choose, install, test & service brakes. Disc- & drum-brake
sign. Brake materials for racing or street. Air cooling &
water ceding. Proportioning valves & balance bar
Practical da'ta & formulas.
Fred Puhn
HPBooks@
11ArlDBOOK
Fred Puhn
Registered
Professional
Fred
Puhn Engineer
Registered Professional Engineer
I
3
3
4
1.
2.
1.
2.
3.
4.
Corvette rotor-ano-caliper assembly by Girlock, modified·for racing by Tilton Engineering.
Neal Products brake-pedal , balance-bar, bracket & dual master-cylinder assembly ; Airheart master
Corvette rotor-and-caliper
for racing
Engineering.
cylinders
shown. ·' . _ _assembly
_ .
. by
- Girlock,
'modifled
.
- by Tilton
-Neal
Products
brake-pedal, balance-bar,
& dual
master-cylinder assembly; Airheart master
Tempilaq
temperature-sensing
paintfrornbracket
Big"Three
Industries;
cylinders
shown.
Alston proportioning
valve.
....
3. Tempilaq temperature-sensing paint from Big-Three Industries.
4. Alston proportioning valve.
Contents
11
2
3
3
4
5
6
6
7
7
8
8
9
9
10
10
11
11
11 22
Introduction
............................................ 33
Introduction ............................................
Basics.................................................
Basics ................................................. 44
Drum
Drum Brakes
Brakes ..........................................
.......................................... 1155
........................................... 23
Disc
Disc Brakes
Brakes ...........................................
23
Friction
Friction Material
Material .......................................
....................................... 34
34
Hydraulic
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 42
Hydraulic Systems
Systems ....
.....................................
42
Brake
Brake Pedals
Pedals &
& Linkages
Linkages ...............................
............................... 66
66
Power Assist ..........................................
.......................................... 77
77
Other Types
Types of Brakes
Brakes .................................
................................. 82
82
HighPerformance Brakes
High-Performance
Brakes ..............................
.............................. 88
88
Testing
Testing .............................................
............................................. 104
104
........................................ 1121
Maintenance
Maintenance ........................................
21
Modifications........................................
Modifications ........................................ 1 37
37
Trouble-Shooting Guide ..............................
.............................. 166
1 66
Suppliers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1
Suppliers List.
List ........................................
169
69
Reference
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 71
Reference Tables .....................................
71
Index ............................................... 174
174
...............................................
THANKS
Thanks to the many brake
brake suppliers and
and experts
experts who helped
helped with technical information
and
Tilton Engineering, Bill
Bill Neal
Neal of Neal
Neal
and photographs.
photographs. Special
Special thanks to Mac Tilton of Tilton
Products, and John Moore of AP Racing
Racing for their personal contributions.
Products,
cohtributions. Thanks also to
Carroll Smith
Carroll
Smith of Carroll
Carroll Smith Consulting for helpful
helpful suggestions given
given after reading
reading the
finished manuscript.
Special thanks to Garrett Van Camp,
Camp, Van Camp Racing
Racing Enterprises, Inc., 25192
Maplebrooke, Southfield, MI
MI 48034. His
His heroic efforts and
and great technical knowledge
gained
Ford Motor brake-design engineer and
and race-car brake-design
gained over the years as a Ford
made a significant contribution to the content and completeness of this book.
consultant made
book. It
could
could not have been
been this quality without him. Thanks Garrett.
NOTICE:
in this book is true and complete to the best of our knowledge. All
NOTICE: The information contained in
guarantees on the part of the author or
recommendations on parts and procedures
procedures are made without any guaranteeson
the quality of parts, materials and methods are beyond
control, author and
HPBooks. Because thequality
beyond our control,
publisher disclaim all liability incurred in connection with the use of this information.
information.
SAE.; Senior
Publisher: Rick Bailey;
Editor: Randy Summerlin; Editorial
Editorial Director:
Monroe, P.E.,
Publisher:
Bailey; Executive Editor:
Director: Tom Monroe,
P.E., S.A.E.;
Editor:
Don Burton;
Editor: Ron
Ron Sessions,
Sessions, A.S.A.E.;
A.S.A.E.; Art Director:
Director: Don
Burton; Book Design:
Design: Paul Fitzgerald;
Fitzgerald; Production
Production Coordinator:
Coordinator:
B. Narducci;
Coatsworth; Typography:
Typography: Michelle
Michelle Carter;
Carter; Director of Manufacturing:
Manufacturing: Anthony B.
Narducci; Photos:
Photos: Fred
Fred
Cindy J. Coatsworth;
Puhn,
Bill Keller
Puhn, others noted;
noted; Cover Photo:
Photo: Bill
Published by HPBooks
A Division of HPBooks, Inc.
P.O.
50
P.O. Box 5367,
5367, Tucson, A2
AZ 85703 6021888-21
602/888-2150
0-89586-232-8 Library of Congress Catalog Number 84-62610
84-62610
ISBN 0-89586-232-8
Inc. Printed in U.S.A.
U.S.A.
©1985 HPBooks,
HPBooks, Inc.
01985
2nd Printing
Printing
2
Introduction
When driving down a long hill on a crowded freeway, a situation can occur that demands good brakes. Many of the cars in this photo are
going over 55 mph . If an emergency were to happen, the resulting chain-reaction braking would result in some drivers locking the wheels.
When driving down a long hill on a crowded freeway, a situation can occur that demands good brakes. Many of the cars in this photo are
Most
of55usmph.
onlyIf an
think
about were
brakes
problems,
too. chain-reaction braking would result in some drivers locking the wheels.
going
over
emergency
to happen,
the resulting
when a panic stop occurs ahead in trafof we
us only
think
about brakes
ficMost
and all
see are
brakelights
and
when
a
panic
stop
occurs
ahead
trafthe undersides of cars. Theseinnearfic and all weillustrate
see are brakelights
and
emergencies
how important
the
undersides
of safety.
cars. These
brakes
are to our
Brakesnearare
emergencies
illustrate
important,
also a vital part
of highhow
performance
brakes
are can
to our
safety.
Brakes are
as
any racer
tell you
.
also
a
vital
part
of
high
performance,
Because everyone wants higher peras
any racerand
cansafety,
tell you.
formance
brakes deserve a
Because
wants
pergreat
deal everyone
of attention.
Wehigher
not only
formance
and
safety,
brakes
deserve
want our car to go fast , but it shoulda
great
dealquickly
of attention.
We not
also stop
and safely.
Anyonly
car
want powerful
our car toand
go fast,
but it should
with
consistent
brakes
also
stopconfidence
quickly andin safely.
Any car
instills
the driver.
It
with
powerful
and
consistent
brakes
also increases driving pleasure.
Bad
instills
confidence
brakes are
terrifying. in the driver. It
also
increases
driving
If racing
is your
game,pleasure.
you needBad
to
brakes are
terrifying.
know
more
about brakes than the
If racing
is your
game, what
you need
to
casual
driver.
No matter
type of
know
more
about
brakes
than
the
racing you do, brake performance is
casual
driver.racing
NO matter
type of
vital. Road
is mostwhat
demanding
racing
you do,
brake drag
performance
is
on
brakes,
although
racing and
vital.
Road
racing
is
most
demanding
oval-track
events
have
special
on brakes, although drag racing and
oval-track events have special
I talk about brakes as a system. This
problems,
too. lines, pedals, levers
includes fluid,
I
talk
about
a system.
This
and linkages, brakes
as wellas as
the brake
includes
fluid,
lines,
pedals,
levers
units. Wheels, bodywork and even
and
linkages,
as well
as the
brake
the frame
structure
become
a part
of
units.
Wheels,
bodywork
and affect
even
the brake
system
when they
the
frame
structure This
become
a part
of
brake
performance.
book
covers
the
brake
system
when
they
affect
each part of the system and how it rebraketoperformance.
book covers
lates
overall brakeThis
performance.
It
each help
part of
andofhow
it rewill
in the
the system
selection
compolates
braketo performance.
It
nents toif overall
you prefer
design a brake
will
help
in
the
selection
of
composystem.
nents
yousection
prefer of
to the
design
a brake
The iffirst
book
deals
system.particular parts of a brake
with
The first
the book
deals
system.
Thesection
secondofsection,
starting
with
particular
parts
of
a
brake
with Chapter 9, describes how to
system.
second
starting
design , The
install,
test,section,
maintain
and
with
9, system
describesfor how
to
modifyChapter
a brake
racing
design,
install,
test,
maintain
and
applications. Race-car concepts also
modify toa brake
system for racing
apply
high-performance
road
concepts
applications.
vehiCles. I alsoace-bar
note where
there also
are
apply
to differences
high-performance
road
important
between racing
vehicles.
I also
note where t'here are
and road use
.
important differences between racing
and road use.
Braking is essential in winning races.
These stock cars are competing on a road
course-the
severe
for automoBraking is most
essential
in duty
winning
races.
tive brakes. cars
Notice
thea right
aresmoke from On
road
front tire on most
car that's
braking
hard
in the
course-the
severe
duty for
automocorner.
tive
brakes. Notice smoke from the right
front tire on car that's braking hard in the
corner.
3
Basics
I
Good brakes are essential to overall vehicle performance. Even though engine performance, suspension and body aerodynamics approach
perfection, race cars, such as this GTP Corvette, will not be competitive without good brakes. Photo by Tom Monroe.
Good brakes are essential to overall vehicle performance. Even though engine performance, suspension and body aerodynamics approach
perfection, race cars, such as this GTP Corvette, will
not be
competitive
goodtobrakes.
by Tomthe
Monroe.
Brake
systems
are without
designed
do Photo
brakes,
friction materials rub
Most production sedans have drum brakes
on the rear and disc brakes on the front.
Drum
brakes are sedans
preferred
on drum
rear wheels
Most ~roduction
have
brakes
because
a parking
brake
is easily
adapted
on the rear
and disc
brakes
on the
front,.
This
drum
on the rear
of awheels
2-ton
Drumlarge
brakes
are ispreferred
on rear
sedan. a parking brake is easily adapted.
because
~
-
- -
This large drum is on the rear of a 2-ton
sedan.
4
one thing-stop the vehicle. Sounds
Brake
designed
to do
easy,
but systems
problemsare
start
when brakes
one
the from
vehicle.
mustthing-stop
stop a vehicle
highSounds
speed
easy,
but problems
startdowhen
brakes
in a short
distance, and
it over
and
must
stop
a
vehicle
from
high
speed
over again . We expect no failures
or
in
distance,All
andbrake
do it over
and
lossa short
of control.
systems
over again.
expectThe
no failures
or
should
stop We
a vehicle.
difference
loss
of
control.
All
brake
systems
between a good system and a bad one
should
stop ita vehicle.
The difference
is how well
will perform
under the
between
a good
system and a bad one
most adverse
conditions.
is All
howvehicles
well it will
the
haveperform
brakes, under
and they
most
adverse
conditions.
always did . Ever since m an discovered
vehicles
have itbrakes,
and they
theAll
wheel
, stopping
was a problem.
always did.
Ever since
discovered
Carts,
wagons
and man
carriages
had
the
wheel,
stopping
it was
a problem.
brakes,
usually
simple
blocks
rubbing
Carts,
wagons
carriagesa basic
had
on a wheel.
This and
established
brakes,
usually
simple
blocks
rubbing
that has yet to change, even with the
on a wheel.
This established
a basic
most
sophisticated
brake system:
All
that
hasuse
yetfriction
to change,
with the
brakes
to stopeven
the vehicle.
most sophisticated brake system: All
brakes usefiiction
BRAKE
TYPES to stop the vehicle.
When two parts rub together, the
BRAKE
resulting TYPES
friction generates heat. In
When two parts rub together, the
resulting friction generates heat. In
against metal surfaces . Different types
brakes,
friction materials
of
brakes the
are arranged
differently,rub
or
against
metal
surfaces.
Different
use different methods of forcing types
rubof
brakes
are together.
arranged There
differently,
or
are also
bing
surfaces
use
different
methods
of
forcing
rubdifferences in dissipating heat once it
bing
surfaces together. There are also
is generated.
differences
in dissipating
heat
once or
it
Either drum
brakes or disc
brakes,
generated. of the two, are used on
ais combination
Either
drum brakes
disc brakes,
most
vehicles.
Theseorterms
refer or
to
ahow
combination
of
the
two,
are
usedand
on
friction surfaces are designed
most
vehicles. These terms refer to
configured.
how
friction
surfaces are
and
Drum
Brakes-All
eadesigned
rly vehicles
configured.
used drum bra kes ; many of today's
Drum
early vehicles
vehicles Brakes-All
still do . The rubbing
surface
used
drum
brakes;called
many
of today's
drum ,
is a metal
cylinder
a brake
vehiclesmade
still do.
Theiron
rubbing
surface
usually
of cast
.
is aEarly
metal drum
cylinderbrakes
called awere
brake drum,
exterusually
made ofsurface
cast iron.
nal-rubbing
was outside of
brakes internal
were extertheEarly
drum.drum
More modern
drum
nal-rubbing
surface
was
outside
of
brakes have the rubbing surface
inside
the
drum.
More
modern
internal
drum
the drum. There are shoes inside the
brakes with
have frict
the ion
rubbing
surface
inside.
drum
material
attached
the drum.
are isshoes
inside
This
frictionThere
material
called
lining.the
It
drum with friction material attached.
This friction material is called lining. It
..
Honda disc brake is typical of front brakes
on small sedans. Exposed rubbing I
surface
of disc
brake
aids cooling.
Honda disc
brake
is typical
of front brakes
Iused
used on small sedans. Exposed rubbing
surface of disc brake aids cooling.
is designed to rub against the drum
without burning, melting or wearing
is
designed
rub are
against
theagainst
drum
The to
shoes
forced
rapidly.
without
burning,
melting
or
wearing
the inside surface of the drum when
rapidly.
Thepushes
shoes are
the driver
the forced
brake against
pedal,
the insidefriction
surfacebetween
of the drum
when
the lining
creating
the
driver
pushes
the
brake
pedal,
and the drum surface . Drum brakes
creating
friction
between
in Chapter
2. the lining
are covered
and
the
drum
surface.
Drum brakes
Disc Brakes - A modern
brake
are
covered
in
Chapter
2.
design is the disc brake. The drum is
Disc
modern
replacedBrakes-A
by a flat metal
disc, or brake
roto;;
design
is
the
disc
brake.
The
drum
is
with a rubbing surface on
each
side.
replaced
by
a
flat
metal
disc,
or
rotot;
The rotor is usually made of cast iron.
with
a rubbing
surface
on each
side.
Friction
materials
are inside
a caliper,
The
rotor
is
usually
made
of
cast
iron.
which surrounds the rotor. Disc-brake
Friction
materials are inside
caliper,
friction material-one
on eacha side
of
which
surrounds
the
rotor.
Disc-brake
the rotor- is called a brake pad, puck
friction
each side of
or
lining.material-one
This caliper on
is designed
to
the rotor-is
a brake
pad,ofpuck
clamp
the padscalled
against
the sides
the
or
lining.
This caliper
designed
to
rotor
to create
friction.is Disc
brakes
clamp
the pads
against 3.
the sides of the
are
covered
in Chapter
Earliest automotive brakes were drum type
with the rubbing surface on the outside of
the
drum.
Because brakes
frictionwere
material
surEarliest
automotive
drum type
rounds
outside
of theon
drum,
coolwith
thethe
rubbing
surface
the little
outside
of
ing air
contacts
the friction
hot rubbing
surface.
the
drum.
Because
material
surExternalthe
drum
brakes
are drum,
simplelittle
and cooleasy
rounds
outside
of the
to
but have
coolingsurface.
ability.
ingservice,
air contacts
thehorrible
hot rubbing
External drum brakes are simple and easy
to service, but have horrible cooling ability.
Finned aluminum drums give better cooling
than plain cast iron.
Caliper
P = Clamping Force
on Rotor
p
P
=
Clamping Force
on Rotor
Caliper Mounting
Bolt
-
-
- Axle
Centerline
Axle
Centerline
rotor to create friction. Disc brakes
are
covered in Chapter 3.SYSTEM
BRAKE-ACTUATING
Wheel
Stud
Between the driver's foot and the
BRAKE-ACTUATING
SYSTEMthat
wheel
brakes are components
Betweenforce
the from
driver'sthefoot
and into
the
translate
driver
wheel
brakes
are
components
that
friction force at the brake-rubbing
translate force
into
surfaces.
I callfrom
this the
thedriver
actuating
friction
force
at
the
brake-rubbing
system. This system can be mechanisurfaces.
I call
this theor aactuating
cal,
hydraulic
, pneumatic
combisystem.
This
system
canvehicles
be mechanination of these . Future
could
cal,
pneumatic
or a combiWhatever
the
use hydraulic,
electric systems.
nation
these. Future
vehicles
could
type ofof
actuating
system,
the result
is
use
electricWhen
systems.
Whatever
the
the same:
the driver
operates
typesystem,
of actuating
the .result is
the
brakessystem,
are applied
the
same:
When
the
driver
operates
Brake Pedal & Linkage-Brake
the system,
brakes areare
applied.
pedals
and linkages
integral parts
Brake Pedal & Linkage-Brake
Stud
pedals and linkages are integral parts
Prewar MG used mechanical brakes. Front
brakes are operated by cables that flex as
the
wheels
steer mechanical
and move up
and down.
Prewar
MG used
brakes.
Front
Finned aluminum
drums
better
brakes
are operated
by give
cables
that cooling
flex as
thanwheels
plain cast
iron.and move up and down.
the
steer
~Rotor
-\
Rotor
Disc brake operates by clamping rotor between two stationary pads. Rotor turns with the
wheel;
caliper is mounted to a fixed part of the suspension, usually the spindle or upright.
I
I
Disc brake operates by clamping rotor between two stationary pads. Rotor turns with the
wheel; caliper is mounted t o a fixed part of the suspension, usually the spindle or upright.
of a brake system. The pedal is the familiar lever that the driver pushes
of
a brake
system.
pedal
the fawith
his foot
to The
apply
the is brakes.
miliar
lever
that
the
driver
pushes
Regardless of the type of brakewith
his system
foot toused,
apply
the applicabrakes.
actuating
system
Regardless
the with
type the
of braketion always ofbegins
driver
actuating
used, system
operating system
a pedal-or
lever applicain rare
tion always
beginsdesign
with determines
the driver
cases.
Brake-pedal
operating
a pedal-or
in rare
the leg force
required tolever
stop the
car.
cases. Brake-pedal design determines
the leg force required to stop the car.
It is also a factor in determining how
solid the brakes feel to the driver.
It Trade-offs
is also a factor
in determining
how
when designing
are made
solid
brakesLong
feel to
the driver.
brakethe
pedals.
pedals
reduce the
Trade-offs
are madetowhen
pedal
force required
stop adesigning
vehicle.
brake
pedals.
Longpedals
pedals have
reducelong
the
However,
long
pedal
force
required
to
stop
a
vehicle.
travel. They can also feel spongy to the
However,
long pedals
long
driver.
Brake-pedal
design have
is detailed
travel.
They6. can also feel spongy to the
in Chapter
driver. Brake-pedal design is detailed
in Chapter 6 .
5
Although most mechanically actuated
brakes are found on antique cars, some are
still
being used.
by APactuated
Racing
Although
most Developed
mechanically
for
useare
onfound
competition
brakes
on antiquerally
cars,cars,
somethis
are
modern
caliper
mechanically
actuated.
still
being
used. isDeveloped
by AP
Racing
Independent
the hydraulically
actuated
for
use on of
competition
rally cars,
this
brakes,
calipers
are used onactuated.
the rear
modern these
caliper
is mechanically
for
high-speed
on slick surfaces.
Independent
of control
the hydraulically
actuated
Photo courtesy
AP Racing.
brakes,
these calipers
are used on the rear
for high-speed control on slick surfaces.
Photo courtesy AP Racing.
Early race cars had no front brakes. Although this Peugeot was a winner with its advanced
high-speed dual-overhead-cam engine, it used cable-operated rear-wheel brakes.
Early race cars had no front brakes. Although this Peugeot was a winner with its advanced
high-speed dual-overhead-cam engine, it used cable-operated rear-wheel brakes.
In the '20s, Duesenberg introduced hydraulic brakes with large finned drums .
This
was
probably
the firstintroduced
road car with
In the
'209,
Duesenberg
hyenough
horsepower
required
great
draulic brakes
with that
large
finned adrums.
improvement
in braking.
It didroad
not car
use with
flex
This
was probably
the first
hoses, but
instead ranthat
fluidrequired
through internal
enough
horsepower
a great
passages
in the
improvement
in suspension.
braking. I t did not use flex
hoses, but instead ran fluid through internal
passages in the suspension.
The brake pedal is connected to a
linkage that transfers force to the acThe brake
pedal
connected
to asa
tuating
system.
Thisislinkage
can be
linkage asthat
transfers force
to the ac-a
simple
a push/pull
rod operating
tuating hydraulic
system. This
linkage
can beOr,
as
single
master
cylinder.
simple
as
a
push/pull
rod
operating
the linkage may be a complicated, ad-a
single
master
cylinder.
Or,
justablehydraulic
balance-bar
system
for changthe
linkage
maybetween
be a complicated,
ading the
balance
front and rear
justable
balance-bar
system
for
changbrakes. Early-design, mechanicaling the balance
between
front
actuating
linkage
extends
all and
the rear
way
brakes.
Early-design,
mechanicalto the brakes themselves. Brakeactuating
linkageis extends
all inthemore
way
linkage design
discussed
to
the
brakes
themselves.
Brakedetail in Chapter 6.
linkage
designBrakes-The
is discussed in
more
Mechanical
simplest
detail
in
Chapter
6.
brake-actuating system is a mechaniMechanical
Brakes-The
simplest
cal
system. The
brake pedal operates
brake-actuating
system
is
a
mechanicables or rods that apply the brakes
cal system.
The isbrake
pedal
operates
when
the pedal
pushed
. Early
sys-
cables or rods that apply the brakes
when the pedal is pushed. Early sys-
6
tems were mechanical and are still
used for parking brakes on presenttemsvehicles.
were mechanical
and are
still
day
The mechanical
linkage
used fortheparking
brakes onin presentmoves
shoes outward
a drum
day vehicles.
The mechanical
linkagea
brake,
or clamps
the pads against
moves
the
shoes
outward
in
a
drum
disc-brake rotor.
brake,
or
clamps
the
pads
against
Hydraulic Brakes-Modern cars usea
disc-brakebrakes.
rotor. In a hydraulically achydraulic
Hydraulic
Brakes-Modern
tuated
system,
the cables or cars
rodsuse
of
hydraulic
brakes.
In
a
hydraulically
the mechanical system are replaced acby
tuated system,
or rods
of
fluid-filled
lines the
and cables
hoses. The
brake'the mechanical
system are
replacedinbya
pedal
linkage operates
a piston
fluid-filled
linestoand
hoses. The
master cylinder
pressurize
thebrake:
fluid
pedal
linkage
operates
a
piston
in a
inside the lines and hoses. Fluid presmaster
cylinder
to
pressurize
the
fluid
sure in each wheel cylinder forces the
inside the
lines and
hoses.the
Fluid
presfriction
material
against
drum
or
sure
eachChapter
wheel cylinder
the
rotor.inSee
5 for aforces
detailed
friction material
against
the drum
or
explanation
of how
a hydraulic
system
rotor.
See
Chapter
5
for
a
detailed
works.
explanation
of how a hydraulic
system,
Pneumatic Brakes-In
a pneumatic
works.
or air-brake, system the brakes are
Pneumatic by
Brakes-In
a pneumatic,
controlled
compressed
air. Air
or
air-brake,
system
the
are
brakes are generally usedbrakes
on large
controlled
compressed
air. Air
commercial by
vehicles
and trucks.
An
brakes are of
generally
used on brake
large
advantage
the pneumatic
commercial
vehicles
and
trucks.
An
system is safety. Small leaks cannot
advantage
of
the
pneumatic
brake
cause a total loss of braking because
system
is safety. supplied
Small leaks
air
is constantly
by acannot
comcause
total stored
loss ofinbraking
because
pressora and
large volume.
air
is constantly
suppliedoperation
by a comPneumatic
brake-system
is
pressor
and
stored
in
large
described briefly in Chapter 8. volume.
Pneumatic brake-system operation is
described
briefly in Chapter 8.
BRAKE HISTORY
The earliest brakes were derived
BRAKE
HISTORY
from
those
used on horse-drawn
The earliest
derived
wagons.
As carsbrakes
becamewere
heavier
and
from
those
used
on
horse-drawn
more
powerful,
these primitive
wagons. As cars became heavier and
more powerful, these primitive
brakes soon were improved to the
early external- type drum brakes, all
brakes
soon were improved
to the
mechanical-actuating
systems.
with
early
external-type
drum
all
Early
brakes were
on brakes,
the rear
with
mechanical-actuating
systems.
wheels
only. The major reason
for this
Early
brakes were
on thean rear
was
the difficulty
in designing
acwheels
only.
The
major
reason
for this
tuating system on wheels that
are
was the difficulty
designing
acsteered.
Engineersinavoided
the an
probtuating
system on
wheels that
are.
lem
by omitting
front-wheel
brakes
steered.
the probAnother Engineers
reason foravoided
not using
front
lem
by
omitting
front-wheel
brakes was concern that the carbrakes.
might
Another
reason
for not
usingbrakes
front
tip over on
its nose
if front
brakesapplied
was concern
were
hard! that the car might
tipEarly
over external-type
on its nose if drum
front brakes
brakes
were
applied
hard!
used a band of friction material outEarly
external-type
brakes
side
the drum.
This typedrum
of brake
was
used to
a band
of but
friction
materialmateouteasy
design,
the friction
side
the drum. thehisdrum
typefrom
of brake
was
rial prevented
cooling.
easy
to
design,
but
the
friction
mateAlso, exposed friction materials were
rial
prevented
the drum
su bject
to dirt,
oil from
and cooling.
water
Also, exposed friction
materials
were
contamination.
When the
brake shoes
subject
to
dirt,
oil
and
water
were relocated inside the drum, a
contamination.
Whenwas
the born.
brake These
shoes
modern drum brake
were
relocated
theRenault.
drum, a
were first
used oninside
the 1902
modern
drumfour-wheel
brake was braking
born. These
Although
was
were
first
used
on
the
1902
Renault.
tried early in the 20th century,
most
Although
was
early
cars hadfour-wheel
rear brakes braking
only. Then,
triedtheearly
in the
20thdiscovered
century, most
in
1920s
it was
that
early
hadadded
rear brakes
front cars
brakes
greatlyonly.
to aThen,
car's
in
the
1920s
it
was
discovered
that
stopping a bility, and they were judged
front
brakes
added
greatly
to
a
car's
safe. Four-wheel brake systems soon
stopping
ability, and they were judged
became universal.
safe.
Four-wheel
brake systems
systems soon
were
Mechanicalac tuating
became
universal.
still used on most cars until the late
Mechanical-actuating
systems came
were
'20s
when hydraulic systems
still
most cars until
late
into used
use . onMechanical
brakesthewere
'20s
when
hydraulic
systems
came
used for auto rac ing long after hydrau-
into use. Mechanical brakes were
used for auto racing long after hydrau-
Internal details of early Duesenberg hydraulic drum brake: Notice fluid passages through axle, kingpin and spindle. Sealing was a problem
solved by use of flexible hydraulic lines.
I
Ieventually
Internal details of early Duesenberg hydraulic drum brake: Notice fluid passages through axle, kingpin and spindle. Sealing was a problem
eventually solved by use of flexible hydraulic lines.
.
This little disc brake started it all-first
disc brake used on a mass-produced car.
Goodyeardiscstarted
brakesit were
ofThis
little Hawley
disc brake
all-first
fered
on Crosley
Hotshot
and Supersports
disc brake
used on
a mass-produced
car.
roadsters
in the early
'50s. A were
Crosley
Goodyear-Hawley
disc brakes
ofHotshot
won theHotshot
first Sebring
12-hour
fered
on Crosley
and Supersports
endurance in
race
with
these
brakes.
In later
roadsters
the
early
'50s.
A Crosley
years,
they
were
for small 12-hour
sportsHotshot
won
thepopular
first Sebring
racing cars.race with these brakes. In later
endurance
years, they were popular for small sportsracing
cars. were developed for passenlic
systems
ger cars. The simple mechanical brake
lic systems
developed
system
waswere
reliable,
easy for
to passenunderger
cars.
The
simple
mechanical
brake
stand and maintain, and not subject
to
system was
easy that
to undersudden
loss reliable,
of braking
could
stand
not subject
happenandto maintain,
a hydrau and
lic system
with toa
sudden
loss
of
braking
that
could
failed line or seal.
happen
to
a
hydraulic
system
with
After World War II, disc brakesa
failed
or seal. The first production
began line
to appear.
War 11,wasdisc
carAfter
with World
disc brakes
thebrakes
1949
began
to
appear.
The
first
production
Crosley Supersport. Disc brakes were
car
disc brakes on
was the
the 1949
usedwithsuccessfully
24Crosley
Supersport. Disc brakes
hours-of-LeMans-winning
Jaguarwere
in
used successfully on the 24hours-of-LeMans-winning Jaguar in
Since the mid-'50s, disc brakes have been highly developed for both racing and road use.
Companies such as JFZ Engineered Products have taken brake development far beyond
the
early
concept.
Rotors,
brake-mounting
haveand
all benefited
Since
thedisc-brake
mid-'50s, disc
brakes
havepads
beenand
highly
developed forhardware
both racing
road use.
from
rigors of
faster
Photo courtesy
Engineered
Products.
JFZ cars.
Engineered
Products.IFZ
have
taken brake
development far beyond
Companies
such
as race
the early disc-brake concept. Rotors, pads and brake-mounting hardware have all benefited
from
fasterbrakes
race cars.
Photo
courtesy JFZ
Engineered
the rigors
'50s. ofDisc
soon
became
design,
there Products.
have been many impor-
popular on many race cars. Indianathe '50s.
Disc used
brakes
became
polis
500 cars
discsoon
brakes
early
popular
on
many
race
cars.
Indianatoo, but they had little effect on the
polis 500 of
carsraces
usedondisc
early
outcome
thisbrakes
fast track.
too, but
had little
effect
the
Only
at they
LeMans,
where
carsonmust
outcome
of
races
on
this
fast
track.
decelerate from 180 to 30 mph every
Only
at do
LeMans,
lap, and
it for 24where
hours,cars
weremust
disc
to limit.
30 mph
every
decelerate
fromto 180
brakes tested
their
Even
in
lap,
anddrum
do it brakes
for 24 hours,
racing,
are stillwere
useddisc
in
brakes classes,
tested tobut
their
Evenrace
in
certain
mostlimit.
modern
racing,
brakes are still used in
cars
use drum
disc brakes.
certain
classes,
but most
modern
race
the basic
changes
in brake
Beyond
cars use disc brakes.
Beyond the basic changes in brake
tant improvements. Brake systems
design,
there
havesafe;
beenand
many
importoday are
very
complete
tant
improvements.
Brake
systems
system failure occurs rarely. Modern
today are
brakes
can very
go forsafe;
yearsand
withcomplete
little or
system
failure in
occurs
rarely.use
Modern
no attention
highway
, but
brakes
years with
or
therein can
lies go
a for
problem:
Whenlittle
really
no
attention
in
highway
use,
but
needed , performance may be marginal
therein
a problem:
When
because lies
of inattention
. This
bookreally
will
needed,
may
be marginal
help you performance
keep that from
happening.
because of inattention. This book will
help
you keep& that
from happening.
FRICTION
ENERGY
Friction is resistance to sliding . Any
FRICTION & ENERGY
Friction is resistance to sliding. Any
7
Type of Energy
..
Friction
Force
Friction
Friction between
the box and floor is what
Force
makes the box difficult to slide. If box
weight
frictionthe
between
floor
and
Friction or
between
box andthe
floor
is what
box
increases,
sodifficult
must theto
force
to slide
it.
makes
the box
slide.
If box
Heat is or
developed
on slidingthe
surfaces
as
weight
friction between
floor and
box is
moved. so must the force to slide it.
increases,
Heat is developed on sliding surfaces as
two isobjects
box
moved. in contact with and trying
to move relative to each other have
two objects
in contact
and
trying
friction.
It can
be high with
or low
dependto move
each other
have
ing
on therelative
types ofto
surfaces
in contact.
friction.
It
can
be
high
or
low
dependFriction helps keep your feet from
ing o n the
in contact.
sliding
outtypes
fromof surfaces
under you.
When
Friction
helps keep
your
feet isfrom
you
are standing
on ice,
friction
low
sliding
fromto prevent
under you.
When
and
it is out
difficult
slipping.
you
standing
on ice,
If are
two
surfaces
in friction
contactis low
are
and
it
is
difficult
to
prevent
sliding, the friction createsslipping.
heat. You
two surfaces
contact your
are
canIf confirm
this byin rubbing
sliding, the friction creates heat. You
can confirm this by rubbing your
KINETIC ENERGY
OF ROTATION
KINETIC
ENERGYan object with
Strictly
speaking,
OF
ROTATION
kinetic
energy can be either moving
Strictly
speaking,
an object
with
in a straight
line or rotating
about
its
kinetic
energyofcan
be either
own
center
gravity
(CG).moving
In a
in a straightcar,
line or
rotating
about its
speeding
kinetic
energy
is
own
gravity
a
mostlycenter
in the of
moving
car. (CG).
UnlessInthe
speeding
car, down
kinetic
is
car
is spinning
the energy
road, less
mostly
in the
moving
Unless
the
than
10%
of the
total car.
kinetic
energy
car
is spinning
downparts
the of
road,
is stored
in rotating
the less
car.
than
10%parts
of theinclude
total kinetic
energy
Rotating
tires, wheels,
is storedengine
in rotating
parts line.
of the
car.
brakes,
and drive
Addi~
Rotating
partsenergy
include
tires, in
wheels,
tional
kinetic
stored
these
brakes, engine
and drive
line. Addirotating
parts must
be absorbed
in
tional
kinetic
energy stored
these
the
brakes.
However,
to makeincalcurotating simpler,
parts must
be absorbed
in
lations
I ignore
the small
the brakes.
However,
to make
calcuamount
of kinetic
energy
stored
in
lations simpler,
I ignore the small
rotating
parts.
amount
of kinetic
in
At high
speed, energy
kineticstored
energy
rotatinginparts.
stored
the rotating tire-and-wheel
At high speed,
kinetic
energy
assemblies
increases
significantly.
stored
If you in
hitthe
therotating
brakestire-and-wheel
hard at high
assemblies
increases
significantly.
speed,
the rotating
parts
must be
If you hitbefore
the brakes
hardcan
at high
stopped
the wheel
lock
speed,
the Itrotating
partsand
must
be
and
slide.
takes time
pedal
stopped
the rotating
wheel can
lock
effort
to before
stop this
weight,
and slide.
takes
time slow
and at
pedal
even
if the Itcar
doesn't
all.
effort to stop this
rotating
weight,
Consequently,
it is more
difficult
to
even
if the
car doesn't
slow at all.
lock the
wheels
when traveling
at
Consequently,
it is Ironically,
more difficultthis
to
higher
speeds.
lock the
wheels
traveling
makes
a car
saferwhen
at high
speed at
if
higher
speeds.
the
driver
panics Ironically,
and hits this
the
makes a
safer
at highinspeed
brakes
toocar
hard.
However,
racing,if
the
driver panics
it increases
pedal and
effort hits
as the
brakestries
too hard.
However,
in racing,
driver
to reach
the traction
limit
it the
increases
pedal effort as the
of
tires.
driver tries to reach the traction limit
of the tires.
8
Example
Heat
Energy stored ina hot brake rotor.
Type of Energy
Example
Sound
Noise from exhaust.
Heat
Energy
stored
in a hot brake rotor.
Ught
Light from
headlights.
Sound
Noise
exhaust.
Stored Mechanical
Energyfrom
stored
in a compressed coil spring.
Light
Light from
headlights.
Energy
in agallon
of gasoline.
Chemical
Stored
Mechanical
Energy stored
a compressed
spring.
Electrical
Current
from a in
battery
turning a coil
starter.
Chemical
Energy in a energy
gallon of
Radiation
Microwave
in gasoline.
a microwave oven.
Electrical
Current
from a ina
battery
turning
a starter.
Kinetic
Energy stored
speeding
bullet.
Radiation
Microwave energy in a microwave oven.
Kinetic
Energy
stored
initacan't
speeding
bullet.
Energy
can be changed from one form
to another,
but
be created
or destroyed. Here
are some different forms of energy. Most forms are transformed into heat after energy
does
itscan
useful
work.
Energy
be changed
from one form to another, but it can't be created or destroyed. Here
are some different forms of energy. Most forms are transformed into heat after energy
does
useful work.
handsitstogether
rapidly back and forth.
varies as the square of speed. To calcu-
You can feel the warmth. This friction
hands
together
back and
can
help
warm rapidly
your hands
on aforth.
cold
You
can
feel
the
warmth.
This
friction
day. In brakes, friction is used
to
can help
warm
handsofo ncreating
a cold
create
heat.
Theyour
process
day.
In brakes,
heat stops
the car. friction is used to
create
heat.
T h eofprocess
creating
The amount
frictionof between
heat
stops
the
car.
two rubbing surfaces depends on the
T h e amount
of friction
between
materials
and their
roughness.
The
two rubbing
surfacesis depends
amount
of friction
describedo nbythea
materials called
and their
e
number
the roughness.
coefficient T hof
amount
of
friction
is
described
by
a
friction. A high number means a large
number ofcalled
the a coefficient
of
amount
friction;
low number
A
high
number
means
a
large
.friction.
means a small amount of friction.
amount
of about
friction;
a low
Read
more
friction
at thenumber
beginmeans
a
small
amount
of friction.
ning of Chapter 4.
Read
moreisabout
frictionto atdothe
beginEnergy
the ability
work.
A
ning of Chapter
4.
moving
car develops
energy. The
Energy
is the ability
to doenergy
work. A
faster
it moves,
the more
it
moving car
energy.
The
develops.
Thisdevelops
type of energy
is called
faster
moves,
thespeed
moreis energy
kinetic it
energy.
When
doubled,it
develops.
This
type
of
energy
is called
four times the kinetic energy
is
kinetic
energy.
W
h
e
n
speed
is
doubled,
developed. That is, kinetic energy
four times the kinetic energy is
developed. That is, kinetic energy
TEMPERATURE & HEAT
The difference between temperature
TEMPERATURE
& HEAT We all
and heat may be confusing.
The familiar
difference
between
temperature
are
with
temperature,
meaand heat
confusing.
We all
sured
in may
eitherbedegrees
Farenheit
are
familiar
with
temperature,
(F) or
degrees
centigrade
(Cl. measured
Farenheit
Heat inis either
a formdegrees
of energy.
When
(F) or isdegrees
(C).itstemheat
added centigrade
to a material,
Heat is arises;
form of
energy.
When
perature
when
heat
is
heat is added
a material, its
temremoved,
its totemperature
drops.
perature
rises; when
heat of
is
Thus,
temperature
is the effect
removed,
its temperature
drops.
adding or subtracting
heat energy.
Thus, ,Itemperature
is the
effect
When
say something
heats
up, ofI
addingheat
or subtracting
mean
is added. heat
Whenenergy.
I say
When
I say
something
heats up, InI
cools off,
I mean
heat is removed.
mean case,
heat is
When of
I say
either
theadded.
temperature
the
cools off,
I mean heat is removed. In
object
changes.
either
case, the
temperature
the
I measure
kinetic
energy inoffootobject changes.
pounds
(It-I b). However, it could be
I measure
footmeasured
in kinetic
British energy
ThermalinUnits
pounds
it could
be
(BTU's), (ft-lb).
just asHowever,
engineers
do .. One
measured
British
Units
BTU
is the in
amount
of Thermal
heat it takes
to
(BTU's),
as engineers
One
raise
the just
temperature
of onedo.
pound
BTU
IS theby
amount
of heat Farenheit.
it takes to
of
water
one degree
raise BTU
the temperature
oneIt-Ib
pound
One
is equal to of778
of
of waterorbyone
oneft-Ib
degree
Farenheit.
energy,
equals
0.0013
One
is equal
to 778 offt-lb
of
BTU. BTU
Although
one pound
water
energy, or one ft-lb equals 0.0013
BTU. Although one pound of water
late kinetic energy of a car, use the folvaries as
the square of speed. To calculowing
formula:
late kinetic energy ofS2a car, use the folWc
lowing
Kinetic formula:
energy = - -
29.9
W,S2
=
Kinetic
energy
in foot-pounds (It-Ib)
29.9
W = Weight of Car in pounds (Ib)
in c=
foot-pounds
S
Speed of(ft-lb)
car in miles per hour
= Weight of Car in pounds (Ib)
W,
(mph)
S = Speed of car in miles per hour
Converting
Energy-The first law of
(mph)
thermodynamics says: Energy can
Converting
law of
never
be Energy-The
created nor first
destroyed.
thermodynamics
can
However,
energy says:
can beEnergy
converted
neveronebeform
created
nor destroyed.
from
to another.
However,
canenergy
be converted
Differentenergy
forms of
are heat,
from
o
n
e
form
to
another.
sound, light, stored mechanical,
Different electrical
forms of energy
heat,
chemical,
and are
radiated.
sound, electrical
light, stored
mechanical,
Stored
energy in
a battery
chemical,
will
convert electrical
energy intoand
heatradiated.
or light
Stored
electrical
energy
by connecting the batteryin toa battery
a light
will
into heat
or light
bulb.convert
Stored energy
mechanical
energy
in a
by connecting
battery to
to kinetic
a light
spring
can be the
converted
bulb. Stored mechanical energy in a
spring can be converted to kinetic
changes temperature one degree F
when one BTU of heat is added,
F
changes
temperature
one react
degree
other
materials
do not
the
when
of heat change
is added,
sallle. one
TheirBTU
temperature
is
other
materials
do BTU
not of
react
different
when one
heatthe
is
same. Their temperature change is
added.
different
when one BTU
of heat
is
The relationship
between
temadded.
perature change and heat-energy
The relationship
temchange
is governed between
by a property
perature
change
andEach
heat-energy
ca
ll1ed specific
heat.
material
change
is governed
by aasproperty
has its own
specific heat
shown
called
specific
heat. in
Each
for
typical
materials
the material
accomhas its own
specific
heatheat
as shown
panying
table.
Specific
is the
for typical materials
thepound
accomtemperature
rise for in
one
of
panying table.
is the
material
when Specific
one BTU heat
of heat
is
temperature
rise forspecific
one pound
added. A material's
heat of
is
material
when one
of heat is
very
important
to aBTU
brake-design
added. A material's
spec~ficheat
is
engineer
for calculating
brakevery important
to a
temperature
change
for brake-design
each stop.
engineer
for calculating
Ideally, brakes
should be brakemade
temperature
change
eachspecific
stop.
from
materials
with for
a high
Ideally,
should inbea made
heat.
This brakes
would result
small
from materials
high specific
temperature
r isewith
for aa given
amount
heat.kinetic
This would
a small
of
energyresult
put ininto
the
temperature
rise for
a given amount
brakes. A small
temperatur
e rise
of
kinetic
energywouput
intofewer
the
means
the brakes
l1d have
brakes. A small temperature rise
problems.
means the brakes would have fewer
problems.
MELTING TEMPERATURE
Material
Degrees
F
Degrees C
MELTING
TE'MPERATURE
Water
Material
Beryllium - pure
Water
Beryllium-QMV
Beryllium-pure
Magnesium-AZ 31 B-H24
Beryllium-QMV
Aluminum-6061- T6
Magnesium-AZ
31 6-H24
Aluminum -2024-T3
Aluminum-6061
-T6
Carbon-pure
Aluminum-2024-T3
Titanium-pure
Carbonpure120VCA
Titanium-B
Titanium-pure
Magnesium-HK 31 A-H24
Titanium-B
120VCA
Stainless Steel-304
Magnesium-HK
31A-H24
Cast Iron
Stainless
Steel-304
Steel-C1020
Cast
Iron
Copper-pure
Degrees F
32
2340
32
2340
2340
1100
2340
1080
1100
940
1080
6700
940
3070
6700
3100
3070
1100
31
00
2600
1100
2750
2600
2750
2750
1980
Steel-C1020
0
1282
0
1282
1282
593
1282
582
593
504
582
3704
504
1688
3704
1704
1688
593
1704
1427
593
1510
1427
1510
151
0
1082
2750
1510
Degrees C
SPECIFIC
HEAT
SPECIFIC
BTU/1 b/F
HEAT
1.00
BTU/l
b/F
0.52
1.oo
045
0.52
0.25
0.45
0 .23
0.25
0.23
0.23
0 .16
0.23
0.14
0.1
6
0 .13
0.1
4
0 .13
0.1
3
0 .12
0.1
3
0.10
0.1
2
0.10
0.10
0 .09
0.10
Specific
heats of various materials are1980
listed from the highest
heat is
Copper-pure
1082 to lowest. Specific
0.09
amount of heat energy required to raise one pound of material by one degree Fahrenheit .
Material heats
with highest
specific
heat are
is not
necessarily
besttoforlowest.
brakes.
To be a
good
Specific
of various
materials
listed
from the the
highest
Specific
heat
is
brake material,
must withstand
temperature,
conduct
heat
and have
a good
amount
of heat it
energy
required tohigh
raise
one pound of
material
by rapidly
one degree
Fahrenheit.
rubbing surface.
Material
with highest specific heat is not necessarily the best for brakes. To be a good
brake material, it must withstand high temperature, conduct heat rapidly and have a good
rubbing surface.
energy
when a wind-up toy car is
released. Chemical energy stored in
energy
whenis converted
a wind-up int
toy
car is
gunpowder
o sound,
released.
Chemical
energy
heat and kinetic
energy
when stored
ignited in
.
gunpowder
is converted
intoroad
sound,
down the
has
A car moving
heat
andenergy.
kinetic energy
kinetic
To stopwhen
the ignited.
car, you
A car
moving
downkinetic
the road
has
must
dispose
of this
energy.
kinetic
stop bethedestroyed,
car, you
Becauseenergy.
energy To
cannot
must
of thistokinetic
it mustdispose
be converted
anotherenergy.
form.
Because
energy
cannot
be be
destroyed,
This
kinetic
energy
could
convertit
be converted
to another
edmust
into any
of the forms
listed onform.
page
This
kinetic
energy
could
convert8, but conversion to heat isbe
easiest.
By
ed
into anyfriction
of the forms
listed on
page
forcing
material
against
8, but conversion
heatis iscreated
easiest.and
By
drums
or rotors , to
heat
forcing
friction
material
against
the car slows
. If the
brakes or
tires
drums, orsome
rotors,
heat energy
is created
and
squeal
sound
is also
the
car
slows.
If
the
brakes
or
tires
produced, but the amount of kinetic
squeal,
some sound
energy isis small
also
energy converted
to sound
produced, tobut
theenergy.
amount of kinetic
compared
heat
energy
soundcaris using
small
If youconverted
had an to
electric
compared
to
heat
energy.
batteries, you could brake the car by
If you had
electric
car inusing
converting
the an
electric
motor
to a
batteries, you
brake
car by
generator.
Thiscould
could
be the
done
by
converting the
motor into
switching
the electric
connections.
Thea
generator.
could
be done
by
motion of This
the car
would
turn the
switching putting
the connections.
generator,
electric energy The
into
motion
of the
the
the
batteries.
Thecarcarwould
would turn
s low begenerator,
putting
electric
energy
into
cause power- kinetic energy in this
the batteries.
The
car would
slowelecbegenerator.
Some
case
- turns the
cause
this
tric carspower-kinetic
maintain their energy
battery in
charge
case-turns
generator.
Somecalled
elecby using thistheform
of braking
tric
cars
maintain
their
battery
charge
regenerative braking.
byItusing
of braking
wouldthis
be form
wonderful
if fuel called
could
regeneralive
braking.
be
put in the
gas tank by hitting the
It would
be 'twonderful
fuelallcould
brakes.
It can
, however,if so
that
be
put
in
the
gas
tank
by
hitting
the
kinetic energy is lost. On the other
brakes.if Ityou
can't,
so allor that
hand,
drivehowever,
more slowly
ankinetic every
energystop,
is lost.
theuseother
ticipate
you On
could
the
hand,
if
you
drive
more
slowly
anbrakes less and, th us , conserveorfuel.
ticipate
every
stop,
you
could
use
the
Try this while driving to work. The
brakes
less and,
conserve
fuel.
fuel
energy
used thus,
to move
the car
is
Try in
thisheat
while
driving
work.
lost
energy
eachtotime
youThe
hit
fuel energy used to move the car is
lost in heat energy each time you hit
the brakes. By minimizing braking ,
you increase mileage.
theIf brakes.
By the
minimizing
braking,
you slow
car without
using
you
mileage.
the increase
brakes, the
kinetic energy can be
If you into
slow two
the different
car without
using
changed
forms.
If
the
brakes,
the
kinetic
energy
can
be
you are driving on a flat road and take
changed
twothrottle,
differenttheforms.
If
your
foot into
off the
car will
you
driving
on a flat
road
take
slow.are
Kinetic
energy
is lost
in and
air drag,
your
foot(heat)
off the
throttle,
theand
cardrive
will
friction
in the
engine
slow.
Kinetic
energy
is
lost
in
air
drag,
line, and rolling resistance of the tires.
friction
(heat)
in items
the engine
andkinetic
drive
Because
these
get hot,
line, and rolling
resistance of
the tires.
energy
is converted
into
heat.
Because these
items slowing
get hot, kinetic
However,
because
takes
energy
longer andis theconverted
items beinginto
heatedheat.
are
However,
slowing
takes
much larger,because
drive-line
components
longer
anddon't
the items
area nd tires
reachbeing
the heated
high tem"
much
larger,
drive-line
components
peratures achieved by the brakes. But,
and
tires isdon't
the heat
therereach
. Put the
yourhigh
handtemon
peratures
by run
the on
brakes.
But,
your
tires achieved
after a fast
the highthe heat
is there.
Put feel
your
hand the
on
way
and see
how they
. Touch
your
tires
after
a
fast
run
on
the
highrear-axle housing and the transway
and. see
how they
feel.
Touch
mission
A portion
of the
power
of the
the
rear-axle
and the
transengine washousing
lost supplying
the energy
mission.
A portion
to heat those
parts. of the power of the
engine
was
lost
The other waysupplying
yo u can the
slowenergy
a car
to
heat
those
parts.
without the brakes is by coasting up a
The
other
way you
can toslow
car
hill.
The
car loses
energy
draga the
without
the
brakes
is
by
coasting
up
same as on a fl at road , but it slowsa
hill. TheThe
car kinetic
loses energy
drag the
quicker.
energyto
is convertsame
as
on
a
flat
road,
but
ed into potential energy as ittheslows
car
quicker.the
The
kinetic energy is convertclimbs
hill.
as another
the car
edPotential
into potetltiol
energyetiel,gy
is just
climbs
the
hill.
form of stored mechanical energy. It
Potential when
energy
is justis raised
another
a weight
to
is increased
of stored
greater
height.mechanical
As the carenergy.
climbs Ita
aform
is increased
a weight
is raised
to
hill,
some ofwhen
its kinetic
energy
is conaverted
greater
height.
As
the
car
climbs
to potential energy. This pote n-a
hill, energy
some ofcan
its be
kinetic
energy
is contial
changed
back
into
verted
potential
energy.
kine
tic to
energy
by all
ow in gThis
the potencar to
tial energy
back
coast
down can
the be
hillchanged
with the
e nginto
ine
kinetic
energy
by
allowing
the
car of
to
shut off. The speed at the bottom
coasthilldown
hill than
with the
the original
engine
the
will the
be less
shut off. The speed at the bottom of
the hill will be less than the original
Car parked at top of hill has zero kinetic
energy. However, its position at top of the
hill gives
it potential
Car
parked
at top ofenergy"
hill hasThis
zeropotential
kinetic
energy is
changeditsinto
kinetic
as
energy.
However,
position
at energy
top of the
car gives
coastsit down
hill. energy. This potential
hill
potential
energy is changed into kinetic energy as
car coasts down hill.
After coasting half way down the hill, car
has lost half of its potential energy, but has
gainedcoasting
kinetic half
energy.
energy
inAfter
way Kinetic
down the
hill, car
creases
as car
increases.
has
lost half
of speed
its potential
energy, but has
gained kinetic energy. Kinetic energy increases as car speed increases.
All potential energy of coasting car is converted into kinetic energy at bottom of the
hill
where carenergy
reaches
speed
and
All potential
of maximum
coasting car
is conkinetic
verted energy.
into kinetic energy at bottom of the
hill where car reaches maximum speed and
speed
kinetic when
energy.you began to coast up the
hill because some energy is lost in fricspeed
when
yougoing
beganuptothe
coast
the
tion and
drag
hill,upplus
hill energy
becauselost
some
energy
losthill.
in fricthe
going
downisthe
tion and drag going up the hill, plus
the energy lost going down the hill. 9
Tempera ture
(OF)
Rubbing Surface
Temperature
(" F)
Brakes Re leased
/
Temper
at ure of
Brakes
Released
Rubbing Surface
of Drum or Rotor
Temperature
of
Rubbing Surface
Interior of Rotor _
Materi al
Interior of Rotor
Material
,/
'\..
"
Te mpe rature of
I nterior of
Drum or Rotorof
Temperature
Mater ia of
l
Interior
In te rior
of Drum
Material
Interior
~
Cross
Section
of Drum
Drum or Rotor
T s L---__~-------------------------Time
of
Stop
Rotor
Cross
Section
Rotor
%
Rubbing
Surface
Drum
Cross
Section
Drum
Cross
T m = Maximum temper ature reached at r ubbing surface .
Section
T a = Average temperature after stop.
temperatur
e before
stop.at rubbing surface.
T, s == Starting
Maximum
temperature
reached
T, = Average temperature after stop.
T, = Starting temperature before stop.
During a stop, brake rubbing-surface temperature increases more rapidly than interior temperature of a drum or rotor. Eventually, temperatures equalize after brake is released . Aver-I
age
brake
temperature
occurs at a point
betweenincreases
rubbing - more
surface
and than
interior
temperaDuring
a stop,
brake rubbing-surface
temperature
rapidly
interior
temtures
before
place. temperatures equalize after brake is released. Averperature
of amuch
drum cooling
or rotor.takes
Eventually,
age brake temperature occurs at a point between rubbing-surface and interior temperatures
before much
cooling
place. in
a brake. The problem is that heat is
Potential
energy
is takes
measured
units of foot-pounds (ft-Ib). PotentialPotential
energy
measured
in
e nergy
change
equalsis the
weight of
units
of foot-pounds
by the Potentialchange in
the object
mUltiplied (ft-lb).
energy
equals
thecoasts
weightup ofa
height. change
If a 3000-1
b car
the
objectghmultiplied
by the
change
in
100-ft-hi
hill , it gains
300,000
ft-lb
height.
If a energy.
3000-lbIf al
car
coasts
up isa
l this
energy
of potential
100-ft-high back
hill, itinto
gains
300,000
ft-lb
converted
kinetic
energy,
of
potential
energy.
If
all
this
energy
is
the speed of the car can be calc ul ated
converted
back into
kinetic
8. Byenergy,
changfrom the formula
on page
the
of the carusing
can bealgebra,
calculatedit
ing speed
the formula
from
the
formula
on
page
8.
By changcomes out as follows:
ing the formula using algebra, it
comes outf29.9E:
as
follows:
Speed
~---p
in miles per hour
We
(mph)
in miles per hour
Ep = Potential energy of car in
foot-pounds (ft-Ib)
Ep =
of car in (Ib)
We
= Potential
Weight ofenergy
car in pounds
foot-pounds (ft-lb)
W,
Weight
of le
car
Fo r=our
examp
, in pounds (Ib)
,.,.."..~";"-~.....,.....,...-,.Speed
(29.9)(300 ,000) = 55
h
For our=example.
3000
mp .
Speed
=
is much faster th an
Obviously,
this3000
would happen if you tri ed it with a real
this is much
faster than
car.Obviously,
The difference
between
this
would
happen
if
you
tried
it
sample problem and a real with
test isa real
the
car. The
difference
this
and friction.
kinetic
energy
lost in dragbetween
samplehot
problem
and aget
realduring
test is one
the
do brakes
How
kinetic
energy
lost
in
drag
and
friction.
stop? -Because the brake-rubbing
How hotaredoheated
brakes
get during
it is one
imsurfaces
by friction,
stop? -Because
the thebrake-rubbing
portant
to know what
temperature
surfaces
are stop
heated
friction,
it istemimsurface
is after one
. P.byhigh
portant
to
know
what
the
temperature
perature can cause fade or damage to
is after one stop. P. high surface temperature can cause fade or damage to
10
=y
constantly being transferred from the
afriction
brake.surface
The problem
is that
heat to
is
of the drum
or rotor
constantly
being
transferred
from
the
air and cooler interior metal. This
friction
surface
of surface
the drumtemperature
or rotor to
makes the
exact
air
and to
cooler
interior
metal. This
calculate.
However,
it is
difficult
makes
exact
surface
temperature
ate the
average
temperaeasy
to the
calcul
difficult
calculate.
it is
ture of a to
drum
or rotor However,
after one stop'.
easy
to
calculate
the
average
temperaThe difference between surface temture
of a and
drum
orrage
rotor
after one stop.
perature
ave
temperature
of a
The
between
surface temn above.
drumdifference
or rotor is show
perature
and average
temperature
of a
In calculating
the average
temperadrum
or
rotor
is
shown
above.
tu re of a drum or rotor, you must
In calculating
theptions.
average
temperamake
so me ass um
This
makes
ture caoflcualatidrum
or rotor,
youanswer
must
on easier
and the
the
make
some
assumptions.
This
makes
more accurate. Tests have shown that
the fo
calculation
easier and are
thevalid:
answer
llowing assumptions
the
more
accurate.
haveenergy
shownfrom
that
• Assume
that Tests
all heat
the
following
assumptions
are
valid:
the stop fl ows into the drum or rotor.
heatteenergy
from
is anall
accura
assum ption
In Assume
fact this that
the
stop
flows
into
the
drum
or
rotor.
because th e frict ion material insulates
In
is an
accurate
assumption
thefact
rest this
of the
brake
from heat
and the
because
the
friction
material
insulates
metal drum or rotor is a very
good
the
of the brake from heat and the
heatrest
conductor.
metal
drumdrag
or rotor
is car
a very
• Assume
on the
fromgood
all
heat conductor.
sources
is zero, including the effects
on the
car fromand
all
of Assume
air drag,drag
rolling
resistance
sourcesbraking.
is zero,This
including
theassumpeffects
is a good
engine
of
rolling100resistance
and
mph because
tionair
for drag,
stops below
engine
braking.
This
is
a
good
assumpair drag is small compared to braking
tion for stops below 100 mph because
forces.
air
drag is kinetic
small compared
braking
in
• Ignore
energy to
stored
forces.
rotating parts of the car. This assumpIgnore
kinetic
energyof stored
in
tion
and the
assumption
zero drag
rotating parts of the car. This assumption and the assumption of zero drag
The heavier a drum or rotor, the lower its
temperature rise during a single stop. Designed
for a a3000-lb
car lower
powered
The
heavier
drum or sports
rotor, the
its
by a 300-HP
large
temperature
rise engine,
during a this
single
stop.drum
Deweighs for
22 lb.
signed
a 3000-lb sports car powered
by a 3 0 0 - H P engine, this large drum
weighs 2 2 Ib.
cause errors in opposi te directions.
Thus, the error in the brakecause
errorscalculation
in opposite
directions.
is sma
ll.
temperature
Thus,
error ofinbrakes
the during
brake• Ignorethecooling
temperature
calculation
is
small.
stop. Heat flo w into rotor or drum
Ignore iscooling
of brakes
during
to coo
ling
material
rapid compared
stop.
time. Heat flow into rotor or drum
material
is step
rapidiscompared
cooling
The first
to calculatetothe
temtime.
perature change of the drum or rotor.
Theincrease
first step
to calculate isthe
temin istemperature
known
Any
perature
change
of the
drum or rotor.
ture rise.
Temperatures
are
as tempera
Any increase
in temperature
is known
to
energy
by
always
related
as tetnperature
Temperatures
change
-not byrise.
the absolute
valuesare
of
always or related
to . It energy
byt
is importan
energy
temperature
change-not
by the
values
of
to think of this
as aabsolute
change in
energy
energy or
temperature.
It is important
in temperature.
Temcausing
a change
change
inused
energy
to think
of this
as abrake
in the
is ca
by
perat
ure rise
causing
a
change
in
temperature.
a kinetic-energy reduction inTemthe
peraturecar.
rise in the brake is caused by
moving
a For
kinetic-energy
in the
a particular reduction
stop, figure
the
moving
car.
change in kinetic energy using th e
For a onparticular
stop,results
figurein the
the
formula
page 8. This
change
kinetic energy using the
followinginrelationship:
formula on page 8. This results in the
=
Kinetic
energy change in footKe
following
relationship:
pounds = Ks - KAin foot-pounds
K c == Kinetic
Kinetic energy
energybefore
change
footKs
the instop
in
K, - K, in foot-pounds
pounds =
foot-pou
nds
K, =
the stop
stop in
in
KA
= Kinetic
Kinetic energy
energy before
after the
foot-pounds
foot-pou
nds
K, = Kinetic energy after the stop in
Obviously, if the car comes to a
foot-pounds
complete halt , KA is zero . The change
if the
car comes
in Obviously,
kinetic energy
is used
to comptoutea
A is of
zero.
change
complete
halt, K rise
the temperature
theThe
brake.
For
in kinetic
used use
to compute
the
weight energy
of the is
brake,
only the
the temperature
rise of and/
the brake.
For
weight
of the drums
or rotors.
the
weight
of
the
brake,
use
only
the
The temperature rise must be added
weight
of the drums
and/or
of the
brake rotors.
before
to
the temperature
The
rise must
the temperature
stop to obtain
finabe
l added
brake
to
the
temperature
of
the
brake
before
temperature .
the stop to obtain final brake
temperature.
The temperature rise of the brakes
is calculated as follows:
The temperature rise of the brakes
is
calculated
as follows:Kc
Temperature rise = - - 77.8
KcW B
Temperature
rise = (F)
in degrees Fahrenheit
77.8the
W, rotors and
W B = Weight of all
in degrees
Fahrenheit (F)
drums
in pounds
W, = Weight of all the rotors and
For inexample,
drums
pounds let 's compare the
temperature rise in the brakes of a
For example,
let's compare
the
3500-lb
sedan stopping
from 60 mph
temperature
rise in rise
the of
brakes
of a
to the temperature
a 3500-lb
3500-lb sedan
stopping
fromfrom
60 rnph
stock-car's
brakes
slowing
120
to
the
temperature
rise
of
a
3500-lb
mph to 60 mph.
stock-car's
from 120
First let'sbrakes
figure slowing
the temperature
rnph
to 60
rise for
themph.
sedan. Assume the brakes
First 5let's
figure forthea temperature
weigh
Ib each,
total brake
rise
for
the
sedan.
Assume the
the change
brakes
weight of 20 lb. Calculate
weigh
5
Ib
each,
for
a
total
brake
in kinetic energy slowing from
60
weight
20 From
Ib. Calculate
mph to of
stop.
page 8, the
the change
kinetic
in kinetic
energy car
slowing
from 60
energy
of a moving
is:
rnph to stop. From
page
8,
the
kinetic
W S2
KinetiC
energy
= _ ccar
_ is:
energy of
a moving
29.9
W,S2
- at 60 mph:
Kinetic
energy
For our
sedan= traveling
29.9
KB = (3500 Ib)(60 mph)2/29.9
For
our sedan traveling at 60 mph:
= 421,000 ft-Ib .
K
,
=
(3500
1nph)~/29.9
KB = Kineticlb)(60
energy
before stop
= 421,000 ft-lb.
Kinetic
energy
after
thestop
stop = 0,
K, = Kinetic energy before
because car now has zero speed.
Kineticin energy
the =stop
= 0,
Change
kinetic after
energy
421,000
because
car
now
has
zero
speed.
ft-Ib. From the above formula temChange
perature in
risekinetic
of the energy
brakes is:= 421,000
ft-lb. From the
above formula tem.
_ (421,000 ft-Ib)
perature rise rise
of the
is: Ib)
Temperature
- brakes
(77.8)(20
Tires on this car have reached their maximum coefficient of friction. Although a car stops
faster if the wheels are not locked, most drivers hit the brakes too hard during a panic stop.
This
being
at Goodyear's
San Angelo,
Texas,
test track,
is to see
howstops
tires
Tirestest,
on this
carconducted
have reached
their maximum
coefficient
of friction.
Although
a car
react during
a paniC are
stop.not
Photo
courtesy
Goodyear.
faster
if the wheels
locked,
most drivers
hit the brakes too hard during a panic stop.
This test, being conducted at Goodyear's San Angelo, Texas, test track, is to see how tires
react during a panic stop. Photo courtesy Goodyear.
time, racing on a medium-speed track
with short straights might result in
time, racing
a medium-speed
tracka
higher
brakeon temperatu
res than
with
short
straights
might
result
in
high-speed track with long straights.
higher
brake
temperatures
than
Both temperature rise per stop anda
high-speed
track
long to
straights.
cooling
time
arewith
critical
brake
Both temperature
riseweighing
per stopmore
and
performance.
Rotors
cooling
time
are
critical
to
brake
than 5 Ib would normally be used on a
performance.
weighing rotors
more
3500-lb
race Rotors
car. Heavier
than 5 Ib
normallyrisebeper
used
on a
reduce
thewould
temperature
stop.
3500-lb race car. Heavier rotors
reduce the temperature rise per stop.
DECELERATION
Deceleration is a measure of how
DECELERATION
quickly
a car slows. Deceleration
(77,i)(20
Decele~.a/ion is a measure of how
(421 000 ft-lb)
Temperature rise =
= 270F (132C)
For stock car slowing from 120 to 60
mph, change in kinetic energy is:
For
stock car slowing from 120 to 60
K = (3500 Ib)(1 20 mph)2
mph,
B change
29.9in kinetic energy is:
(3500 IbI(l20
= 1,686,000
ft-IbmphI2
K, =
29.9
K = (3500
Ib)(60 mph)2
A = 1,686,000
29.9 ft-lb
(3500 lb)(60
=
421,000
ft-Ib rnphI2
K, =
29.9
Kc = KB - KA
= 421,000 ft-lb
Kc = (1,686,000) - (421,000)
Kc = 1,265,000 ft-Ib.
KA
energy
K, == Kinetic
1,265,000
ft-lb.after stop
KB = Kinetic energy before stop
energy after
stop
K, =
Kc
= Kinetic
Kinetic-energy
change
K, Notice
= Kinetic energy before stop
how much greater this
change
Kc = Kinetic-energy
change
in kinetic energy
is compared
howEven
much
greater
this
to Notice
the sedan.
though
the speed
change
in was
kinetic
is compared
reduction
the energy
same 60
mph, the
to the reduction
sedan. Even
thoughatthe
speed
speed
occurring
a higher
reduction
was
the
same
60
mph,
the
initial speed resulted in much greater
speed reduction
occurring
a higher
energy
put into the
brakes at
. The
teminitial speed
in much
perature
rise resulted
for the stock
car greater
in the
energy
put
into
the
brakes.
The temrace is:
perature rise for the stock car in the
Temperature rise =
(1,265,000 ftrace
is:
Ib)/(77.8)(20Ib) = 813F (434C).
Temperature
rise = of
(1,265,000
ftHowever, because
less cooling
lb)/(77.8)(20Ib) = 81 3F (434C).
However, because of less cooling
means slowing the car-acceleration
quickly
a car itslows.
Deceleration
means speeding
up.
means
the car-acceleration
Both slowing
acceleration
and deceleration
means
speedinginit units
up. of gravity-g's.
are measured
Both
acceleration
and deceleration
One g is the force exerted
by an object
are
in units
gravity-g's.
due measured
to gravity
at ofthe
Earth ' s
One g is the
exerted
by anweighs
object
surfacehowforce
much
an object
due
to
gravity
at
the
Earth's
while at rest. One g is also a measure
surface-how
object weighs
of
accelerationmuch
or an
deceleration
- 22
while
at rest.
One Zero
g is also
a measure
mph per
second.
g occurs
in a
of acceleration
or deceleration-22
weightless
environment.
Acceleration
rnph
per second.
Zero isg negative.
occurs in a
is positive;
deceleration
weightless
environment.
Acceleration
Once the brakes are applied, a car is
is positive;
negative.
stopped
by deceleration
the friction is
force
between
the brakes
are applied,
a car is
theOnce
tires
and the
road. During
stopped
by
the
friction
force
between
braking, friction acts on the tires in a
the tiresopposite
and the
road. During
direction
to movement.
The
braking,the
friction
acts on the
in a
higher
deceleration,
thetires
greater
direction
opposite
to movement.
The
this friction
force becomes
. Maximum
higher the
deceleration,
the greater
possible
deceleration
occurs
at the
this
friction
force
becomes.
Maximum
maximum coefficient of /riction
bepossible
occursThis
at hapthe
tween
the deceleration
tires and the road.
maximum
fiiction
bepens just as coeflicient
the tires areofabout
to skid.
tween
the
tires
and
the
road.
This
hapOnce tires lose traction and skid,
pens just as the
tires are
about
deceleration
drops.
Read
on to
forskid.
an
Once tires of
losecoefficient
traction ofand
skid,
explanation
friction,
deceleration
drops.
Read on for an
or
si mply friction
coefftcient.
explanation of coefficient of friction,
or simply ,f,.ictiot7 coeJficient.
INERTIA FORCES
More than 200 years ago, Sir Isaac
INERTIA
FORCES
Newton
wrote
the basic law relating a
More
200 years
Sir Isaac
force
on than
an object
to itsago,
acceleration.
Newton
wrote Newton's
the basic Law
law relating
a
Simply stated,
is:
force on an object to its acceleration.
Acceleration of an object = ~ in g's
Simply stated, Newton's Law is:
F
of an object
in g's in
Acceleration
force =
on object
F = Unbalanced
pounds
F == Weight
Unbalanced
force
on object in
W
of object
in pounds
pounds
In this formula, the force F causes
W = Weight of object in pounds
acceleration. If a car weighing 3000 Ib
formula,
causes
hasIna this
braking
forcethe
of force
-1500F lb,
the
acceleration.
weighing
3000 Ib
Ib
stopping
forceIf isa car
-1500
Ib -7- 3000
has
a
braking
force
of
1500
Ib,
the
= -0.5 g.
stopping
force pushes
is - 1500
+ 3000 to
Ib
If the force
in aIbdirection
= -0.5theg.object to speed up , the force
cause
the force
in a direction
to
is If
positive
andpushes
acceleration
is a posicause
the
object
to
speed
up,
the
force
tive number. If the force causes the
is positive
and acceleration
a posiobject
to slow,
the force is isnegative
tive
number. If the
force causes
the
and acceleration
is negative.
We call
object
to
slow,
the
force
is
negative
the negative acceleration deceleration .
and
acceleration
is negative.
We call
The
force referred
to in Newton's
the
acceleration
Lawnegative
is unbalanced
force. decele~.arion.
That means
Theforce
forceis referred
to inby Newton's
if the
not resisted
opposing
unbalanced
force.
That
means
Law
is
force, the object is free to
move,
or
if
the
force
is
not
resisted
by
opposing
accelerate. If I push on a tree with a
force,
freewill
to not
move,
or
force ofthe
100object
Ib, theistree
move.
accelerate.
I push
on a tree
with
The
100-lb If
force
is resisted
by the
treea
force
100a Ib,
the tree
will so
notthere
move.
roots of
with
100-lb
force,
is
The
100-lb
force
is
resisted
by
the
no unbalanced force on the tree.tree
To
roots with
a 100-lb either
force, positive
so there or
is
cause
acceleration,
no unbalanced
force
tree.
To
negative,
the force
on on
the the
object
must
cause
acceleration, either positive or
be unbalanced.
negative,
the force on
the object
must
To understand
how
unbalanced
be unbalanced.
forces
work on a car, assume you are
To understand
how strip.
unbalanced
driving
a car on a drag
At the
forces
work
on
a
car,
assume
youpush
are
start, you let out the clutch and
drivingona the
car accelerator,
on a drag strip.
At fricthe
down
and the
start,
you let
out thetheclutch
tion force
between
tires and
and push
road
down
on
the
accelerator,
and
thestart,
fricpushes the car forward . At the
tion force between the tires and road
pushes the car forward. At the start,
11
air drag is zero, so the forward force is
not resisted by anything but drive-line
friction and tire drag, or rolling
resistance. The forward force is
almost unbalanced. Consequently, acstart.
celeration is maximum at the start.
As the car gains speed, air drag
increases. It opposes the forward force
on the tires that is trying to accelerate
the car. The unbalanced force is the
forward force minus the rearward
force. As speed increases, the unbalanced force becomes smaller because
of air drag. Consequently, acceleration
also gets smaller.
Near the end of the drag strip, the
car is moving so fast that the air-drag
force approaches the forward force of
the tires against the road. Assuming
engine rpm and track length aren't
limiting factors,
factors, speed will increase
until no force unbalance exists and acceleration becomes zero. The car has
reached its maximum speed. The only
way to accelerate the car to a higher
speed would be to increase the forward
force (more engine power), or reduce
(Jess air drag).
the rearward force (less
drag).
Every race-car designer knows that
more power or less drag will increase
car speed.
speed.
In addition to the basic relationship
between force
force and acceleration,
Newton came up with other important
laws of
of nature.
nature. He
t l e discovered that
every moving object has inertia. That
is, an object always
always moves at the same
same
speed and in the same
same direction until
acted on by an unbalanced force.
force. Inertia is
is what keeps the Earth moving
around the Sun and keeps satellites in
orbit.
orbit. There is no air drag in outer
space,
space, so
so once an
an object is
is at speed, it
keeps moving forever.
forever. Only a force
force
can change its speed or direction.
direction.
A car also acts
acts according to Newton's laws.
laws. Once
Once it is moving, a car
wants to continue in a straight line
line at
the
the same
same speed.
speed. Every part of the
the car
and its passengers also want to keep
moving.
moving. When the brakes are applied,
applied,
a force
force is
is applied to
to the
the car by the
tires, causing deceleration.
deceleration.
Because
Because passengers
passengers tend to
to continue at the
the same
same speed,
speed, they will
will
move forward
forward in
in the seat
seat and strike
strike
the
the instrument panel unless held by
restraint devices,
devices, legs or friction
friction
against the
the seat.
seat. This
This forward
forward force
force
that tends
tends to
to "throw"
"throw" a passenger forforward during
during braking is
is called
called inertia
force.
,force. Inertia force
force acts
acts on
on everything
in
in aa car as
as its
its speed
speed changes.
changes.
12
--
. . Inertia Force
Friction Forces
ForCes on Tires
Friction
-
-
Tire friction forces are external forces that cause deceleration.
deceleration. The road
road pushes
pushes on the
opposite direction
direction of motion.
tires in
in the opposite
motion. Inertia
lnertia force of the car acts in the same direction
as motion
equals friction
friction force.
force.
motion and equals
Therefore, if a car accelerates, the
inertia force acts toward the rear; if it
decelerates, the inertia force acts
forward.
forward.
Inertia force in g's is equal to car's
car's
acceleration or deceleration.
deceleration. Inertia
forces are easy to calculate in pounds
if you know the acceleration.
acceleration.
W
object in
W == Weight of the
theobject
in pounds
a=
= Acceleration of the object in
in g's
Inertia force is measured in pounds. If
the car is decelerating,
decelerating, the inertia
force is negative-it
negative-it acts in a forward
direction.
direction.
Try visualizing
visualizing what happens when
a car decelerates.
decelerates. It is easier to visualize the forces if you imagine a driver
trying to stop
stop so
so quickly that he locks
the wheels.
wheels. Imagine a car skidding
with all
all four wheels locked and smoke
smoke
pouring off the
the tires.
tires. Assume the
the car
weighs 3000 lb
Ib and the coefficient of
friction
friction between the tires and road is
is
0.7. The
The friction
friction force
force on all
all four tires
0.7.
is:
is:
Friction
p FN
FN
Friction force == f.L
p =
= Coefficient
Coefficient of friction
friction between
between two
f.L
Inertia
lnertia forces
forces act on
on every
every part of a car.
car.
This passenger resists
resists inertia
inertia force on
on his
his
This
body with his
his arms
arms against the
the dash,
dash, feet
body
against the floor,
floor, and
and seat belt around
around his
his
against
waist.
waist. Inertia
lnertia force
force on
on his
his hat is
is not
not resisted by
by anything,
anything, so
so it
it flies
flies forward
forward into
into the
ed
windshield.
windshield.
Acceleration of car == F
F/Wc
IW c
F == Unbalanced
Unbalanced force
forceon
in pounds
~ounds
F
on car in
We
Wc == Weight of car in
in pounds
pounds
Acceleration of
of car
Acceleration
Ib) == -0.7
-0.7 g.
g.
Ib)
=
=
00 Ib)/(3000
lb)/(3000
(-2100
Friction
Friction force
force =
= (0.7)(3000
(0.7)(3000 Ib)
Ib) =
= 2100
lb.
Ib.
The unbalanced force
force has a minus
minus
The
sign because it acts
acts in
in a direction
direction
sign
car. Remember:
Remember: Negaopposite to the car.
tive acceleration means deceleration;
deceleration;
tive
car to
to slow.
slow.
itit causes the car
deceleration is
is 0.7
0.7 g,
E., every
everv
Because deceleration
part of the car has an inertia force
force on it
g. The inertia force
force on a 200-lb
of 0.7 g.
passenger is:
is:
passenger
This
This friction
friction force
force on the
the tires tries
tries to
to
decelerate
decelerate the
the car.
car. The
The deceleration
deceleration is
is
easy to calculate
calculate from
from Newton's law,
law,
easy
page 11:
11:
Inertia
lnertia force
force == Wa
Wa
w == Weight
Weight of
of the
the passenger
passenger in
in
W
pounds
pounds
Acceleration of the
the passenger
passenger in
in
aa == Acceleration
g's
g's
sliding surfaces
sliding
FN
F, == Force
Force pushing
pushing the
the two surfaces
together in
nds
in pou
pounds
In this
this example,
example,
p == 0.7
0.7 and
and FN
FN== 3000lb
3000 Ib
f.L
-
- - -
~
~-~
If there were some way to support a car at
its center of gravity (CG), it would be
balanced.
Rotate
the tocar
to another
If there were
some way
support
a car at
position,
as on a (CG),
side, and
it would
its centersuch
of gravity
i t would
be
remain
balanced.
CGcar
is the
supbalanced.
RotateThe
the
to only
another
port pointsuch
where
exists
regardless
position,
asbalance
on a side,
and
it would
of
position.
remain
balanced. The CG is the only sup-
port point where balance exists regardless
of position.
I nertia force = (200 Ib) (-0. 7 g)
=-140Ib.
Inertia force = (200 Ib)(-0.7g)
The minus =
sign
the force is
-1 40means
Ib.
forward. If there is little friction beThe
sign means
the seat,
forcethe
is
tweenminus
the passenger
and the
forward.
If
there
is
little
friction
be140-lb inerti a force acts on his seat
tween
belt or the
legs.passenger and the seat, the
140-lb
forcetheacts
his seat
In thisinertia
example,
car on
decelerates
belt
or
legs.
at only 0.7 g. With the wheels locked
In sliding,
this example,
the car decelerates
and
the coefficient
of friction
at
g. With
the wheelspossible
locked
is only
lower0.7
th an
its maximum
and
sliding,
the
coefficient
of
friction
value. Maximum deceleration of a car
is determined
lower than by
itsmany
maximum
lis
factors,possible
includvalue.
Maximum
deceleration
car
aerodynamic
forces,of aroad
ing
tires,
pis
determined
by
many
factors,
includcondition and brake-system design.
ing tires,
forces,
road
Most
cars aerodynamic
on street tires
can reach
condition
and deceleration
brake-system on
design.
about
0.8-g
dry
Most
cars Race
on street
tires
can reach
pavement.
cars can
decelerate
at
about
well over0.8-g
1 g. deceleration on dry
pavement. Race cars can decelerate at
well over 1 g.
WEIGHT TRANSFER
A car's inertia force acts at its center
WEIGHT
TRANSFER
of gravity, or
CG, of the whole cal'. The
forcewhich
acts atthe
its entire
center
CGA iscar's
the inertia
point about
of
graviry,
or
CG,
of
the
whole
car,
car is balanced. If you could hang The
the
CG by
is the
pointattached
about which
car
a cable
a t itsthe
CGentire
, the
car would
is balanced.
you
hang the
car
balanceIf in
anycould
position.
carThe
by aCG
cable
at its
is attached
the center
ofCG,
all the
the
car
would
balance
in
any
position.
weight. All the inertia forces on the inof togethall the
The CG
dividual
partsis ofthe
the center
car added
weight.
inertia
on the
iner are All
the the
same
as forces
a single
inertia
dividual
parts
of
the
car
added
togethforce for the whole car acting at its
er
the same
as a CO
single
inertia
CG.areBecause
a car's
is always
force for
whole
car acting
its
above
thethe
road,
inertia
force at
from
CG.
Because
car'sto CG
braking
always atries
load isthealways
front
above
theliftroad,
inertia
force
from
tires and
the rears
. This
effect
is
brakingweight
always
tries to load the front
transfer.
called
tires
and lift
the rears.
This that
effectthe
is
Weight
transfer
means
called
weightare
transfer.
front tires
loaded more during a
Weight
transfer
means
that the
stop,
and the
rear tires
are unloaded.
front tires are loaded more during a
stop, and the rear tires are unloaded.
A front-wheel-drive car, such as this VW, has majority of weight at front. When brakes are
applied hard, more weight is transferred to the front. The nose drops and tail rises during
braking
due to weightcar,
transfer.
A
front-wheel-drive
such as this VW, has majority of weight at front. When brakes are
applied hard, more weight is transferred to the front. The nose drops and tail rises during
braking due to weight transfer.
t
~I
F, = vertical force on front tires Ob)
F, = vertical force on rear tires (Ib)
Xeg
horizontal
Ff ==vertical
forcedistance
on frontfrom
tiresfront
(Ib) axle to
CG
.)
F, =(in
vertical
force on rear tires (Ib)
I = wheelbase
length
(in.) from front axle to
Xcg
= horizontal
distance
Y
CG height (in.)
CG
(in.)
eg =
(Ib) (in.)
We
Car weight
I = =wheelbase
length
fJ.
==
Coefficient
friction
Ycg
CG heightof(in.)
Wc = Car weight (Ib)
F
,
=
W _F
e
,
+ We fJ.I Y cg
wc P YYCg
I eg
F =WcXCg·_W c fJ.Y
'I
I
wc xc;WC P Ycg
F, = I
I Yea
Weight transfer
= W efJ.
Ff=Wc-F,+-
I
Weight transfer
= Wcfi
Ycq
p. = Coefficient of friction
I
Ignoring
aerodynamic forces, these forces act on a car during hard braking.
Maximum
weight transfer can be calculated if tire coefficient of friction is known.
Ignoring aerodynamic forces, these forces act on a car during hard braking. Maximum
weight transfer can be calculated if tire coefficient of friction is known.
The weight of the whole car does not
change. Weight added to the front
The
of the whole
car rear
doestires
not
tires weight
is subtracted
from the
change.
Weight
added
to
the
front
during weight transfer. The forces
tires is on
subtracted
from the
rear tires
acting
a car during
braking
are
during
transfer. Thedrawing
forces.
shown inweight
the accompanying
acting
on a car
during aerodynambraking are
In this simple
illustration,
shown
in
the
accompanying
drawing.
ic forces are not shown. Aerodynamic
In this simple
aerodynamforces
changeillustration,
the amount
of the
ic
forcesbut
arenot
not the
shown.
forces,
basicAerodynamic
principle of
forces
change the amount of the
weight transfer.
forces,
but weight
not thetransfer
basic principle
of
Because
loads the
weight
transfer.
front tires,
additional friction force
weight transfer
loads tires
the
canBecause
be developed
by the front
front tires, additional friction force
can be developed by the front tires
before they skid. To produce this
extra friction force, front brakes have
before
skid.
produce
to
work they
harder
thanToif there
was this
no
extra
force,
front
brakes
weightfriction
transfer.
At the
same
time,have
the
to
hardercan
than do
if there
no
rearwork
brakes
less was
work.
weight
transfer.
At
the
same
time,
the
Typically, front brakes supply about
rear
brakes
less force
work.
two-thirds
of thecan
totaldo
braking
in
Typically,
front
about
Thebrakes
ratio issupply
even higher
a hard stop.
two-thirds
of the total
braking car.
forceBein
on
an extremely
nose-heavy
acause
hard the
stop.
T
h
e
ratio
is
even
higher
front brakes do most of the
on an they
extremely
car. rear
Bework,
need tonose-heavy
be larger than
cause
front
brakes
most higher
of the
brakes.the
The
forces
are do
usually
work,
they
need to
larger
than
rear
on front
brakes,
so be
they
must
absorb
brakes.
The
forces
are
usually
higher
more heat energy.
on front brakes, so they must absorb
more heat energy.
13
BRAKE FADE
Brake fade is loss of braking due
to overheating. It can cause lo'nger
pedal travel as the brakes get
hotter-maybe to the paint where
the pedal goes to the floor. Pedal
effort may also increase as heat
bu'ilds up, even to the point where
pushing with maximum force won't
lock the wheels! Many times, fade
causes a combination of both
longer pedal travel and increased
pedal effort.
Whatever fade is, the driver is
faced with a panic situation. Brake
fade typically occurs at the worst
posSible moment-going down a
long hill pulling a trailer, at the end
of a long race, or during a panic
stop from freeway speed in heavy
traffic. This is when you need your
brakes the most. Consequently,
brake fade is always scary, and
often dangerous.
Geoff Brabham is at the traction limit of his Toyota Celica in this turn. Combination of braking and cornering forces causes tires to slip and pOint at extreme angles to the direction of
travel.
When carisisatat
tractionlimit
limit,
attempt
to corner,
or brakeofharder
Geoff Brabham
theitstraction
of any
his Toyota
Celica
in thisaccelerate
turn. Combination
brakwill
throw
it into a forces
skid. causes tires to slip and point at extreme angles to the direction of
ing and
cornering
travel. When car is at its traction limit, any attempt to corner, accelerate or brake harder
will throw it into a skid.
BRAKING LIMITS
With a modern brake system, how
BRAKING
LIMITS
good
can brakes
be? What determines
a modern
brakeperformance?
system, how
theWith
limits
to brake
good
can
brakes
be?
What
determines
What makes your car stop
quicker
the
limits
than the
nextto
car,brake
or vice performance?
versa?
What
quicker
Theremakes
are your
limits car
thatstop
determine
than
the
next
car,
or
vice
versa?
how quick a car can stop. Some of
There
arecanlimits
that determine
these
limits
be altered
by design
how
quick
a
car
can
Somelaws
of
or maintenance, so onlystop.
the basic
these
limits
cana car
be ' altered
by ability.
design
of
nature
limit
s stopping
or
maintenance, so only
Brake-performance
limitsthe
are:basic laws
of l.nature
limit
a
car's
stopping
ability.
Force
Brake-performance
limits are:
2. Deflection
1. Wear
Force
3.
2.
Deflection
4. Temperature
3.
Wear
5. Tire traction
4. Temperature
5.
A Tire
braketraction
system should be designed
and maintained so that tire traction
A brake system
should your
be designed
determines
how quickly
car can
and maintained
so other
that tire
stop.
If any of the
fourtraction
limits
determines
howstopping
quickly quicker,
your caryour
can
keep you from
stop.
any
the other four limits
brakesIfare
notofadequate.
keep
you from
your
Force
limit stopping
means quicker,
the driver
brakes
are
not
adequate.
pushes as hard as possible with his
Force
means
foot
and limit
the car
can't the
stopdriver
any
pushes as
possible
with
his
quicker.
In hard
otheraswords,
if the
driver
foot
carthecan't
stop stop
any
could and
push the
harder,
car would
quicker. This
In other
the driver
quicker.
limitwords,
can beif altered
by
could push harder, the car would stop
quicker. This limit can be altered by
14
reducing master-cylinder size, putting
on different lining, using power-assist
reducing
size,I putting
brakes, ormaster-cylinder
other methods.
discuss
on
different
lining,
using
power-assist
how to reduce the force a driver
has to
brakes,later
or inother
methods.
I discuss
exert
the book.
In some
cases,
to reduce
the force
a driver
has to
ahow
force
limit occurs
when
the brakes
exert
later
in
the
book.
In
some
get hot . This is called brake fade.cases,
The
a force limit
occurs
when the
answer
here is
dissipating
heat.brakes
Perget
brake fade.
The
hapshot.
theThis
forceis called
limit you've
encounanswer
is dissipating
heat. limit.
Pertered is here
really
a temperature
haps to
the
forceexcess
limit heat
you've
encounHow
handle
is discussed
tered
is
really
a
temperature
limit.
in Chapters 10 and 12.
How
to handlelimit
excess
is discussed
Deflection
is heat
reached
as the
in Chapters
andat12.
brake
pedal 10
stops
the floor or stop.
Deflection
limit
is reached
as the
This means the pedal
is moving
too
brake
pedal
stops
at
the
floor
or
stop.
far to get maximum efficiency from
This
means Athedeflection
pedal is limit
moving
the brakes.
can too
be
far to get maximum
efficiency
from
eliminated
by design changes
such
as
deflection limit
can be
the brakes.theA pedal-support
stiffening
structure,
eliminated
design changessize,
such inas
increasing by
master-cylinder
stiffeningstiffer
the pedal-support
stalling
brake hoses , structure,
changing
increasing
master-cylinder
size,
into stiffer calipers,
or other
modistalling
stiffer
brake
hoses,
changing
fications. Maintenance can eliminate
stiffer calipers,
other
modiato deflection
limit if or
air is
trapped
in
fications.
Maintenance can eliminate
the brake lines.
a deflection
limit
if airhappen
is trapped
in
Wear limit
won't
when
the
brake
lines.
brakes are new. However, if friction
Wear limit
happen it when
material
is wornwon't
excessively,
may
brakes
friction
be
wornare
outnew.
just However,
when you ifneed
the
material
is worn excessively,
it may
brakes most-such
as at the end
of a
be worn out just when you need the
brakes most-such as a t the end of a
long race. Wear limits can be eliminated or reduced by changing linings,
long
Wear
limitsorcanbybedissipating
eliminatusingrace.
larger
brakes,
ed
reduced
changing inlinings,
heat.orBrake
wear by
is discussed
Chapusing
larger
ters 4 and
12. brakes, or by dissipating
heat.
Brake wearlimit:
is discussed
ChapTemperature
Brakesincannot
ters 4 and
absorb
the12.full power of an engine
Temperaturewithout
limit: some
Brakes time
cannot
continuously
to
absorb
the
full
power
of
an
engine
cool. When the temperature limit
is
continuously
without
time
to
reached , you can
reachsome
a force
limit,
cool.
Whenlimit,
the temperature
limit is
deflection
or greatly increase
reached,
you
can
reach
a
force
limit,
the wear at the same time. Other
deflection
limit,
or
greatly
increase
things can happen , too , such as comthe
at theofsame
time. orOther
pletewear
destruction
the brakes
total
things can
too,part.
suchExcessive
as comcollapse
of ahappen,
structural
plete
destruction.
the brakescause
or total
temperature
is aofcommon
of
collapse
of a structural part. Excessive
brake problems.
temperature
is a Ifcommon
of
Traction limit:
brakes arecause
properbrake
problems.
ly designed and maintained, and don't
If brakes
are propergetTraction
too hot,limit:
the only
stopping
limit is
ly
maintained,
and
don't
tiredesigned
traction.and
If you
try to stop
quicker
get
hot,traction
the onlylimit
stopping
limitthe
is
thantoothe
allows,
tjre
traction.
If
you
try
to
stop
quicker
wheels lock up and the tires skid. The
than
thelimit
traction
limittheallows,
the
traction
is always
limit with
wheelsbrakes,
lock upbut
andit the
The
good
cantires
be skid.
increased
the limit
with
traction
is always
through limit
correct
adjustment
of brake
good
brakes,
but
it
can
be
increased
balance. Adjusting brake balance is
through correct
adjustment
of brake
discussed
in Chapter
10. Modificabrake balance
is
balance.
tions
to Adjusting
allow brake-balance
adjustdiscussed
in
Chapter
10.
Modificament are described in Chapter 12.
tions to allow brake-balance adjustment are described in Chapter 1 2 .
2
DrumBrakes
Drum Brakes
Backing
~~
PI"e~
Hole Covers
~
!;
Wheel Cylinder
Assembly
&(
)
Anchor-Pin Plate
~Secondary
fJ
a ~
Hold-Down
Pin or Rod
Adjusting Lever
Return
Spring
rr;;
r
Cup
Spring
Retainer
Retainer
hoe Hold-Down
Modern drum brake automatically adjusts shoes outward as friction material wears. Drum is not shown. Drawing courtesy Chrysler
Corporation.
Modern drum brake automatically adjusts shoes outward as friction material wears. Drum is not shown. Drawing courtesy Chrysler
Most cars have used internal drum
Corporation.
brakes over the years. They continue
carson
have
to Most
be used
theused
rear internal
of most drum
road
brakes over the years. They continue
cars.
to Even
be used
on thedrum
rear brakes
of most share
road
though
cars.
common features, details may differ.
Even
Each
hasthough
a metaldrum
drum,brakes
usuallyshare
cast
common
iron. Thefeatures,
drum details
rotates may
withdjffer.
the
Each
a metalthedrum,
cast
wheel.has
Within
drumusually
are brake
iron.
The with
drum
rotates
with This
the
shoes lined
friction
material.
wheel.
Within
the
drum
are
brake
material, consisting of various organic
lined with
friction material.
This
shoesmetallic
and
compounds,
is the brake
material,
consisting
of
various
organic
lining. The brake shoes are moved
and metallic
compounds,
is thebybrake
against
the inside
of the drum
pis*The
brake
shoes
are moved
lining.
tons inside the wheel cylinders.
Hyagainst the
of the
drum by
draulic
fluidinside
under
pressure
in pisthe
Hytons inside
the wheel
wheel
cylinders
moves cylinders.
the pistons.
draulic
fluid under
in the
Wheel cylinders
and pressure
brake shoes
are
wheel
cylinders
moves
the
pistons.
mounted on a metal backing plate.
Wheelbacking
cylinders
and isbrake
shoes
are
This
plate
bolted
to the
plate.
mounted
a metal orbacking
car's
axleonhousing
suspension
This
backing plate is bolted to the
upright.
car's axle housing or suspension
upright.
Cable Guide
~
Adjuster cable!
Cable Guide
""
Adjuster-Lever
Spring
I
rgIiUli€l4S---'
Pa ingBrake Strut
" t"
Ad JUS
109
Shoe Hold-down Parts
Nt/~~
u
Pivot
Adjusting Screw
Automatic-Adjuster Parts
Shoe Hold-down Parts
Automatic-Adjuster Parts
Bendix duo-servo rear brake is typical of drum brakes found on American cars. Brake features automatic adjuster and high servo action. Included is linkage to operate shoes from
the
parking-brake
Drawing
courtesy
Bendix
Corp.found on American cars. Brake feaBendix
duo-servo cable.
rear brake
is typical
of drum
brakes
tures automatic adjuster and high servo action. Included is linkage t o operate shoes from
the parking-brake cable. Drawing courtesy Bendix Corp.
15
r
Trailing Shoe
Leading Shoe
Wheei Cylinder
Hydraulic Force
\Trailing
Shoe
Pressurized
Hydraulic
on Leading
Shoe Fluid
r Hvdraulic~Leading
Force
~
Shoe
Friction
Force
on
Friction
Trailing
Force
Shoe
on
Trailing
Shoe
Pivots
Away
From
Drum
Friction
Force on
Leading
Shoe
Trailing
Shoe
-
1//
'Leading
Shoe
Pivots
Toward
Drum
~Friction
Force
on Shoe
~
Drum
Rotation
I
L ~ h o Pivots
e
Single leading-shoe drum brake-sometimes
called a lea dingand-trailing-shoe brake-has one leading and one trailing shoe. As
drum
clockwise,
friction
force on leading
shoea forces
it
Singlerotates
leading-shoe
drum
brake-sometimes
called
leadingagainst
drum, creating
servo one
action,
or force
multiplication.
Drum
and-trailing-shoe
brake-has
leading
and one
trailing shoe.
As
rotation
tends clockwise,
to reduce shoe-to-drum
of trailing
shoe.
drum
rotates
friction forceforce
on leading
shoe
forces it
I
against drum, creating servo action, or force multiplication. Drum
rotation tends to reduce shoe-to-drum force of trailing shoe.
Drum
Shoes in this single leading-shoe
brake both pivot toward the right
Rotation
when acted on by friction forces. Although wheel-cylinder force
keeps
both
the drum,
friction
forces
modify
Shoes in
thisshoes
singleagainst
leading-shoe
brake
both pivot
toward
thepresright
sure
shoe.
Leading-shoe
pressure increases;
when exerted
acted onbybyeach
friction
forces.
Although wheel-cylinder
force
trailing-shoe
pressure
decreases.
is forces
little overall
keeps both shoes
against
the drum,There
friction
modify servo
presaction
with thisbytype
of shoe.
brake, Leading-shoe
as friction-force
effectsincreases;
on shoes
sure exerted
each
pressure
cancel
out each
other. decreases. There is little overall servo
trailing-shoe
pressure
action with this type of brake, as friction-force effects on shoes
cancel out each other.
SERVO ACTION
There are many varIatIOns of
SERVO
ACTION design. Designs
simple drum-brake
There
variations
of
differ in are
the many
amount
of forcesimple
drum-brake
design.
Designs
multiplication, or servo action . Imagine
forcediffer
amount
of brakes
driving in
one the
car with
standard
servo action.
multiplication,
and
another or
equipped
with Imagine
powerdriving
one car
withamount
standardofbrakes
assist brakes
. The
pedal
and
another
equipped
force is greatly reduced with
with powerpowerassist
brakes. Servo
The amount
of much
pedal
assist brakes.
action acts
force
is greatly
reduced
withthepowerlike power
assist-it
reduces
force
assist
brakes.
Servobrake
actionpedal
acts much
required
on the
for a
reducesHowever,
the force
like power
assistof- itbraking.
given
amount
required
on
the
brake
pedal
for a
servo action occurs within the brake
given
itself. amount of braking. However,
servo
action
occurs withinhelp
theunderbrake
Leading
or Trailing-To
itself.
stand servo action, let's look at how
or Trailing-To
under-a
Leading
brake
shoes
are mounted.help
Imagine
stand
look
howa
brake servo
shoe piaction,
voting let's
at one
endatand
brake
shoes
are
mounted.
Imagine
wheel cylinder pushing on the other.a
brake shoe
pivoting
at mount
one enda brake
and a
There
are two
ways to
wheel ascylinder
the other.
shoe,
leading pushing
shoe or ason/railing
shoe.
Theredepends
are two ways
to mount
This
on which
end aofbrake
the
shoe, aspivots
leaditillginshoe
or as trailing
shoe.
shoe
relation
to drum
This
depends
whichdrum
end rotates
of the
rotation
. If theonbrake
shoe
pivots
in relation to end
drum
from the
free (wheel-cylinder)
of
rotation.
If
the
brake
drum
rotates
the shoe toward the pivoted end, it is
from
the free
(wheel-cylinder)
of
a leading
shoe.
If the brake end
drum
the
shoeistoward
the pivot
pivoted
it is
motion
from the
endend,
toward
atheleading
shoe.
If the
brake drum
free end,
the shoe
is trailing.
motion
is
from
the
pivot
end applied
toward
Now let's look at the forces
the
free
end,
the
shoe
is
trailing.
to each type of brake-shoe arNow let's The
look at
the forces
rangement.
friction
forceapplied
on a
to eachshoe
type
arleading
tendsof to brake-shoe
rotate the shoe
rangement.
The
friction
force
on
around its pivot and against the drum.a
leading
shoethe
tends
to rotate
theinshoe
This
assists
wheel
cylinder
ap-
around its pivot and against the drum.
This
assists the wheel cylinder in ap16
Single leading-shoe
found on rear wheels
has
low leading-shoe
servo action,
Single
in bothon
directions.
found
rear wheels
brake is generally
only. Although brake
itbrake
works is
equally
well
generally
only. Although brake
has low servo action, it works equally well
in both directions.
plying the brake shoe. A trailing shoe
is just the opposite-the friction force
plying
shoe.from
A trailing
shoe
moves the
the brake
shoe away
the drum,
is
just
the
opposite-the
friction
force
thus counteracting the force of the
moves
the shoe away from the drum,
wheel cylinder.
thus
counteracting
the drum
forcerotation
of the
With a leading shoe,
wheel
cylinder.
increases
pressure between the shoe
With
a leading
drum rotation
and
drum,
givingshoe,
increased
friction
increases
pressure
between
theaction.
shoe
and braking force. This is servo
and driver
drum, doesn't
giving increased
friction
The
have to push
the
and
force.
Thisa isleading-shoe
servo action.
pedalbraking
as hard
with
The
have the
to push
the
drumdriver
brake.doesn't
It is just
opposite
pedal
as
hard
with
a
leading-shoe
with a trailing-shoe brake. The driver
drum
brake.
It hard.
is just the opposite
has to push
very
with
a trailing-shoe
brake.leading-shoe
The driver
When
car with
has
to
push
very
hard.
brakes on all wheels is backed up, the
a
When a car with leading-shoe
brakes on all wheels is backed up, the
reversed direction of the wheel rotation changes all the leading shoes into
reversed
direction
the wheel
trailing shoes.
The of
driver
noticesrotathis
tiona changes
all the leading
as
huge increase
in pedalshoes
forceinto
retrailing toshoes.
Thecar.
driver
this
quired
stop the
For notices
this reason,
as
a huge
increase
in pedal of
force
redrum
brakes
have a mixture
leading
quired
to stop
the -car.
For
this reason,
and trailing
shoes
two
leading
shoes
drum
a mixture
of leading
leading
on thebrakes
front have
wheels
and one
and
trailing
shoes-two
leading
and one trailing shoe on eachshoes
rear
on the front
wheelssome
and one
leading
wheel.
This gives
amount
of
and one
trailing
shoe
on one
eachsetrear
servo
action
and still
allows
of
wheel. toThis
some shoes
amount
of
shoes
workgives
as leading
when
servo
action
and
still
allows
one
set
of
braking in reverse.
shoes
to work as leading
when
Duo-Servo-Another
typeshoes
of brake,
braking
in reverse.
which differs
from leading- or trailingDuo-Servotype of brake,
shoe types, Another
is the duo-servo
drum
which
differs
from
leadingbrake. Its features are shownorintrailingthe acshoe types, drawing.
is the duo-servo drum
companying
brake.
featuresbrake
are shown
acThe Its
duo-servo
does in
notthe
have
companying
drawing.
a simple pivot on its brake shoes. The
The are
duo-servo
brake
have
shoes
connected
to does
each not
other
at
athe
simple
on its
shoes.
The
end pivot
opposite
thebrake
wheel
cylinder
shoes
are connected
to link
eachtransmits
other at
by a floating
link. This
the
end
opposite
the
wheel
the force and motion of one cylinder
shoe to
by
floating
link.
linkpin
transmits
the aother
shoe.
AnThis
anchor
next to
the
motionkeeps
of one
to
the force
wheeland
cylinder
theshoe
shoes
the
shoe.with
An anchor
pin next
to
fromother
rotating
the brake
drum.
the
wheel
cylinder
keeps
the
shoes
The two shoes are called the primary
from
rotating
with the shoe.
brakeThe
drum.
the secondaty
prishoe and
primary
The
shoes
are called
mary two
shoe
pushes
on thethe
secondary
shoe and
the secondary
The prishoe
through
the link; shoe.
the secondary
mary
shoe
pushes
on
the
secondary
shoe pushes on the anchor pin. When
shoe
through
the link;
the secondary
braking
in reverse,
the action
reverses
shoethe
pushes
onchange
the anchor
When
and
shoes
roles.pin.
The
pribraking
in reverse,
the action
reverses
mary
shoe
then becomes
a secondary
and the
shoes
shoe
in the
way change
it works.roles. The pri-
mary shoe then becomes a secondary
shoe in the way it works.
Anchor Pin
Anchor Pin
Anchor Pin
Anchor Pin
rimaf
hoe
Forward Braking
Typical duo-servo front brake used on
large front-engine, rear-drive American
cars;
pin is front
above brake
wheel used
cylinder.
Typicalanchor
duo-servo
on
Adjuster
joins lower rear-drive
ends of shoes.
Only
large front-engine,
American
.cars;
rigid connection
between
backing
plate
anchor pin is
above wheel
cylinder,
and
shoesjoins
is at anchor
pin. of shoes. Only
Adjuster
lower ends
rigid connection between backing plate
and shoes is at anchor pin.
Duo-servo brakes have servo
action regardless of rotation. The
Duo-servo
brakes
have forward
servo
brake
is designed
for mostly
action
regardless
of
rotation.
motion or rotation. Lining wearThe
is
brake is designed
forward
equalized
betweenforthemostly
primary
and
motion or shoes
rotation.by Lining
is
secondary
puttingwear
more
equalized
between
the
primary
and
lining on .the face of the secondary
secondary
shoes the
by driver
puttingcanmore
shoe.
However,
feel
liningdifference
on .the face
of theaction
secondary
when
little
in servo
shoe.
driver can
feel
brakingHowever,
in reversethe
. Duo-servo
brakes
little
difference
in
servo
action
when
were used on most American cars
brakingrear-wheel
in reverse. drive
Duo-servo
with
and brakes
drum
were
onthe
most
cars
brakesused
before
use American
of disc brakes.
with
rear-wheel
duo-servo drive
brakesand
havedrum
the
Because
brakes
before
the use
disc well
brakes.
most servo
action,
theyofwork
on
Because
brakes have the
heavy carsduo-servo
.
most
action, they
work well the
on
Pedal servo
Effort-Let'
s compare
heavy
three cars.
types of brake-shoe arrangePedal
Effort-Let's
compare
ments and
see how the servo
action the
afthree
types
of
brake-shoe
fects pedal effort. Pedal effortarrangeis the
mentsthe
anddriver
see how
the servo
action
afforce
applies
to the
pedal.
fects
effort. Pedal
effort
the
accompanying
ch art
, it is isobviIn thepedal
forcethat
thethe
driver
appliesbrake
to thehaspedal.
ous
duo-servo
less
In
the
accompanying
chart,
is obvipedal effort for a given it rate
of
ous that the duo-servo brake has less
deceleration.
pedal
for bad
a given
rate
of
Now effort
comes the
part-we
never
deceleration.
get something for nothing. Let 's see
Nowhappens
comes the
bad brakes
part-we getnever
what
when
too
get
nothing. Let's
see
brake-lining
material,
hot. something
With most for
what happens
when with
brakesincreasing
get too
friction
decreases
hot.
With
most
brake-lining
material,
temperature. As an example, assume
friction
decreases
withbetween
increasing
the friction
coefficient
the
temperature.
As lining
an example,
assume
brake
drum and
drops from
0.5
the
between
the
gets hot. The
comparito 0.4friction
when itcoefficient
brakeisdrum
andinlining
from 0.5
son
shown
the drops
accompanying
to
0.4
when
it
gets
hot.
The
comparitable for each type of drum brake . The
son is shown
the loses
accompanying
duo-servo
druminbrake
the most
table
for force.
each type
of ,drum
brake. The
braking
Thus
the brake
that
duo-servo
drum brake
servo loses
actiontheis most
also
has
the greatest
braking
Thus,
the
one force.
affected
the the
mostbrake
by a that
dehas thein greatest
crease
friction . servo action is also
the one affected the most by a decrease in friction.
Primary
Shoe
Reverse Braking
Forward
Braking
Duo-servo drum-brake
operation:
Notice that primary shoe Reverse
is pushedBraking
away from anchor pin
in forward braking. It moves until it is stopped against the drum. When backing up, rotation
reverses
and
other shoeoperation:
acts as primary
courtesy
Bendix
Corp.
Duo-servo
drum-brake
Noticeshoe.
that Drawing
primary shoe
is pushed
away
from anchor pin
in forward braking. I t moves until i t is stopped against the drum. When backing up, rotation
reverses and other shoe acts as primary shoe. Drawing courtesy Bendix Corp.
160
Single Leading-Shoe or
Leading-and- TrailingShoe
Brake
SingleDrum
Leading-Shoe
or
140
Leading-and-TrailingShoe Drum Brake
120
Two Leading-Shoe
Drum Brake
Two Leading-Shoe
100
Pedal
Effort
80
(I b)
60
40
40 -
20
20 .2
.3
.4
I
I
I
Lining Coefficient of Friction
.5
I
I
.4
.5
Duo-servo drum brake gives lowest
pedal
effort for
all practical friction coefficients.
Lining
Coefficient
of Friction
.2
.3
Duo-servo drum brake gives lowest pedal effort for all practical friction coefficients.
Pedal Effort at
Pedal Effort at
Percent Increase
CF=O.5
CF=O.4
in Pedal Effort
Pedal Effort at
Pedal Effort at
Percent Increase
Duo-servo
107.61b
115.2%
50lb
Brake Type
CF = 0.5
CF
= 0.4
in
Pedal Effort
50lb
99.81b
Two-leading shoe
99.8%
176.0%
15.2%
50
1b
107.6
Ib
Duo-servo
Leading-trailing
50lb
88.01b
50 Ib
99.8
Ib
99.8%
Two-leading
Disc brake shoe
50lb
62.51b
25.0%
88.0 1b
76.0%
50 Ib
Leading-trailing
25.0%
50 could
Ib
62.5 fade.
1b Pedal effort
brake
0.1Disc
friction-coefficient
drop
occur from brake
more than doubles
Brake Type
A
with duo-servo drum brakes. Disc brakes have no servo action, so effect of fade is considA
0.1 friction-coefficient
drop could occur from brake fade. Pedal effort more than doubles
erably
less.
with duo-servo drum brakes. Disc brakes have no servo action, so effect of fade is considerably less.
17
I
Cast-iron brake drum is large and heavy
compared to disc-brake rotor of equal
effectiveness.
Many
'60s
and '70s
Cast-iron brake
drum
is large
and Ameriheavy
can cars have
drums of this
This
compared
to disc-brake
rotortype.
of equal
front-brake drum
has'60s
integral
wheel
hub
effectiveness.
Many
and '70s
Ameriand
can bearings.
cars have drums of this type. This
During later days of race-car drum-brake
development, a great deal of work was
spent
cooling-fin
design. This
type of
Duringon
later
days of race-car
drum-brake
radial-finned drum
pumps
air was
bedevelopment,
a great
dealcooling
of work
tween
wheel and drum.
spent the
on cooling-fin
design. This type of
front-brake drum has integral wheel hub
Duo-servo
and
bearings. brakes are most sus-
ceptible to the type of brake fade
Duo-servo
brakes
are most
suswhere
a force limit
is reached.
Thus
, if
ceptible
to the
brake
fade
they are ever
usedtype
in a of
racing
or highwhere
a force limit
is reached.
Thus,
if
performance
application,
care
must
they
are
ever
used
in
a
racing
or
highbe taken to use linings that do not
performance
carewith
must
have a drastic application,
drop in friction
inbe takentemperature.
to use linings
do with
not
creasing
Carsthat
fitted
have a drastic
in friction
induo-servo
frontdrop
brakes
have a with
tendencreasing
temperature.
Cars
fitted
with
cy to pull to the right or left if the fricduo-servo
front
brakes
have a tendention in one
brake
is slightly
higher
cy
to the
pullother.
to the right or left if the fricthan
tion
in one
slightlyin higher
More
is saidbrake
aboutis linings
Chapthan
the
other.
ter 4.
More is said about linings in Chapter
4.
BRAKE
DRUMS
The brake drum is a large, critical
BRAKE
brake system. If the drum is
part of a DRUMS
brake
is athe
large,
critical
tooThe
small
or drum
flexible,
brake
will
part
of a poorly
brake system.
If the drum
is
perform
under severe
use, no
too
small
flexible,
the brake
matter
howorgood
the system
may will
be.
perform
severe ause,
no
Let
' s seepoorly
what under
constitutes
good
matter
how
good
the
system
may
be.
brake drum. The important properties
Let's see what constitutes a good
are:
brake
drum.
properties
• Must
haveThe
a important
hard wear-resistant
are:
rubbing surface and the surface finish
Must
a the
hardlining.
wear-resistant
must
not have
damage
rubbing
surface
the surface
finish
strongand
enough
to withstand
• Must be
must
not
damage
the
lining.
the hardest braking, while at high
Must be strong
enough to withstand
temperatures
.
the
hardest
braking,
while toatdistorhigh
• Must be stiff and resistant
temperatures.
tion and warping.
Must bedissipate
stiff and heat
resistant
to distorrapidly
and
• Must
tion
and
warping.
withstand excessive temperatures.
Must
dissipate
rapidlyof grey
and
Most brake
drumsheat
are made
withstand
excessive
cast iron, because
it temperatures.
is hard and wearMost brake
are madecarbon,
of grey
resistant.
Castdrums
iron contains
cast
iron,
because
it
is
hard
and
wearwhich prevents galling and seizing
resistant.
Cast
iron
contains
carbon,
when hot. It's also a good d,y rubbing
which without
preventslubrication.
galling and seizing
surface
when
also arigid
good
dry rubbing
Casthot.
ironIt's
is very
, compared
to
surface
without
lubrication.
most metals. Therefore, the drum reCastdistortion
iron is very
rigid,load
compared
to
sists
under
. Because
most
metals.
Therefore,
the drum re-,
the drum
is cast
at high temperature
sists distortion under load. Because
the drum is cast at high temperature,
18
Racers soon discovered that bigger brakes
are better. This old Talbot Grand Prix car
used
wheels-brake
drums
are
Racers18-in.
soon discovered
that bigger
brakes
bigger!
Fitting
into wheel
its
are
better.
Thisdrum
old Talbot
Grandlimits
Prix car
size.
used 1 8-in. wheels- brake drums are
bigger! Fitting drum into wheel limits its
size.
it resists warpage when repeatedly
heated and cooled.
it However,
resists warpage
whenis repeatedly
cast iron
not the
heated andmetal
cooled.
strongest
in the world; it tends
cast iron Tois avoid
not this,
the
to However,
crack if overstressed.
strongest
metal
in
the
world;
it
tends
thick sections are used in a drum .
to crack
if overstressed.
Tostrengthens
avoid this,
This
extra
metal not only
thickdrum,
sections
used the
in astiffness
drum.
the
but itare
increases
This
extra
metal
not
only
strengthens
of the drum. It also reduces temperathe
but during
it increases
turedrum,
buildup
hard the
use.stiffness
When
of thearedrum.
also help
reduces
temperafins
used,It they
reduce
tem'ture
buildup
duringby hard
use. When
peratures
quickly
exposing
more
fins
used, tothey
help reduce
temmetalare
surface
the cooling
air. When
peratures
quicklyarebyused,
exposing
all
design tricks
a drummore
will
metal
surface to strength.
the cooling
When
have adequate
In air.
addition,
all
tricks are
used, a drum
heatdesign
dissipation
is improved
with will
the
have
adequate
strength.
In
addition,
fins and extra metal.
heat dissipation
is improved with the
Drum
Cooling-High-performance
fins
anddrums
extra metal.
brake
must be BIG; bigger the
Drum
Cooling-High-performance
befter is the
key for reducing temperathe
brake
drums
must be BIG;
tures and eliminating
fade. bigger
A large
the key has
for reducing
temperabetter is
drum
diameter
the added
advantures ofand
eliminating
fade. A
large
tage
reducing
pedal effort
because
drum
diameter
has
the
added
advanof the increased "leverage" of the
tage of reducing
pedal effort
friction
material-similar
to abecause
longer
of
increased
"leverage"
the
pry the
bar. Racing
drum
brakes are of
usualfriction
material-similar
to
a
longer
ly the largest possible diameter that
pry bar.
Racing
brakes are usualwill
fit inside
thedrum
wheel.
ly The
the largest
possible
that
size and
weightdiameter
of a brake
will fit inside
the wheel.in determining
drum
are important
Themuch
size heat
and energy
weightit of
brake
how
can aabsorb.
drum
are
important
in
determining
Brake drums are measured by the
how much
heat of
energy
it can
inside
diameter
the drum
andabsorb.
width
Brake
drums The
are drum
measured
by surthe
of
the linings.
rubbing
inside
diameter
of
the
drum
and
width
face is slightly wider than the lining to
of the linings.
The Don
drum
allow
clearance.
' t rubbing
measuresur-a
face istoslightly
widerlining
than width.
the lining to
drum
determine
allow clearance. Don't measure a
drum to determine lining width.
radial-finned drum pumps cooling air between the wheel and drum.
Swept Area-The brake-drum inside
circumference multiplied by lining
Swept
inside
width isArea-The
the brake brake-drum
swept area, an
imcircumference
multiplied
by
lininga
portant measure of how effective
width
is. the
brakea car's
sweptbrake
area, specifian imbrake is
Usually
portant
measurea ratio
of how
effective
cation includes
of brake
swepta
brake tois. the
Usually
a car's brake
specificar weight.
A figure
of
area
cation
ratioin.)of brake
swept
square includes
inches a(sq
per ton
is
figurearea
of
area
to Athecarcar
weight.
typical.
with
a highAswept
square
in.) per ton
is
per ton inches
will have(sqlong-wearing,
fadecar with
a high
swept
area
typical. Abrakes,
resistant
with
all other
factors
per
tonequ
will
long-wearing,
being
al. have
A typical
road carfadehas
resistant
brakes,
with
all
other
about 200 sq in. per ton of
sweptfactors
area;
equal.
typical
car has
abeing
race car
may A
have
twice road
this amount.
about
200 sqdrum-brake
in. per ton of
swept
area;
Calculate
swept
area
by
athis
race
car
may
have
twice
this
amount.
formula:
Calculate drum-brake swept area by
Swept area = 3.14 DL in square inches
this formula:
D = Brake-drum inside diameter in
Swept
inches area = 3.14 DL in square inches
D
Brake-drum
inside diameter in
L = =Lining
width in inches
inches
ToLining
calculate
area per ton,
L=
width swept
in inches
divide swept area of all four brakes by
calculate
swept
theTo
car's
weight in
tons. area per ton,
divide
swept
area
of
all four
by
To help remove heat
andbrakes
cool the
the
car's
weight
in
tons.
drum, fins are necessary. If the fins
Towheel
help remove
heat and
and
are designed
as acool
unitthe
to
drum,
are necessary.
If as
theanfins
promotefins
airflow,
they can act
air
and
wheel
are designed
as a unit
to
pump.
Some
older race-car
drum
promote
airflow,
they
can
act
as
an
air
brakes were highly sophisticated in
pump. air
Some
older
race-car
drum
forcing
around
the hot
parts, as
the
brakes show.
were highly sophisticated in
photos
forcing
air around
the hot further
parts, as imthe
Bimetallic
Drums-To
photos
show.
prove cooling, a high heat-conducting
Bimetallic
Drums-To
further
immaterial
is used
outside the
cast-iron
prove cooling,
a highThis
heat-conducting
rubbing
surface.
is usually
material is used
outside
the has
cast-iron
aluminum,
although
copper
been
rubbing
surface.
This
is
usually
tried. Such drums are called bimetaflic.
aluminum,
although
copper
Aluminum carries
heat
from has
the been
rubtried.
Such drums
called fins
bimetallic.
to theare
cooling
more
bing surface
Aluminum
heat
from thebenerubrapidly than carries
iron. An
additional
bing surface to the cooling fins more
rapidly than iron. An additional bene-
Drum
l
+
A
Bellmouthing, which results from overheating and hard use, createsBrake
angle Shoe
A between
drum and shoe. This angle causes shoe
distortion, extra pedal movement, and
faster lining wear on inside edges.
Airflow
Vintage sports car is powered by fuel-injected Chrysler hemi. Because of its high weight
and a top speed of over 160 mph, it needed all the brakes it could get. Buick
aluminum/cast-iron bimetallic drums were some of the best ever produced for passengercar use.
Bellmouthing, which results from overheating and hard use, creates angle A between
drum and shoe. This angle causes shoe
distortion, extra pedal movement, and
faster lining wear on inside edges.
Airflow
Vintage sports car is powered by fuel-injected Chrysler hemi. Because of its high weight
and a top speed of over 160 mph, it needed all the brakes it could get. Buick
aluminum/cast-iron bimetallic drums were some of the best ever produced for passengercar use.
A
Plate
lron
Sheet Steel
.
Cast- lron
Drum
Composite
Drum
Cast Iron
'
Sheet Steel
y
Composite
Drum
Aluminum
Cast-Iron
Drum
cast 1.0"
Bimetallic
Drum
Cast
Aluminum
Centrifugally
Cast Composite
Drum
Of commonly used designs, bimetallic drums cool best due to high heat transfer of
aluminum. Bimetallic drums are also the lightest.
Bimetallic is lighter.
Centrifugally
minum around
the iron, known as the
fit is that aluminum
Cast Composite
A /-fin process.
For an Drum
aluminum/iron drum to
There Drum
are four basic types of brakework properly, the aluminum must be
drum
construction.
The simplest is
attached
tightly
to
the
iron.
The
drum
Of commonly used designs, bimetallic drums cool best due to high heat transfer of
cast
in
one
piece
from
iron. Another,
will
not
cool
sufficiently
if
there
are
aluminum. Bimetallic drums are also the lightest.
lighter drum style, is the composite
air gaps between the two metals. A
drum. This type uses a sheet-steel
once-popular type of bimetallic drum
fitused
is that
aluminum
is lighter.
around
therim
iron,
the
h u b with
an iron
castknown
to it. Aasvariaa special
process
for casting alu- minum
For an aluminumliron drum to
work properly, the aluminum must be
attached tightly to the iron . The drum
will not cool sufficiently if there are
air gaps between the two metals. A
once-popular type of bimetallic drum
used a special process for casting alu-
A I-fin process.
There are four basic types of brakedrum construction. The simplest is
cast in one piece from iron. Another,
lighter drum style, is the composite
drum. This type uses a sheet-steel
hub with an iron rim cast to it. A varia-
Wheel Rim
Angled lip on drum can help cooling. If lip
has fins, drum rotation can pump air between the wheel and drum. If lip extends inboard past wheel and backing plate, additional cooling is realized.
tion of the composite drum uses a
stamped sheet-steel drum with a castAngled
lip on drum
can inside
help cooling.
lipa
iron rubbing
surface
it. LastIf is
has fins, drum rotation can pump air bebimetallic
drum,
made
of
aluminum
tween the wheel and drum. If lip extends inand cast
board
pastiron.
wheel and backing plate, addiDrum
Design-The
tional
cooling
is realized. design of the
open edge of the brake drum is critical
tion
of the performance.
composite drum
uses a
to a drum's
The stiffness
stamped
sheet-steel
drumwill
withkeep
a castof the lip
at the edge
the
rubbing
it. Last (egg
is a
iron
drum
from surface
going inside
out-of-round
bimetallic
, made of
aluminum
bellmouthing
(diameter
inshaped) ordrum
and
cast iron
creasing
at . open end) under severe
Drum
Design-The
design of Also,
the
loads and
high temperatures.
open
edge ofofthethe
brake
is critical
the shape
lip drum
can determine
tohow
a drum's
stiffness
well aperformance.
drum cools. The
An angled
lip
of
lip promote
at the edge
will around
keep the
canthehelp
airflow
the
drum
going
out-oj-round
(egg
drum.from
Because
airflow
around a drum
shaped)
or bel/mouthing
(diameter
inis complicated
and affected
by other
creasing
at
open
end)
under
severe
parts on the car, drum cooling can
loads
and
high temperatures.
Also,
only be
determined
by tests.
the Besides
shape of
the lip and
can cooling
determine
stiffening
the
how
wellthe
a lip
drum
lip
drum,
alsocools.
matesAn
withangled
the backcan
airflow
around
ing help
plate.promote
This helps
keep
dirt the
and
drum.
around
a drum
water Because
out of airflow
the drum.
The
usual
isdesign
complicated
and affected
by other
has a groove
at the edge
of the
parts
the car,
brakeondrum.
T h e drum
outer cooling
edge ofcan
the
only be determined by tests.
Besides stiffening and cooling the
drum , the lip also mates with the backing plate. This helps keep dirt and
water out of the drum. The usual
design has a groove at the edge of the
brake drum . The outer edge of the
19
Fins on Alfa-Romeo aluminum/cast-iron
drum are designed to pump air between
drum
and Alfa-Romeo
tight-fitting aluminum/cast-iron
wheel. Drum goes
Fins on
with brake
assemblyto
pictured
on page
22.
drum
are designed
pump air
between
Photo and
by Ron
Sessions. wheel. Drum goes
drum
tight-fitting
with brake assembly pictured on page 22.
Photo by Ron Sessions.
backing plate is flanged. This flange
fits into the groove, but does not
backing
is This
flanged.
Thisfor
flange
touch theplate
drum.
is a seal
dirt
fits water,
into the
groove,
but does
not
and
making
it difficult
for fortouch
the
drum.
This
is
a
seal
for
dirt
eign matter to blow or splash into the
and water,
it difficult
for fordrum.
The making
brake-lining
surfaces
are
eign
to from
blow contamination.
or splash into the
thus matter
protected
A
drum.
are
problemThe
withbrake-lining
this seal is surfaces
it also prethus protected
contamination.
A
vents
cooling from
air from
entering the
problem
with
this
seal
is
i
t
also
preinterior of the brake.
vents cooling air from entering the
interior of the
brake.
BACKING
PLATE
The backing plate is a bracket on
BACKING
which
the PLATE
brake shoes and wheel
The backing
is serves
a bracket
on
cylinders
mount.plate
It also
to prowhich
brake ofshoes
and wheel
tect thetheinterior
the drum
from
cylinders mount. as
It also
serves
to procontamination,
just
discussed.
tect
the
interior
of
the
drum
from
Braking torque is transmitted from
contamination,
as just discussed.
the shoes to the suspension
of the car
Braking
is transmitted
from
through torque
the backing
plate. A good
the
shoes
to
the
suspension
of
the
car
backing plate must be stiff and strong
through
the
backing
plate.
A
good
so the shoes stay in alignment with
backing
plate
musta be
stiff and
strong
the drum.
When
backing
plate
deso
the excessively
shoes stay inunder
alignment
flects
load, with
the
the drum.
driver
feels When
this asa abacking
spongy plate
pedaldeor
flects
excessively
under load, the
as
excessive
pedal travel.
driver
this asplates
a spongy
pedal or
Mostfeels
backing
are stamped
as
excessive
pedal
travel.
from heavy sheet steel. Ridges,
Most and
backing
plates
are stamped
bumps
edge lip
stamped
into the
from
heavy
sheet
steel.
Ridges,
backing plate increase its strength
and
bumps andCritical
edge lipareas
stamped
into the
stiffness.
for strength
backing
increase its strength
and
are
the plate
brake-shoe-pivot
and wheelstiffness.
Critical
areas
for
strength
cylinder mounting points. Any cracks
areother
the brake-shoe-pivot
wheelor
weakness in thoseand
areas
can
cylinder
mountingsituation.
points. Any cracks
cause
a dangerous
or Some
other backing
weaknessplates
in those
areas race
can
on older
cause
a
dangerous
situation.
cars are cast aluminum or magnesium
backingThese
plates are
on older
race
forSome
lightness.
not good
cars
are cast
or magnesium
materials
for aluminum
this application
because
for
These are
not good
they lightness.
lack sufficient
stiffness
and
materials
for
this
application
because
strength. By the time an aluminum
or
they lack sufficient stiffness and
strength. By the time an aluminum or
20
Early race-car drum brake has finned backing plate to help cooling. Unfortunately, the
designer
neglected
usehas
vents.
And,
beEarly race-car
drum to
brake
finned
backcause
thetobacking
plate Unfortunately,
doesn't get very
ing plate
help cooling.
the
hot, theseneglected
cooling fins
help much.
designer
to don't
use vents.
And, because the backing plate doesn't get very
hot, these cooling fins don't help much.
magnesium casting is sufficiently
beefed up to equal the strength of a
magnesium
castingit will
is be
sufficiently
steel
backing plate,
nearly as
beefed up to equal the strength of a
heavy.
steel
plate,
it will
nearly as
Thebacking
backing
plate
is be
a precision
heavy.
part. Brake-shoe mounting points
Thebebacking
is brake
a precision
must
aligned plate
with the
drum
part.proper
Brake-shoe
points
for
operation.mounting
A bent or twisted
must be aligned
the brake
drum
backing
plate is with
useless,
so inspect
for
proper
operation.
A
bent
or
twisted
each one carefully for damage when
backing plate
is useless,
so inspect
working
on your
car. You
should
each one
for damage
when
never
pry carefully
on a backing
plate
to
working a on
your
car.This
Youwillshould
remove
brake
drum.
bend
neverbacking
pry onplate
a backing
plate the
to
the
and misalign
remove
a
brake
drum.
This
will
bend
brake shoes.
theA backing
plate isand
misalign
backing plate
usually
boltedthe
to
shoes. upright or axle flange
abrake
suspension
A backing
plate high-strength
is usually bolted
to
with
tight-fitting,
bolts.
aIt suspension
upright
or
axle
flange
is important that this joint is tight
with tight-fitting,
and
cannot shift high-strength
under load. bolts.
This
It
is important
that this joint
tight
brings
up an important
point. isWhen
and
cannot
working
on shift
brakes,under
makeload.
sure This
the
brings
up
an
important
point.
bolts are the correct lengthWhen
and
working for
on the
brakes,
make sure the
strength
application.
bolts are theCooling-The
correct length
and
Drum-Brake
backing
strength
for
the
application.
plate has little brake-cooling effect. It
Drum-Brake
never gets as Cooling-The
hot as the otherbacking
brake
plate has
little brake-cooling
It
parts.
Therefore,
fins or air effect.
blowing
never
as hot
other brake
on
the gets
backing
plateasisthe
ineffective.
Efparts. to
Therefore,
fins orbrake
air blowing
forts
cool a drum
should
on
the
backing
plate
is
ineffective.
Efalways be directed to the drum.
forts
to backing
cool a drum
brake
should
Some
plates are
vented
or
always
be directed
to theon
drum.
have scoops
mounted
them. The
Some backing
plates
are vented
or
purpose
is to direct
cooling
air into
have
scoops
mounted
on
them.
The
the interior of the brake drum. This
purpose
is to direct
cooling
into
setup
is found
on most
drumair
brakes
the interior
of the
brake
drum.
This
used
for racing,
if the
rules
allow
it.
setupproblem
is found with
on most
drumbacking
brakes
The
ventilated
used for racing, if the rules allow it.
The problem with ventilated backing
Large forward-facing scoop was used on
520-HP Auto Union Grand Prix cars from
the
mid-'30s.
These cars
usedwas
huge
drums
Large
forward-facing
scoop
used
on
and
butPrix
brake
cooling
5 2 0 -hydraulic
H P Auto actuation,
Union Grand
cars
from
withmid-'30s.
that muchThese
powercars
was used
a realhuge
problem.
the
drums
and hydraulic actuation, but brake cooling
with that much power was a real problem.
Although most brake shoes are made of
steel plate, cast aluminum has been used.
Aluminum most
is lighter,
weakens
at exAlthough
brakebut
shoes
are made
of
treme
temperatures.
If youhas
arebeen
building
a
steel plate,
cast aluminum
used.
car
with aluminum
make sure
Aluminum
is lighter,shoes,
but weakens
at they
exwon't temperatures.
be subjected Iftoyouextremely
high
treme
are building
a
temperatures.
Never
use metallic
racingcar with aluminum
shoes,
make sure
they
brake linings
on aluminum
won't
be subjected
to shoes.
extremely high
temperatures. Never use metallic racingbrake linings on aluminum shoes.
plates is that the venting may allow
entry of water, dirt or other
plates is that the
venting
maybraking
allow
contamination.
This
creates
entry
of particularly
water, dirt
or side
other
problems,
if one
of
contamination.
This more
createsthan
braking
the car is affected
the
problems,
particularly
if one
sideside
of
other.
Grabbing
or pulling
to the
the
car
is
affected
more
than
the
while braking can result.
other.
Grabbing
to the
side
A scoop
shouldorbepulling
designed
to keep
while
braking can result.
out contamination.
To do this, some
A scoop
should
be designed
to keep
people
place
a screen
flush with
the
out
contamination.
To
do
this,
some
scoop intake. This restricts airflow
to
people
place
a screen
flush
the
the
brake,
thus
defeating
the with
purpose
scoop
intake. AThis
to
of
the scoop.
goodrestricts
solutionairflow
is to use
the
brake,
thus
defeating
the
purpose
a long air duct with a coarse screen re-
of the scoop. A good solution is to use
a long air duct with a coarse screen re-
Adjuster
Cab le
Hold -
Return springs and hold-downs have been
removed from these brake shoes. Springloaded hold-downs
the shoes
against
Return
springs and keep
hold-downs
have
been
flats on the
backing
shoeSpringedges
removed
from
these plate.
brakeThe
shoes.
rub against
these flats
asthe
they
moveagainst
in and
loaded
hold-downs
keep
shoes
out. on the backing plate. The shoe edges
flats
rub
against
they Thus
move ,inonly
and
cessed
intothese
the flats
duct asinlet.
out.
Adjuster
Levers
1
~)
~
.,-
fine partic les are likely to reach the
cessed
ductwill
inlet.
Thus,
only
brake . into
The the
screen
tend
to repel
fine
particles
are
likely
to
reach
the
stones and other large objects entering
brake.
Thebut
screen
tendairflow
to repel
the duct,
won'twill
block
as
stones
other large
objectsthat
entering
much . and
However,
be aware
dust
the
but brake
won't and
block
as
will duct,
enter the
mayairflow
increase
much.
However,
be
aware
that
dust
lining wear and drum-surface scoring.
will enter the brake and may increase
lining
wear
and drum-surface scoring.
BRAKE
SHOES
Brake shoes are rigid metal assem-
BRAKE
blies to SHOES
which friction material is
Brake shoes
are rigid
metalorassemattached.
Friction
material,
brake
blies
material
is
lining, tois which
ri veted friction
or bonded
to the
brake
attached.
Friction
material,
or
brake shoe. Brake shoes are usually
or basis
bonded
to can
the
lining,
sold
on isan riveted
exchange
so they
brake
shoe.by Brake
shoes
usually
be rebuilt
installing
newarelining
on
sold
on an
exchange
so they
the old
shoes.
Brakebasis
shoes
can can
be
be
rebuiltandby used
installing
new lining
on
relined
repeatedly
unless
the
Brake shoes can be
they old
haveshoes.
been damaged.
relined
and used
unless
Most brake
shoesrepeatedly
are fabricated
of
they
have
been
damaged.
sheet steel with a tee-shaped cross
Most brake
fabricated
of
section.
Someshoes
are are
made
of cast
sheet steel. The
with shoe
a tee-shaped
cross
is shaped
to
aluminum
section.
Some
made ofof cast
match the
insidearediameter
the
aluminum.
shoe is shaped
to
drum
, with The
new full-thickness
lining
match the
inside diameter
of the
installed
. Accurate
fit between
the
drum, and
withdrum
newisfull-thickness
lining
lining
assured by machininstalled.
Accurate
fit
between
the
ing the lining after it is attached to the
lining This
and drum
is assured
by machinshoe.
machining
process
is called
it is exact
attached
to the
ing thethe
lining
afterThe
arcing
lining.
radius
of
shoe.
This
machining
process
is
called
the arc is determined by the inside
arcing the
lining.
TheIfexact
radiushas
of
radius
of the
drum.
the drum
the arc
is determined
by the
inside
been
turned
to an oversize
diameter,
drum has
radius
of the drum.
the
lining-arc
radius Ifis the
increased
to
been
turned
to
an
oversize
diameter,
match.
theBrake
lining-arc
increased
to
shoes radius
have is
rubbing
points
match.
that
are contacted by wheel-cylinder
Brake shoesand
havebrake
rubbing
points
mechanisms
adjusters.
that
are
contacted
by
wheel-cylinder
Also, there's a mechanical linkage
mechanisms
andparking
brakebrake
adjusters.
connected
to the
, which
Also, there's
a mechanical
operates
the rear
brake shoes. linkage
These
connected
to the
which
rubbing
points
areparking
subjectbrake,
to wear
and
operates the rear brake shoes. These
rubbing points are subject to wear and
Adjusting-Hole
Cover
Adjusting-Screw
Spring
~~ ~
Adjust in g-Screw Assemb ly
Assembly
in the typical drum
brake. This is a duo-servo rear brake
Various types of springs are usedAdjusting-Screw
with an automatic adjuster. Drawing courtesy Bendix Corp.
Various types of springs are used in the typical drum brake. This is a duo-servo rear brake
with an automatic
adjuster.
should
be lubricated
withDrawing
specialcourtesy
high- Bendix Corp.
temperature grease for maximum life .
should
lubricated
with special
highBrakebeshoes
have holes
in them
for
temperature
grease
for
maximum
life.
locating pins and return springs.
Brakebuying
shoes new
have shoes,
holes inmake
themsure
for
When
locating
pins
and ones
return
springs.
the holes in
the new
match
those.
When
new shoes,
in the buying
old shoes.
Shoes make
often sure
get
the
holes
in
the
new
ones
match
those.,
mixed up when relining is performed
in carefully
the old comparing
shoes. Shoes
so
old ofter!
to newget
is
mixed
up when
relining
is performed,
worthwhile.
When
installing
the new
so
carefully
oldwhere
to newthe
is
shoes,
pay comparing
attention to
worthwhile.
When
installing
the
new
return springs connect. Some shoes
shoes,
pay attention
the
have
extra
holes toforwhere
various
return springs
applications.
If aconnect.
spring isSome
placedshoes
in a
have hole,
extra poor
holes
various
wrong
brake for
performance
applications.
a spring
is grabbing
placed inora
can
result, in Ifthe
form of
wrong hole,
poor brake performance
dragging
brakes.
canBrake
result,
in
grabbing
or
shoesthe
getform
very ofhot
in racing
dragging
brakes.
use, but not nearly as hot as the drum .
Brake
shoes
hot the
in racing
If the
shoe
gets get
too very
hot and
lining
use,
butworking,
not nearly
as hotofasthe
the liningdrum.
is still
failure
If the shoe
gets toocould
hot and
the lining
to-shoe
bonding
occur.
Foris
still
working,
failure
of
the
tunately, most heat generatedliningby a
to-shoebrake
bonding
occur.
drum
goes tocould
the drum
andFornot
tunately,
heat generated
the
shoes,most
so overheated
shoesbyarea
drumBrakes
brake goes
theed
drum
and linnot
rare.
using to
bond
metallic
the
shoes,
so
overheated
shoes
are
ings are the type for which bonding
rare. Brakes
using bonded
metallic linstrength
is extremely
important.
ings
are the type design
for which
bonding
Lining-material
is more
imstrength
is
extremely
important.
portant than brake-shoe design . See
Lining-material
design is discussion
more imChapter
4 for an in-depth
portant
than brake-shoe design. See
of
brake linings.
Chapter
for anshoes
in-depth
discussion
Usually4, brake
are held
to the
of brake linings.
Usually, brake shoes are held to the
Girlock of Australia manufactures this
lightweight mechanically-operated brake
for
use asofa parking
brake
on '84-and-later
Girlock
Australia
manufactures
this
Chevrolet
It has all the features
lightweightCorvettes.
mechanically-operated
brake
of
standard
drum brake,
including
an adforause
as a parking
brake on
'84-and-later
juster
and Corvettes.
return springs.
in
Chevrolet
It hasDrum
all theinstalls
features
the
hat. including
Photo courtesy
of a disc-brake-rotor
standard drum brake,
an adGirlockand
Ltd.return springs. Drum installs in
juster
the disc-brake-rotor hat. Photo courtesy
backing
plate with a spring clip or
Girlock Ltd.
spring-loaded pin. This pin lightly
backing
platebrake
with shoe
a spring
clip the
or
presses the
against
spring-loaded
pin.
This
pin
lightly
backing plate. Flats are provided on
presses
brakeforshoe
against
the
the backithe
ng plate
the edge
of the
backing
plate.against.
Flats are
provided
on
shoe
to rest
Pressure
of the
the
backing
plate
for
the
edge
of
the
shoe hold-down springs is low, so fricshoe
rest against. Pressure of the
tion isto
minimal.
shoe hold-down springs is low, so friction is minimal.
RETURN
SPRINGS
Drum-brake shoes are pulled away
RETURN SPRINGS
Drum-brake shoes are pulled away
21
Brake adjuster is operated by turning star
wheels. This type adjuster is used between
the
on byaturning
leadingBrake brake
adjuster shoes
is operated
star
and-trailingdrum brake.
Adjuster
wheels. This shoe
type adjuster
is used between
housing
is mounted
to backing
plate.leadingthe
brake
shoes
on
a
and-trailing-shoe drum brake. Adjuster
housing is mounted to backing plate.
from the drum-retracted-after application by a set of return springs. Befrom the
apcause
the drum-retracted-after
force exerted by these
plicationisbyhigh,
a set of
return springs.
springs
a special
tool is Berecause to
theinstall
forcethem.
exerted
quired
Thereby
are these
varisprings
is high, a and
special
tool for
is the
reous arrangements
mounts
quired
install them.
There are
return tosprings,
depending
on varithe
ous arrangements
and mounts for the
specific
design.
return
on thea
If the springs,
brake hasdepending
any servo action,
specific
design.
loss of return-spring force can cause
the brake
hasorany
theIf brake
to lock
grabservo
. Thisaction,
may bea
lossdangerous
of return-spring
can cause
as
as a lossforce
of braking.
For
the
brake if
to only
lock or
grab.
Thisloses
may be
instance,
one
wheel
its
as
dangerous as
a loss
of side
braking.
For
return-spring
force
, that
can lock
instance,
if only
one swerve
wheel or
loses
up and cause
a sudden
skidits
.
return-spring
force, that side
can lock
Some manufacturers
provide
difup and return
cause a springs
sudden swerve
or skid.
ferent
that give
a difSome
manufacturers
provide
different force when installed. Springs
ferent
return
springs by
thatcolor.
give Check
a difare
usually
identified
ferent
force
when
installed.
Springs
with your
parts
supplier
to be sure
you
are
usually
identified
by
color.
Check
have the correct ones on your vehicle.
with your
parts supplier
to be if
sure
This
is particularly
important
theyou
car
have
the correct
ones on yourorvehicle.
is
fitted
with heavy-duty
racing
This
is particularly important if the car
brakes.
is fitted with heavy-duty or racing
brakes.
BRAKE ADJUSTERS
The return springs pull the brake
BRAKE
ADJUSTERS
shoes
away
from the drum a minimum
The
return
springs
pulldistance
the brake
specified distance
. If the
the
shoes
away
from
the
drum
a
minimum
shoes must travel before contacting
specified
If theexcess
distance
the
the drum distance.
is too great,
brakeshoes
must results.
travel before
pedal travel
Thus , contacting
some adthe drum must
is toobegreat,
excessto brakejustment
provided
minipedal
travel
results.
Thus,
admize shoe clearance and to some
compenjustment
mustwear.
be provided to minisate for lining
mize
shoeare
clearance
and to of
compenThere
two types
brake
sate
for
lining
wear.
adjusters, ma nua I and a uloma lie.
There
are two and
types automaticof brake
Both manualadjusters,designs
man~/aland
adjuster
use aautomatic.
cam or screw-
Both manual- and automaticadjuster designs use a cam or screw-
22
Prior to disc brakes, some drum-brake designs got pretty exotic. This three-leading-shoe
drum brake was used on some Alfa Romeo sports cars. Although they did a good job of
stopping
the little
sports
cars,
they weredesigns
heavy and
Notice
that
each shoe has its
Prior to disc
brakes,
some
drum-brake
got complex.
pretty exotic.
This
three-leading-shoe
own
drumwheel
brakecylinder.
was used on some Alfa Romeo sports cars. Although they did a good job of
stopping the little sports cars, they were heavy and complex. Notice that each shoe has its
own wheel cylinder.
thread mechanism to move the brake
shoes toward or away from the drum.
thread mechanism
move the
brakea
The
duo-servo tobrake
uses
shoes
toward
or
away
from
the
drum.
turnbuckle-like threaded link between
The
duo-servo
brake uses
the primary
and secondary
shoes.a
turnbuckle-like
threaded
link between
There
are right-hand
threads
on one
the primary
and secondary
shoes.
end
and left-hand
threads on
the
There
are
right-hand
threads
on
other. A star-shaped wheel, whichone
is
end
and
left-hand
on thea
rotated
manually
withthreads
a tool through
star-shaped
wheel,
is
other.
hole inA the
brake drum
or which
backing
rotated
manually
with
a
tool
through
plate, turns the threaded link. This ro-a
hole
the brake
or backing
tation in makes
the drum
link shorter
or
plate,
the threaded
link. This
rolonger,turns
increasing
or decreasing
shoetation makes
the link shorter or
to-drum
clearance.
longer,
increasing
or decreasing
shoeAutomatic adjusters
have a linkage
to-drum
clearance.
that
rotates
the star wheel as the vehihave
a linkage
cleAutomatic
is backedadjusters
up and
brakes
are
that
rotates
the
star
wheel
as
the vehiapplied. This is a ratchet-type
cle
is backed only
up and
brakes
are
mechanism-it
works
in one
applied. . Automatic
This is adjusters
a ratchet-type
direction
are not
mechanism-it
only
worksThere
in one
actuated
in forward
driving.
is a
direction.
Automatic
adjusters
are not
limit to the stroke of the actuating
in forward
driving.
There the
is a
actuated
linkage. When
clearance
between
limit and
to the
of the actuating
shoe
the stroke
drum reaches
a certain
linkage.the
When
clearance
between
the
value,
actuating
linkage
jumps
shoe
and
the
drum
reaches
a
certain
over the next tooth on the star wheel.
value,feature
the actuating
jumps
That
prevents linkage
the automatic
over the next
tooth
on the star wheel.
adjusters
from
overtightening
the
That
brakes.feature prevents the automatic
adjusters
from
overtightening
thea
Other types
of brake
adjusters use
brakes.
cam
or an eccentric bolt for adjusting
Other types of brake adjusters use a
cam or an eccentric bolt for adjusting
the shoes. These are actuated manually by turning a bolt that protrudes
the
shoes.the
These
are actuated
manualthrough
backing
plate or by
using
ly
by
turning
a
bolt
that
protrudes
a screwdriver through a hole in the
through
the backing plate or by using
brake drum.
a screwdriver
throughisa covered
hole in the
Adjusting brakes
in
brake
drum.
Chapter 11 .
Adjusting brakes is covered in
Chapter
1.
WHEEL1CYLINDERS
Brakes are applied by hydraulic
WHEEL
CYLINDERS
fluid
inside
wheel cylinders. One or two
Brakesin are
pistons
eachapplied
cylinderbyarehydraulic
moved
fluid
inside
cylinders.
One orwhen
two
outward
by wheel
brake-fluid
pressure
pistons
in
each
cylinder
are
moved
the driver pushes on the brake pedal.
outward
by brake-fluid
pressure when
Piston movement
is transmitted
to
the
pushes
onthe
thebrake
brakeshoe
pedal.
the driver
movable
end of
by
movement
is transmitted to
aPiston
pushrod
or other linkage.
theThere
movable
of the
brakeofshoe
by
are end
many
types
wheel
acylinders.
pushrod or
other linkage.
Cylinders
are made from
There are
types are
of singlewheel
aluminum
or many
iron. There
cylinders.
Cylinders
are made
from
or dual-piston
cylinders,
depending
aluminum
or iron. Duo-servo
There are singleon brake design.
brakes
or
cylinders,
depending
havedual-piston
one cylinder
operating
two
on brake
brakes
shoestwodesign.
pistons Duo-servo
are used with
this
have
cylinder
operating
design. one
Others
have one
cylinder two
on
shoes-two
pistons are used
with this
each shoe-one-piston
cylinders
are
design.
used. Others have one cylinder on
each
shoe-one-piston
cylinders
are
Wheel
cylinders and other
hydraulic
used.
components are discussed in more
Wheel
cylinders5. and other hydraulic
detail
in Chapter
components are discussed in more
detail in Chapter 5.
Disc Brakes
3
Racing-brake setup on this March Indy Car uses four-wheel disc brakes with dual master cylinders pressurized by remotely adjustable balance bar. Brake cooling is critical at Phoenix International's one-mile oval. Photo by Tom Monroe.
Racing-brake setup on this March lndy Car uses four-wheel disc brakes with dual master cylinders pressurized by remotely adjustable balance bar. Brake cooling is critical at Phoenix International's one-mile oval. Photo by Tom Monroe.
Rotor
Caliper
Shield
Transfer Tube
Splash Shield
Major parts of disc brake are caliper, rotor
and splash shield. A transfer tube connects
hydraulic
cylinders
on opposite
sides
of
Major parts
of disc brake
are caliper,
rotor
this
fixed caliper.
othertube
fixedconnects
calipers
and splash
shield. Many
A transfer
have
internal
fluid passages.
Photosides
courtehydraulic
cylinders
on opposite
of
sy Bendix
Corp. Many other fixed calipers
this
fixed caliper.
have internal fluid passages. Photo courtesy Bendix Corp.
Disc brakes are used on the front of
most modern road cars, and on all
Disc
brakesofaremost
usedrace
on the
front
of
four
wheels
cars.
Disc
most
modern
road
cars,
and
on
all
brakes were first introduced on cars in
four
wheels
race cars.
the late
'40s. ofBymost
the early
'70s, Disc
disc
brakes
first introduced
on carson
in
brakes were
had replaced
drum brakes
the
late
'40s.
By
the
early
'70s,
disc
the front.
brakes
had replaced
brakes
on
Two common
typesdrum
of disc
brakes
the
front.
are single and multiple disc, both with
Two common
of disc
brakes
rotating
discs or types
rotors.
Single-disc
are
single
and
multiple
disc,
both
with
types have a rotor, which is clamped
rotating
discs
or
rotors.
Single-disc
on by friction material called brake
types Multiple-disc
have a rotor, which
clamped
pads.
types, is
commonly
brake
on byonfriction
used
aircraft,material
have acalled
number
of
Multiple-disc
types,
commonly
pads.
rotating discs separated by stators, or
used on aircraft,
have a number
stationary
discs. Operation
is by ofa
stators,
or
rotating
discs
separated
by
large-diameter hydraulic piston in the
stationary
discs.
Operation
by a
backing plate
moving
outward,isclamplarge-diameter
piston
in the
ing the rotors hydraulic
and stators
together.
backing
plate
moving
outward,
clampMultiple-disc
brakes
are
100%
ing the , rotors
stators types
together.
metallic
while and
single-disc
use
Multiple-disc brakes are 1000/o
organic/metallic friction material.
metallic, while single-disc types use
organic/metallic friction material.
ADVANTAGES OF DISC BRAKES
The auto industry changed from
ADVANTAGES
DISC
BRAKES
drum
brakes toOF
disc
brakes
for a
The
auto
industry
changed
from
number of reasons:
drum
brakes
to
disc
brakes
for
a
• More resistant to brake fade.
number
reasons:
• Better of
cooling.
More resistant
to brake fade.
and dirt resistant.
• Water
Better
cooling.
• Less maintenance.
Water andsurface
dirt resistant.
• Greater
area for a given
Less of
maintenance.
weight
brake.
Greater
surface
area for
given
The
main
advantage
disc a brakes
weight
of
brake.
have over drum brakes is their inThe main
advantage
disc reasons
brakes
creased
resistance
to fade . The
havethisover
for
are : drum brakes is their increased
resistance
to fade.
Theexposed
reasons
• Friction
surfaces
directly
for
this
are:
to cooling air.
surfacesis directly
exposed
Drum deflection
eliminated.
• Friction
to
cooling
air. have no servo action.
• Disc
brakes
Drum
deflection
eliminated.
The
lack
of servoisaction
is a disadDisc
brakes
have
no
action.
vantage with a heavy servo
car. Resulting
The
lack
of
servo
action
is
disadpedal effort is too high. As aa result,
vantage
with almost
a heavyalways
car. Resulting
brakes
require
disc
pedal effort is too high. As a result,
disc brakes almost always require
23
AHeatlnput
Air
Cooling
Heat Input
" I_\J"
~
Drum
Drum
Heat lnput
Drum Brake
Drum Brake
Rotor
Disc Brake
Rotor
Why a disc brake has superior cooling is illustrated here. Heat generated by brake drum
Disc Brake
must flow through drum before air can cool the brake. On a disc brake, hot rubbing surfaces
are
directly
exposed
to
cooling
air;
heat-to-air
transfer
begins
immediately
Why a disc brake has superior cooling is illustrated here. Heat generated
by upon
brakebrake
drum
application.
must
flow through drum before air can cool the brake. On a disc brake, hot rubbing surfaces
are directly exposed t o cooling air; heat-to-air transfer begins immediately upon brake
application.
Expansion
Adapted to a hot rod, early Chrysler Imperial disc brake looks like a drum brake and
works like
Adapted
toaaclutch.
hor rod,Although
early ~ nneat
r y s llooking,
e Imper
it
worklooks
as well
a modern
rialdoesn't
disc brake
like as
a drum
brakedisc
and
brake. like
Rubbing
surfaces
on brake
are on
works
a clutch.
Although
neat looking,
inside
of finned
i t doesn't
work housing.
as well as a modern disc
brake. Rubbing surfaces on brake are on
inside of finned housing.
Direction
Expansion
Direction
Expansion
Direction
Expansion
Direction
Pad
Drum
Drum
_
d$$
... -..._.
..
. _ . ..__-_....
, .
Drum
Brake
&pad
...
..,..
8 .
...
..I
Shoe
Drum
Brake
Rotor
Disc
Brake
Disc
Expansion of hot brake drum is away from brake shoes. This requires
extra pedal travel. A
Brake
disc-brake rotor expands slightly toward the pads. Therefore, extra pedal travel due to
heat
expansion
is brake
not a problem
hot disc
brake.
Expansion
of hot
drum is with
awaya from
brake
shoes. This requires extra pedal travel. A
disc-brake rotor expands slightly toward the pads. Therefore, extra pedal travel due to
heat expansion is not a problem with a hot disc brake.
SPOT BRAKES &
-,
DISC BRAKES
SPOT
BRAKE9
& first called a
The
disc
brake was
Disc brakes were used on many race cars
in the mid-'50s. This car, built in 1955, is
powered
by were
a 300-HP
Chevy.
Disc brakes
used on
many Tiny
race solid
cars
rotors
would never
becar,
used
today
on such
in the mid-'50s.
This
built
in 1955,
is
a
powerfulby
car.a 300-HP Chevy. Tiny solid
powered
rotors would never be used today on such
assist,
apower
powerful
car. while drum brakes with
high servo action may not. On race
power
assist, while
drumless,
brakes
cars
, weight
is much
so with
disc
high
servo
action
may
not.
On
race
brakes usually do not require power
cars, weight is much less, so disc
assist.
brakes
usually part
do not
The hottest
of arequire
brake power
is the
assist.
metal surface contacted by the friction
The hottest
a brake
the
On a part
drumofbrake,
thisis surmaterial.
metal
surface
contacted
by
the
friction
face is inside the drum; on a disc
material.
Onthe
a drum
brake,
thisrotor.
surexterior
of the
brake, it is
face
is
inside
the
drum;
on
a
disc
For a drum brake to cool, the tembrake,
it
is
the
exterior
of
the
rotor.
perature of the entire drum must first
For aThen
drumthebrake
theattemdrumto iscool,
cooled
the
rise.
perature of the entire drum must first
rise. Then the drum is cooled at the
24
DISC
BRAKES
spot brake
or spot disc brake.
The dlsc
brake was
first acalled
a
This
distinguished
it from
type of
spot brake
brake that
or spot
brake.
disc
has adisc
clutch-like
a type
of
This
dlstlnguished
full circle
of frictionIt from
material.
This
disc brake
thatof has
ctufcblike
unusual
type
disca brake
was
full
of frlction
material.
This
Chrysler
Imperial
in
usedcircle
on the
unusual
was
the
early type
'50s, of
butdisc
was brake
discOritintheofChryder
Imperial
in
used
ued i'non
favor
the traditional
drum
the
early '50s, but was discolltln-brake.
ued
In favor ofmultidisc
the traditional
Full-circle
brakesdrum
are
brake.
Full-circle multidisc brakes are
exterior by surrounding air. A disc
brake is cooled immediately by air
exterior
A disc
the disc'sair. rubbing
blowing byonsurrounding
brake
is
cooled
immediately
by air
surfaces.
blowing
on
the
disc's
rubbing
drum
expands-ID
A
brake
surfaces.
increases-when
it gets hot, increasbrake
expands-ID
ingA pedal
travel.drum
The drum
can also
increases-when
it
gets
warp from temperature hot,
or increasbraking
ing
travel. The deflection
drum can also
deforce.pedalBrake-drum
warp
temperature
or braking
creasesfrom
performance
and causes
fade.
force.
Brake-drum
derotor is essenHowever,
a disc-brake deflection
creases
performance
and
causes
fade.
tially a flat plate. Temperature expanHowever,
disc-brake
rotortheisfriction
essension of thearotor
is toward
tially a flat plate. Temperature expansion of the rotor is toward the friction
used on large aircraft. Light aircraft
typically use more conventional
used on large
Light
alrcraft
spot-type
discaircraft.
brakes.
There's
a
typlcelb
use more
convent~onal
brief discussion
of aircraft
brakes
spot-type
disc brakes. There's a
in Chapter 9.
brief
discussion
aircraft
brakes
To keep
things of
simple,
I call
the
in Chapter automotive
9.
standard
disc ', brake
-simply
To keep
th'inggsimple,
I call the
a disc
brake because
the
standard
brake
brake is nodisc
longer
in
term spot automotive
simply a use.
disc And,
brake I beaause
the
common
call aircraft
term
spotbrakes
brake simply
Is no longer
in
multidisc
multidisc
cbrakes.
m m n use. And, I oall aircraft
multidisc brakes simply multidiso
brakes.
material rather than away from it.
Squeezing a disc cannot cause suffimaterial
rather tothan
from it.
cient
deflection
affectaway
performance.
Squeezing
a
disc
cannot
cause
The lack of servo action meanssuffithat
cient
deflection
performance.
a disc
brake to
is affect
affected
little by
The lack
servo action
that
changes
in of
friction.
As I means
mentioned
aearlier,
disc drum
brake brakes
is affected
little by
with maximum
changes
in friction.
As I mentioned
servo action
are also affected
the most
earlier,
drum
brakes
maximum
by friction changes. Awith
slight
drop in
servo action
most
friction,
suchare
as also
thataffected
caused the
by heat,
by
friction changes.
A slight
drop
in
is magnified
by the servo
action
. The
friction,
such
as
that
caused
by
heat,
driver senses this as fade. Disc brakes
is magnified
by the
servo action.
The
as sensitive
as drum
are
simply not
driver senses this as fade. Disc brakes
are simply not as sensitive as drum
JFZ disc brake is designed to stop a
oval-track race car. Four-piston, I
lightweight
caliper is
is massive
to reduce
JFZ disc brake
designed
to stopde-a
flections
minimize
temperature.
Photo
powerful and
oval-track
race
car. Four-piston,
courtesy
JFZ
Engineered
Products.
lightweight
caliper
is massive
to reduce de-
Changing brake pads on most disc brakes
is easy. Pads are sometimes retained with
quick-release
pins.
New
being
inChanging brake
pads
on pads
mostare
disc
brakes
stalled
thisare
transaxle-mounted
caliper
is easy. in
Pads
sometimes retained
with
for
bedding in. pins. New pads are being inquick-release
flections and minimize temperature. Photo
courtesy JFZ Engineered Products.
stalled in this transaxle-mounted caliper
for bedding in.
Ipowerful
Rotor bolts to lightweight aluminum hat.
Assembly then bolts to wheel hub or axle . .
Deep
flexes
when rotor aluminum
expands from
Rotor hat
bolts
to lightweight
hat.
high
temperature
and to
minimizes
brake
heat
Assembly
then bolts
wheel hub
or axle.
transferred
to thewhen
wheelrotor
hub expands
and bearings.
Deep hat flexes
from
Photo
courtesy JFZ
Engineered
high
temperature
and
minimizesProducts.
brake heat
transferred to the wheel hub and bearings.
Photo courtesy JFZ Engineered Products.
brakes to changes in friction.
The shape of a drum brake also conbrakes
in friction.
tributestotochanges
fade. Many
organic brake
The
shape
of
a
drum
con-.
linings expel gases brake
when also
heated
tributesgases
to fade.
Many
brake
These
can act
as aorganic
lubricant
belinings
expel
when causing
heated.
tween the
lininggases
and drum,
These
as a lubricant
befrictiongases
loss can
andact
severe
brake fade.
tween
the
lining
and
drum,
causing
The cylindrical surface of a brake
friction
and severe
brake infade.
drum is loss
similar
to bearings
an
The
cylindrical
surfacehigh-pressure
of a brake
engine.
For example,
drum
is similar
bearings
in an
oil
between
a main tobearing
and crankengine.
For
example,
high-pressure
shaft journal keeps the surfaces apart
oil between
bearing and
and
friction atomain
a minimum.
A crankbrake
shaft journal
keeps
the surfaces
drum
and shoes
act much
like an apart
oiled
and
friction
to a minimum.
A gas
brake
bearing
and journal
when hot
is
drum and shoes
act much
an oiled
expelled
between
them.like
They
are
bearing
when
hot gas is
pushed and
apartjournal
by the
high-pressure
expelled
between
them.andThey
are
gas
, reducing
friction
causing
pushed
apart
by
the
high-pressure
brake fade.
gas,
frictionarea
andof causing
Thereducing
small surface
a discbrake
brake fade.
pad and the flat face of the rotor
surface
area of
a discdoThe
not small
simulate
a bearing
container.
brake
pad
and
the
flat
face
of
the
There may be some gas coming rotor
from
do
simulate
a bearing
the not
lining,
but because
it iscontainer.
not conThere
someisgas
coming
tained may
well,bethere
little
effect.from
To
the
lining,
it is on
nota conrepeat,
any but
dropbecause
in friction
disc
tained
well, there
littleon
effect.
To
it lessis than
a drum
brake affects
repeat,
any
drop
in
friction
on
a
disc
brake because the disc brake has no
brake action
affects. it less than on a drum
servo
brake
because cooling
the discisbrake
no
Disc-brake
betterhasthan
servo
action.
drum-brake cooling because the rotorDisc-brake
cooling
is better
than
contact
surfaces
are directly
exposed
drum-brake
cooling
becausethis
themakes
rotorto cooling air.
However,
contact
surfaces
are directly
exposed
the contact
surfaces
"potentially"
to
cooling
air.
However,
this
makes
more vulnerable to damage from
corthe
contact
surfaces
"potentially"
rosive dirt or water contamination.
more vulnerable
corFortunately,
theto damage
constantfrom
wiping
rosive dirt or water contamination.
Fortunately, the constant wiping
action of the pads against the rotor
keeps the surfaces clean. Also, cenaction
the tends
pads to
against
rotor
trifugal of
force
throwthe
material
keeps
the
surfaces
clean.
Also,
cenoff the rotor. Because water is wiped
trifugaltheforce
tends
throw material
from
rotor,
discto brakes
are less
off
the rotor.
Because
water is wiped
sensitive
to this
contamination
than
from
the
rotor,
disc
brakes
less
drum brakes. On the otherarehand,
sensitive
to
this
contamination
than
water lubricates a drum brake well.
drum more
brakes.
On action
the other
And,
servo
meanshand,
less
water
lubricates a drum brake well.
braking.
And,
more servo
action
less
Disc-brake
pads are
easymeans
to change
braking.
on most cars. Usually, disc pads can
padsremoving
are easy the
to change
beDisc-brake
changed after
wheel
on most
cars.locking
Usually,
disc Some
pads 'can
and
a simple
device.
inbe
changed after
removing
the wheel
stallations
requires
removing
the
and
a simple locking device. Some incaliper.
stallations
requires removing
the
Another advantage
of disc brakes
caliper.drums is adjustment. Drum
over
Another
of disc
brakes
brakes
mustadvantage
be manually
adjusted
or
over
drums
is
adjustment.
must have the added complexityDrum
of an
brakes must be manually
adjusted
or
automatic-adjusting
system
. Disc
must
added to
complexity
an
brakeshave
are the
designed
run with of
little
automatic-adjusting
system. each
Disc
clearance,
and are self-adjusting
brakes
are
designed
to
run
with
little
time they are applied .
clearance,
and are rotor
self-adjusting
each
The disc-brake
has a contact
time
they
are
applied.
surface on each side; the brake drum
rotor has
contact
hasThe
a disc-brake
contact surface
onlya on
the
surface
on each side;
thearea
brake
drum
inside. Disc-brake
swept
is larger
has
contact surface
only brake
on the
whena compared
to a drum
of
inside.
Disc-brake
swept
area
is
the same diameter and weight. larger
More
when
compared
a drum
brake of
swept area
means to
better
cooling.
the same diameter and weight. More
swept
area &
means
better cooling.
ROTORS
HATS
The rotor, usually made of cast
ROTORS
HATSand heaviest part of
iron,
is the&largest
The
rotor,
of disc
cast
a disc brake. Itusually
is a flatmade
circular
iron,
is
the
largest
and
heaviest
part
of
with a contact surface on each side.
a disc brake. It is a flat circular disc
with a contact surface on each side.
The rotor may either be solid or it can
be vented with cooling passages
The
rotorit.may either be solid or i t can
through
be vented
with iscooling
passages
HatsThe rotor
usually attached
through
to a hat, it.
which in turn is attached to a
Hats-The
rotor
is flange.
usually The
attached
wheel
hub or
axle
hat
to
a
hat,
which
in
turn
is
attached
to a
gives a long path for heat to travel
wheelthe
hub
or rubbing
axle flange.
The
hat
from
brake
surface
to the
gives
long pathThis
for heat
travel
wheel a bearings.
keepsto wheelfrom
thetemperature
brake rubbingdown.
surface
to the
bearing
The
hat
wheel
bearings.
This
keeps
wheelsometimes is cast integral with the
bearing
temperature
hat
rotor, and
sometimes down.
it is a The
separate
sometimes
is cast integral with the
part.
rotor,
it is aorseparate
Hatsand
are sometimes
made of iron
lighter
part.
material, such as aluminum. ProHats are hats
madeareof usually
iron oriron
lighter
duction-car
and
material,
such
aluminum.
Prointegral with
the as
rotor.
Most race-car
duction-car
hats are
iron
and
hats are separate
and usually
made of
alumiintegral
with
the
rotor.
Most
race-car
num alloy.
hats
are non-integral
separate and rotors,
made ofthe
alumiWith
hatnum
alloy.attachment can be either of
to-rotor
With
rotors, the
hattwo
typesnon-integral
, bolted or dog-drive.
A dogto-rotor
attachment
can
be
either
of
drive is a series of radial slots in the
two
types,
bolted
or
dog-drive.
A
dogrotor with metal driving dogs attached
drive
seriesact
of asradial
slots
the
to the is
hat.a They
a spline
to in
transrotor
with metal
driving
dogs and
attached
mit torque
between
brake
hat.
to the hat.
actthe
as arotor
splinetotoexpand
transThese
dogsThey
allow
mit
torque
between
brake
and
hat.
freely while keeping the rotor cenThese
dogsthe
allow
rotorfreedom
to expand
tered on
hat.theThis
to
freely
keeping
cenexpand while
eliminates
loadsthe
therotor
hat would
tered
on get
thewhen
hat. the
This
freedom
otherwise
rotor
gets hot.to
expand
loadstothe
would
If the eliminates
hat is bolted
thehat
rotor,
it
otherwise
get when
the rotor
rotor gets
must
expand
with the
as it hot.
gets
If the
hathat
is bolted
to the thin
rotor,andi t
hot.
If the
is relatively
must
expand
with
the
rotor
as
i t gets
flexible, it works without breaking.
hot. Ifbolted
the hat
is relatively
thin and
The
connection
between
the
flexible, it works without breaking.
The bolted connection between the
25
Slots on
Surface
Slots on
Surface
,
Rotor
Rotation
Direction
Curved
Vent
Holes
Curved
Vent
Holes
Racing rotor from AP Racing uses a dogdrive rather than bolts to transfer braking
action
the from
hat. Dogs
on hatuses
fit ina slots
Racing to
rotor
AP Racing
dogmachined
in than
edge bolts
of rotor
10. Slightbraking
cleardrive rather
t o transfer
ance between
hatDogs
dogsonand
action
t o the hat.
hat rotor
fit in slots
allow rotorintoedge
expand
uniformly,
but remain
machined
of rotor
ID. Slight
clearcentered.
Cleverhat
mounting
arrangement
is
ance
between
dogs and
rotor slots
called rotor
castel/a
ted drive
by AP
allow
t o expand
uniformly,
but Racing.
remain
Photo courtesy
APmounting
Racing. arrangement is
centered.
Clever
called castellated drive by AP Racing.
Photo courtesy AP Racing.
On this racing rotor, metal is removed at
outer edge to reduce weight and slots are
cut
in rotor
faces
to reduce
of
On this
racing
rotor,
metal ispossibility
removed at
fade. Photo
courtesy
Racing.
outer
edge to
reduceAP
weight
and slots are
cut in rotor faces to reduce possibility of
fade. Photo courtesy AP Racing.
Highly developed AP Racing Sphericone
rotor-notice projections cast inside ventJ
holes-transmits
cooling
air more
Highly developedheat
AP to
Racing
Sphericone
efficiently
standardcast
vented
rotor-noticethan
projections
insiderotor.
vent
Design is used onheat
Grand
Prix cars,
holes-transmits
t o cooling
airwhere
more
every
ouncethan
of rotor
weight vented
counts. Photo
efficiently
standard
rotor.
courtesy
Racing.
Design isAP
used
on Grand Prix cars, where
every ounce of rotor weight counts. Photo
courtesy
AP Racing.
two items
must use high-strength
bol ts wi th close-fitting, un threaded
two items
mustbolts
use are
high-strength
shanks
. Aircraft
often used
boltsthiswith
close-fitting,
for
purpose,
because unthreaded
they come
shanks. Aircraft bolts are often used
for
this purpose, because they come
26
A rotor that has curved vent holes or
angled slots must rotate in a particular direction
be has
effective.
rotation
A
rotor tothat
curvedCorrect
vent holes
or
relative slots
to vents
and
slots in
is ashown.
angled
must
rotate
particular di-
rection to be effective. Correct rotation
relative t o vents and slots is shown.
Here's what eventually happens to a rotor
when thermal stresses are high. Because
race-car
rotors
undergo
such atobeating,
Here's what
eventually
happens
a rotor
they should
inspected
and
when
thermalbestresses
are frequently
high. Because
replaced ifrotors
cracksundergo
are detected.
race-car
such a beating,
they should be inspected frequently and
replaced if cracks are detected.
with accurately machined unthreaded
shanks.
with
accuratelyhats
machined
Aluminum
reduce unthreaded
weight and
shanks.
thermal stress on the rotor. Because
Aluminum
hatse xpands
reduce atweight
and
aluminum
alloy
a gre ater
thermal
the to
rotor.
Because
rate thanstress
iron , itontends
equalize
the
aluminum alloy
expands
at a greater
expansion
difference
caused
by exrate
thantemperature
iron, i t tends of
to equalize
ther.
treme
the roto
expansion
difference
caused
by
exAdditionally , aluminum alloy is about
treme temperature
of the
rotor.
one-third
as rigid as iron,
so there
is
Additionally,
aluminum
alloy
is about
much less force
put on the
rotor
fo r a
one-third
as rigid
as iron, .so
there
is
given
amount
of e xpansion
The
lightmuch
less
force
put
on
the
rotor
for
er aluminum hat aids the car ' s per-a
given
amount
of expansion.
lightformance
and handling
. One The
disadvaner
aluminum
hat
aids
the
car's
tage of the aluminum-alloy hat is perthal
formance
handling.
One iron.
disadvanit conductsand
heat
better than
This
tage of the
causes
the aluminum-alloy
wheel bearingshattois that*
run
ithotter.
conducts heat better than iron. This
causes
the wheel bearings
run
Rotor Design-A
disc-braketo rotor
hotter.
has many features common with that
Rotor
Design-A
rotor
of
a brake
drum. The disc-brake
material is usualhas
many
that
ly grey
castfeatures
iron forcommon
the samewith
reasons
of
a
brake
drum.
The
material
is
usualit is popular for brake drums. Cast
ly greyhas
cast good
iron for
the same
iron
wear
and reasons
friction
itproperties,
is popularis rigid
for brake
drums.
and strong
at Cast
high
iron
has good
and friction
temperatures,
and wear
is inexpensive
and
properties,
is rigid and strong at high
easy
to machine.
temperatures,
and is inexpensive
and
A rotor is measured
by its outside
easy
to
machine.
diameter and its total thickness across
rotorcontact
is measured
by its
theA two
surfaces.
A outside
vented
diameter
and its total
thickness
rotor is always
thicker
than aacross
solid
the two
surfaces.
A vented
rotor.
Thecontact
diameter
of the rotor
is usurotorlimited
is always
than a solid
ally
by thethicker
wheel size.
rotor.
Thearea
diameter
of theisrotor
is usuSwept
of a brake
an imporally
by of
theitswheel
size.
tant limited
measure
effectiveness.
The
Swept
area
a brake
imporswept
area
of of
a disc
brakeis isanthe
total
tant measure
effectiveness.
The
area
contactedofbyitsboth
the brake pads
swept
of a disc brake is the total
in one area
revolution.
area
contacted
by both
thearea
brakeofpads
The
combined
swept
a ll
in
one
revolution.
brakes divided by the weight of the
combined
swept area
all
carThe
is one
way of indicating
how of
effecbrakes
by the
the
tive its divided
brakes are
likelyweight
to be.ofWith
car is one way of indicating how effective' its brakes are likely to be. With
Tiny cracks on race-car-rotor surface are
caused by thermal stresses. Rotor should
be replaced
before
larger cracks
form.
Tiny
cracks on
race-car-rotor
surface
are
Small
cracksstresses.
can oftenRotor
be removed
caised surface
by thermal
should
by
be grinding.
replaced before larger cracks form.
Small surface cracks can often be removed
by
grinding.
good
brake design, high swept area
per ton indicates a high-performance
good
design,
swept
brake brake
system.
Brake high
swept
area area
for
per ton cars
indicates
a on
high-performance
various
is given
page 28 .
brake
Brakeslots
swept
area mafor
Somesystem.
rotors have
or holes
various
cars
is
given
on
page
28.
chined in their contact surfaces .
Some
rotorshot-gas
have slots
holes maThese
reduce
and or
dust-particle
chined
in their pad
contact
surfaces.
buildup between
and rotor.
AlThese
reduce
hot-gas
and
dust-particle
though fade caused by gas buildup is
buildup
padthan
and for
rotor.
Alless for abetween
disc brake
a drum
though
fade
caused
by
gas
buildup
is
brake , some fade can still occur. This
lessmore
for a prevalant
disc brakewith
than large
for a brake
drum
is
brake,
some fade
stillhas
occur.
This
pads , because
the can
hot gas
a harder
is
more
prevalant
with
large
brake
time escaping than with small pads.
pads, because
theorhot
gas have
has a greater
harder
Therefore,
slots
holes
time escaping
withpads
small
effect
in racing,than
where
are pads.
large
Therefore,
slots orareholes
and temperatures
veryhave
high.greater
Holes
effect
in racing,
where pads
large
increase
the tendency
for are
cast-iron
and
temperatures
are
very
high.
Holes
rotors to crack, so they should be
increase
used only the
whentendency
required. for cast-iron
rotors
crack, so they
be
Vented to
Rotors-Many
rotoshould
rs are cast
used
only
when
required.
with radial cooling passages in them.
Ventedact
Rotors-Many
rotors
are cast
These
as an air pump
to circulate
withfrom
radial
passages
in them.
air
thecooling
rotor center
through
the
These act as an air pump to circulate
air from the rotor center through the
Tension
Tenslon
1m
I
Compression
Compression
Shear
Three ways stress act on a material: Tension pulls; compression crushes; and
and shear rips
rips
Each stress occurs simultaneously in
in a hot brake component, particularly
particularly if one
sideways. Each
area
area of the part is hot and
and another is cool.
.' THEflMALSTRESS
Lightweight race-car rotor has
has no hat.
Rotor heat flows directly from rotor to
t o aluminum
minum hUb.
hub. Such a design
design should only be
be
used
used on light cars with small
small engines,
where little heat is generated. Wheel bearings
ings in
in this hub
hub have to
t o be
be replaced
replaced several
times a season.
'Stress is a measure of the internal
force' inasolio material, usually
giVen. in pounds per square inch
(psj).:.,..the same units for measuring
'l1y<;lraulic pressure. Stress acts in
compressIon, tension orin a sliding.
dfrectioti '.. called ,shear. Typically,
. only 'tension
stress-pulling..:.causes cast ironto crack., The
stress at wl1ich. a material breaks, in
tension is called.its fensiJes.trengt1:),
. Tl1e tensile 'strength of g(eyca~t
,jrortJs apout 25,000 psI. .
,".
Wh~m . a metal is heated, it;·
expands. If the metal is' restrained"
so it can't expand freely, it,r:lI:essss .,
against its restraint with atorce:.··
The restraining force ,causes,ao',
additional stress in the: metaLt'hi.S" '
streS$ caused by a changeinlem,,;. "
peratl,Jre is called a thermalsfr.ess,'.~'·
Thermal stress occurs.' .WR,el'] ,
metal is hotter in one area.l(acqlo
brake rotor is suddenlyusedfcir' a
Rp
Rp == radius to outside of pad
pad
RR
RR == radius to the outside of the rotor
wp
wp == pad
pad width
passages to the outside of the rotor.
This type of rotor is referred to as a
vented rotor.
rotor. Vented rotors are used
on most heavy cars requiring the larglargest possible rotors.
rotors. Lighter cars usually use solid rotors.
Powerful race cars use vented
Sometimes there is a difference
rotors. Sometimes
sidewalls.
in the thickness of the rotor sidewalls.
On many race-car brakes, the rotor
side closest to the wheel is thicker
than the side away from the wheel.
This is done to try to equalize the temperature on each side of the rotor.
The wheel tends to prevent cooling
air from reaching the outboard rubbing surface of the rotor, making it
run hotter than the inboard surface.
The extra thickness next to the poorly
cooled outboard surface tends to
equalize temperatures.
Racing rotors often have curved
cooling passages, which increase airpumping efficiency.
efficiency. Because these
vents are curved, there are different
rotors for the right and left sides of
the car.
car. If your brakes use curved-vent
up!
rotors, don't get them mixed up!
A problem with vented rotors used
in severe service is cracking.
cracking. This is
caused by thermal stresses and by
brake-pad pressure against the unsupported metal at each cooling passage.
passage.
Thermal stresses on a rotor with a
cast- or bolted-on hat are caused by
the contact portion of the rotor being
hotter than the hat portion. Because
heat causes expansion, the outer portion of the rotor expands more than
the cooler hat. This distorts and bends
the rotor into a conical shape.
shape. Repeated expansion and contraction cause
If Rp
R, nearly equals RR.
RR, use the following
following
formula
formula to find swept area of brake:
brake:
Disc-brake
swept area
=
=
6.28 wp
wp)
w, (2RR
(2RR-- w
),
Disc-brake swept area is area on both
both
sides of rotor rubbed
rubbed by pads.
pads. It
I t is more
more
accurate to use
use Rp
R, instead
instead of RR'
R,. However,
However,
because the two radii
radii are nearly equal
in
R, is used
used for convenin most brakes, RR
ience. RR
R, is easier to
t o measure than Rp.
R,.
cracks to appear.
appear. Even though crackcracking may not occur, coning causes
uneven lining wear.
Rotor cracking is greatly reduced
for two reasons with curved vents:
First, curved vents provide better support for the sides.
sides. And, because
curved-vent rotors cool better, therless.
mal stresses are less.
Rotors-The
Composite RotorsThe latest
rotor material was developed for
heavy aircraft brakes and is being
27
TYPICAL SWEPT AREAS PER TON OF VEHICLE WEIGHT
Swept Area·
TYPICAL Sq
SWEPT
AREAS PER TONCar
OFMake
VEHICLE
WEIGHT
Car Make and Model
In.lTon
and Model
Swept Area
Alta Romeo Spyder Veloce
Mercury Lynx RS
259
Car Make
Model
S q In./Ton
Car
Make and
Model
Audi
5000 and
Turbo
245
Mitsubishi
Cordia
LS
R
S Turbo
Alfa
Romeo
Spyder
Veloce
259
Mercury
Lynx
Audi Quatro
254
Mitsubishi Starion
Audi
245
Mitsubishi
Cordia LS
BMW5000
528eTurbo
Nissan
Sentra
259
Audi
254
Mitsubishi
Starion Turbo
745i
Nissan
Stanza
BMWQuatro
302
BMW 528eCamaro Z28
259
Nissan Sentra
Peugeot
505 STI
Chevrolet
176
BMW 7451Citation X11 HO
302
Nissan Stanza
Chevrolet
Pontiac
Firebird Trans-Am
180
Chevrolet Corvette
Camaro 228
176
PeugeotGrand
505 ST1
Pontiac
National Racer
Chevrolet
284
Chevrolet
Citation X 1 1 HO
180
Pontiac J2000
Firebird Trans-Am
Pontiac
Datsun
200SX
266
Chevrolet
284
Pontiac Grand
Porsche
944 National Racer
Delorean Corvette
346
266
Pontiac J2000
DatsunAries
200SX
Dodge
Wagon
Renault
Alliance
145
346
Porsche Fuego
944 Turbo
Delorean
Renault
Dodge
Challenger
230
145
Renault Alliance
Dodge Aries
Wagon
Charger
2.2
161
Renault
LeCar ISMA GTU Turbo
Dodge Challenger
230
Renault 5Fuego
Ferrari
308GTSi
Renault
TurboTurbo
263
Dodge
Charger 2.2
161
Renault LeCar
I S M A GTU Turbo
Renault
18i
Fiat
Brava
154
Ferrari
308GTSi
5 Turbo
263
Renault
Spyder
Saab
900
Fiat
Turbo
221
Fiat Brava
154
Renault GL
18i
Ford
Mustang GT 5.0
162
Subaru
Fiat Turbo
Spyder
221
Saab
Honda
Accord
Toyota900
Celica
177
162
SubaruCelica
GL Supra
Ford Mustang
Honda
Civic GT 5.0
Toyota
171
HondaI-mark
AccordLS
177
Toyota Starlet
Celica
Isuzu
209
Toyota
Honda Civic
171
Toyota CelicaQuantum
Supra
Jaguar
XJ-S
219
Volkswagen
S
209
Toyota
Starlet
lsuzu I-mark LJalpa
Lamborghini
227
Volkswagen
Rabbit GTI
21 9
Volkswagen
Quantum
Jaguar
XJ-S Carlo GP.5 Turbo
Lancia Monte
537*
Volkswagen Sci
rocco
Larnborghini
227
Volkswagen
Rabbit
GTISCCA GT3
Mazda
GLC Jalpa
174
Volkswagen Sci
rocco
Lancia
Monte Carlo
GP.5 Turbo
537*
Volkswagen
Scirocco
Volvo GLT Turbo
Mercedes-Benz
380SL
237
Mazda
GLC
174
Volkswagen
Scirocco
Mercury
LN7
173
*Indicates race
car. SCCA GT3
Swept Area
Sq In.lTon
Swept
Area
188
S196
q In./Ton
188
236
196
272
236
174
272
269
174
277
269
236*
277
173
236*
303
173
190
303
185
190
348*
185
175
348'
189
175
275
18 9
169
275
208
169
224
208
196
224
183
196
216
183
198
21 6
304*
198
242
304*
Volvo GLT Turbo
242
and '82 cars as published in Road & Track magazine. Notice that high-performance
'Indicates race car.
economy sedans. Those for race cars are indicated by asterisks. Race-car brakes are
237
Mercedes-Benz 380SL
ListedMercury
are brake
swept areas per ton for typical 1981
LN7
173
cars tend to have higher swept areas per ton than
larger and race cars are generally lighter. The 537 sq-in./per ton area for the Lancia Monte Carlo GP 5 Turbo long-distance racer indicates
long-wearing
powerful
brakes.
cars
tend to have
higher
swept areas per ton than economy sedans. Those for race cars are indicated by asterisks. Race-car brakes are
larger and race cars are generally lighter. The 537 sq-in./per ton area for the Lancia Monte Carlo GP 5 Turbo long-distance racer indicates
long-wearing powerful brakes.
Curved-vent AP Racing rotor has slots
angled so rotor rotation will tend to throw
off
dust. As viewed,
rotorrotor
should
inCurved-vent
AP Racing
hasbeslots
stalled
sorotor
it rotates
angled so
rotation counterclockwise.
will tend to throw
Photo courtesy AP Racing.
Off dust. As
rotor
be in-
stalled so it rotates counterclockwise.
Photo courtesy AP Racing.
used on Grand Prix cars. These new
rotors are made of carbon-graphite,
used
Grand Prix
These rotor
new
borononcomposite.
A cars.
composite
rotors
are
made
of
carbon-graphite,
is lighter than a cast-iron rotorA composite
boron 30-lb
composite.
about
less total
weight onrotor
the
is
lighter F-l
than
a cast-iron
rotorBrabham
car-and
it can operate
about
30-lb
less temperatures.
total weight onTemthe
at much
higher
Brabham
F-1
car-and
it
can
operate
peratures up to 1700F (927C) have
at
muchobserved
higher temperatures.
Tembeen
without damage.
peratures
up to 1700F
7 0 have
Graphite-composite
pads( 9 2are
used
been composite
observed rotors
without
with
due damage.
to high
Graphite-composite
pads are used
operating temperatures.
with
composite
rotorsrotors
due to
Because
composite
are high
exoperating
perimentaltemperatures.
for racing use, there is no
Becausethey
composite
are way
excertainty
will everrotors
find their
perimental
for
racing
use,
there
is
no
into production cars. However, if the
certainty
they will ever
find their
way
car
manufacturers
continue
to work
into production cars. However, if the
car manufacturers continue to work
Brabham Grand Prix car is fitted with graphite-composite brake rotors. Exotic material
from the aerospace industry can operate at extreme temperature. Brakes work while rotors
glow
red! Grand Prix car is fitted with graphite-composite brake rotors. Exotic material
Brabham
from the aerospace industry can operate a t extreme temperature. Brakes work while rotors
glow red!
28
on weight reduction and the cost of
composites become reasonable, there
on
reduction
and on
theyour
cost car
of
mayweight
be composite
brakes
composites
become
reasonable,
there
some day. The problem is that commay be composite
brakes on your
car
posite
brakes experience
extreme
some
day.toThe
problem
is that comwear due
road-dirt
contamination.
posite brakes experience extreme
wear
due to road-dirt contamination.
CALIPERS
Disc-brake calipers contain brake
CALIPERS
pads and hydraulic pistons that move
calipers
contain
brake
theDisc-brake
pads against
the rotor
surfaces.
pads
and
hydraulic
pistons
that
move
There are many types of calipers.
the pads
against
the rotor structural
surfaces.
They
differ
in material,
There are
types arrangement.
of calipers.
design
andmany
piston
They
differ all
in material,
Regardless,
disc-brake structural
calipers
design
and
piston
arrangement.
operate on the same principle-when
Regardless,
all disc-brake
the
driver pushes
the brake calipers
pedal,
operate
on
the
same
brake fluid forces theprinciple-when
pistons against
the
driverpads
pushes
the them
braketo pedal.
the brake
, causing
clamp
brake
fluid
forces
the
pistons
against
the rotor.
theCalipers
brake pads,
them
to clamp
usedcausing
on most
production
the rotor.
cars
are made of high-strength nodular
Calipers
used low-cost
on most material
productionis
cast
iron. This
cars
are
made
of
high-strength
suited to mass production, andnodular
makes
cast
This
low-costcast-iron
materialcaliis
a rigidiron.
caliper.
However,
suited
to mass
and cars
makes
pers tend
to beproduction,
heavy. Race
or
ahigh-performance
rigid caliper. However,
cars cast-iron
usually caliuse
pers tend to be heavy.
cars or
aluminum-alloy
brake Race
calipers.
A
high-performance
carscaliper
usuallyweighs
use
light aluminum-alloy
aluminum-alloy
calipers.
A
about half as muchbrake
as cast-iron
caliper
light
aluminum-alloy
caliper
weighs
of the same size.
about
much as cast-ironarecaliper
Fixed half
& as
Floating-There
two
of the same size.
Fixed & Floating-There are two
I
Rotor on dragster rear axle has been given
the swiss-cheese look by cross-drilling.
Care
must
be exercised
when
Rotor on
dragster
rear axle has
beendrilling
given
rotors
to avoid weakening
or ruining
the
swiss-cheese
look bythem
cross-drilling.
their
Drilling
reduceswhen
rotor drilling
weight
Care balance.
must be
exercised
and, therefore, the
heat it can
absorb.
This
weakening
them
Or ruining
is no balance.
problem Drilling
for a dragster
the
their
reduces because
rotor weight
brakes
are coolthe
for heat
each itstop.
drilling
and,
therefore,
can Such
absorb,
This
is
more
critical
oval- or because
road-racing
is no
problem
foron
a dragster
the
cars. Beare
careful!
brakes
cool for each stop. Such drilling
JFZ racing caliper is typical fixed-caliper design; caliper is fixed and only pistons move.
Two pistons on each side are housed in cylinders bored in caliper body. Caliper assembly is
bolted
to axle
housing
or suspension
upright
through
ears at
Fluid-transfer
is
LFZ
racing
caliper
is typical
fixed-caliper
design;
caliper
is bottom.
fixed and
only pistonstube
move.!
sometimes
prevent
fluid boil.
Photo courtesy
Engineered
Products.
TWO
pistonsinsulated
on each to
side
are housed
in cylinders
bored inJFZ
caliper
body. Caliper
assembly is
bolted to axle housing or suspension upright through ears at bottom. Fluid-transfer tube is
sometimes insulated t o prevent fluid boil. Photo courtesy JFZ Engineered Products.
is more critical on oval- or road-racing
cars. Be careful!
~
Guide-Pin Boot
.; " I
,
1984 Corvette floating caliper uses
finned-aluminum caliper housing with one
piston
inboard floating
side of rotor.
Mounting
1984 on
Corvette
caliper
uses
bracket is darker caliper
portiol housing
to right of
finned
finned-aluminum
with
one
housing.
on rotor.
two guide
pins
piston onHousing
inboardslides
side of
Mounting
are applied
rotor
bewhen brakes
bracket
is darker
portiol to
t oclamp
right of
finned
tween
pads.
See separate
in followhousing.
Housing
slides on parts
two guide
pins
ing drawing.
courtesy
Girlock
Ltd .bewhen
brakesPhoto
are applied
t o clamp
rotor
tween pads. See separate parts in following
drawing.
basic
typesPhoto
of courtesy
calipers:Girlock
fixedLtd.and
floating. The difference is obvious
basic
types
calipers:
fixedcaliper
and
when you
lookofat them.
A fixed
floating.
The
obvious
twodifference
pistons on isboth
sides
has one or
A fixed usually
caliper
when
looka at
them. caliper
of
the you
rotor;
floating
has
one
or
two
pistons
on
both
has one piston on only one side ofsides
the
of
theThe
rotor;
a floating
usually
rotor.
housing
of a caliper
fixed caliper
is
has
onerigidly
piston to
on the
onlyspindle
one sideorofaxle
the
bolted
rotor.
TheAhousing
a fixed
caliper is
is mounted
housing.
floating of
caliper
bolted
rigidly
to
the
spindle
or axle
so it moves in the di recti on opposite
housing.
floating
caliper
is mounted
the pistonA(s).
Because
a floating
caliso
moves
direction
per itonly
has in
thethe
piston
(s) onopposite
the inthe piston(s).
Because
caliboard
side of the
rotor, athefloating
entire caliper
only
has
the
piston(s)
on
the
inper must shift inward for the outboard
board
of the
pad
to side
contact
the rotor,
rotor. the entire cali-
per must shift inward for the outboard
pad to contact the rotor.
Outer Pad & Spring
Assembly
I
Blowup of '84 Corvette floating caliper. Guide pins are retained in close-fitting holes in
anchor plate. Pins are in line with piston to minimize twisting of housing as it slides. Drawing
courtesy
Ltd.
Blowup ofGirlock
'84 Corvette
floating caliper. Guide pins are retained in close-fitting holes in
anchor plate. Pins are in line with piston t o minimize twisting of housing as it slides. Drawing
courtesy Girlock Ltd.
Floating-caliper mountings vary.
Some are mounted on guide pins and
mountingssurfaces
vary.
areFloating-caliper
held between machined
Some
are
mounted
on
guide
pins
anda
to take braking torque. Others have
are
held
between
machined
surfaces
flexible mount or are mounted on a
to take braking
torque.
have a
linkage.
Depending
on Others
their mountflexible
mount
or
are
mounted
ing, they are also called slidingonora
linkage.
Depending on their mounthinged calipers.
ing,
they
also are
called
or
Floating are
calipers
usedsliding
on most
hinged
calipers.
production
cars; fixed calipers are preFloating
are used on most
ferred
for calipers
racing applications.
This
production
cars;
fixed
calipers
are predoes not mean one type
is good
and
ferred
foris bad-each
racing applications.
This
the other
has advantages.
does
mean
one has
typemore
is good
and
Thenot
fixed
caliper
pistons
the
other
is
bad-each
has
advantages.
(two or four) and is bigger and heavier
The fixed caliper has more pistons
(two or four) and is bigger and heavier
than a floating caliper. In severe use,
it will take more hard stops to make
than
a floating
caliper.
In severe
use,a
the fixed
caliper
overheat.
And,
it
will
take
more
hard
stops
to
make
fixed caliper generally will flex less
the fixed
caliper
overheat. And, a
than
a floating
caliper.
fixed
calipera generally
will flex
less
However,
floating caliper
is more
than a floating
compact,
thuscaliper.
packages better in a
However,
floating
is more
wheel.
With athe
pistoncaliper
an d fluid
on
compact,
thus
packages
better
in a
the inboard side of the rotor, a floating
wheel.
With better.
the piston
fluidcalion
caliper cools
The and
floating
the
side
of the parts
rotor, and
a floating
per inboard
has fewer
moving
seals,
caliper
cools
better.
The
floating
so
is less
likely
to leak
or wear
out.caliOn
per
fewerside,
moving
andfeature
seals,
the has
negative
the parts
floating
is cause
less likely
to leak
or wear
out.
On
so
may
the pads
to wear
at an
angle
the
negative
side,
the
floating
feature
due to caliper motion. One advantage
may cause the pads to wear at an angle
due to caliper motion. One advantage
29
Anti-Rattle Clip
ffiJ
Dust Boot-
~
~
Seal
Piston
Seal
Steel Balls
/
~
Operating Shaft
Th'''' Be,,,o,
End Retainer
@
~.
•
a)~
/~~"W
'o't·Ro"tioo Pto
Pad and Plates
Thrust Screw
B"'eLe,.,
Seal
Pad and Plates
Thrust Screw
Floating caliper used on rear of some larger Ford cars features an integral parking-brake mechanism. As parking-brake shaft rotates, steel
balls roll up ramps and push on piston to apply brake. Drawing courtesy Bendix Corp.
r l u a i l l l y CiaIIper useu UII rear UI aume laryer roru cars raarures an lnregral parnlng-urane meclnanlsm. n s parnlng-urane snarr roiares, ateel
balls roll up ramps and push on piston t o apply brake. Drawing courtesy Bendix Corp.
Bridge
0-._
\1
Deflection
DuetoP
Caliper
I
I
Rotor
One-piece AP RaCing caliper is used on
race cars using 10-in.-diameter,I
small
I
0.375-in.-thick
solid rotors.
Caliper
is
One-piece AP Racing
caliper is
used on
available
withcars
1.625
or 1.750-in.
pistons.
small
race
using
10-in.-diameter,
Photo courtesy AP
Racing.
0.375-in.-thick
solid
rotors. Caliper is
available with 1.625 or 1.750-in. pistons.
Photo courtesy AP Racing.
of the floating caliper on road cars is
the ease of using a mechanical parking
of
the floating
caliper on road
cars is
The single-piston
design
is
brake.
the easeoperated
of using abymechanical
parking
easily
a parking-brake
brake. while
T h e asingle-piston
is
cable,
fixed caliper design
with piseasily
a parking-brake
tons onoperated
both sidesbyof the
rotor is more
cable, while a fixed caliper with pisdifficult.
tons
bothbody
sidescan
of the
is more
A on
caliper
be rotor
one piece
of
difficult.
metal or it can be several pieces
A caliper
body Boiled
can be one
pieceuse
of
bolted
together.
designs
metal
or it can be
pieces
only high-strength,
highseveral
torque-value
bolted
together.
Boltedmust
designs
use
bolts because
a caliper
not flex
only
high-strength,
high
torque-value
during heavy brake application. Bebolts because
caliper
must
flex
rotor,
thenot
caliper
cause
it spansa the
during
heavy
brake
application.
by
body acts as a curved beam loadedBecause
spanseach
the pad
rotor,
forces it
against
. If the
the caliper
caliper
body acts
a curved
beam
by
theasdriver
senses
thisloaded
as a soft
flexes,
forces
againstIteach
thetocaliper
brake pedal.
will pad.
also If
tend
cock
flexes,
the driver
senses this
as aconsoft
the pistons.
This reduces
braking
brake pedal.
It will the
alsopads
tendwear
to cock
sistency
and makes
in a
the
pistons. This reduces braking contaper.
sistency and makes the pads wear in a
taper.
30
Two-piece caliper is for small race cars
10.5- in.-diameter,
0.44- in.-thickI
solid rotors.caliper
Caliperisuses
pistons.
Two-piece
for 2.00-in.
small race
cars
Photo courtesy
AP RaCing. 0.44-in.-thick
using
10.5-in.-diameter,
Iusing
solid rotors. Caliper uses 2.00-in. pistons.
Photo courtesy AP Racing.
You can visualize caliper flex using
a C-clamp. The frame of the C-clamp
You cantovisualize
caliper flex body.
using
is similar
a disc-brake-caliper
aAsC-clamp.
The
frame
of
the
C-clamp
the C-clamp is tightened , it simuis similar
a disc-brake-caliper
lates
the to
clamping
action of a body.
discAs
the caliper.
C-clampAfter
is tightened,
it simubrake
the C-clamp
is
lates
clamping
action
of ahandle
disctight, the
continued
turning
of the
brakedistort
caliper.
the This
C-clamp
is
will
the After
C-frame.
is what
tight,
continued
turning
of
the
handle
happens to a flimsy caliper when the
will
distort
the C-frame.
brakes
are applied
hard. This is what
happens
to a flimsy
the
The portion
of the caliper
caliper when
body that
brakes
are
applied
hard.
spans the outside of the rotor is called
portion
of the
caliperdetermines
body that
theThe
bridge.
Bridge
stiffness
spans
outside
of the Bridge-design
rotor is called
overallthe
caliper
stiffness.
bridge. Bridge
determines
the
requirements
call stiffness
for stiffness,
which
overall
caliper
stiffness.
Bridge-design
requires a thick cross section and
requirements
call the
for caliper
stiffness,
which
weight. Because
must
fit
requires
cross side
section
between athethick
outboard
of and
the
fit
weight.
the wheel
caliperrim,
must
rotor andBecause
inside the
space
between the dictate
outboard
side ofcross
the
requirements
a thinner
rotor and inside
the wheel rim,
section.
Unfortunately,
this space
may
requirements dictate a thinner cross
section. Unfortunately, this may
Fluid pressure in disc-brake-caliper body
exerts a force P on each side of caliper and
tries
bend caliper
bridge. Caliper-bridge
Fluid to
pressure
in disc-brake-caliper
body
stiffness
is critical
caliper
design.
If
exerts a force
P onpart
eachofside
of caliper
and
caliper
is too bridge.
thick, wheel
may not
tries to bridge
bend caliper
Caliper-bridge
fit over it. is
On
the inside, of
most
car deSigners
stiffness
criticalpart
caliper
design. If
want largest
rotorwheel
diameter,
so
caliper
bridge possible
is too thick,
may not
bridge
limited.
fit overthickness
it. On the is
inside,
most car designers
want largest possible rotor diameter, so
bridge thickness is limited.
allow caliper flexing.
Because
bridge design
is a
allow caliper flexing.
compromise,
most calipers have
Because
bridge
about
the same
bridge design
thickness.is Buta
compromise,
most
calipers
havea
racing calipers are designed with
about
the
same
bridge
thickness.
But
wider bridge to gain additional
racing calipers are designed with a
stiffness.
wider
bridge piston
to gain
additional
is installed
in a
A disc-brake
stiffness.
machined bore in the caliper body.
A disc-brake
is have
installed
in a
Usually,
floatingpiston
calipers
a single
machined
boreside
in of
thethecaliper
body.
on one
rotor. Fixed
piston
Usually, have
floating
calipers
a single
calipers
one
or twohave
pistons
on
piston
on
one
side
of
the
rotor.
Fixed
each side of the rotor.
calipers
one or are
tworequired
pistons on
on
When have
big calipers
each side
of the rotor.
heavy,
powerful
cars, a single piston
big the
calipers
areis required
not do
job. It
difficult on
to
willWhen
heavy, powerful cars, a single piston
will not do the job. It is difficult to
caliPer
Pad
;;
.. .
-
'
Brakes
Applied
..
,
.
'
,'
,
.
*
.
Seal
.
... .
Brakes
Applied
Piston
Piston
,
Piston
Frank Airheart, working for Alston Industries, designed this racing
caliper with noncircular pistons. Kidney-shaped pistons closely
match
the pads,
resulting
in more
even pad-to-rotor
clamping
Frank Airheart,
working
for Alston
Industries,
designed this
racing
pressure.
Drawing
courtesy
Alston Kidney-shaped
Industries.
caliper with
noncircular
pistons.
pistons closely
match the pads, resulting in more even pad-to-rotor clamping
pressure. Drawing courtesy Alston Industries.
Cross section through caliper-piston seal shows position of seal
brakes applied and released. When brakes are released, seal I
retracts
piston through
from rotor.
As pad wears,
slides
on piston
to
Cross section
caliper-piston
seal seal
shows
position
of seal
compensate.
with brakes applied and released. When brakes are released, seal
Iwith
retracts piston from rotor. As pad wears, seal slides on piston to
compensate.
Flu id
Pressure
Fluid
Pressure
Fluid
Pressure
Fluid
Pressure
Piston
Piston
Y'
Pad
Pad
Pad
. .-:. -:-;
,. .
Single-Piston
Caliper
Single-Piston
Caliper
Pressure of Lini ng
on Rotor
Pressure of Lining
on Rotor
-.;:: :::,.'
11113-1
Dual- Piston
Caliper
Dual-Piston
Pressure of Lining
on Rotor
Pressure of Lining
on Rotor
Caliper
Wide brake pad used with large single piston results in uneven pressure on rotor. Unsupported ends of pad deflect and apply little pressure.
Wide pads should be used with multiple-piston calipers. More-even pad-to-rotor pressure resulting from two smaller pistons gives improved
braking.
Wide
brake pad used with large single piston results in uneven pressure on rotor. Unsupported ends of pad deflect and apply little pressure.
Wide pads should be used with multiple-piston calipers. More-even pad-to-rotor pressure resulting from two smaller pistons gives improved
braking.
make a large single-piston caliper that
fits inside a wheel. As the caliper gets
make
caliper
that
larger, aitlarge
gets single-piston
wider. If a single
piston
fits
the caliper
gets
wereinside
useda wheel.
with a As
wide
rectangular
larger,
getssurface
wider. would
If a single
piston
pad, theit pad
not contact
were
used
with
a
wide
rectangular
the rotor evenly. If the pad overhangs
pad,
pad surface
contact
the the
piston,
it will would
bend not
when
the
the
rotor
If Only
the pad
brakes
areevenly.
applied.
thatoverhangs
pad porthe
will bend
tion piston,
directly it behind
the when
piston the
is
brakes
are
applied.
Only
that
pad porloaded aga inst the disc. Multiple
pistion
directly this.
behind the piston is
tons minimize
loaded
thespread
disc. caliper-piston
Multiple pisIn anagainst
effort to
tons
minimizethis.
load evenly against the pad and
In an effort
to spread
caliper-piston
achieve
maximum
piston
area for a
load
evenly
against
pad and
given-size
caliper,
FranktheAirheart
deachieve
maximum
piston
area
veloped a racing caliper with a for
non-a
given-size
caliper,
decircular piston
for Frank
AlstonAirheart
Industries.
veloped
a racingkidney-shaped
caliper with apiston
nonThis
unusual
circular
for the
Alston
Industries.
roughly piston
matches
shape
of the
This
unusual
kidney-shaped
piston
brake lining . Consequently, there
is
roughly
matches
the and
shape
of disthe
little piston
overhang
lining
brake lining. Consequently, there is
little piston overhang and lining dis-
tortion with this design .
Multiple-piston calipers are used on
tortion
with this
most large
and design.
powerful cars. Most
Multiple-piston
calipers
are used
on
race
cars with over
lS0-HP
engines
most
large
and
powerful
cars.
Most
use multiple-piston calipers. These
race
carshave
with four
over or150-HP
usually
more engines
pistons .
use
These
The multiple-piston
largest calipers calipers.
are found
on
usually
haveand
fourGTorcars.
more
pistons.
racing stock
These
caliThe
largest
calipers
arerotor.
found
on
pers cover
nearly
half the
Usualracing
stock
and
G
T
cars.
These
calily larger, multiple-piston calipers use
pers
cover
nearlyFloating
half thecalipers
rotor. Usuala fixed
mount.
using
ly
larger, pistons
multiple-piston
multiple
are rare incalipers
racing,use
alathough
fixed mount.
calipers
BMW Floating
uses a big
ATE using
twomultiple
pistons aluminum
are rare in caliper
racing, alpiston f10ating
on
though
BMW uses a big ATE twothe M 1 coupe.
piston
Most floating
caliper aluminum
pistons arecaliper
made on
of
the
M1
coupe.
steel, aluminum or cast iron. MoldedMost caliper
are made
of
phenolic
plastic pistons
is becoming
popular
steel,
aluminum
or
cast
iron.
Moldedon road cars because of its low cost
phenolic
is becoming
popular
and
lowplastic
thermal
conductivity.
on
road cars
becausehasn't
of its found
low cost
However,
phenolic
its
and low thermal conductivity.
However, phenolic hasn't found its
way into many racing app lica tions yet,
even though it should work quite well
way
into
many
applications yet,
where
f1uid
boilracing
is a problem.
even
it should
workisquite
well
A though
disc- brake
piston
usually
where
is a problem.
sealed fluid
with boil
a square
cross-section 0A This
disc-brake
piston as istheusually
ring.
seal stretches
piston
0sealed
a square
cross-section
moves with
toward
the rotor.
When the
ring.
stretchesthe
as the
piston
brakesThis
areseal
released,
stretched
moves
toward
the rotor.
Whenelimthe
rubber seal
retracts
the piston,
brakes
are need
released,
the stretched
inating the
for return
springs.
rubber
elimBecauseseal
the retracts
pad and the
rotorpiston,
surfaces
are
inating
the
need
for
return
springs.
flat, only a slight movement is needed
Because
the pad
and rotor surfaces
are
to obtain
pad-to-rotor
clearance.
flat,
only a slight
movement
is needed
Consequently,
disc
brakes never
need
to
obtain The
pad-to-rotor
clearance.
adjusting.
piston moves
to take
Consequently,
disc brakes never need
up wear.
adjusting.
The piston
to with
take
Some calipers
are moves
designed
up
wear.springs on the pistons. Airheart
return
Somecalipers
calipershave
are this
designed
with
racing
mechanical
return
springs
on theto pistons.
Airheart
retraction
feature
make sure
the
racing
calipers
mechanical
pad never
dragshave
on this
the rotor.
With
retraction feature to make sure the
pad never drags on the rotor. With
31
Caliper
r------1 -
-
~FF
- - - _
- ..
- - - 1- --"'--------,
-
Rotor
- - - - - - -FF- R
T
. - , - - - Caliper
Mounting
y Caliper
~
Bracket
Mounting
Bracket
Bolt
Bolt
Forces on brake pads, indicated by FF' are resisted by a force R at
caliper bracket. Because force R is not in line with the rotor, twisting
torque
T is pads,
also applied
toby
the
Effect
twisting
Forces
on brake
indicated
Ffibracket.
are resisted
by aofforce
R at
torque
on the bracket
shown
If mounting
R isinnotlower
in linedrawing.
with the rotor,
twistcaliper bracket.
Becauseisforce
bracket
is not
sufficiently
rigid,tocaliper
cocks against
causing
torque
T is
also applied
the bracket.
Effect rotor,
of twisting
ing uneven
wear, is spongy
pedal,
excessive
pedal
torque
on thepad
bracket
shown in
lowerand
drawing.
If mounting
movement.
Usesufficiently
a stiff caliper
bracket
and
this will
not happen.
bracket
is not
rigid,
caliper
cocks
against
rotor, caus-
Husky bracket attaches caliper to spindle on this sprint car. Because spindle was not designed to mount a disc-brake caliper,
mounting
bolts attaches
are too far
from to
caliper.
Risk
twisting
Husky bracket
caliper
splnale
on of
tnlsbracket
sprlnr car.
Beexcessively
is reduced
heavy plate.
cause
spindle
was notbydesigned
t o mount a disc-brake caliper,
mounting bolts are too far from caliper. Risk of bracket twisting
excessively isreducedby heavy plate.
ing uneven pad wear, spongy pedal, and excessive pedal
movement. Use a stiff caliper bracket and this will not happen.
Racing stock cars use the largest calipers.
This is the popular Hurst! Airheart caliper
with
twostock
pistons
onuse
each
side
of rotor.
Racing
cars
the
largest
calipers.
This is the popular Hurst/Airheart caliper
with two pistons on each side of rotor.
Tilton Engineering sells sturdy calipermounting brackets for popular race-car
applications. Bracket
adapts caliper to
"
four-bolt
normally
used to
mounting pattern
brackets
for popular
racemount
:;&
drum-brake
plate.
Disc brakes
applications.backing
Bracket
adapts
caliper can
to
be fitted pattern
in place normally
of drum used
brakes
a
four-bolt
t o with
mount
bracket suchbacking
as this. plate. Disc brakes can
drum-brake
-<
be fitted in place of drum brakes with a
bracket such as this.
mechanical-retraction calipers such as
this, a slightly different mastermechanical-retraction
calipers
as
cylinder
design is used.
This such
is disthis, ain Chapter
slightly 5.different mastercussed
cylinder design
is used. This is disCaliper
Mounting-It is essential
5.
cussed
in
Chapter
that a caliper not move or flex as the
Caliper
Mounting-It
brakes are applied-other is
thanessential
the latthat movement
a caliper not
or flex
as the
eral
ofmove
a floating
caliper.
If
brakescaliper-mounting
are applied-other structure
than the latthe
is
eral
movement
of a floating
caliper.
If
flexible,
the caliper
can twist
on its
the caliper-mounting
structure
is
mount.
This causes uneven
pad wear,
caliper
twist on
its
and can
excessive
pedal
aflexible,
spongy the
pedal
mount.
This causes uneven pad wear,
movement.
a spongy
pedalrace-car
and excessive
pedal
A common
design error
is
movement.
using thin, flexible brackets to mount
common
race-car
design
errorthe
is
theA caliper
to the
spindle.
Because
using thin, flexible brackets to mount
the caliper to the spindle. Because the
32
rotor and caliper-mounting bracket lie
in two different planes, the caliper
rotor
andhas
caliper-mounting
bracket
lie
bracket
a twisting force on
it when
in
different
planes,If the
the bracket
caliper
the two
brakes
are applied.
bracket
has aittwisting
forcecocking
on it when
is
too thin,
will twist,
the
the
brakes
are
applied.
If
the
bracketa
caliper against the rotor. Generally,
is
too thin, bracket
it will twist,
cocking
the
mounting
at least
I/2-in.
caliper
againstbethe
rotor.
Generally,ona
thick should
used,
particularly
mounting
bracket
least
large race cars
such asatstock
cars 112-in.
.
thick should be used, particularly on
large
race cars
such as stock cars.
SPLASH
SHIELDS
The inboard side of the rotor on
SPLASH
SHIELDS
most
production
cars is shielded by a
The
inboard
the rotor
on
steel plate that side
looksof similar
to the
most
production
cars
is
shielded
by
backing plate on a drum brake. This isa
steel
plateshield.
that looks
similar
to prethe
the splash
This shield
only
backing plate on a drum brake. This is
the splash shield. This shield only pre-
vents mud, dirt and water from being
thrown up against the inboard surface
vents
and water
from
being
of
the mud,
rotor. dirt
It does
not have
a structhrown
up against
the inboard
. If splash
shields surface
are not
tural function
of
the road
rotor. debris
It doesmay
not have
strucused,
cause a excess
tural
function.
If
splash
shields
are
not
scoring and wear on the inboard side
used,
road debris may cause excess
of
the rotor.
scoring
and wear on
the shields
inboard tend
side
Unfortunately,
splash
of
the
rotor.
to block cooling air from reaching the
Unfortunately,
rotor.
This is why splash
splash shields
shields tend
norto
block
cooling
air
from
reaching
the
mally are not used on race cars. Racerotor.
This usually
is why need
splashallshields
norcar brakes
the cooling
mally
are get.
not Road-debris
used on race contaminacars. Racethey can
car
brakes
usually
need
all
the
tion is a secondary problem. cooling
Therethey
get. Road-debris
fore, can
deleting
the splash contaminashield is a
tion is a secondary
Therecompromise
betweenproblem.
brake cooling
fore,
deleting
the splash shield is a
and rotor
protection.
compromise between brake cooling
and rotor protecti.on.
BRAKE PADS
Disc-brake
friction
material
is
BRAKE
mounted PADS
on a brake-pad backing plare,
Disc-brake
material
is
which
is usuallyfriction
a steel plate
. This asa brake-pad
plare,
mountedis on
sembly
called
a brake backirlg
pad. Friction
which
steel plate.
This
asmateri aisl isusually
usu allya bonded
to the
backsembly
is
called
a
brake
pad.
Friction
ing plate during the lining-molding
material
usually
bondedit to
the backbut
sometimes
is joined
in
process, is
plate during
the with
lining-molding
operation
rivets and
aingseparate
process, but sometimes
it is joined in
conventional
bonding adhesives.
a separate
operation
with
rivets
and
Brake pads are sold with
friction
conventional
bonding
adhesives.
material attached
as are
brake shoes.
Brakedrum-brake
pads are sold
withpadfriction
Unlike
shoes,
backmaterial
attached
as
are
shoes.
reused.
To
ing plates usually are notbrake
Unlike
drum-brake
shoes,your
pad partsbackmake sure,
check with
ing plates
usually
are discarding
not reused.used
To
house
before
supply
make
sure,
check
with
your
partsdisc-brake pads.
supply
used
The house
piston before
in thediscarding
brake caliper
disc-brake
often doespads.
not bear directly against
piston
in many
the brake
caliper
theThe
brake
pad . On
cars, there
is
often does not bear directly against
the brake pad. On many cars, there is
an anti-squeal shim between the
piston and brake pad. This sheet-metal
an anti-squesl
between
the
shim
is supposed shim
to reduce
the noise
piston
and
brake
pad.
This
Sheet-metal
caused when the pad chatters against
shimrotor.
is supposed
reduce the noise
the
Follow to
manufacturer's
incaused
when
the
pad
chatters
structions when servicing
the against
brake
the
Follow
inpads.rotor.
These
shimsmanufacturer's
may require restructions
when with
servicing
the brake
placement along
the pads.
pads.
Theserace
shims
requirehave
recars,may
insulators
On some
placement
along
with
the
pads.
been used between the brake pads
Oncaliper
some race
cars,This
insulators
have
is done
to
and
pistons.
been
used
between
the
brake
pads
reduce brake-fluid and piston-seal
and
caliper pistons.
Thistemperature
is done to
temperature.
Excessive
reduce
brake-fluid
and
piston-seal
can cause seal failure or fluid
boiling.
temperature.
Excessive
temperature
If an insulator is used, it must be stiff,
can cause
or fluid
boiling.
andseal
notfailure
too large.
These
constrong,
If an insulator
is used,make
it must
stiff,
flicting
requirements
thebedesign
strong,
not toovery
large.
These conofa goodand
insulator
difficult.
flicting
requirements
make
the design
in
Friction materials are covered
of a good
insulator
verychapter.
difficult.
detail
in the
following
Friction materials are covered in
detail in the following chapter.
••
1984 Corvette rear brake less rotor shows
splash shield. Thin circular plate mounted
behind
rotor protects
it from
and
1984 Corvette
rear brake
lessroad
rotordirt
shows
water.
cars
usecircular
splash plate
shields
to prosplash Road
shield.
Thin
mounted
vide
good
braking
in ait dirty
environment.
behind
rotor
protects
from road
dirt and
bettershields
off without
Most race
aresplash
water.
Road cars use
t o prosplash
shields
because
cooling
vide good
braking
in a they
dirty block
environment.
air.
Photo
courtesy
Girlock
Ltd. off without
Most
race
cars are
better
splash shields because they block cooling
air. Photo courtesy Girlock Ltd.
Racing brake pads look similar to those for
road use. Pads come with lining bonded to
a
steel brake
backing
plate.
are deRacing
pads
lookThese
similarpads
to those
for
signed
forPads
JFZ come
racingwith
calipers
use on
road use.
liningfor
bonded
to
dragsters.
Photoplate.
courtesy
JFZpads
Engineered
a steel backing
These
are deProducts.
signed
for JFZ racing calipers for use on
dragsters. Photo courtesy JFZ Engineered
Products.
33
Friction Matarial
Friction Matefzl
4
Stock car running on road course is hard on brakes. Stock cars are the heaviest road-racing vehicles, and are powerful. Brake ducts and
heavy-duty linings are a must on hot day at Riverside Raceway.
Stock car running on road course is hard on brakes. Stock cars are the heaviest road-racing vehicles, and are powerful. Brake ducts and
heavy-duty linings are a must on hot day at Riverside Raceway.
The material that rubs on a brake
drum or rotor is called friction material
material
rubs
on afriction
brake
or The
brake
lining. that
Drumbrake
drum
or rotor
is called friction
material
is attached
to thematerial
brake
or brake
Drum-brake
friction
shoes.
In alining.
disc brake,
friction material
material
is to
attached
to the plates.
brake
is
attached
steel backing
shoes.
a disc brake,
friction material
composition
is simiFrictionInmaterial
is
to steel
backing
lar attached
in both types
of brakes,
but itplates.
is deFriction
material
composition
disc
signed for higher temperaturesisinsimilar
in both types of brakes, but it is debrakes.
signed for higher temperatures in disc
brakes.
WHAT IS FRICTION?
Friction exists when two contacting
WHAT ISeither
FRICTION?
surfaces
try to or do slide
Friction
exists
whenThere
two contacting
each
other.
is always
against
surfaces
either
try
to
do slide
resistance to sliding. This or
resistance
is
againstfriction
each force.
other. The
There
is always
friction
force
called
resistance
to sliding.
resistance
is
on the
sliding This
surfaces
at their
acts
called
friction
force.
The
friction
force
point of contact in a direction opposite
acts
on the sliding surfaces at their
to movement.
point
contact
in aisdirection
In aofbrake,
there
friction opposite
between
to
movement.
the friction material and the drum or
In a brake, there is friction between
the friction material and the drum or
34
rotor rubbing surface. The problem is
controlling the amount of friction
rotor and
rubbing
The
is
usingsurface.
it to stop
theproblem
car.
force
controlling
theforce
amount
of friction
The friction
depends
on two
force
usingof
it tosurfaces
stop theincar.contact
things:andtypes
The
friction
force
depends the
on surtwo
and amount of force pressing
things:together.
types of surfaces in contact
faces
andEach
amount
of force
surof these
haspressing
its ownthe
name.
faces
together.
The force pressing the two surfaces
Each ofis called
these normal
has its force
own, or
name.
together
perThe
force force.
pressing
the two
surfaces
pendicular
Because
only
engitogether
is called
or perneers use
the normal
word force,
normal
for
Because
only
engipendiclrlar
force.
pelpendiculal; I'll use perpendicular
to
neers confusion.
use the Itword
for
avoid
should normal
be obvious
perpendicular,
1'11 perpendicular
use perpendicular
to
that a higher
force
avoid
confusion.
It
should
be
obvious
causes a higher friction force. Ifsliding
that a are
higher
perpendicular
force
surfaces
slippery,
friction force
is
causes
higher
friction
force.
If sliding
low. If athe
surfaces
resist
sliding,
fricsurfaces
force is
"slipperiness"
tion forceare
is slippery,
high . Thefriction
low.
If
the
surfaces
resist
sliding,
fricof a surface is described by a number
tion force
high. Theof"slipperiness"
called
its iscoefficient
friction. The
of
a surface
is described
a number
value
of this
friction by coefficient
called its coefficient of jiction. The
value of this friction coefficient
varies, usually between 0 and 1. The
friction coefficient for surfaces trying
varies,
between
0 and
1. The
to slideusually
is given
by the
following
friction :coefficient for surfaces trying
formula
to slide is given by the following
Friction Force
formula:
f.1. = Perpendicular Force
Friction Force
If Perpendicular
the coefficientForce
of friction is low )
=
'the surfaces are slippery - the friction
If the
coefficient
of friction
is low,
If the friction
coefficient
force
is low.
the
surfaces
are
slippery-the
friction
is high, the surfaces grip each other
force
is the
low. If
the friction
betterfriction
force coefficient
is high.
is high,
griphave
eacha other
Tires
on the
dry surfaces
pavement
high
better-the
friction but
force
on is
ice high.
they
friction
coefficient,
Tires
n dry
pavement
have a high
have a olow
friction
coefficient.
friction
coefficient,
but on ice
life complicated,
the they
fricTo make
have
a
low
friction
coefficient.
tion coefficient has two different
To make
complicated,
fricvalues.
It is life
somewhat
higher the
if there
tion
coefficient
has
two
different
is no sliding. As soon as the surfaces
values.
is somewhat
there
start
to Itmove
relative higher
to eachif other,
is nofriction
sliding. coefficient
As soon as drops
the surfaces
the
to a
start
move
relative
other,
lower to
value
. This
is whytoit each
is harder
to
the friction coefficient drops to a
lower value. This is why it is harder to
W = Weight
FF = Friction Force
W = Weight
W = Perpendicular Force
FF = Friction Force
Coefficient of Friction =~
W = Perpendicular Force
IL
Coefficient
Friction
To slide box,
tractorofhas
to pull=
with
W a force
equal to friction force Fp Friction force is
related
perpendicular
force
two
To
slideto
box,
tractor has to
pull pushing
with a force
sliding
this example,
equal t osurfaces
friction together.
force F, In
Friction
force is
the
perpendicular
force force
is boxpushing
weighttwo
W.
related
perpendicular
Frictionsurfaces
coefficient
is friction
force
divided
sliding
together.
In this
example,
by
force,
theperpendicular
perpendicular
forceorisFF/W.
box weight W'
Friction coefficient is friction force divided
by perpendicular force, or F,/W.
start something sliding than It IS to
keep it sliding. The friction coefficient
start
slidingis than
is to
calledit static
beforesomething
sliding occurs
keep
it
sliding.
The
friction
coefficient
coefficien t of friction. After sliding
static
before it's
sliding
occurs
is called
called
dynamic
coefficient
starts,
coefficient
of
friction. of friction. After sliding
dynamic
coefficient
starts,
called
Eitherit'stype
of friction
coefficient
is
of
friction.
calculated by the previously given
Either type
friction coefficient
is
Justof remember
that the
formula.
calculated
previously
value
drops by
oncethe
sliding
starts. given
formula.
Justweremember
thatabout
the
In a brake,
are concerned
value
drops
once
sliding
starts.
the coefficient of friction between the
In a brake,
we are
about
friction
material
andconcerned
the drum
or
the coefficient
between
the
For most
brake
rotor
surface.of friction
friction
and the
drum or
rna terials,material
the friction
coefficient
is
rotor
surface.
For
most
about 0.3. I'll discuss later howbrake
the
materials, the
friction affects
coefficient
is
coefficient
of friction
brakeabout
0.3. I'll discuss later how the
pedal effort.
coefficient of Friction-The
friction affects friction
brakeTire-to-Road
pedal
effort.
coefficient between the tires and road
Tire-to-Roadhow
Friction-The
determines
fast a car canfriction
stop.
coefficient
between
the tires
This value varies from
less and
thanroad
0.1
determines
how0.5fast
car can roads
stop.
on wet ice and
on arain-slick
This
value
varies
less than
than
l.0 from
for racing
tires 0.1
on
to more
on
wet
ice
and
0.5
on
rain-slick
roads
dry pavement. The friction coefficient
to more
1.0 for racing
tires for
on
for
tires than
on pavement
is critical
dry
pavement.under
The friction
coefficient
all conditions.
It
performance
for
tires onhow
pavement
critical
for
determines
fast a caris can
accelerperformance
all as
conditions.
as well
how fast It
it
ate
and cornerunder
determines
how fast a car can accelercan
stop.
ate and corner as well as how fast it
can stop.
FRICTION-MATERIAL
CHARACTERISTICS
FRICTION-MATERIAL
A good friction material must have
CHARACTERISTICS
these
characteristics:
A good friction material must have
these characteristics:
As first car brakes in turn, inside front wheel locks. Tire smokes as it slides on pavement
due to heat from friction. Following car can slow quicker because its wheels aren't locked.
Static-nonsliding-coefficient
of front
friction
is higher
dynamic-sliding-coefficient
of
As
first car brakes in turn, inside
wheel
locks. than
Tire smokes
as i t slides on pavement
friction.
due t o heat from friction. Following car can slow quicker because its wheels aren't locked.
Static-nonsliding-coefficient
of friction is higher than dynamic-sliding-coefficient
of
friction.
• Friction coefficient must be high.
• Friction coefficient must not
Friction
be high.
change
withcoefficient
increasingmust
temperature.
Frictionnot coefficient
• Should
wear rapidly. must not
change
with
increasing
• Should
not
damage temperature.
surface it rubs
Should
not
wear
rapidly.
against.
not damage
it rubs
Must withstand
highsurface
temperature
• Should
against. failing.
without
Must withstand
high when
temperature
not be noisy
brakes
• Should
without
failing.
are applied.
Should
not be there
noisy iswhen
brakes
Unfortunately,
no perfect
are
applied.
friction material. Instead, there are
Unfortunately,
thereeach
is no
many
different types,
oneperfect
made
friction material. Instead, there are
many different types, each one made
FRICTION & SURFACE AREA
For sliding surfaces, the friction
FRICTION
& SURFACE
AREA
force
depends
only on the
coeffiFor sliding
surfaces,
the friction
cientot
friction
and perpendicular
force
only
the or
coeffiforce. depends
The amount
of on
sliding
rubcient
of friction
anddoes
perpendicular
bing surface
area
not affect
force. The
amount
of sliding
rubfriction.
This
holds true
for all or
condibing surface
does
not affect
tions
of s lidingarea
where
matertal
isn't
friction.
true for
all condiremovedThis
fromholds
the sliding
surface.
tions
sliding
where
material
Skidofmarks
result
from
lockingisn't
up
surface.
removed
from
the
brakes
onthe
drysliding
pavement.
Each
Skid
marks
up
skid
mark
is result
rubberfrom
thatlocking
was torn
the brakes
on and
dry deposited
pavement.onEach
the tires
the
from
skid
mark Because
is rubber material
that wasistorn
pavement.
refrom
the
tires
deposited
on the
theand
tires
during sliding,
moved
from
pavement.
material
is resurface
ar eaBecause
does affect
the friction
movedConsequently,
from the tires the
during
sliding,
force.
greater
the
surface
area does
thethe
friction
area
in contact,
theaffect
greater
fricforce.force.
Consequently,
greater
the
tion
To makethethe
friction
area in contact,
greater
the fricwork forthe
tires
on pavement,
formula
tion force. To make the friction
formula work for tires on pavement,
to emphasize a particular characteristic
or several of them. The ideal friction
to emphasize
a particular
characteristic
material
for severe
or racing
use is not
or
friction
theseveral
same ofasthem.
that The
for ideal
lowest-cost
material
for
severe
or
racing
use
is not
passenger-car use.
thePopular
same friction
as thatmaterials
for lowest-cost
fall into
passenger-car
use.categories:
one
of these basic
Popular
friction
fall into
• Organic material materials
held together
by
one
of
these
basic
categories:
resin binders. Contains asbestos, glass
together
by
or Organic
syntheticmaterial
fibers, held
and may
contain
resin
binders.
Contains asbestos, glass
metallic
particles.
or
syntheticmaterial
fibers, fused
and may
• Metallic
or contain
sintered
metallic
particles.
together. Almost entirely made of
@ Metallic material fused or sintered
together. Almost entirely made of
engineers choose to change the
coefficient of friction rather than the
engineers
choose to change the
fric
t ion formula.
coefficient
friction
rather
than
the
with
all but
width
being
For tires of
friction
formula.
coefficient of friction inequal, the
For tires
but widthThis
being
creases
as with
widthallincreases.
is
equal,
coefficient
of friction
infactor
that makes
the friction
a
majorthe
creases
as greater
width increases.
This
is
coefficient
than 1.0 for
wide
a
majortires.
factorSo,
thatthe
makes
the friction
racing
friction
coefficoefficient greater
than 1.0than
for wide
cientcannot
be greater
1.0
racing
So,isthe
frictionfrom
coeffiunless tires.
material
removed
the
cient
slidingcannot
surface.be greater than 1.0
unless
is removed
from
the
discussing
handling,
I call
Whenmaterial
sliding
surface.of friction of a tire its
the
coefficient
When
discussing
handling,
call
This
differentiates
grip I from
grip.
the coefficient
of friction
of a tirebeits
ordinary
coefficient
of friction,
grip. This
differentiates
grip from
cause
tire area
affects "coefficient
ordinary
coefficient
of friction,
beof friction."lf
the subject
of tires and
cause
tire area
affects
"coefficient
grip
interests
you,
read my
HPBook
of
friction."
If the
subject
of tires and
"How
to Make
Your
Car Handle."
grip interests you, read my HPBook
"How to Make Your Car Handle."
35
Metallic linings for 1962 Corvette drum
brakes were highly successful for racing.
Prior to the use of disc brakes, drum
brakes
with these
werefor
relatively
brakes were
highly linings
successful
racing.
fade-free,
even
3000-lb,
300-HP
Prior to the
useonof a disc
brakes,
drum
sports
brakescar.
with these linings were relatively
fade-free, even on a 3000-lb, 300-HP
sports car.
metal particles.
• Semi-metallic material held together
metal
particles.
by resin
binders. Contains steel fibers
Semi-metallic
material held together
and metallic particles.
by resin binders. Contains steel fibers
and metallic MATERIALS
particles.
ORGANIC
Most brake friction material on the
ORGANIC
MATERIALS
market is organiC.
This means that the
Most brake
friction
on the
friction
material,
suchmaterial
as petroleummarket
is organic.
meanswas
thatonce
the
based products
andThis
plastics,
friction
material,
such
as
petroleuma living plant or animal. Early friction
based
products
plastics,leather
was once
materials
wereandwood,
or
a living impregnated
plant or animal.
friction
cotton
withEarly
asphalt
or
materialsThese
were old-fashioned
wood, leather
or
rubber.
linings
cotton
impregnated
with
asphalt
or
did
not
have many desirable
rubber. These Ifold-fashioned
characteristics.
used severely,linings
they
did
have
many desirable
tendednot
to catch
on fi re!
characteristics.
If used
severely,
Superior friction
material
was they
obtended
to
catch
on
fire!
tained
by
weaving
asbestosSuperior friction
was with
obimpregnated
fibers material
together
tained
by
weaving
organic
material
to glueasbestosthem
impregnated
fibers
together
with
together.
Today,
asbestos
is still used
organic
material
to
glue
them
in most brake linings, along with varitogether.
Today,
still used
ous
binders
andasbestos
frictionis modifiers.
in most brake
along
with holds
variBinder,
usuallylinings,
a plastic
resin,
binders
and
friction
modifiers.
ous
the friction material together. The
Binder, provide
usually astrength
plastic resin,
fibers
and holds
resist
the friction
material
together.
wear.
Glass and
synthetic
fibers The
are
fibers
provide
strength
andin some
resist
beginning
to replace
asbestos
wear. Glass and
synthetic
fibers
are
organic-lining
material.
Friction
modibeginning
to
replace
asbestos
in
some
fiers tune the friction of the material
organic-lining
material. Friction modito the desired level.
fiers
tune
the
friction
the first
material
Molded brake
liningsofwere
proto
the
desired
level.
duced in the '30s. Woven lining matebrake fibers
linings was
were manufacfirst prorialMolded
with small
duced
in the a'30s.
Woventechnique.
lining matetured using
molding
In
rial
fibers was
manufacof friction
material,
the
this with
type small
tured using
a molding
In
binder,
modifiers
andtechnique.
fibers are
this
type
of friction
material,
the
pressed
together
in a mold
under heat
binder,
modifiers
and fibers
are
and
pressure
to produce
a curved
pressed
together
in
a
mold
under
heat
brake-shoe lining.
and pressure to produce a curved
brake-shoe lining.
36
In a molded lining, other materials
such as mineral or metallic particles
In aadded
molded
lining, the
other
materials
were
to change
characterissuch
as
mineral
or
metallic
Later,
tics of the friction material.particles
were
added
change were
the characterispads for
discto brakes
developed
tics of
the friction
from
molded
material,material.
as well as Later,
semipads
for disc
brakes were developed
metallic
high-temperature
friction
from
moldedWoven
material,
as wellgradually
as semimaterials.
linings
metallic
high-temperature
friction
became less popular because
the
materials.
Woven was
linings
gradually
range of materials
limited.
Today,
became material
less popular
because
the
woven
is found
in clutch
range
of
materials
was
limited.
Today,
discs, but not in brakes.
woven
material
found has
in a clutch
Organic
friction is
material
variediscs.
but not in brakes.
ty of ingredients.
Manufacturers keep
material has
varietheOrganic
'exact friction
specifications
a asecret.
ty
of
ingredients.
Manufacturers
keep
Generally, a typical organic brake
the
specifications
a secref.
lining.exact
contains
these components:
• Asbestos fia bers for friction andbrake
heat
lining
contains
thesematerial
components:
resistance.
Friction
is usually
Asbestos
fibers
for friction and heat
more
than 50%
asbestos.
resistance.
Friction
material
such is
as usually
oil of
• Friction modifiers,
more than 50%
asbestos.
cashew-nut
shells,
give the desired
Friction
modifiers, such as oil of
friction
coeffici~nt.
cashew-nut
shells, give the desired
• Fillers, such
friction
coefficient.as rubber chips,
reduce
noise.
Fillers, such as rubber chips,
• Powdered lead, brass or aluminum
reduce
noise.
improves
braking performance.
Powdered
lead, as
brass
or aluminum
• Binders, such
phenolic
resin,
improves
braking together.
performance.
hold the material
Binders, agents
such as provide
phenolic proper
resin,
• Curing
hold
the
material
together.
chemical reactions in the mixture
Curing
agents provide proper
during
manufacturing.
chemical
reactions
in the mixture
The friction coefficient and wear
during
manufacturing.
properties of friction material can be
The friction
coefficient
and wear
modified
by changing
the components
properties
of
friction
material
can be
in this magic brew. When you change
modified
by changing
theprobably
components
lining material
, you are
getin this
magic brew.
WhenWhat
you ischange
ting
a different
mixture.
actuliningin material,
you are
probably
getThe
actual perally
it is a secret.
ting a different
is actuformance
of themixture.
materialWhat
is also
diffially
in determine.
it is a secret.
actual
percult to
YouThe
must
resort
to
formance
of
the
material
is
also
diffia trial-and-error method based on excult
to determine.
resort
to
perience
to find the You
best must
friction
matearialtrial-and-error
based on exfor a particularmethod
car.
to find theorganic
best friction
mateperience
Conventional
materials
rial
for
a
particular
car.
work well at low temperatures, but
Conventional
organic
their
friction coefficient
tendsmaterials
to drop
work well
low also
temperatures,
but
when
hot. atThey
usually wear
their
friction
coefficient
tends
to
drop
rapidly at high temperature. Above
when
hot. They
usually
wear
400F (204C),
mostalso
organic
materials
rapidly
at highandtemperature.
Above
have fade
wear problems.
400F (204C),
mostoforganic
materials
their good
wear
However,
because
have
fade
and
wear
problems.
properties when cool, low noise and
However,
because linings
of theiraregood
low cost, organic
usedwear
on
properties
when
most road cars
. cool, low noise and
low cost,
organic linings
are Friction
used on
HighTemperature
Organic
most
road
cars.
Material-A special organic lining,
High-Temperature
Organic
called
high-temperature
organiCFriction
materMaterial-A
special
organic
lining,
ial, has improved
wear
properties
at
called
high-temperature
organic mate/high temperatures.
However,
it has
improved
wearfriction
properties
at
ial, has wear
poorer
and low
at low
high
temperatures.
However,
it has
temperatures.
It is also
harder on
the
poorer and
wearrotors
and than
low low-temperature
friction at low
drums
organic materials. High-temperature
organic materials usually have a high
organic materials.
High-temperature
concentration
of metai
particles in
a high
organic
materials
usually
have coeffithem to increase the friction
concentration
metaiMost
particles
in
cient
and resistof heat.
popular
them
increase
friction coeffihigh-temperature
racing tolinings
are the
cient
resist heat.
Most
popular
organicand
materials.
The best
ones
work
racing
linings
high-temperature
well
up to
1250Fare
(677C).
organic
materials. Theorganic
best ones
work
High-temperature
material
well
up to
(677C).
is stiff
and1250F
brittle
compared to lowHigh-temperature
organic material.
material
temperature
organic friction
is
and itbrittle
compared
As stiff
a result,
is harder
to attachtoitlowto a
temperature
friction material.
shoe
or pad. organic
The old-fashioned
rivetAs
result, itwon't
is harder
attach
it to a
worktowell
because
ing amethod
shoe
or pad. tends
The old-fashioned
the material
to crack at therivetrivet
ing
method
workbonding
well because
holes.
And won't
ordinary
techthe material
to crack
at the rivet
niques
have tends
too low
a temperature
holes.
And
ordinary
bonding
techlimit. Therefore , great care must
be
niques
too low
a temperature
used inhave
attaching
high-temperature
limit.
great care
mustonly
be
organicTherefore,
friction material.
Trust
used
in
attaching
high-temperature
an expert. The best attachment is one
organic
material.
Trust
only
in whichfriction
the friction
material
is mold
an
expert.
is one
bonded
to The
the best
metalattachment
backing during
mold
in
which the friction
materialofisbondmanufacture.
A combination
to
the
metal
backing
during
bonded
ing and riveting also works well.
manufacture.
A combination
High-temperature
organicof bondlining
ing and
riveting
also works
well. operamay
require
a special
finishing
High-temperature
organic
on the drums or
rotors. lining
The
tion
may
require
a
special
finishing
operamanufacturer of the lining material
tion specify
on the what
drumsshould
or rotors.
The
will
be done.
manufacturer
of
the
lining
material
Always follow his instructions, or you
will
should be
done.
won'tspecify
achievewhat
the superior
performAlways
follow
instructions, or you
ance
of this
ma his
terial.
won't achieve the superior performance of this material.
METALLIC MATERIALS
In the mid- '50s, Chevrolet was
METALLIC
MATERIALS
competing
in road
races with its new
In
the
mid-'50s,
Chevrolet
V8 Corvette. Using drum
brakeswas
to
competing
in road
its new
stop
a 3000-lb
car races
with with
its 300-HP
V8
Corvette.
drum brakes
to
engine
was a Using
big technical
problem,
stop
a
3000-lb
car
with
its
300-HP
particularly in the 12-hour endurance
engine
a big To
technical
problem,
race at was
Sebring.
make the
Corparticularly
in the with
12-hour
endurance
vettes competitive
the lighter
forTo make
the Cor-a
race cars,
at Sebring.
eign
the company
developed
vettes
competitive
with the lighter
forceramic-metallic
brake-lining
material
eign
cars, the
company
developed
that could
operate
at extremely
higha
ceramic-metallic brake-lining material
temperatures.
that
couldcerametallic
operate at extremely
high
These
linings worked
temperatures.
well, but at the brutal Sebring 12-hour
These
linings
worked
race
they cerametallic
tended to wear
through
the
well,
at the brutal
brakebutdrums!
AfterSebring
these12-hour
early
race they tendedless-harsh
to wear through
the
experiments,
materials
brake
drums!
After
these
early
were developed, using an iron base
experiments,
less-harsh
materials
rather than abrasive
ceramic.
Ironusing
an offered
iron base
were
developed,
base metallic
linings
were
by
rather thanforabrasive
ceramic.
Chevrolet
street use
prior toIronthe
base metallic of
linings
offered
by
introduction
disc were
brakes
on the
Chevrolet The
for street
use metallic
prior to linthe
Corvette.
Chevrolet
introduction
of disc
onOnly
the
for brakes
the time.
ings were excellent
Corvette.
The
Chevrolet
metallic
linthe superior characteristics of the disc
ings
excellent
the time. Only
brakewere
has made
themfor
obsolete.
theMetallic
superior linings
characteristics
of the disc
are designed
to
brake
has
made
them
obsolete.
operate at higher temperatures than
Metallic linings are designed to
temperatures. It is also harder on the
drums and rotors than low-temperaf~rre operate at higher temperatures than
Organic friction material attached by bonding only didn't stay attached long under
racing
conditions.
Organic
friction material attached by bonding only didn't stay attached long under
racing conditions.
Grand Prix cars frequently run on courses with long straights and tight turns, which is extremely hard on brakes. Friction-material hardness is selected to match the course. "Hard"
linings
are required
when running
race likewith
this one
the streets
Long
Beach.
Grand Prix
cars frequently
run ona courses
longon
straights
and of
tight
turns,
which is extremely hard on brakes. Friction-material hardness is selected to match the course. "Hard"
linings are
requiredmaterials.
when running
race like this one on the streets of Long Beach.
organic
friction
Alla organic
materials, such as plastic resin, disinorganic
friction
materials. All reached
organic
tegrate at
high temperatures
materials,
such
as
plastic
resin,
disinin severe braking conditions. The
astegrate
at
high
temperatures
reached
bestos fiber in organic linings can
in severe braking
conditions. but
Thewith
aswithstand
high temperature,
bestos
fiber
in organic
linings
no
binder
to hold
it together
it hascan
no
withstand. The
highmetallic
temperature,
but solve
with
strength
materials
no
to . hold it together it has no
thisbinder
problem
strength.
The metallic
materials
solve
Sintering-Metallic
linings
are manuthis
problem.
factured using a sintering process . A
Sintering-Metallic
linings
are manumetal-powder mixture
is compressed
factured
using
a
sintering
process.
A
in a mold at high temperature and
metal-powder
is compressed
pressure. The mixture
metal partially
fuses
in a mold
high material.
temperature and
together
intoata solid
pressure.
The
metal
partially
fuses
Sintered friction material
can be
attogether
solid or
material.
tached tointo
the ashoe
pad by brazing,
can sinterbe ator Sintered
it can be friction
fused onmaterial
during the
tached
to
the
shoe
or
pad
by
brazing,
ing process . Sometimes, the material
or
i t can be to
fused
onplate
during
is sintered
a thin
andthe
thesinterplate
ingthen
process.
Sometimes,
the material
is
riveted
to the shoe
or pad .
is sintered
to a eliminates
thin plate and
plate
This
processes
the the
ne~d
for
is
then
riveted
to
the
shoe
or
pad.
organic adhesive.
This
processes
eliminates
the need
Metallic
friction
material
that for
is
organicon
adhesive.
glued
loses some of its highMetallic friction
material
is
temperature
capability.
This that
is beglued
on
loses
some
of
its
highcause the organic adhesive will fail at
temperature that
capability.
Thismaterial
is betemperatures
the friction
cause
the organicWhen
adhesive
will failure
fail at
can withstand.
such
temperatures
that the
frictioncomes
material
occurs,
the friction
m aterial
off
can
withstand.
failure
its backing,
and When
brakingsuch
is severely
occurs, the
affected
. friction material comes off
itsMetallic
backing,friction
and braking
severely
materialis does
not
affected.
fade at high temperature, but it does
Metallic
material does
not
have
otherfriction
bad properties.
It costs
fade
at
high
temperature,
but
it
does
more than organic material, works
have other
It costs
worse
when bad
cold, properties.
wears the drum
or
more
than and
organic
material,
works
rotor more,
is harder
to attach
to
worse when cold, wears the drum or
rotor more, and is harder to attach to
the shoe or pad . Many metallic racing
linings are dangerous if not warmed
the
pad. Many
up. shoe
Whenorcold,
some metallic
metallic racing
matelinings
are
dangerous
if
nothave
warmed
rials either grab viciously or
very
up. When
matelow
friction.cold,
In some
racing,metallic
warming
up
rials
either prior
grab viciously
or have
very
the brakes
to using them
may
be
low friction.butInnotracing,
warming
acceptable,
for street
usage . up
theSintered-metallic
brakes prior to using
themmaterial
may be
friction
acceptable,
but
not
for
street
usage.
is used extensively in heavy aircraft
Sintered-metallic
friction material
brakes,
and some high-performance
is
used clutches
extensively
heavy aircraft
racing
andin brakes.
Some
brakes,
and
some
high-performance
motorcycle disc brakes use st ainlessracingrotors
clutches
and brakes.
steel
and sintered
linings. Some
motorcycle disc brakes use stainlesssteel
rotors and sintered
linings.
SEMIMETALLIC
MATERIALS
To solve some of the problems with
SEMIMETALLIC
MATERIALS
organic
and sintered-metallic
maTo ,solve
some of the
problems
with
terial
semimetallic
friction
material
organic
and sintered-metallic
mawas developed.
Semimetallic linings
terial,
semimetallic
friction
material
contain no asbestos. This material is
was
Semimetallic
linings
madedeveloped.
of steel fibers
bonded together
contain
no asbestos.
This characterismaterial is
wi th organic
resins to give
made
steel fibers
together
tics ofof both
organicbonded
and sinteredwith
organic
resins
to
give
characterismetallic materials. Semi metallic lintics
both well
organic
and sinteredings of
operate
at temperatures
of
metallic
materials.
linup to lOOOF
(538C).Semimetallic
The steel fibers
ingstheoperate
at totemperatures
of
in
materialwell
tend
melt and weld
up
to
lOOOF
(538C).
The
steel
fibers
to the rotor when operated at higher
in
the material tend to melt and weld
temperatures.
to the rotor when operated at higher
temperatures.
FRICTION-MATERIAL
HARDNESS
FRICTION-MATERIAL
Racers often talk about hard or SO/I
HARDNESS
brake
pads. This is slang for how high
often talk
about hard
or soft
theRacers
coefficient
of friction
is. "Soft"
brake
pads.
This
is
slang
for
how
high
friction material has a high friction
the coefficient
of friction
coefficient;
"hard"
materialis.has"Soft"
a low
friction coefficient.
material has a high friction
friction
coefficient; "hard" material has a low
friction coefficient.
Why does a racer want to use a
"harder "
friction material ? The
Why isdoes
racer
to use a
reason
wear aand
fadewant
characteristics
"harder"
friction
material?
The
of the material. Unfortunately, " soft"
reason ismaterial
wear and
fadetocharacteristics
friction
tends
wear rapidly ;
of
the material.
Unfortunately,
"soft"is
it also
fades easier.
"Soft" material
friction
material
tends
to
wear
rapidly;
usuaJly organic. "Hard" material may
it alsoa fades
"Soft" ofmaterial
is
have
highereasier.
percentage
metallics.
usually
may
A
racer organic.
usually "Hard"
chooses material
soft material
haveshort
a higher
of metallics.
for
racespercentage
or on tracks
that are
A
racer
usually
chooses
soft
material
easy on brakes. Hard materials
are
for
races
or is
on high,
tracksorthat
are
usedshort
where
wear
where
easy
on brakes.
Hardlittle
materials
are
very hard
braking and
brake coolused
where wear is high, or where
ing occurs.
very hard braking and little brake cool-
ing occurs.
FRICTION-MATERIAL
ATTACHMENT
FRICTION-MATERI
Friction m aterial is AL
attached to a
ATTACHMENT
metal backing . On a drum brake, the
Friction
material
attached
backing
is the
brake isshoe.
On a to
disca
metal
a drum
brake,
the
brake, backing.
a metal On
backing
plate
is used.
backing
is
the
brake
shoe.
On
a
disc
The friction material is either riveted
brake,
a metal
used.
or
bonded
to backing
the shoeplate
or is
backing
The
is eitheris riveted
plate.friction
This material
attachment
very
or
bonded If
to itthecomes
shoe or
backing
important.
apart
, the
plate.
This
attachment is very
brakes can
fail suddenly.
important.
If it comes
Riveted-Although
rivetingapart,
is an the
old
brakes
fail suddenly.
way of can
attaching
friction material, and
Riveted-Although
riveting
is ,anrivet
old
the method is very
reliable
way
of
attaching
friction
material,
and
holes can cause cracks in the friction
the
method
reliable,
rivet
material
whenisit very
gets hot.
The rivets
holes can
cause cracks
the friction
friction
seldom
fail-usually
it in
is the
material
gets hot.
Thefriction
rivets
material when
itself. i tAlso,
if the
i
t
is
the
friction
seldom
fail-usually
material wears out, the rivets can conmaterial
itself.or Also,
if thewillfriction
tact
the drum
rotor. This
score
material
wears
the ruin
rivets
the surface
and out,
usually
it. can contact
the drummore
or rotor.
Thisa ttachment
will score
Bonded-A
modern
the
surface
and
usually
ruin
it.
is bonding with high-temperature
Bonded-A
more ismodern
attachment
adhesive. There
less tendency
for
is
with high-temperature
the bonding
friction material
to crack because ·
adhesive.
less iftendency
for
it has no There
holes. is
And,
the friction
the
friction
material
to
crack
because
m aterial wears out, a bonded attachit has does
no holes.
And, to
if the
the rotor
friction
ment
less damage
or
materialsurface.
wears out,
a bondedbondedattachdrum
In addition,
ment does less damage to the rotor or
drum surface. In addition, bonded37
Brake-specialty shop is best place to get facts for comparing
lining materials. Because they often work with repeat customers,
shop
personnel see
long-term
of using
different
materials.
Brake-specialty
shop
is best results
place to
get facts
for comparing
Stores
selling brake
linings
typically
don'twith
seerepeat
resultscustomers,
of actual
lining materials.
Because
they
often work
use. personnel see long-term results of using different materials.
shop
Passenger car used for towing should have heavy-duty brake
linings. Cheap linings may work in light-duty use, but will have high
wear
and may
towing should
heavy have
loads. heavy-duty
Consider vehicle
Passenger
car fade
used when
for towing
brake
use when
selecting
linings.
linings.
Cheap
linings
may work in light-duty use, but will have high
wear and may fade when towing heavy loads. Consider vehicle
Stores selling brake linings typically don't see results of actual
use when selecting linings.
use.
with
the
posItIve
mechanical-
attachment feature of riveting. Most
with
the positive
racing disc-brake
pads aremechanicalmade this
attachment
feature
riveting.
way. Unfortunatelyof
, due
to Most
their
racing
disc-brake
pads
are
made
this
curved shape , it is difficult to produce
way.
Unfortunately,
due toassemtheir
drum-brake
shoe-and-lining
curved
shape,
it is difficult to produce
blies with
this process.
drum-brake shoe-and-lining assemSELECTING
blies with this process.
FRICTION MATERIAL
Riveted linings should be replaced when
rivets get close to touching the drums.
Here's what
happens
warning when
signs
Riveted
linings
shouldwhen
be replaced
are
ignored.
Most to
of touching
lining andthe
rivets
are
rivets
get close
drums.
gone
shoe
is wornwhen
part warning
way through!
Here'sand
what
happens
signs
Drumignored.
was alsoMost
ruined.
are
of lining and rivets are
gone and shoe is worn part way through!
Drum
also ruined.
only was
linings
lasl longer because they
have more usable thickness; there are
onlyrivet
linings
longer because
they
no
headslast
to contend
with.
have
more
usable
thickness;
there
The disadvantage of bonding isarea
no
rivetresistance
heads to contend
with.
lower
to high temperature.
The disadvantage
of bonding
Sometimes,
riveting and
bonding isarea
lower resistance
to high
temperature.
combined
to secure
brittle
material
Sometimes,
riveting and
bondingRivare
for high-temperature
operation.
combined
to
secure
brittle
material
ets are much stronger at extreme
for
high-temperature operation. Rivtemperatures.
etsThe
arebest
much
strongeris achieved
at extreme
attachment
by
temoeratures.
bonding during the lining-molding
is achieved
process.best-attachment
This is called mold
bonding by
or
bonding
during During
the lining-molding
integral molding.
this process,
process.
is calledin mold
or
holes areThis
punched
the bonding
brake-pad
integral
molding.
During
this
process,
backing plate. A high-temperature
holes are ispunched
in theto brake-pad
adhesive
then applied
the plate
backing
plate. is Aputhigh-temperature
and
the plate
into the lining
adhesive
is thentheapplied
to the
plate
mold. During
molding
process,
and
the
plate
is
put
into
the
lining
pressure forces the lining material
mold.
During
process,
into these
holes the
and molding
high temperature
pressure the
forces
the lining
activates
adhesive.
This material
process
into these holes
and high temperature
combines
the advantages
of bonding
he
activates the adhesive. This process
combines the advantages of bonding
38
SELECTING
Selection of t he proper friction
FRICTION
MATERIAL
material depends
on the following:
of the proper
friction
street driving,
• Selection
Vehicle use-easy
material
depends
theracing.
following:
hard street
dri vingon
, or
use-easy
• Vehicle
Cost versus
budget. street driving,
hard
street
driving,
racing.
• Maintenance youorare
willing to put'
upCost
with.versus budget.
Maintenance
you are willing
put'
Easy
Street Driving-For
streettouse,
up
with.
most people choose the lowest-cost
Easy Street
Driving-For
friction
material.
However,street
you use,
get
most
people
the lowest-cost
what you
paychoose
for. Cheap
linings or
friction
However,
youfaster
get
pads maymaterial.
squeal and
wear out
what
you
pay
for.
Cheap
linings
or
than the more expensive ones.
pads
may
squeal
and
wear
out
faster
Consequently, they may end up costthan
the Worse
moreyet expensive
ones.
ing more.
, they may fade
in
Consequently,
they may
up costsome
unexpected
hard end
usage.
So ,
ing more.
Worse
yet, street
they may
fade in
even
though
most
driving
is
some
unexpected
hard
usage.
So,
easy, it is best to get high-quality friceven
though most street driving is
tion material.
easy,
is best to get
high-quality
fric-' t
An itauto-parts
store
usually can
tion
material.
judge friction-material wear or fade
An auto-parts
store
usually a can't
resistance.
Therefore
, consult
spejudge
friction-material
fade
cialty shop
that deals in wear
brakes.orThere
resistance.
consult
a speare
usually Therefore,
a number of
brake-repair
cialty
shop
that
deals
in
brakes.
shops in every city or locale. There
They
are
brake-repair
deal usually
with alla number
sorts of of
brake
failures.
shops
in every
city customers
or locale. allow
They
And their
repeat
deal
all sorts
of brake performfailures.
them with
to judge
the long-term
And of
their
repeat
customers
ance
various
materials.
The allow
shop
them
to judge
the long-term
foreman
or service
manager isperformusually
ance
of various
materials.
Theadvice
shop
the person
to ask.
Take his
foreman
or
service
manager
is
usually
rather than that of an overthe person to ask. Take his advice
rather than that of an over-
Shoes are fitted with different types of
lining. Upper shoe is darker due to extra
metallics
lining. with
This different
"harder" types
lining of
is
Shoes
arein fitted
used
severe
use.is darker due to extra
lining.for
Upper
shoe
metallics in lining. This "harder" lining is
used for severe use.
the-counter general parts salesman.
1
The problem with
easy street drivthe-counter
generalboth
parts salesman.
ing
is getting
good lowThe problem
withperformance
easy street drivtemperature
brake
and
is gettingEven
both
goodleisurelowing resistance.
fade
the most
temperature
brake
performance have
and
ly
street driver
will occasionally
fade
resistance.
Even
the
most
leisureto make a hard stop from high speeds.
ly street
driver
The
brakes
mustwill
be occasionally
capable of a have
hard
to make
a hardlinings
stop from
speeds.
stop.
Organic
are high
the best
for
The
brakes
must be as
capable
of a hard
this type
of service,
they work
best
stop.
liningsThe
areone
thehard
beststop
for
at
lowOrganic
temperature.
this
type
of
service,
as
they
work
best
should be within their capability, but
at
temperature.
The one
hardfrom
stop
notlownecessarily
repeated
stops
should
be
within
their
capability,
but
high speed.
notIf you
necessarily
repeated
stops
from
' ve selected a lining correctly
high
speed.
matched
to easy street driving, dan',
you've
selected
lining
LlseIf it
for racing
or ahard
use.correctly
If you
matched
to aeasy
street
driving,
don't
have to pull
trailer
in the
mountains,
use
it
for
racing
or
hard
use.
If
either change friction material oryou
go
have to
pull a down
trailer hills
in theinmountains,
very
slowly
low gear
either
friction
material or go
withoutchange
riding the
brakes.
very
slowly
down
hills
in lowheavygear
Hard Street Driving-Use
without riding the brakes.
Hard Street Driving-Use
heavy-
duty friction material for hard street
driving or hauling heavy loads. This is
duty
friction
material for
hardHeavystreet
usually
a semimetallic
lining.
driving
or
hauling
heavy
loads.
This
is
duty material has greater wear resisusually
a
semimetallic
lining.
Heavytance and better braking performance
duty
material
has greater
wearusually
resisat high
temperature.
It will
tance
and better
braking
performance
cost more
initially,
but will
be more
at
high temperature.
It will usually
economical
overall .
cost
more
initially,
but
will bebe more
Heavy-duty linings should
pureconomical
chased
onlyoverall.
after consulting an expeHeavy-duty
shouldSelect
be pur-a
rienced
brake linings
specialist.
chased
only
after
consulting
a
n expebrand that he is familiar with and
has
rienced
brake
specialist.
Select
confidence in . Ask him what hea
brand that
he his
is familiar
with for
andsimihas
would
use on
own vehicle
confidence
in. Ask him
he
lar driving conditions.
Go towhat
several
would
use
on
his
own
vehicle
for
simishops , if possible, to see if the advice
lar driving
conditions.
G o toBeseveral
you
are getting
is consistent.
aware
shops,
if possible,
to see
if the
advice
that many
American
cars
produced
you
getting
is consistent.
Be aware
afterare
1979
are fitted
with semimetallic
that
many
American
cars
produced
disc- brake linings. Most European
are fittedcars
with semimetallic
aftzr
and 1979
Japanese
use
highdisc-brake
Most European
temperature linings.
organic linings.
and
Japanese
cars , use
highFor hard
street driving
you may
be
temperature
organic
linings.
tempted to use a high-temperature,
For hard
street
driving,
you may
be
organic
racing
friction
material.
This
tempted
to
use
a
high-temperature,
may
work
well
under severe
organic racing
material.
This
conditions,
but friction
be prepared
for troumay
worknormal
welldriving.
underTheysevere
ble during
actuconditions,
but be
troually have some
of prepared
the samefor
characble
during
normal
driving.
They
actuteristics when cold as organic linings
ally have
when
hot. some of the same characteristics
coldmaterial
as organic
linings
Racingwhen
friction
cannot
be
when
hot.
kept hot enough to work on long trips
friction This
material
cannot
be
onRacing
the highway.
would
require
kept hot enough
to work on long
trips
repeated
brake applications
to keep
on
thewarm.
highway.
This
would
require
them
A panic
stop
caused
by an
repeated
brake
applications
to
keep
unexpected emergency could have
them
warm.
A
panic
stop
caused
by
disastrous results with cold brakes. an
unexpected
emergency
couldfriction
have
Racing-Selecting
the correct
disastrous
results
with
cold
brakes.
material for racing is easier than for
Racing-Selecting
correct
friction
the street because the
driving
conditions
material
racing is easier than
for
are more for
predictable-always
severe.
the
street
driving
Exact
brakebecause
use depends
on conditions
the particare
severe.
ular more
track, predictable-always
driver's technique and
race
Exact
brake
use
depends
on
the
length. Friction material mustparticmeet
ular
driver's technique and race
thesetrack,
requirements:
length.
Friction
must meet
• No fade
during material
race.
these
requirements:
• Will not wear out during race.
No fade during
race. to withstand
• Correct
composition
Will not wear
out during.race.
temperatures
encountered
Correct
withstand
Because composition
road racing istousually
the
temperatures
encountered.
hardest on brakes, let's look at how to
Because
road racing
is usually
the
select
friction
material
for this
hardest on .brakes, let's look at how to
application
select
friction
material
for this
It turns
out that
most road-racing
application.
cars use the same ma terial , Ferodo
thatallmost
road-racing
OSItIIturns
. And out
, nearly
road-racing
cars
cars
use brakes.
the same
material,
Ferodo
use disc
OS 11
is so common
DS11.
nearly all brakes
road-racing
becauseAnd,
road-racing
are cars
deuse
disc
brakes.
D
S
l
l
is
so
common
signed to be as light as possible, relabecause
road-racing
tive to the
power a ndbrakes
weightare
of dethe
signed
be as
light
as possible,
relacar. Big,to fast
cars
have
bigger brakes
tive
the slow
power
weight
of that
the
than to
light,
carsand
. This
means
car. Big, fast cars have bigger brakes
than light, slow cars. This means that
Racing caliper is fitted with Ferodo DS11
lining material. This lining is popular for all
types
racing. is
Photo
courtesy
AP Racing.
Racingofcaliper
fitted
with Ferodo
DSll
lining material. This lining is popular for all
types of racing. Photo courtesy AP Racing.
Super Vee brake is typical of those used
on small race cars. Rules require using VWbrake
components.
cast-iron
singleSuper Vee
brake is VW
typical
of those
used
piston-one
piston
side-caliper
on
small race cars.
Rulesper
require
using VWclamps
on solid rotor.
rotor bolts
to
brake components.
VWVW
cast-iron
singlespecial
aluminum
hat that
quickpiston-one
piston
per allows
side-caliper
change
wheel
is adeclamps on
solidmounting.
rotor. V WDesign
rotor bolts
to
quate
light hat
carsthatwith
160-mph
special for
aluminum
allows
quickcapability.
change
wheel mounting. Design is ade-
quate for
capability.
light
cars
with
160-mph
Compare Indy Car brake with Super Vee
brake in photo, above right. Indy car uses
dual-piston
aluminum
caliper
vented
Compare lndy
Car brake
with and
Super
Vee
rotor.
diameter
slightly
bebrake Rotor
in photo,
aboveisright,
lndylarger
car uses
cause
15-in. aluminum
wheels arecaliper
used. Indy
has
dual-piston
and car
vented
210-mph
capability,
is hundreds
of
rotor.
Rotor
diameter and
is slightly
larger bepounds15-in.
heavier
than are
Super
Vee.
Carcar
speed
cause
wheels
used.
lndy
has
and
weightcapability,
show in the
Photo by
210-mph
andbrakes.
is hundreds
of
Tom
Monroe.
pounds
heavier than Super Vee. Car speed
and weight show in the brakes. Photo by
Tom Monroe.
most road-racing brakes operate at
about the same temperature .
most
road-racing
brakesproperly
operateatata
Ferodo
OSII operates
about
the
same
temperature.
disc temperature of 780-1100F
1 operates
at a
Ferodo DSl The
(416-593C).
frictionproperly
coefficient
disc
780-of 1100F
rises totemperature
its operatingofvalue
about
(41 6-593C).
The friction
coefficient
0.3
and is reasonably
constant
in this
rises
to
its
operating
value
of about
temperature range. Outside this
tem0.3
and isrange,
reasonably
constant
in this
perature
the friction
coefficient
temperature
range. Outside this temis lower.
perature
range,
Most race carsthe
canfriction
use thecoefficient
same fricis
lower.
tion material because car designers
Most
cars can
use the same
size
therace
brakes
in proportion
to fricthe
tion
because
speedmaterial
and weight
of thecarcar.designers
Try the
size
in proportion
to theit
OS 11themabrakes
terial first
and see how
speed
and
weight
of
the
car.
Try
works. Check rotor temperature tothe
be
D S l l itmaterial
firsttheand
see how
sure
is within
correct
range,it
works.
rotor temperature paint.
to be
temperature-indicating
using aCheck
sure
it
is
within
the
correct
range,
Read Chapter 10 for more information
using
a testing.
temperature-indicating paint.
on
brake
Read
Chapter
10 wear
for more
If the
linings
too information
fast or the
on
brake
testing.
brakes fade, and cooling cannot be
If the linings wear too fast or the
brakes fade, and cooling cannot be
Scoop for Indy Car rear brake projects
above body and into airstream. Because
drag
smallestScoopisforcreated,
lndy Cartherear
brake possible
projects
scoop body
shouldand
be into
used
. Smaller Because
scoops
above
airstream.
mean aisfaster
car, but
brakes. Maxidrag
created,
thehotter
smallest-possible
mum
necessary
on shortscoops
ovals
scoopducting
shouldis be
used. Smaller
such
asfaster
Phoenix
International
Raceway.
mean a
car, but
hotter brakes.
MaxiPhotoducting
by Tom Monroe.
mum
is necessary on short ovals
such as Phoenix International Raceway.
Photo by Tom Monroe.
improved, a harder friction material is
required. There are materials that can
improved, atemperatures
harder frictionover
material
is
withstand
1200F
required.
There
are
materials
that
can
(649C), but these have disadvantages.
withstand
over 1200F
Raybestostemperatures
M 19 and Hardie-Ferodo
(649C), are
but these
have disadvantages.
1103
ultra-high-temperature
RaybestosThese
M 19 and
Hardie-Ferodo
materials.
friction
materials
1103
are
ultra-high-temperature
tend to wear out rotors and also take a
materials.
friction
little time toThese
work after
they materials
coolon a
tend to
wear outConsequently,
rotors and alsoFerodo
take a
long
straight.
little
time
to
work
after
they
cool
on a
OS 11 is more popular than higherlong
straight.mConsequently,
Ferodo
temperature
aterial. It is better
to
D
S l lbigger
is more
popular
than higheruse
brakes
or improve
brake
temperature
It is extremely
better to
cooling
than material.
to live with
use bigger brakes or improve brake
cooling than to live with extremely
39
high brake temperatures.
If brakes run cool, that's good. You
high
temperatures.
have brake
two options:
Use softer linings to
If brakes
run cool,
that's
good. You
give
lower pedal
effort
or reduce
airhave
two
options:
Use
softer
to
flow to the brakes. However,linings
because
give
lower
pedal
effort
or
reduce
airchanges occur during a race that can
flow
to thethebrakes.
overheat
brakes,However,
reducing because
cooling
changes
occur choice.
during Cooling
a race that
can
air is a better
airflow
overheat
the
brakes,
reducing
cooling
increases aerodynamic drag , so slightair
is a better
choice.
Cooling
airflow
ly smaJler
ducts
or none
at all
will
increases
aerodynamic
drag,
slightreduce drag
and make
theso car
go
ly
smaller
or none
at allbrake
will
faster.
Thisducts
will also
increase
reduce
drag. and
makethethe
go
temperature
Usually,
onlycarvalid
faster.
will alsosoft
increase
excuse This
for running
liningsbrake
is a
temperature.
Usually,
only
very high pedal
effort. the
If you
canvalid
run
excuse
for
running
soft
linings
is a
soft linings, Hardie-Ferodo Premium
very
If you can
run
workshigh
well.pedal
It iseffort.
a low-copper
organic
soft
linings,
Hardie-Ferodo
material
, with
a high Premium
friction
works
well. It is a low-copper organic
coefficient.
material,
with
a high
Always run
the same
frictionfriction
matecoefficient.
rial on the front and rear. If you use
Always
run material
the sameatfriction
mateOS11
friction
one end,
use
rial
front
If youwarm
use
it aton
thethe
other
endand
, toorear.
. Brakes
D
l l friction
material
at one
end, use
upSduring
a race
and reach
steady-state
it
at the otherafter
end,atoo.
warm
temperature
few Brakes
la ps . If
the
up
during
a racefriction
and reach
steady-state
brakes
change
differently
from
temperature
a fewthe
laps.warmup
If the
front to rearafter
during
brakes
change
friction
defer-encly
from
period, front-to-rear brake balance
front
rear during
will alsotochange.
This canthe
causewarmup
loss of
period, If
front-to-rear
brakedifference
balance
control.
you find a great
will
also
change.
This
can
cause
lossand
of
in temperature between the front
control.
If
you
find
a
great
difference
rear brakes, modify the cooling airflow
in temperature
between
the front
and
or
the brake size,
not brake
friction
rear
brakes, modify the cooling airflow
material.
or the brake size, not brake friction
material.
STOCK-CAR
BRAKE LININGS
Because of their high weight, speed
STOCK-CAR
BRAKE
LININGS
and horsepower,
a racing
stock car is
Because
of
their
high
weight,
the hardest on brakes. The
mostspeed
diffiand
horsepower,
a racing
car is
cult track
for brakes
is onestock
consisting
the medium-length
hardest on brakes.
The most diffiof
straightaways
and
cult
track
for
brakes
is
one consisting
slow corners. And, racing
stock-car
of
medium-length
straightaways
anda
brakes
require more
attention on
slow
corners.
And,
stock-car
road course
than
on aracing
superspeedway.
brakes require
more attention
Certain
medium-speed
ovals are on
alsoa
road
course
than
on
a
superspeedway.
hard on brakes.
Certain
medium-speed
ovalscars
arewere
also
Disc
Brakes
- Before stock
hard
on
brakes.
used on road courses , most used
Disc Brakes-Before
stockdrums
cars were
drum
brakes . Their huge
with
used onlinings
road were
courses,
mostforused
metallic
adequate
sudrum
brakes. Their
hugesmaller
drums with
perspeedways
and most
oval
metallic
liningshave
werechanged
adequatein for
sutracks. Things
stockperspeedways
andnow
most
oval
car
racing. They
use smaller
disc brakes.
tracks.calipers
Things are
havehuge,
changed
in stockThe
even
when
car
racing.
They
now
use
disc
brakes.
compared to the high-horsepower
The
calipers
huge, speed
even potenwhen
Indy cars.
The are
200-mph
compared
to the
high-horsepower
tial of a stock
car combined
with a
Indy cars.
The3000
200-mph
weight
over
Ib , speed
makes potenlarge
tial of necessary.
a stock car combined with a
brakes
weight
over road-racing
3000 lb, makes
large
As with
cars, brake
brakes
necessary.
lining must be chosen according to
withof road-racing
cars, ofbrake
theAstype
track and length
the
liningTracks
must can
be chosen
according
to
race.
vary from
short dirt
the type
track
and length
of the
ovals,
to of
road
courses,
to 200-mph
race. Tracks can vary from short dirt
ovals, to road courses, to 200-mph
40
Size of caliper used on a stock car indicates how much energy brakes must
absorb.
Usually,
Size
of caliper
usedthe
on abiggest-possible
stock car indibrakes how
are used.
Linings
are brakes
varied tomust
suit
cates
much
energy
track and length
of race.
absorb.
Usually,
the biggest-possible
brakes are used. Linings are varied to suit
track and length of race.
superspeedways. The type of lining
that works best for each type of racing
superspeedways.
The over
type of
lining
has been developed
years
of
that
works
best
for
each
type
of
racing
experience . If you are new to the
has
developed
over yearssupof
sport,been
consult
your brake-lining
experience.
you forareadvice.
new to the
plier or other Ifracers
sport,
brake-liningracing
supManyconsult
gradesyour
of high-quality
plier
or
other
racers
for
advice.
linings are available for stock cars.
Many racing-brake
grades of high-quality
Many
suppliers racing
offer
linings
are available
stockPremicars.
Hardie-Ferodo
linings.for
Again,
Many
racing-brake
suppliers
offer
um is the softest lining. HardieHardie-Ferodo
linings.
Again, PremiFerodo Premium
is recommended
for
um is the ovals
softestandlining.
high-banked
tracks, Hardiesuch as
Ferodo Premium where
is recommended
for
superspeedways,
little braking
high-banked
ovals
and
tracks,
such
as
is required . These soft pads are easiest
superspeedways,
where
little
braking
on rotors and require no warm-up'
is
required.
These
soft pads areIf easiest
time
for full
effectiveness.
brake
on
rotors andarerequire
no warm-up
temperatures
low enough
to avoid
time or
forexcess
full effectiveness.
If brake
fade
pad wear, Premium
is
temperatures
the best choice.are low enough to avoid
fade
Premium
is
Foror excess
runningpad atwear,higher
temthe
best choice.
peratures,
try the Hardie-Ferodo
For pads.
running
temOPll
These atare higher
the mediumperatures,
try material.
the Hardie-Ferodo
hardness racing
The DPll
D P l l pads.
the mediummaterial
hasThese
more are
copper
content
hardness
racing
material.
The itD Phas
ll
than Premium . Consequently,
material has
more copper
content
increased
temperature
resistance
and
thanwear.
Premium. Consequently, it has
less
increased
resistance
and
For roadtemperature
racing, a hard
lining mateless
wear.
rial will be required on most stock
For Hard
road racing,
a hard
matecars.
materials
willlining
withstand
rial will
be requiredbeston ofmost
high
temperatures
all. stock
They
cars. operate
Hard materials
will withstand
will
above 1200F
(649C)
high temperatures
best ofOSall.
They
while
the popular Ferodo
11 comwill operate
above 1200Fat (649C)
pound
loses effectiveness
about
while
popular Ferodo D S l l com1100F the
(593C).
pound
loses
effectiveness
about
Two hard materials
are theatHardie1IOOF (593C).
Ferodo
1103 and Raybestos M19.
Twohave
hard high
materials
arecontent,
the HardieBoth
copper
but
Ferodo
1103
and
Raybestos
M19.
are still considered organic linings.
Both only
have do
highthey
copper
content, high
but
Not
withstand
are still considered
organic
linings.
temperatures.
they wear
long enough
Notlastonly
do they
withstand
high
to
in a long
hard race.
The draw-
temperatures. they wear long enough
to last in a long hard race. The draw-
back is that 11 03 or M 19 material
tends to wear rotor surfaces more
thatcompounds.
1103 or M19
material
back
than is
other
Also,
pedal
tends
to
wear
rotor
surfaces
effort will be higher and they more
take
than
compounds.
Also,usepedal
longerother
to bed
in. Therefore,
the
effort
will be higher
theyto, take
hard compound
if youand
have
but
longer
to bed results
in. Therefore,
use the
better overall
will be obtained
hard
compound
if
you
have
if you can use the softer to,0 Pbut
11
better
overall results will be obtained
material.
if Other
you can
use theracing
softerpads
D Pare
ll
heavy-duty
material.
available from various manufacturers.
Other
racing
pads are
They
alsoheavy-duty
tend to be hard
on rotors.
available
from
various
manufacturers.
If you race on supers peed ways,
Thev
to material.
be hard onSuch
rotors.
don't also
use tend
a hard
mate1
f
you
race
on
superspeedways,
rial cools off too much and the brakes
don't
matedon't use
worka hard
well material.
when an Such
emergency
rial
cools off too much and the brakes
occurs.
don't
well when an emergency
Drum work
Brakes-Although
racing
occurs.
stock cars now use disc brakes, there
Drum
Although racing
are still Brakessome restricted-class
mastock
cars
now
use
brakes,
chines using drums.disc
If you
racethere
in a
are
restricted-class
class still
that some
is so limited,
you mightmabe
chines
using
drums.
If
you
race in a
required to use original-equipment
class
is so
limited,
drum that
brakes
at the
rear. you might be
required
to several
use original-equipment
There are
metallic or semidrum
brakes
at the for
rear.use in stock-car
metallic
materials
There
aredrum
several
metallic
semiracing
with
brakes.
Oneorpopular
metallic
materials
for
use
in
stock-car
brand is made by the Grey Rock diviracing
drum brakes.
One popular
sion ofwith
Raybestos
Manhattan
Corp.
brand make
is made
the Greylinings
Rock diviThey
twoby metallic
with
sion
of Raybestoscapability:
Manhattan
high-temperature
5262Corp.
and
They
two metallic
linings
519l. make
The 5262
compound
was with
first
high-temperature
5262
developed for use capability:
on fast ovals
andand
su5191.
The
5262
compound
was
first
perspeedways with the characteristic
developed
for use on
ovals and
suof low change
in fast
friction
under
perspeedways
with
the
characteristic
extreme-temperature conditions. The
of
change
in friction
under
5191low
material
is softer,
but is said
to
extreme-temperature
conditions.
The
wear faster.
5191
is softer,
but is said
to
For material
some types
of oval-track
racing,
faster.
awear
semi
metallic or heavy-duty street
For some
types
of oval-track
racing,
lining
may be
suitable.
This assumes
athat
semimetallic
or
heavy-duty
speeds are low, cornersstreet
are
lining
suitable.
banked,may
andbe races
are This
short.assumes
Here,
that
low, forcorners
are
brakesspeeds
are usedaremostly
setting the
banked,
races and
are for
short.
Here,
car
up forand
cornering
unexpectbrakes
are used mostly
for setting
the
ed
emergencies.
The Chevrolet
semicar
up
for
cornering
and
for
unexpectmetallic linings or Bendix EOF heavyed emergencies.
Themight
Chevrolet
semiduty
service linings
be suitable.
metallic
linings
or
Bendix
E
D
F
heavyCareful testing is required to see if a
duty
service linings might
be suitable.
medium-temperature
material
will
Careful
testing
is
required
work properly on your car. to see if a
medium-temperature material
work
properly
your car.
BEDDING
INon
LININGS
will
New linings must be bedded in
BEDDING
I N LININGS
before they are
raced to ensure proper
New
linings
be inbedded
brake operation. must
Bedding
brakes in
is
before
they
are
raced
to
ensure
proper
similar to breaking in a new engine.
If
brake
operation.
Bedding
in brakes
is
an
attempt
is made
to race
on new
similar
breaking
a new
engine.
If
linings, togreen
fade in
can
occur.
Green
an attempt
is made
racecaused
on new
fade
is severe
brake to
fade
by
linings,
green
fade
can
occur.
Green
gas or liquid coming out of the friction
fade
is severe
fadethecaused
by
material
and lubrake
bricating
rubbing
gas or liquid
of the
friction
surfaces.
Thecoming
driver out
feels
green
fade
material
andbrake
lubricating
the rubbing
as
a sudden
loss.
surfaces. The driver feels green fade
as a sudden brake loss.
Oval-track cars running on dirt are not extremely hard on brakes. For light cars such
as
this late-model
stockon
car,
softer
racing
Oval-track
cars running
dirt
are not
exlinings or
heavy-duty
linings
may
tremely
hard
on brakes.street
For light
cars such
work.
testing
during
long practice
as
thisCareful
late-model
stock
car,a softer
racing
session
is desirable
before
trying
new may
linlinings or
heavy-duty
street
linings
ings inCareful
a race. testing during a long practice
work.
session is desirable before trying new linOrganic
material in the lining tend~
ings
in a race.
to boil off rapidly when first heated.
Organic
material
in the
tends
This
material
not only
actslining
as a lubrito
boil
off
rapidly
when
first
heated.
cant between the lining and rotor, but
This
notthe
only
acts surface.
as a lubriit canmaterial
also glaze
lining
A
cant between
lining by
andthe
rotor,
but
glazed
surface the
is caused
organic
it
can also
glaze the
surface. on
A
material
cooling
and lining
resolidifying
glazed
surface
is
caused
by
the
organic
the pad surface. A glazed surface is
material
and
resolidifying
on
hard and cooling
slick, and
never
has the right
the pad coefficient.
surface. A Once
glazedglazed,
surfacethe
is
friction
hard andmaterial
slick, andmust
neverbehas
the right
friction
refaced
or
friction
replaced.coefficient. Once glazed, the
friction
material
mustshould
be refaced
or
Bedding
in brakes
be done
replaced.
during a practice session, not during a
Bedding
brakes isshould
done
race.
If theinpractice
long be
enough,
during
a
practice
session,
not
during
a
you can bed in more than one set of
race.
If
the
practice
is
long
enough,
pads and have them race-ready for
you
in to
more
one set
of
later.can
It isbed
wise
havethan
a spare
set of
pads
andbedded-in
have them
unworn
pads race-ready
as spares. for
later.
is wise to procedure
have a spare
set by
of
TheI tbedding-in
starts
unworn
bedded-in
pads
as
spares.
taking the car out and gradually warmstarts by
ingThe
up bedding-in
the brakes. procedure
This is followed
by
taking
out and
gradually
warmusing the
the car
brakes
very
hard several
ing
up the
followedinto
by
times.
Thebrakes.
car is This
then isbrought
using
the
brakes
very
hard
several
the pits for a cooling-off period.
times.
car is DS
then
into
WhenTheFerodo
11 brought
is properly
the
pits for
period.
bedded
in, aitcooling-off
changes from
a black or
When
Ferodo
D Sgrey
l l or
is brownish
properly
dark
grey to
a lighter
bedded
in,
it
changes
from
a
or
tone near the surface. Variousblack
brands
dark
grey
to
a
lighter
grey
or
brownish
of lining material have similar colortone nearcharacteristics,
the surface. Various
change
whichbrands
you
of
lining
material have similar colorlearn
by experience.
change
which on
youa
Metalliccharacteristics,
particles are visible
learn
by
experience.
worn racing-lining surface. Check
Metallic
are visibleGet
onfa-a
your
brake particles
linings frequently.
worn
surface. of
Check
miliar racing-lining
with the appearance
the
your
linings
frequently.
G e t are
faliningbrake
surface
when
the brakes
miliar with
the appearance
of you
the
working
correctly.
This will help
lining surface
the abrakes
are
visually
detectwhen
when
problem
working
correctly.
This
will
help
you
occurs. Make sure the surface is not
visually
detect when
a problem
polished, crumbling
or cracking.
Also
occurs. Make sure the surface is not
polished, crumbling or cracking. Also
Brake-pad appearance changes greatly
after bedding in. Pad on left is bedded in,
but
not raced.
Pad at right
is new. greatly
If new
Brake-pad
appearance
changes
pad were
used
hard,ongreen
could
after
bedding
in. Pad
left isfade
bedded
in,
result.
should
bedded
in
but
not Pads
raced.
Pad atalways
right isbenew.
If new
first. were used hard, green fade could
pad
result.
be bedded
in
inspectPads
theshould
rotoralways
surface.
Friction
first.
material should not transfer from the
inspectto the
the rotor.
rotor surface. Friction
lining
material should not transfer from the
lining to the rotor.
MACHINING
FRICTION MATERIAL
MACHINING
When installing new drum-brake
FRICTION
MATERIAL
linings,
you may
need to turn or grind
drum-brake
theWhen
drums.installing
However,new
do not
turn the
linings,
you
may
need
to
turn
or grind
drums unless they are out-of-round
the
drums.
However,
do
not
turn
the
or deeply grooved. Regardless, brake
drums
unless be
theymachined
are out-of-round
linings should
to fit the
or
deeply
grooved.
Regardless,
brake
drums
for best
braking
performance.
linings
should
be
machined
to
fit
the
Because brake-lining material
drums
for
best
braking
performance.
usually contains asbestos fiber,
Because results
brake-lining
material
machining
in dangerous
asusuallydust.
contains
asbestos
fiber,
bestos
Due to recent
discoveries
machining
results
dangerous
of
the hazards
of in
asbestos
dust asto
bestos
dust.
Due
to
recent
discoveries
human health, many new safety preof the hazards
of asbestos
to
cautions
are required
in brakedust
shops.
human health, many
safety have
preConsequently,
many new
of them
cautions
are required
in brake
shops.
stopped machining
brake
linings.
You
Consequently,
many
of
them
may have to search for a shop tohave
do
stopped
linings.
You
this, but machining
it is worth brake
it in terms
of optimay have
search for a shop to do
mum
braketoperformance.
this,
but
it
is
worth
it in terms
of optiThe drum-brake-shoe
machining
m
u
m
brake
performance.
process is called arcing the shoes. The
The must
drum-brake-shoe
drums
be measured,machining
so bring
shoes.
The
process
them to isthecalled
brakearcing
shop.the
The
machine
drums
must
be
measured,
so
bring
cuts the correct radius on the shoe so
them
to thecontact
brake shop.
The machine
the shoes
the drum
over a
cuts
correct
on the
shoebeso
large the
area.
If a radius
mismatch
exists
the shoes
contact
drum
over
tween
the drum
andthe
shoes,
brake
fric-a
large
area. be
If atoomismatch
betion may
high or exists
too low,
tween
the
drum
and
shoes,
brake
fricdepending on where the shoe contacts
tion
may beThetooworst
high possibility
or too low,
the drum.
is
depending
on where
thewheels
shoe contacts
when the right
and left
have a
the drum.fit The
worstthepossibility
is
different
between
shoes and
when
the
right
and
left
wheels
have
drums. This will cause dangerous pull-a
different
fit between the shoes and
ing to the side.
drums.
This will
cause
Disc-brake
pads
for dangerous
racing usepullare
ing
to
the
side.
often machined to make them flat.
Disc-brake
padsonfor
racing machine
use are
This
can be done
a milling
often
machined
to
make
them
flat.
or surface grinder. Be careful. Some
This
be done
on a dull
milling
machine
typescan
of brake
lining
milling
cutor
grinder. Be careful. Some
terssurface
in a hurry.
types
of
brake
lining
dullthey
milling
As brake pads
wear,
tendcutto
ters in a hurry.
As brake pads wear, they tend to
This machine was used to arc, or grind correct radius, on brake linings before asbestos
was was
discovered
to be
a health
This
machine
used to arc,
or grind
corproblem.
Consequently,
many shops
rect radius,
on brake linings
beforehave
asstopped was
arcingdiscovered
brake shoes.
health
bestos
to Better
be a braking
is achieved
with arced shoes
drumshave
are
problem.
Consequently,
many ifshops
turned. arcing brake shoes. Better braking
stopped
is achieved with arced shoes if drums are
turned.
get tapered. In that condition, the
braking gets worse, with higher pedal
get
that condition,
the
efforttapered.
and In
longer
pedal travel
braking
with full
higherbraking
pedal
required.gets
Toworse,
restore
effort and longer
travel
effectiveness,
machine pedal
the pads
so
required.
To
restore
full
braking
the rubbing surface is parallel to the
effectiveness,
theandpads
so
back of the pad.machine
Deglazing
minor
the rubbingmay
surface
is parallel to the
flattening
be accomplished
by
back of the
Deglazing
and minor
rubbing
thepad.
lining
on medium-grit
flattening laid
may onbea accomplished
by
sandpaper
flat surface, such
rubbing
the
lining
on
medium-grit
as a mill table or a piece of glass.
sandpaper
on a flat after
surface,
such
Rebedding laid
is necessary
machinas
table or a piece of glass.
ing aor mill
sanding.
Rebedding
is necessary
after
machinAlso, it sometimes
helps
to machine
ing
or
sanding.
a groove in the surface of the brake
it sometimes
helps to
machine
padAlso,
to get
rid of the lining
dust.
Most
apads
groove
surface
of theforbrake
haveina the
groove
in them
this
pad
to getIfrid
of the seems
lining dust.
purpose.
it always
to be Most
filled
pads
have aa second
groove groove
in themmay
forhelp.
this
with dust,
purpose.
it always seems
be stock
filled
A grooveIfmachined
90° totothe
with
a second plan.
groove
help.
one isdust,
a reasonable
Seemay
Chapter
A
groove
machined
90"
to
the
stock
12 for details on modifying brake pads.
one
a reasonable
See Chapter
If is
you
machine theplan.
linings,
be care12 for
on modifying
pads.
ful
notdetails
to breathe
the dust brake
and chips.
If you
linings, be
Wear
an machine
approvedtherespiralOr
andcaredo
ful
to dust
breathe
and chips.
not not
blow
withthe
andust
air hose.
Pick
and do
Wear
an approved
up asbestos
dust respirator
with a vacuum
not
blowThe
dustdust
with
hose.
cleaner.
in an
the air
shop
mustPick
be
up
asbestos
dust the
withoperation,
a vacuum
cleaned
up after
so
cleaner.
The dust
the shop
be
other people
won'tinbreathe
themust
potencleaned
up stuff.
after the operation, so
tially deadly
other
won't
breathe
the potenSee people
your local
health
authorities
for
tially
stuff. before you take a
safetydeadly
regulations
See your
local health
authorities
for
chance.
Remember,
many
organic linsafety
regulations
before
you
take
ings contain more than 50% asbestos.a
chance.
organic
Most, if Remember,
not ali, new many
road cars
will linuse
ings contain more
than 50% asbestos.
asbestos-free
semimetallic
or nonMost,
if not
all, new
road
will use
asbestos
organic
linings
by cars
1990.
asbestos-free semimetallic or nonasbestos organic linings by 1990. 41
Hydraulic Systems
5
Modern fast-fill tandem master cylinder, page 50, has plastic reservoir and integral proportioning valves. Cylinder must be mounted so fluid
is level in reservoir.
Modern fast-fill tandem master cylinder, page 50, has plastic reservoir and integral proportioning valves. Cylinder must be mounted so fluid
is level in reservoir.
All modern cars use a hydraulic
system to operate the brakes. This hyAll modern
use ofa cylinders,
hydraulic
draulic
system cars
consists
system
to
operate
the
brakes.
Thisfilled
hyvalves, hoses and tubing, all
draulic
system fluid.
consists
cylinders,
with hydraulic
The oftype
of hyvalves,
hosesused
andin tubing,
all filled
brake systems
is
draulic fluid
with liydra~ilic
jlirid.
type properof hycalled
brake fluid.
TheThe
special
draulic
fluid used
systems
is
ties of brake
fluid in
arebrake
discussed
later
called
brake fluid. The special properin
this chapter.
tiesA of hydraulic
brake fluid system
are discussed
has later
two
in this chapter.
functions
: move brake linings into poA hydraulic
system
has and
two
sition
against drums
or rotors;
functions:
move
brake
linings
into
poapply a force to brake linings, creating
sition against
friction
force. drums or rotors; and
apply
a force
brakeabout
linings,
creating
When
you tothink
a hydraulic
friction
force.
system, remember these important
When you
think about
a hydraulic
functions:
movemenf
and force.
A hysystem,system
remember
important
draulic
has tothese
do both
jobs to
A hyfunctions:themovement
operate
brakes. and
Theforce.
movement
draulic
system
has
to
do
both
jobs
to
must be enough to take up all clearoperateand
the deflections
brakes. Theinmovement
a brake
ances
must be The
enough
to take
all clearsystem.
force
mustup be
great
ances
and
deflections
in
a brake
enough to stop the car.
system. The force must be great
enough to stop the car.
42
BASIC HYDRAULICS
To understand how a hydraulic
BASIC operates,
HYDRAULICS
we must first considsystem
To
understand
a hydraulic
er the basics. For ahow
hydraulic
system
system
operates,
first
considto function
it mustwebemust
closed
and
comer
the basics.
hydraulic
pletely
filled For
witha fluid
, andsystem
leakto function
it must
free
- no fluid
ou t orbeairclosed
in. and completely
filled properly
with fluid,
andhydrauleakIn a closed,
sealed
free-no
or air in.laws are true:
lic
system,fluid
the out
following
In a closed,
sealed hydrauto a
Fluid
cannot properly
be compressed
lic
system,
the
following
lawsare
lesser volume, no matter
how true:
high
Fluid
cannot. Pressure
be compressed
the pressure
is equal to
overa
lesser
volume,
matter how
high
all
surfaces
of theno
containing
system.
theTurn
pressure.
equal
to pagePressure
63 for is
more
on over
hyall surfaces
containinguse.
system.
draulic
fluidofforthe
automotive
Turn to Fluid
page 63
for more on
Pressureis pressurized
by hythe
draulicoffluid
for automotive
a piston
. The pistonuse.
moves in
force
pressurized
by the
aPressure-Fluid
cylinder and isis sealed
to prevent
force
of
a
piston.
The
piston
moves
in
fluid from leaking out or air leaking
ain. cylinder
and
is
sealed
to
prevent
The piston must move with little
fluid from
leaking
out or air leaking
friction
in the
cylinder.
in.There
The piston
must
move
withof little
is air on one
side
the
friction
in
the
cylinder.
piston and hydraulic fluid on the
There is air on one side of the
piston and hydraulic fluid on the
other. The area of each piston is determined by its diameter.
other. The area of each piston is deterPiston area = 0.785 Dp2
mined by its diameter.
Ap = Area of piston in square inches
0.785 DP2
Piston
area =
Dp
= Piston
diameter
in inches
A, = Area of piston in square inches
applied to the piston creates
D pForce
= Piston diameter in inches
pressure in the hydraulic fluid . Th e
Force applied
to thediv
piston
is the force
ided creates
by the
pressure
pressure
in
the
hydraulic
fluid. The
area of the piston:
pressure is the forceF divided by the
Hydraulic
area of thepressure
piston: =----E.
Ap
F
Hydraulic
=
A
in
pounds pressure
per square
inch
P
F p = Force on piston inApounds
in pounds per square inch
' t refer to pressure In
= Force on piston in pounds
FpDon
pounds-it is pounds per square in ch
Don't
refer to pressure in
(psi).
pounds-it
is pounds
per sqimre
Let 's illustrate
pressure
with itich
an
(psi).
example. See accompanying drawing
illustrate
with one
an
of Let's
a simple
hydraulicpressure
system with
example.
See accompanying
drawing
piston. Fluid
pressure is measured
of a simple
hydraulic
system
one
by a with
formula.
with
a gage or
calculated
piston.
Fluid
pressure
is
measured
The amount of pressure depends on
with a gage or calculated by a forn~ula.
The amount of pressure depends on
Stop Prevents
Movement of Piston 2
Piston 1
100POUNDS
100 POUNDS
-".. . . . .,. >'-..1"1 in.
1 in.",
t
'./'<-'---.1 in.
.> 1 in.
PRESSURE
PRESSURE
--Force
Force
Area
=--
100 Pounds
Pounds
100
1.0
Square Inch
Inch
1.OSquare
= 100
100 Pounds-Per-Square-Inch
=
Pounds-Per-Square-I nch
Pressure is
is force per unit area. A hydraulic
piston
piston exerts force on
on fluid like
like this table
leg
leg exerts pressure on
on the floor. Pressure
Pressure
is
is force divided by area on
on which force is
exerted. If leg-to-floor contact area is
reduced, pressure on
on floor is
is proportionally
proportionally
increased. Drawing
Drawing by Tom
Tom Monroe.
how much force you put on the piston.
If the piston has an area of 2 sq in.
in.
and the force is 400 Ib, the pressure is
follows:
calculated as follows:
400lb
.
4001b
= -2--'
= 200 pSI.
psi.
Pressure =
=
In.
2 SQ
sq In.
A smaller piston gives a higher
in.
pressure. If a piston with only 1-sq
I-sq in.
in.
area is substituted for the 2-sq in.
piston, a pressure of 400 psi is obforce.
tained with the 400-lb force.
Force Multiplication-Pistons
Multiplication-Pistons can be
used to multiply force in a hydraulic
difsystem. By choosing pistons of different sizes, any relationship with
forces is possible.
A simple hydraulic system with two
pistons is shown in the accompanying
difdrawing. The pistons can have difareas. The relationship between
ferent areas.
forces depends on the relathe two forces
tionsllip
areas.
tionship between the piston areas.
Assume piston 1 has an area of 2 sq
in. and a 400-lb force
force applied to it.
it. I
in.
showed in the previous example that
this created 200-psi fluid pressure.
pressure.
Piston 2 now is sUbjected
subjected to this
fluid pressure. Remember
200-psi fluid
that fluid pressure acts equally on all
Hydraulic
Fluid
P
A, =
= Area of Piston
Piston 1
A1
A2
A2 =
= Area of piston
piston 2
F, =
= Force
Force on Piston
Piston 11
F1
F2 =
= Force
Force on Piston
Piston 2
F2
P
P=
= Fluid
Fluid Pressure
=~(PSi)
A1
A
F P = F, l ( l b )
A1
Forces
Forces can
can be
be multiplied
multiplied with
with a simple hydraulic system. In
In this drawing, force F1
F, is
is applied
applied
to
F, is created. If
t o a small piston
piston with area A
A,.1 . If large piston
piston A2
A, is resisted
resisted by a stop,
stop, force F2
be the bottom
bottom of a car. Force
Force F,2 is greater than F
F1
in a
this were a hydraulic jack, stop could be
1 in
ratio that's directly related
related to
t o piston areas.
areas. Because
Because fluid pressure
pressure is
is same throughout,
ratio
bigger piston
piston has bigger force.
surfaces of the surrounding container.
Fluid pressure acts on the contact surface of the piston, causing movement.
face
Force 2 will depend on the area of
piston 2.
Force
Force on
on piston
piston == P A,
P =
= Hydraulic pressJ're
pressure in
in pounds per
square inch
inch
Ap
A, == Area of piston
piston in
in square inches
This is the same formula as on page
42, in a different format.
format. In the
example,
example, assume piston 2 has an area
of 1 sq in.
in. The force
force on
011 it at a fluid
pressure of 200 psi is 200 lb.
Ib. If we
change piston 2 to an area of 4 sq in.,
in.,
the force
force increases to 800 lb.
Ib. The pressure does not change-only
change-only the force
on the piston. The larger the piston,
the greater the force
force with the same
pressure.
We can write a simple
s i m ~ l eformula
formula for
for
the relationship between the forces
forces on
the two pistons:
_ F1A2
F --2
A1
F1
F, == Force
~ o r c on
on
e piston
piston 11 in
in pounds
F
on piston
F,2 == Force
Forceon
piston 2 in
in pounds
A, == Area of piston
piston 1 in
in square
A1
inches
inches
A, == Area
~ r e of
a piston
is ton 2 in
in square
sauare
A2
inches
inches
Piston
= Ap
Piston Area
Area =
A, (sq
(sq in.)
in.)
iI
Hydraulic Fluid
Fluid
Sealed Container
W (psi)
P=
W
=(psi)
Ap
A
,
Simple hydraulic system with one piston
piston
and
and pressure gage. By putting
putting force on
on
piston, fluid is pressurized. Pressure is the
force-weight
force-weight in
in this instance-divided
instance-divided by
area of piston. Fluid
Fluid pressure
pressure acts equally
on
on all surfaces of container.
To increase the force on piston 2,
you can reduce piston-l
piston-I area or increase piston-2 area.
area. Force can only
be changed in a brake system by
changing piston area
(s).
area(s).
Do not use piston diameter in place
area! Piston area varies as the
of area!
43
A*x
Output
Force
Output
Force
Piston
Area Ap
Area
Piston
Direction--.,,-/
of
Movement
Direction
t
--I
1-
of
Movement
I
+
Input
Movement
+
Movement Mp
/
=
~~---
lnput
Movement
Piston
ApMp (cu in.)
Movement M,
Fluid Displacement
Output
Movement
I
Displacement
= ApMp
(cuarea
in.) of
Fluid Fluid
displaced
by piston
equals
piston
multiplied by distance it moves. LikeI
I
aFluid
car engine,
displacement
can be given
in
displaced
by piston equals
area of
cubic
(cu in.).
pistoninches
multiplied
by distance it moves. Like
a car engine, displacement can be given in
cubic inches (cu in.).
t
Hyraulic-brake system operates like this simple lever; increases force and reduces
movement. Input side is the brake pedal. Input force and movement are supplied by your
leg. Output side is the brake. Output force is exerted perpendicular by brake linings against
rubbing surfaces.
Output
movement
takeslnput
up all
clearance
in system
brakes by
canyour
be
movement.
lnput side
is the
brake pedal.
force
and'movement
aresosupplied
applied.
leg. Output side is the brake. Output force is exerted perpendicular by brake linings against
rubbing surfaces. Output movement takes up all clearance in system so brakes can be
applied.
To calculate movements in a hydraulic system, you need to consider
To calculate
movements
a hyfluid
displacement
when ain piston
draulic system,
you need
to consider
moves.
Displacement
is the
area of
fluid
displacement
a pistonit
the piston
times when
the distance
moves.
Displacement
is
the
areadisof
moves , or the same as cylinder
the
piston of times
thein distance
placement
a piston
an engine.it
moves, stroke
or the issame
as cylinder
dis-;
Piston
piston
movement
placement
of
a
piston
in
an
engine.
greater piston movement means
Piston displacement.
stroke is piston movement;
greater
greater piston movement means
Fluid displacement = Ap M~
greater
displacement.
Ap = Area of piston in square
Floor jack illustrates relationship between
force and movement in a hydraulic system.
Handle
hasillustrates
a low forcerelationship
and high movement
Floor jack
between
versusand
high
force and
movement
at
force
movement
in alow
hydraulic
system.
jack
pad.
Handle
has a low force and high movement
versus high force and low movement at
jack pad.
square oj the diameter. Calculate all
piston areas first so you won't make
squaremistakes.
of the diameter. Calculate all
costly
piston
areas
first so you won't make
Piston Movement-Hydraulic
syscostly
tems mistakes.
must provide both force and
Piston
Movement-Hydraulic
sysmovement.
We just looked at how
tems
must
provide
both
force
and
forces relate. Piston movement also
movement.
We
just
looked
at
how
depends on piston areas, but not on
forces
relate. Piston
movement
also,
fluid pressure.
Pressure
affects force
depends
on piston areas, but not on
not movement.
fluid
affects force,
If apressure.
system is Pressure
filled completely
with
not
movement.
fl uid, that fluid cannot change
If a system
filled completely
volume,
no ismatter
how high with
the
fluid,
fluid is cannot
change
pressure.that This
hydraulic-la'v
volume,
no This
mattermeans
how that
high any
the
number 1.
pressure.
This
is
hydraulic-la-v
motion inward on a piston must result
number
1. This
means
that any
in an outward
motion
elsewhere
in
motion
inward
o n a piston
mustsystem
result
the system
. A good
hydraulic
in rigid,
an outward
motion should
elsewhere
in
is
so movement
occur
the
A good
hydraulic
onlysystem.
at another
piston.
If the system
hoses ,
is rigid,
so movement
occur
lines
or cylinders
expand should
when the
hyonly
at
another
piston.
If
the
hoses,
draulic fluid is pressurized, the
lines or will
cylinders
expandaswhen
the hysystem
not function
designed
.
draulic fluid
is
pressurized,
the
system will not function as designed.
44
Fluid inches
displacement = A, M,
of piston
in square
A
, =
Mp
= Area
Movement
of that
piston in
inches
inches
M, = Movement of that piston in
Because
hydraulic fluid cannot be
inches
compressed, the following relationBecause
fluiddisplacement
cannot be
ship
exists: hydraulic
In ward flUid
compressed,
the
following
= Outwardfluid displacement. relationship
exists:
Inward
fluid has
displacement
If the
hydraulic
system
only two
=
Out
wardfluid
displacement.
pistons, such as shown in in the acIf the hydraulic
system
only distwo
companying
drawing,
thehas
inward
pistons, such
in the
acplacement
of as
oneshown
pistoninmust
equal
companying
drawing,
the
inward
disoutward displacement of the other
placement
onerelationship
piston must
equal
piston. Thisofbasic
remains
outward displacement
the other
constant
regardless of of
system
compiston. This
relationship
remains
plexity.
All basic
inward-displa
cement
tolals
constant
regardless
of system commust total
all outward-displacem
ent
plexity.
totals. All incva1.d-displacemenr totals
must
Now,total
let's alluseoutwat,d-displacemen(
a simple example
totals.
with a two-piston system . Assume
Now,1 let's
usearea
a simple
piston
has an
of 2 sq example
in. If it
with
two-piston
system.
Assume
movesa inward
1 inch,
its inward
dispiston
1 has
of 2outward
sq in. If
placement
is 2ancuarea
in. The
dis-it
moves inward
1 inch,
its inward
dis-2
placement
of piston
2 must
also be
placement
is
2
cu
in.
The
outward
cu in. If piston 2 has an area of 1dissq
placement
of piston
2 must will
also be
be 22
movement
in.,
its outward
cu
in. change
If pistonthe2 move
has an
area
1 sq
in. To
men
t ofofpiston
in.,
its
outward
movement
will
be
2, you must change its area . A larger-2
in. Topiston
changewill
themove
movement
piston
area
less; aofsmaller
2, you
mustAssume
change now
its area.
larger-2
one
more.
that Apiston
area
piston towill
is changed
an move
area ofless;
4 sqa insmaller
. for 2
one more. Assume now that piston 2
is changed to an area of 4 sq in. for 2
cu in. of fluid displacement, piston 2
must move 1/2 in.
cuThe
in. ofrelationship
fluid displacement,
betweenpiston
piston2
must
move 112
movement
in in.
a simple two-piston
The relationship
piston
system
is given by between
the following
movement
in
a
simple
two-piston
formul a:
system is given by the following
M1A1
formula:
M =-2
A2
M, = Movement of piston 1 in inches
M 2 = Movement of piston 2 in inches
M, == Area
Movement
of piston
1 in inches
A1
of piston
1 in square
M, = inches
Movement of piston 2 in inches
piston 21 in
in square
A,2 =
A
= Area of piston
inches
A, = Area of piston 2 in square
To inches
increase the movement of
piston 2, increase the area of piston 1
increase
movement
of
or To
reduce
the area the
of piston
2.
piston
2,
increase
the
area
of
piston
Remember that fluid mo vement1
or
reduce the
of piston
depends
on area
piston
area 2.and disRemember
that fluid
place
ment. Mistakes
in movement
calcul ation
depends
ondiameter
piston isarea
disoccur when
usedand
in place
placement.
Mistakes
in
calculation
of area, and movement in place of
occur when diameter
is used
in place
displacement.
Use care
with
your
of area, and. Double-check!
movement in place of
calculations
displacement.
Use care
with your
Force/Movement
Relationshipscalculations.
Double-check!
As seen from previous formulas,
Force/Movement
there is a relationshipRelationshipsbetween force
As a seen
previous
formulas,
on
pistonfrom
and its
movement.
Both
there
is
a
relationship
between
force
are related to piston area . It is possible
on
a piston
its movement.
forceand
without
movementBoth
, or
to have
are
related to
piston force
area. .ItHowever,
is possiblea
movement
without
to
havesystem
force without
movement,
or
has both
forces and
brake
movement
without
force.
However,
movements. The relationships be-a
brake system
has and
bothforce
forces
and
tween
movement
is very
movements.
The relationships beimportant.
tween
movement
andand
force
is v&y
Formulas
for force
movement
important.
both depend on piston area. However,
Formulas changes
for force cause
and movement
piston-area
opposite
both depend
on piston
However,
changes
in forces
andarea.
movements.
piston-areain changes
opposite
Changes
area thatcause
create
more
changes
in
forces
and
movements.
force on a piston result in less move-
Changes in area that create more
force on a piston result in less move-
ment of that piston. The system
works like a simple lever, as shown in
ment
of that piston.
The system
the accompanying
drawing.
works
a simple
lever, as hydraulic
shown in
One like
simple
two-piston
the
accompanying
drawing.
system is used in a hydraulic jack. The
One
simpleboth
two-piston
hydraulic
jack
supplies
force and
movesystem
in a hydraulic
jack. as
Thea
ment atis used
the same
time , such
jack
movesystem .both
Theforce
jack and
handle
is
brakesupplies
ment
theforce.
same
time,
as a
movedatwith
This
forcesuch
is applied
brake
system. ofThe
jack
is
to the bottom
a car
and handle
it moves
moved
force.When
This force
is applied
the car with
upward.
using
a jack,
to
thethat
bottom
of a car
andis less
it moves
note
the handle
force
than
the
car
upward.
When
using
a jack,
the force on the car. You can easily
lift
that the
force
is less
than
anote
2000-lb
car handle
using less
than
50 Ib
at
the
on Force
the car.is You
can easily
lift
increased
by the
the force
handle.
a 2000-lb car
thanNote
50 Ib
at
difference
in using
piston less
sizes.
also
the
handle.
Force
is
increased
by
the
how great the movement of the
difference
in piston tosizes.
Note also
handle is compared
the movement
howthegreat
the ormovement
of the
of
jack pad
car. Movement
is
handle
compared
the movement
reduced,is but
force istoincreased
by inof the jack
padsize
or car.
is
that Movement
operates the
creased
piston
reduced,
but
force
is
increased
by
injack pad.
creased
that Operates
the
Input & piston
Outputsize
Pistons-A
hydraulic
jack
pad.uses force and movement apsystem
Input
& Output
an inputPistons-A
piston and hydraulic
provides
plied to
system
uses
force
and movement
apforce and movement
on an ourput
plied
to
an
input
pistoil
and
provides
piston. With a hydraulic jack, the
force
movement
an o~ltput
handleand
operates
an inputonpiston.
The
piston.
With
a
hydraulic
jack,
the
piston is connected to the jack pad,
handle
operates
an
input
piston.
The
which raises th e car. With a brake
piston is aconnected
to the the
jack input
pad,
system,
pedal operates
which
the car.
Withapply
a brake
piston raises
and output
pistons
the
system,
brakes . a pedal operates the input
To
Front
Brakes~
To
Front
Brakes*
--w- To Rear Brakes
-
Front-And-Rear
Split System
Front -And-Rear
Split System
Input
Force
Right Front Brake
Master
Cylinder
Right Rear Brake
~
Right Front Brake
Right Rear Brake
Diagonally
Split
System
Diagonally
Input
Split
System
~Force
lnput
Force
-
Left Rear Brake
Left Front Brake
I
I
Most modern carsLeft
useFront
tandem
master cylinders-two pistons
oneBrake
bore. Each piston operLeft in
Rear
Brake
ates brakes at two wheels. If one system fails, 50% braking is left. Most tandem master
cylinders
operate
front
and rear
systems. Another
used
on road
hasopera diMost modern
cars separate
use tandem
master
cylinders-two
pistonsone
in one
bore.
Eachcars
piston
agonally
splitatsystem
as shown.
I deal
only fails,
with front-and-rear
because
it's
ates brakes
two wheels.
If one
system
50% braking issplit
left.systems,
Most tandem
master
the
type most
high-performance
use. systems. Another one used on road cars has a dicylinders
operate
separate front cars
and rear
agonally split system as shown. I deal only with front-and-rear split systems, because it's
the type most high-performance cars use.
Filler Cap
~:;::::::::::::Lr-
Pushrod
piston and output pistons apply the
brakes.
BRAKE-SYSTEM HYDRAULICS
These laws of hydraulics explain
BRAKE-SY
HYDRAULICS
how a basic STEM
brake system
works. AlThese
laws
of
hydraulics
though the basics are simple,explain
there
how acomplications
basic brake system
Alare
with works.
the autothough
the basics
are simple,
there
motive-brake
system.
I'll describe
are separately.
complications with the autoeach
motive-brake
system. I'll describe
The input piston is in the master
each
separately.
cylinder. Modern brake systems use
Theinput-piston
input piston master
is in the
master
dual
cylinders.
cylinder.
Modern
brake
systems
use
Each piston operates two brakes.
dual
input-piston
master
front brakes
are cylinders.
on one
Usually,
Each piston
operates
system
and rear
brakes two
are brakes.
on the
Usually,
front
brakes
are
one
other. But some dual systems on
operate
system
and
rear
brakes
are
on
the
a diagonal pair of brakes with each
other.
dual
systemsand
operate
piston,But
suchsome
as the
right-front
leftarear,
diagonal
of brakes with each
and vicepair
versa.
piston,
such
as
the
leftOutput pistons right-front
are locatedand
inside
rear,
and
vice
versa.
the brakes. Disc-brake calipers use
Output
pistons
arepistons
locatedto inside
one
or more
output
move
the
brakes.clamping
Disc-brake
calipersDrum
use
the pads,
the rotor.
one
or
more
output
pistons
to
move
brakes use one or more output pistons
the moving
pads, clamping
thetorotor.
Drum
for
the shoes
contact
the
brakes use
one or moreoutput
output pistons
drums.
Drum-brake
pistons
for moving
thesame
shoesdiameter
to contact
are
about the
as the
the
drums.
Drum-brake
output
pistons
master-cylinder input pistons. Disc
are
about
the
brakes
havethenosame
servodiameter
action, soas they
master-cylinder
Disc
require
higher input
force pistons.
to operate.
brakes have nodisc-brake-caliper
servo action, so they
Consequently,
pis-
require higher force to operate.
Consequently, disc-brake-caliper pis-
Dust Boot
Residual-Pressure
Check Valve
dual-Pressure
CheckFluid
Valveenters cylinSingle master cylinder is basic. Fluid reservoir is directly above cylinder.
der through ports in reservoir. Pushrod moves piston to right to pressurize brake fluid.
Drawing
courtesy
Bendix
Corp. Fluid reservoir is directly above cylinder. Fluid enters cylinSingle
master
cylinder
is basic.
der through ports in reservoir. Pushrod moves piston to right to pressurize brake fluid.
Drawing
tons arecourtesy
usually Bendix
twice Corp.
the diameter of
quired to place the lining in contact
master-cylinder pistons.
tons
usually
twice the
of
A are
simple
approach
to diameter
hydraulics
master-cylinder
seems
to "say"pistons.
that large-diameter
A simple
pistons
could approach
be used at to
thehydraulics
brakes to
seems
to
"say"
that
large-diameter
produce high forces at the brakes.
pistonswould
could give
be used
to
This
lowat the
pedalbrakes
effort.
produce high
forces
the brakes.
Therefore,
power
assistatwould
not be
This
would
give low pedal
effort.
required.
Unfortunately,
this doesn
't
Therefore,
power
assist
would
not
be
work. The problem is input-piston
required.
Unfortunately,
this doesn't
movement,
which translates
into
work. brake-pedal
The problem
is input-piston
Let's take a
excess
travel.
movement,
which
translates
into
closer
look at why
this is
true.
excess
brake-pedal
travel.
Let's
take
Pedal Travel-To take up clearancesa
closer
looksystem,
at why this
is true.
in a brake
pistons
must move .
Pedal Travel-To
takeeach
up brake,
clearances
Clearance
is built into
and
in
a
brake
system,
pistons
must
move.
is equal to the piston movement
re-
Clearance is built into each brake, and
is equal to the piston movement re-
with each rubbing surface. The total
quired
the fluid
liningmust
in contact
volume toofplace
moving
equal
with
each rubbingofsurface.
The total
the displacement
all pistons
that
volume
move. of moving fluid must equal
theThis
displacement
of all
pistons that
displacement
is provided
by
move.
master-cylinder-piston
movement.
This displacement
is provided
by
Because
fluid volume doesn't
change,
master-cylinder-piston
movement.
the inward displacement of
the input
Because
fluid volume
doesn't
change,
pistons must
equal the
outward
disthe
inward
displacement
of
the
input
placement of all output pistons in
the
pistons. This
must rule
equal
the outward
dissystem
assumes
a hydraulic
placement
all that
output
pistonsdeflects
in the
system
so of
rigid
nothing
system.
This
rule
assumes
a
hydraulic
from forces in the system.
system
so rigid that nothing
deflects
If a small-diameter
master-cylinder
from
in with
the system.
pistonforces
is used
large pistons at the
If a small-diameter
master-cylinder
brakes,
greater movement
is required
piston is used with large pistons at the
brakes, greater movement is required
45
Typical master-cylinder piston with seals;
larger seal at right seals high-pressure
system. master-cylinder
Left seal keepspiston
fluid with
that's
beTypical
seals;
tween
from
leaking
open end of
larger seals
seal at
right
sealsouthigh-pressure
master
Both
are cup-type
seals.besystem.cylinder.
Left seal
keeps
fluid that's
Girling single master cylinder is type found
on many race cars, typically in dual mastercylinder
setup.
It iscylinder
small, issimple
and
Girling single
master
type found
lightweight.
cap/reservoir
exon
many raceWhite
cars, nylon
typically
in dual mastertension setup.
increases
capacity.
cylinder
It is reservoir
small, simple
and
Cylinders
areWhite
also used
operate hydraulightweight.
nylontocapheservoir
exlic clutches.
tension
increases reservoir capacity.
tween seals from leaking out open end of
master cylinder. Both are cup-type seals.
Cylinders are also used to operate hydraulic clutches.
Fluid-Inlet Port
Compensating Port
Force
On Piston-_~~
From
ForcePushrod
On Piston
From Pus
Cup-Type
Seal
Cup-Ty pe
Seal
L
Cylinder
As master-cylinder piston is pushed forward, seal
slides past compensating port and traps
fluid inside bore. Piston in this position can now pressurize brake fluid to apply brakes.
As master-cylinder piston is pushed forward, seal slides past compensating port and traps
fluid inside bore. Piston in this position can now pressurize brake fluid to apply brakes.
at the master cylinder to take up
clearances. The problem is, only so
at
the pedal
master
cylinder
to take
up
much
travel
is available
at the
clearances.
The This
problem
only
so
master cylinder.
is whyis,you
can't
much
pedal
travel
is
available
at
the
design a system for forces without
master cylinder.
This is why you can't
considering
movement.
design
a system for
without
Unfortunately,
the forces
characteristics
considering
movement.
of a real brake system are worse than a
Unfortunately,
characteristics
theoretically
perfectthe
hydraulic
system.
of a real
brake system
are worse
For
example,
the forces
are asthan
cal-a
theoretically
perfect
hydraulic
system.
culated
except
for a small
loss of
force
For the
example,
forces are
calat
outputthepistons
fromas seal
culated
except
for
a
small
loss
of
force
friction. However, input-piston moveat
theinaoutput
pistons
from larger
seal
ments
real system
are much
friction.
However,
input-piston
movethan those of the theoretically perfect
larger
ments in'a
system areormuch
system
due real
to deflections,
hydraulic
than
those
of
the
theoretically
perfect
hose and line expansion, and bending
system
due toofdeflections,
or hydraulic
and
twisting
brake components.
hose
and line expansion,
bending
Specifically,
additional and
movement
and
twisting
of
brake
components.
comes from places other than clearSpecifically,
movement
ances
in a brakeadditional
system . Pedal
movecomes
from
places
other
than
ment comes from the total ofclearthe
ances in a brake system. Pedal movefollowing:
ment comes from the total of the
following:
46
• Brake clearances.
• Designed clearances and wear in
Brakeclearances.
linkage.
Designed of
clearances
wearand
in
• Swelling
hydraulicandhoses
linkage.
other parts of the hydraulic system.
of of
hydraulic
• Swelling
Compression
hydraulichoses
fluid. and
other
parts of theofhydraulic
system.
• Compression
air bubbles
in hyCompression
of hydraulic fluid.
draulic
fluid.
air bubbles
in hyBending of ofpedal,
linkage
or
• Compression
draulic
fluid.
brackets.
Deflection ofof pedal,
calipers, linkage
drums or
or
• Bending
brackets.
other parts of brake system.
Deflection
calipers,atdrums
or
When total of
movement
the pedal
other
parts of brake
system.
is excessive,
the pedal
will hit the
When
total movement
the pedal
floor
before
the brakesat are
fully
is
excessive,
the
pedal
will
hit the
applied. Keeping pedal movement
floor
the limits
brakes is are
fully
within before
reasonable
a major
applied.
pedaldesign.
movement
problem inKeeping
brake-system
within
reasonable limitsproblems
is a major
Brake-system-design
are
problem
in
brake-system
design.
discussed in Chapter 9.
Brake-system-design problems are
discussed
Chapter 9.
MASTERinCYLINDERS
Brake-fluid movement and pressure
MASTER CYLINDERS
Brake-fluid movement and pressure
are created by the master-cylinder
piston . This piston is connected to the
are
by athe
master-cylinder
brakecreated
pedal with
simple
linkage and
piston.
This piston is connected to the
pushrod.
brake
withmodern
a simpleroad
linkage
The pedal
typical
car and
has
pushrod.
one master cylinder containing two
T h e typical
has
pistons,
while modern
race carsroad
are car
usually
one master
containing
two
equipped
withcylinder
a separate
master cylinpistons,
while
cars are usually
der
for each
pair race
of brakes.
equipped
with
a
separate
master cylinSingle Master Cylinder-The
simder
each pair
of brakes.
plestformaster
cylinders,
such as those
Single
Cylinder-The
simused on Master
production
cars with hydraulic
plest
master
such
as
brakes up to the early '60s, have a
used on piston
production
with hydraulic
single
to cars
operate
all four
brakes upSeeto the
early '60s, have
brakes.
accompanying
photo.a
single
piston
to
operate all four
Today's safety laws have made them
brakes. See
accompanying
photo.
obsolete.
Regardless,
single masterToday's safety
laws
made them
systems
are have
still worth
lookcylinder
obsolete.
Regardless,
mastering at because
they single
are easy
to
cylinder
systems
stillare
worth
lookunderstand.
And,are
they
used
on
ing
they are easy to
most at
racebecause
cars.
understand.
theyhydraulic-fluid
are used on
Note thatAnd,
most
most race cars.
reservoirs
are integral with their
Note cylinders
that mostand hydraulic-fluid
master
are directly
reservoirs
are integral
with
their
above the piston.
The piston
is moved
master in
cylinders
and by
area pushrod
directly
forward
the cylinder
above the to
piston.
piston
is moved
attached
the The
brake
pedal.
The
forward
in
the
cylinder
by
a
piston is returned by a springpushrod
against
attached
to when
the brake
the piston
pedalpedal.
forceThe
is
piston
is returned by a spring against
removed.
theThere
piston
when
force
is
are two
holes,pedal
or ports,
in the
removed.
reservoir that allow fluid to enter the
There are
two holes,
or ports,
the
These
are called
the in
fluidcylinder.
reservoir
that compensating
allow fluid toport.
enter
the
inlet port and
When
arethe
called
the fluidacylinder.
piston isThese
at rest,
compensating
inlet
port
and
compensating
port.
port is ahead and the fluid inlet When
port is
a piston
is attherest,
the compensating
just
behind
lip forming
the front
port of
is ahead
and the
fluidposition,
inlet portthe
is
face
the piston.
In this
just
behind
the lip forming
front
piston
rests against
a clip or the
retaining
face
theprevents
piston. Inthe
thisreturn
position,
the
ring of
that
spring
piston
rests
against
a
clip
or
retaining
from pushing the piston out the end
ring
prevents the return spring
of thethat
cylinder.
from
pushing
outa pushrod
the end
As the brakesthe
arepiston
applied,
of
the
cylinder.
moves the piston forward in the
As the brakes
are applied,
The piston
movesa pushrod
forward
cylinder.
movesthethe
piston
forward
in the
lip of
the seal
covering
the
with
cylinder.
The port.
pistonBefore
moves
compensating
thisforward
port is
with
the piston
lip of the
seal forces
covering
the
covered,
motion
excess
compensating
port.
Before
this
port
is
fluid back into the reservoir. Look
covered,
piston motion reservoir
forces excess
into a master-cylinder
and
fluid
back
into
themotion
reservoir.
Look
you see
slight
fluid
just as
the
into
a
master-cylinder
reservoir
and
piston begins to move. Once the comyou
see slight
fluidismotion
just asfluid
the
pensating
port
covered,
piston
Once thesystem
comtrappedbegins
in to
themove.
hydraulic
pensating
portprovided
is covered,
cannot
escape,
there arefluid
no
trapped
in
the
hydraulic
leaks. Beyond this position, thesystem
piston
cannot
escape,
provided
there are no
moves fluid
to apply
the brakes.
leaks.
Beyond
position, thereduces
piston
Initial
fluidthismovement
moves fluid into apply
the brakes.
clearances
the brakes.
When all
Initial fluid
reduces
clearances
in movement
the
system
are
clearances
in
the
brakes.
'When
all
eliminated, fluid stops moving and
clearances
system
are
pressure rises.inThethe
driver's
foot coneliminated,
fluid
moving
trols how high
fluidstops
pressure
gets. and
As
pressure rises. The driver's foot controls how high fluid pressure gets. As
C up-Type Seal
Cup-Type
Seal
During rapid retraction of master-cylinder piston, fluid flows
through small holes in front face of piston and past seal. This prevents
bubbles
from forming
in front of seal.
Fluid-inlet
port
Duringairrapid
retraction
of master-cylinder
piston,
fluid flows
keeps
fluid
behind
seal
at all face
times.
through
small
holes
in front
of piston and past seal. This pre-
vents air bubbles from forming in front of seal. Fluid-inlet port
keeps fluid behind seal at all times.
Force _ _. -04
on Piston
Piston
Cup-type seal expands outward against cylinder-bore walls when
fluid is pressurized, making a tight seal. Flat end of cup-type seal
goes
toward
piston
face;outward
cup end against
toward high-pressure
fluid. when
Cup-type
seal
expands
cylinder-bore walls
fluid is pressurized, making a tight seal. Flat end of cup-type seal
goes toward piston face; cup end toward high-pressure fluid.
Cup-type seal can withstand high pressure
while sliding easily within cylinder bore.
Seal
lips seal
press
against
cylinder
Cup-type
cantightly
withstand
high pressure
walls sliding
when pressurized.
higherbore.
the
while
easily withinThe
cylinder
pressure,
tighter
the seal.
Seal
lips the
press
tightly
against cylinder
Residual-pressure valves are used in special applications. For example, Airheart
Residual-pressure
valves areretracted
used in specalipers
using mechanically
piscia1
For example, valve
Airheart
tons applications.
require a residual-pressure
to
prevent pistons
from retracting
too far. piscalipers
using mechanically
retracted
walls when pressurized. The higher the
pressure, the tighter the seal.
tons require a residual-pressure valve t o
prevent pistons from retracting too far.
Some Airheart calipers use a padretraction system to prevent pads from
dragging
on rotors.calipers
Two cylindrical
Some Airheart
use aobjects
padprotruding system
from body
of Airheart
X
retraction
to prevent
pads1 75
from
206 caliper
are Two
partcylindrical
of mechanical
dragging
on rotors.
objects
retractors. from
Residual-pressure
valve 175
should
X
protruding
body of Airheart
be
with these
courte206used
caliper
are calipers.
part ofPhoto
mechanical
sy Hurst Performance.
retractors.
Residual-pressure valve should
be used with these calipers. Photo courtesy Hurst Performance.
force on the pedal is reduced, hydraulic pressure drops,
the drumforce
on thereturn
pedal springs
is reduced,
brake-shoe
and /hydrauor disclic
pressure
drops,
the
drumbrake-piston seals retract, and
the
brake-shoe
returnreturn
springs
and/ormoves
discmaster-cylinder
spring
brake-piston
seals
retract,
and the
the piston back
against
the retaining
master-cylinder
return
spring
moves
ring.
theThe
piston
back
against
the
retaining
fluid-inlet-port function is
ring.
more complicated . To understand it
The look
fluid-inlet-port
function
is
better,
at the drawings
of the
more
complicated.
To
understand
it
piston and seals. Note that the piston
better,
look
at
the
drawings
of
the
has sma ll holes drilled through the
piston and lip
seals.
that the
front-face
. TheNote
cup-type
sealpiston
is in has
small
holes
drilled
through
stalled ahead of this face , with the the
lip
front-face
The cup-type
seal is inextending lip.
forward.
The fluid-inlet
stalled
aheadfluid
of this
face, the
withfront
the lip
port allows
behind
lip
extending
forward.
of the piston;
the holesThe
in thefluid-inlet
lip allow
port
allows
behind
theface
front
lip
this fluid
to fluid
contact
the seal
. This
of
the
piston;
the
holes
in
the
lip
allow
is to help during brake release when
this
fluid toreturns.
contact the seal face. This
the piston
is to help during brake release when
the piston returns.
As the brakes are released, the
return spring may move the piston
As than
the brakes
the
faster
the fluidare
can released,
move . When
return
springthemay
the piston
this occurs,
seal move
lip is drawn
away
faster
thancylinder
the fluid
can
move. When
from the
wall
, allowing
fluid
this
occurs,
the
seal
lip
is
to flow through the small drawn
holes inaway
the
from
theThis
cylinder
seal lip.
keepswall,
fluidallowing
ahead offluid
the
to
flow at
through
the small
holes in the
piston
a ll times
and prevents
the
seal
lip. This
fluid ahead
of the
formation
of keeps
a gas bubble
in front
of
piston
at all
times andthe
prevents
the
the piston
. Otherwise,
gas bubble
formation
of aa gas
in front
of
would cause
soft bubble
pedal with
excesthe piston.
the gas
sive
travel. Otherwise,
The secondary
sealbubble
keeps
would
cause
a softout
pedal
with excesfluid from
leaking
the open
end of
sive
travel.
The
secondary
seal keeps
the cylinder.
fluid
from
leaking
outat the
end of
Let's
look
closely
theopen
function
of
the
cylinder.sea l in the accompanying
a cup-type
Let's The
look closely
at the faces
function
of
photo.
cup always
highapressure
cup-typefluid.
seal inFluid
the accompanying
pressure acts
photo.
alwaysasfaces
highequally The
on allcup
surfaces
it contacts
pressure
fluid.
pressureagainst
acts
the cup face
and Fluid
lip. Pressure
equally on all surfaces as it contacts
the cup face and lip. Pressure against
the lip forces it against the cylinder
wall, creating a tight seal. The higher
the
forces the
it against
the lip
pressure,
tighter the
the cylinder
cup lip
wall,
a tight
seal.wall.
The This
higheris
seals creating
against the
cylinder
the
pressure,
the
tighter
the
cup
lip
a reliable, long-life seal.
seals
against
the
cylinder
wall.
This
is
Residual-Pressure Valve-A cupatype
reliable,
long-life
seal.
seal has one problem when used
Residual-Pressure
Valve-A
with a drum-brake wheel
cylinder.cupAs
type
seal ishas
one problem
used
the seal
retracted,
its lipwhen
is relaxed
with
wheel cylinder.
As
and aairdrum-brake
can be introduced
in the
the
seal
is
retracted,
its
lip
is
relaxed
system . On drum-type brakes, this
and
air ofcan
introduced
the
motion
the be
cup-type
seals ininwheel
system.
brakes,
cylinders On
will drum-type
draw in air each
time this
the
motion
of released.
the cup-type seals in wheel
brakes are
cylinders
will two
drawdevices
in air each
the
There are
that time
prevent
brakes
are, released.
this . One
called a cup expander, is a
There
arecup
twoinstalled
devices that
prevent
thin
metal
between
the
this.
One,
called
a
cup
expander,
is a
seal and the return spring . This device
thin
cup on
installed
between
the
exertsmetal
pressure
the lip an
d prevents
seal
and the
return the
spring.
device
air from
passing
sealThis
when
the
exerts pressure on the lip and prevents
air from passing the seal when the
47
Reservoir Diaphrag
Return
Spring
Secondary
Piston
Secondary
Cups
Primary Cup
Primary
Piston
Secondary
Cup
Cross section of typical tandem
master
cylinder with integral fluid reservoirs. Pushrod is
Piston-Stop
Bolt
retained on pedal, which is out of view to right, not on master-cylinder piston. Drawing
courtesy
Bendix
Cross section
ofCorp.
typical tandem master cylinder with integral fluid reservoirs. Pushrod is
retained on pedal, which is out of view to right, not on master-cylinder piston. Drawing
courtesy Bendix Corp.
Reservoir Cover - - - - - ,
Cover Retainer/Bail
Cover Retainer/Bail
Piston-Stop Bolt
Hydraulic lines from tandem master cylinder to front and rear brakes install in outlet ports.
Reservoir cover is retained with spring clip, or bail. Drawing courtesy Bendix Corp.
Hydraulic lines from tandem master cylinder to front and rear brakes install in outlet ports.
Reservoir cover is retained with spring clip, or bail. Drawing courtesy Bendix Corp.
DIAGONALLY
SPLIT SYSTEMS
DIAGONALLY
Most front-wheel-drive cars are
SPLIT
SYSTEMS
designed
with tandem master
Most front-wheel-drive
are
cylinders
plumbed so theycars
operate
designed opposite
with tandem
diagonally
wheels.master
Each
cylinders
so they operate
half of the plumbed
cylinder operates
a diagdiagonally
opposite
wheels.
onally
opposite
pair of
brakes.Each
The
half offront
the cylinder
operates
diagbrake and
left rearabrake
right
onally oppos~te
of brakes.
The
comprise
one pair
system.
Opposite
right front
brake and
rear brake
pair
of brakes
are left
operated
by
comprise
other
half one
of thesystem.
master Opposite
cylinder.
pair
of brakes
by
Because
a front are
andoperated
rear brake
other half
of together,
the master
always
work
thiscylinder.
system
Because
an3 inrear
is
claimedatofront
be safer
the brake
event
always work together, this system
is claimed to be safer in the event
48
one system fails.
Brake balance cannot be adjustone
system
fails. way withadiagoed inthe
normal
Brake
balance
be I'm
adjustnally
split
brake cannot
system.
not
ed in the
waycars
with or
a diagoaware
of normal
any race
highnally split brake
system.
I'm not
performance
sports
cars using
diaware
any brakes,
race cars
or highagonallyof split
so hopefully
performance
sports
cars using
diyou
won't have
to concern
yourself
agonally
brakes,
hopefully
with
them.split
If you
have asocar
with di~
you
won't split
havebrakes,
to concern
agonally
the yourself
system
with them.
car with diwould
haveIftoyou
be have
totallya redesigned
agonally
split brakes, front-to-rear
the system
to
use conventional
would
have techniques
to be totally redesigned
balancing
discussed
to
usebook.
conventional front-to-rear
in this
balancing techniques discussed
in this book.
brakes are released.
The second is a simple spring
brakes are
released.
loaded
valve
in the master cylinder.
The
second
is a simple spring
This valve, the reSidual-pressure
valve,
loaded
valve in
the pressure
master cylinder.
keeps slight
fluid
on the
residual-pressure
This
valve,
thetimes-even
system
at all
whenvalve,
the
keeps
slight
fluid
pressure
on the
brakes are released. When fluid
resystem
all master
times-even
when
the
turns toat the
cylinder
as the
brakes
fluid
rebrakes are
are released.
released, When
a spring
closes
turnsvalve
to the
master
cylinder
the
when
pressure
dropsas tothea
brakes value-usually
are released, a6-25
spring
preset
psi.closes
This
the
valve
when
pressure
drops
to a
pressure is enough to keep the cuppreset
value-usually
6-25 psi.
This
type seals
in wheel cylinders
against
pressure
is enough
to keep
the cuptheir
cylinder
walls, but
not enough
to
type
seals
in
wheel
cylinders
overcome return-spring force. against
Excess
their
cylinder
walls,
but not
enough
to
pressure
would
cause
brakeresidual
overcome
shoe drag. return-spring force. ~ x c e s s
residual
cause
brakeIf youpressure
change would
master
cylinders,
shoe
drag.
make sure you get one designed for
you change
theIf specific
system. master
It must cylinders,
have the
make sure
you get one designed
for
correct
residual-pressure
valve. Most
the specificsystems
system. and
It must
have
the
some
drumdisc-brake
residual-pressure
Most
brake systems
do not use residualdisc-brake
systems
and
some
drumpressure valves, so master cylinders
do not even
use residualbrake not
systems
may
interchange,
if they
pressureto valves,
so master
appear
be identical.
Checkcylinders
mastermay notspecifications
interchange,to even
if they
cylinder
be sure.
appear
to
be
identical.
Check
masterResidual-pressure valves are used
cylinder
specifications
to be
sure. that
on Airheart
disc-brake
calipers
Residual-pressure
valves aresystem
used
have
a mechanical-retraction
on
Airheart
disc-brake
calipers
that
to pull the pads away from the rotors.
have
a residual-pressure
mechanical-retraction
valve system
is also
A
2-psi
to pull the padsbyaway
from the
rotors.
recommended
Airheart
for use
on
A
2-psi
residual-pressure
valve
are
brake systems where calipersis also
recommended
by Airheart
use on
mounted
higher
than thefor masterbrake systems
are
This iscalipers
to prevent
cylinder
reservoir.where
mounted
higher
than
masterfluid
flowing
back to
the the
reservoir
by
cylinder Other
reservoir.
This ismanufacturto prevent
gravity.
disc-brake
fluid do
flowing
to the reservoir
by
ers
not back
recommend
residualgravity.
pressureOther
valves.disc-brake manufacturersThisdobrings
not up
recommend
residualan important
point:
pressure
valves.
If you have a special car or a race car
This
brings up
an important
point:
with
modified
brakes,
always consult
If
have a special
car or a race
car
theyou brake
manufacturer
before
with
brakes,
making any changes.
the brake
manufacturer
before
Tandem
Master
Cylinders - Master
making any
changes.
cylinders
with
two pistons in a single
Tandem
Master
bore are used
on Cylinders-Master
modern road cars.
cylindersarewithcalled
two pistons
in amaster
single
They
tandem
bore
are
used
on
modern
road
cars.
cylinders. Tandem master cylinders
They
are introduced
called tandem
master
were first
on American
cylinders.
Tandem
master
cylinders
passenger cars
in 1962;
they've
been
were
first
introduced
on
American
universal since 1967. A typical
passenger
cars incylinder
1962; they've
been
tandem master
is illustrated
universal since 1967. A typical
nearby.
tandem
master cylinder
is illustrated
Each section
of a tandem
master
nearby.
cylinder works as a single cylinder.
Each
of and
a tandem
master
compensating
Each
hassection
fluid-inlet
cylinder
a single
cylinder.
ports. Theworks
pistonasclosest
to the
brake
Each
andpiston
compensating
pedal has
is fluid-inlet
the primary
and the
ports. isThe
closest
to the
brake
other
thepiston
secondary
piston.
Usually,
primary
piston
and
the
is
the
pedal
the primary operates the front brakes
piston.
Usually,
othertheis secondary
the secondary
and
the rear
brakes.
the primary operates the front brakes
and the secondary the rear brakes.
Primary
Piston
Force
,-L-----,_. Force
Force
Force
To Rear
Brakes
To Rear
Brake
If leak develops in front-brake system, primary piston moves forBrakes
System
ward until it bottoms against secondary piston. Force from pushrod
is develops
transmitted
to secondary
piston
by piston
piston-to-piston
If leak
in front-brake
system,
primary
moves forcontact.
allows against
secondary
piston to
pressurize
rear-brake
ward untilThis
it bottoms
secondary
piston.
Force from
pushsystem.
rod
is transmitted to secondary piston by piston-to-piston
contact. This allows secondary piston to pressurize rear-brake
system.
As the driver operates the brake
pedal, the primary piston moves
As the closing
driver operates
the brake
forward,
the primGlY
compedal, theport.primary
moves
Fluid ispiston
trapped
bepensating
forward,
the and
primary
comprimary
secondary
tween theclosing
pensating
port. trapped
Fluid is fluid
trapped
bepiston. This
cannot
tween
the
primary
and
secondary
compress, so it moves the secondary
piston. forward
This trapped
fluidsecondary
cannot
piston
to seal the
compress, so itport.
moves
the both
secondary
compensating
With
compiston forward
seal the
secondary
pensating
ports toclosed,
trapped
fluid
compensating
With
both
comin front
of the
secondbuilds pressure port.
pensating
closed, trapped
primary fluid
and
ary
piston,ports
and between
builds pressure
in front
of the for
secondExcept
the
secondary
pistons.
ary
piston, and return
between
primary
primary-piston
spring,
thereand
is
secondary
pistons. Except
for the
the
no direct mechanical
link moving
primary-piston
return spring,
there
is
secondary
piston-only
pressure
from
no
directfluid
mechanical
link moving the
trapped
.
secondary
piston-onlyin the
pressure
When clearances
brakesfrom
are
trapped
fluid.
taken up, the pistons stop moving ,
When
clearances
in theand
brakes
pressure
increases
forceare
is
fluid
taken up,to the
moving,
applied
thepistons
brakes.stop
When
the
fluid pressure
and the
forcetwo
is
driver
reduces increases
pedal force,
applied
to
the
brakes.
When
the
piston-return springs plus brakedriver
reduces move
pedal the
force,
the to
twoa
return springs
pistons
piston-return
springs
plus
brakeretracted position. As mentioned
return , springs
the pistons
to a
before
holes inmove
the front
lip of each
retracted
Asto flow
mentioned
piston
allowposition.
brake fluid
to the
before,ofholes
in the front
of each
front
the cup-type
seal lip
when
the
piston
allow
brake
fluid
to
flow
to the
brakes are released. Compensating
front of
theexcess
cup-type
ports
allow
fluidseal
to when
return the
to
brakes
are released.
Compensating
when the
brakes are
the reservoir
ports
allow
excess fluid to return to
released
.
theThe
reservoir
brakes
are
purposewhen
of a the
tandem
master
released.
cylinder is to protect against total loss
purpose
of a tandem
mastera
of The
brakes
when failure
occurs. With
cylinder
is to
protect
loss
leak in the
front
brakeagainst
systemtotal
, almost
of
brakes
when
failure
occurs.
With
no pressure exists in the front brakea
leak
in the
front
system,
almost
system.
Note
thebrake
metal
pushrod
beno
pressure
brake
tween
the exists
primaryin the
and front
secondary
system.
Note
theleaks
metal
bepistons. As
fluid
out pushrod
of the fronttween
the
primary
and
secondary
brake system, the primary piston conpistons.
As fluid
out of until
the fronttinues to
moveleaks
forward
this
brake
primary
conmetal system,
pushrod the
contacts
thepiston
secondary
tinues
move
forward untilmovethis
piston. to
Then,
primary-piston
metal pushrod contacts the secondary
piston. Then, primary-piston move-
To Front
Brakes
To Front
Brake
Brakes
If rear-brake
system should
leak, secondary piston moves forward
System
until it contacts end of master cylinder. This allows trapped fluid
between
pistons
to be
pressurized
by primary
piston,
actuating
If rear-brake
system
should
leak, secondary
piston
moves
forward
front
brakes.
until it
contacts end of master cylinder. This allows trapped fluid
between pistons to be pressurized by primary piston, actuating
front brakes.
Cross section of fast-fill master cylinder used on front-wheel-drive cars shows fluidcontrol valve below primary reservoir (arrow). In-line proportioning valves are in rear-brake
ports
bottom of
of cylinder.
portsused
are not
Crossatsection
fast-fill Front-brake
master cylinder
on shown.
front-wheel-drive cars shows fluidcontrol valve below primary reservoir (arrow). In-line proportioning valves are in rear-brake
ports
of cylinder.
ports arethe
not shown.
mentatisbottom
transmitted
to Front-brake
the secondary
pedal moves closer to the
piston , moving it forward and applying
ment
is brakes.
transmitted
thecondition,
secondarya
the rear
With tothis
piston,
moving
it
forward
and
applying
driver will have to exert more
pedal
the
rear
brakes.
With
this
condition,
a
force than normal to stop the car.
driver
exert in
more
Whenwilla have
leak to
occurs
the pedal
rear
force thanfluid
normal
to stop the
car. the
system,
is trapped
between
When
a
leak
occurs
in
the with
rear
primary and secondary pistons,
system,
fluid
is
trapped
between
the
fluid leakage behind the secondary
primary
and secondary
pistons,
allows both
pistonswith
to
piston . This
fluid
leakage in
behind
the secondary
move forward
the cylinder
until the
piston.
both piston
pistonsconto
pushrod This
of theallows
secondary
move
forward
in
the
cylinder
until
the
tacts the end of the master cylinder.
pushrod contact
of the secondary
conWhen
occurs, piston
secondarytacts
end stops,
of the allowing
master cylinder.
motion
pressure
pistonthe
When
occurs,
secondaryto build contact
up between
the two
pistons.
piston
motion
stops,
allowing
This pressure operates thepressure
front
to
build Again,
up between
the two
brakes.
the driver
will pistons.
have to
This
pressure
the Also,
front
exert more
force operates
on the pedal.
brakes. Again, the driver will have to
exert more force on the pedal. Also,
floor- travel is higher. During an
the pedal moves
to
the
emergency,
with closer
one
system
floor-travel
is
higher.
During
m alfunctioning, stopping distance an
is
emergency,
withbecause
one only
system
greatly increased
two
malfunctioning,
stopping distance is
wheels are braking.
greatly
two
When increased
designingbecause
a brakeonly
system
wheels
are
braking.
using a tandem master cylinder,
When designing
a brake
remember
that all force
appliedsystem
to the
using
tandem
master to cylinder,
master acylinder
is applied
primary
remember
that pistons
all forceequally.
applied to
the
and secondary
Force
master
cylinder
is
applied
to
primary
it is not split like a dual masterand secondary
equally. bar.
Force
cylinder
system pistons
using a balance
it Some
is notmaster
split cylinders
like a dual
masterare designed
cylinder
usingata balance
bar. to
to be system
mounted
an angle
Some
master
cylinders
are
designed
horizontal. If so , the cylinder may
to
mounted
angle
to
havebe
a bleeder
screw.at
Thisanscrew
allows
horizontal.
If the
so, master
the cylinder
air
trapped in
cylindermay
to
have
a bleeder
screw.
Thisfluid.
screwBleeder
allows
be bled
from the
brake
air trapped in the master cylinder to
be bled from the brake fluid. Bleeder
49
Dual master-cylinder setup manufactured by Neal Products, fitted
with Howe cylinders, is popular for use in racing stock cars and
other
special vehicles.setup
Hurst!
Airheart, Girling
or Lockheed
Dual master-cylinder
manufactured
by Neal
Products,master
fitted
cylinders
can
be used with
this setup.
with Howe
cylinders,
is popular
for use in racing stock cars and
Single master cylinders found on most race cars; from left to right
they are Airheart, Lockheed, Girling and Howe.
Single master cylinders found on most race cars; from left to right
they are Airheart, Lockheed, Girling and Howe.
other special vehicles. HursVAirheart, Girling or Lockheed master
cylinders can be used with this setup.
Rubber bellows in nylon- reservoir cap
seals air from brake fluid. When reservoir
is
full, bellows
is compressed.
Bellows cap
exRubber
bellows
in nylon-reservoir
tends
as from
fluidbrake
level fluid.
drops.
Vented
cap
seals air
When
reservoir
allows
air to enter
and exit above
bellows
is full, bellows
is compressed.
Bellows
exto compensate
fluid-volume
changes.cap
tends
as fluidforlevel
drops. Vented
allows air t o enter and exit above bellows
t o compensate for fluid-volume changes.
Some reservoir caps have a float. When
fluid level falls too low, float activates an
electrical
switch caps
that have
turns aonfloat.
a warning
Some
reservoir
When
light on
instrument
This light,
instead
fluid
level
falls toopanel.
low, float
activates
an
of brake loss,
warns
of low
fluid.
electrical
switch
that
turns
on a warning
light on instrument panel. This light, instead
of brake loss, warns of low fluid.
Large translucent nylon reservoirs used on
this Indy Car make it easy to check fluid
It
levels.
Caps don't nylon
have reservoirs
to be removed.
Large translucent
used on
helpslndy
to have
good i tlight
checking
this
Car make
easywhen
t o check
fluid
fluid
this
way. don't have to be removed. I t
levels.
Caps
helps t o have good light when checking
fluid this way.
screws look similar to grease fittings. 1
have seen unknowing persons try to
screws
look similar
grease
shoot chassis
greaseto into
thefittings.
bleeder1
have seen
persons
try to
The internal
screws
with unknowing
a grease gun!
shoot chassis grease into the bleeder
screws
with a grease gun! The internal
50
end of the bleeder has a taper that
seals when it is tightened down on its
end ofWhen
the bleeder
has ais taper
that
loosened
seat.
the bleeder
seals
when
it
is
tightened
down
on
its
slightly, this seat seal is opened, then
seat.
When
the
bleeder
is
loosened
brake fluid and trapped air can come
slightly,
thisthe
seathole
sealinisthe
opened,
out through
bleeder.then
brake
fluidusing
and this
trapped
come
cylinder,
When
typeairofcan
out
through
the
hole
in
the
bleeder.
make sure you mount it where it can
using
this type
of cylinder,
beWhen
bled. For
a master
cylinder
that is
make suretoyou
it where
can
designed
be mount
mounted
level, itmake
be bled.
For a master cylinder that is
sure
it's level.
designed
be mounted
level, make
Fast-Fill toMaster
Cylinders-Note
sure
it's
level.
the master-cylinder drawing, page 49.
Fast-Fill
Master
Cylinders-Note
It
differs from
a straight-bore
master
the master-cylinder
49.
in two ways:drawing,
It has a page
stepped
cylinder
It
differs
from
a
straight-bore
master
primary, or fast-fill bore, and second,
cylinder
in twovalve.
ways: It has a stepped
a fluid-control
primary,
fast-fill
bore,
and second,
Duringorinitial
brake
application,
the
alarger
fluid-control
fast-fill valve.
bore provides fluid for
Duringtakeup
initial by
brake
application,
the
forcing
fluid past
system
larger
fast-fill
bore
provides
fluid
for
the primary-piston seal into the main
system
takeup
by forcing
fluid uppast
in
bore. After
clearances
are taken
the
primary-piston
seal into
main
the rotors
and/or drums,
any the
pressure
bore. After clearances are taken up in
the rotors and/or drums, any pressure
buildup in the fast-fill bore would
result in high pedal effort. The fluidbuildup valve
in the
fast-fillthisbore
would
by divertcontrol
prevents
result
in
high
pedal
effort.
The
fluiding fluid from the fast-fill bore to
the
control
prevents
this bycylinder
divertprimary valve
reservoir.
The master
ing
from the
the brakes
fast-fillinbore
to the
a conventhenfluid
operates
primary
reservoir.
The
master
cylinder
tional manner using the smaller main
then
a convenbore. operates
During the
the brakes
return instroke,
the
tional mannervalve
usingallows
the smaller
main
fluid-control
fluid unresbore.
thereturn
fast-fill stroke,
bore. the
tricted During
return tothe
fluid-control
valve
allows
fluid
unresThe major advantage of fast-fill
tricted
return
to
the
fast-fill
bore.
master cylinders is to increase fluid
The major advantage
of fast-fill
displacement
during initial
pedal
master
cylinders
is
to
increase
fluid
travel. This allows smaller masterdisplacement
during
initial
pedal
cylinder main-bore diameter, and retravel. pedal
This effort
allowsand
smaller
duced
travel masterand/or
cylinder main-bore
and redisc-brake
calipers diameter,
with increased
duced
pedal effort
and travel
and/or
piston retraction
distance,
or rollback,
disc-brake
calipers
with
increased
for brake-drag reduction.
piston
retractionCylinders-Most
distance, or ~~ollback,
Dual Master
race
for brake-drag
reduction.
cars
use two single
master cylinders
Dual
Master
Cylinders-Most
side with a link race
bemounted
side by
cars
use
two
single
tween them called a master
balance cylinders
bar. Balmounted
by side fully
with ina Chapter
link beance
bars side
are covered
tween
called
a balance
bar:a Bal6.
Dualthem
master
cylinders
with
balance bars
are covered
fullyofinforce
Chapter
ance
bar allow
the ratio
be6 . Dualfront
master
with ato balbe
tween
andcylinders
rear brakes
ance bar This
allowadjustment
the ratio of
force beadjusted.
is necessary
tweento front
and track
rear conditions
brakes to be
changing
or
due
adjusted.
This
adjustment
is necessary
arrangevariations in car setup. This
due
track system
conditions
or
menttois changing
also a fail-safe
similar
variations
in car
setup.
This arrangeto
the tandem
master
cylinder.
Racing
ment is cylinders
also a fail-safe
system similar
master
are usually
paired
to
the
tandem
master
cylinder.
Racing
single master cylinders, often
the
masterascylinders
are usually
same
those found
on olderpaired
road
single
cars. master cylinders, often the
same as those found on older road
cars.
RESERVOIRS
The fluid reservoir is often integral
RESERVOIRS
with
the master cylinder. However,
fluid accommodation
reservoir is oftenonintegral
forThe
service
some
with
the
master
However,
is separate,
or
cars the reservoircylinder.
for
service
accommodation
some
reservoir
remote.
This
type of fluid on
cars
reservoir
is separate,
or
usuallytheis made
of translucent
plastic
remote. This type of fluid reservoir
usually is made of translucent plastic
Dust
Dust Bc
Piston
s t Boot
'
Piston
Cup'
cup
I
Expander
kpring
Wheel cylinders with two pistons are used
and-trailing-shoe drum brakes. Spring keeps
brakes cylinders
are released.
are used
this
Wheel
withPushrods
two pistons
are inused
courtesy
Bendix Corp.
and-trailing-shoe
drum brakes. Spring keeps
CUP'
Expander
'cup
'
piston
At left is remote reservoir for dual master
cylinders; reservoir at right mounts directly
on left
Girling
master-cylinder
port.
At
is remote
reservoir for outlet
dual master
Reservoirsreservoir
are large
enough
for directly
racing
cylinders;
at right
mounts
disc-brake
on
Girling systems.
master-cylinder outlet port.
Reservoirs are large enough for racing
disc-brake systems.
on most modern duo-servo or leadingpistons or pushrod against shoes when
cylinder
operateduo-servo
brake shoes.
on most tomodern
or Drawing
leading-
pistons or pushrod against shoes when
brakes are released. Pushrods are used in this cylinder to operate brake shoes. Drawing
courtesy Bendix Corp.
so the fluid level can be checked without opening the reservoir. Many of
so
thehave
fluid graduations
level can beon
checked
withthem
the side
inout opening
the low
reservoir.
of
dicating
full and
levels. Many
Separate
them
have
graduations
on
the
side
influid reservoirs are mounted above
dicating
full to
andthelow
levels.
Separate
and
connect
master
cylinder
by
fluid
reservoirs
are mounted above
flexible
hose.
andThe
connect
to the master
by
fluid reservoir
mustcylinder
not allow
flexible
hose.
any contamination of the brake fluid.
The
fluid reservoir
must
not on
allow
The
reservoir
cap, which
screws
or
any
contamination
of
the
brake
fluid.
is fastened by nuts, clamps or bolts, is
The
reservoir
which screws
on or
vented
to thecap,
atmosphere,
allowing
is fastened
by nuts,
clamps
is
the
fluid level
to rise
and or
fallbolts,
freely.
vented
to
the
atmosphere,
allowing
Water vapor in the air will contamithe
to so
risemany
and fall
freely.
nate fluid
brakelevel
fluid,
reservoirs
Water
vapor diaphragm
in the air under
will contamiuse a rubber
the cap
nate
brake fluid,
so the
many
reservoirs
that isolates
it from
atmosphere.
use
a
rubber
diaphragm
under
the cap
This diaphragm flexes easily, allowing
that
isolates
it
from
the
atmosphere.
the rise and fall of fluid , while sealing
This
diaphragm
flexes The
easily,
allowing
out air
and moisture.
diaphragm
the
rise
and
fall
of
fluid,
while
must be removed on some sealing
master
out
air and
diaphragm
cylinders
to moisture.
check or The
replenish
fluid.
mustbest
be overall
removed
on issome
master
The
design
a translucent
cylinders
to check
or replenish
reservoir with
a rubber
diaphragm.fluid.
The
best
overall
design
is a translucent
Reservoir capacity must
be large
reservoirtowith
a rubber
diaphragm.
enough
allow
fluid to
fill a system,
Reservoir
capacitylinings
must are
be worn
large
even
when brake
enough
to
allow
fluid
to
fill
a
system,
totally. A brake system must never
even
whenofbrake
are worn
run short
fluid. linings
Otherwise,
total
totally.
system
must never
braking A
lossbrake
can occur.
Disc-brake
pisrun
of more
fluid.fluid,
Otherwise,
tons short
displace
so they total
usubraking
loss can
occur.
Disc-brake
pisally
require
more
reservoir
capacity
tons
displace
more
fluid,
so
they
usuthan drum brakes. Reservoir volume
ally
reservoir capacity
mustrequire
exceed more
the displacement
of all
than
drum
brakes.
Reservoir
output pistons, plus allow forvolume
lining
must exceed the displacement of all
wear.
output pistons, plus allow for lining
wear.
With either a tandem or dual
master-cylinder system, two separate
With either
a tandem
or with
dual
reservoirs
or a single
reservoir
master-cylinder
system,
two
compartments
shouldtwo
be separate
used. If
reservoirs
or a single
with
this isn't done,
a leak reservoir
in one system
two
compartments
should
be
used.
If
will drain the fluid available to both
this isn't eliminating
done, a leakthein fail-safe
one system
systems,
feawill
fluid available
both
ture drain
of thethe
tandem
and dual tomaster
systems,
eliminating
the
fail-safe
feacylinders.
ture
of
the
tandem
and
dual
master
Race-Car Reservoirs - Most race cars
cylinders.
use remote reservoirs from road cars.
Race-Car
Most race
cars
If your raceReservoirs
car uses aroad-car
master
use remote and
reservoirs
from calipers,
road cars.a
cylinder(s)
large racing
If
yourreservoir
race car uses
master
larger
may aberoad-car
installed.
The
cylinder(s)
and
large
racing
calipers,
reservoir normally used with road-cara
larger
be small
installed.
The
masterreservoir
cylindersmay
is too
for large
reservoir
normally
used
with
road-car
racing calipers. Larger reservoirs are
master cylinders
is too small
for large
available
from Tilton
Engineering,
racing
calipers. Larger
reservoirs
are
Neal Products
and other
suppliers.
available
fromreservoirs
Tilton Engineering,
Custom-built
can also be
Neal
Products
used on
race cars.and other suppliers.
Custom-built
reservoirs
alsoused
be
Remote reservoirs
are can
often
used strength
on race cars.
for
and reliability. Most
Remote
reservoirson are
often used
remote
reservoirs
modern
road
for
strength
and
reliability.
cars are plastic. However, withMost
the
remote
reservoirs
modern
road
risk of heat,
fire oron
physical
damage
cars
are plastic.
However,
the
associated
with race
cars, with
all-metal
risk
of
heat,
fire
or
physical
damage
reservoirs offer extra protection.
associated
with raceis cars,
all-metal
Another advantage
that mounting
reservoirs
offer can
extra
protection.
lugs or brackets
be added
to a
Another
advantage
that mounting.
mounting
metal reservoir
for iseasy
lugs or brackets
canreservoir
be addedcanto bea
Obviously,
a metal
metal
reservoir
for
easy
made in any size and shape mounting.
you need.
Obviously,
can the
be
Remember, aairmetal
mustreservoir
never enter
made in r-any
size and shape youpassage
need.
reservoi
to- master-cylinder
Remember,
air must never
enter the
during
hard cornering,
acceleration
or
reservoir-to-master-cylinder passage
during hard cornering, acceleration or
Custom-built remote metal reservoir
mounted atop fro':,t bulkhead on this Indy
Car
is stronger remote
than plastiC
reservoir.
Cap
Custom-built
metal
reservoir
must
be removed
to check
fluid on
level.
mounted
atop front
bulkhead
this lndy
Car is stronger than plastic reservoir. Cap
braking,
so a tall
reservoir
is better
must
b e removed
to check
fluid level.
than a short one.
braking,
so a tall
reservoir
is better
Often, special
remote
reservoirs
are
than
a
short
one.
used on off-road race cars. These cars
Often, special
remote reservoirs
are
experience
incredible
up-and-down
used
on off-road
race cars.This
These
cars
bouncing
and pounding.
results
experience
incredible
up-and-down
in severe slosh
and aeration
of brake
bouncing
and
pounding.
results
fluid. To prevent this, tallThis
reservoirs
in
severe
and .aeration of brake
with
bafflesslosh
are used
fluid. To prevent this, tall reservoirs
with
baffles are used.
DRUM-BRAKE
WHEEL CYLINDERS
DRUM-BRAKE
There are a number of drum-brake
WHEEL
CYLINDERS
wheel-cylinder
designs . However, all
There
are
a number
drum-brake
share common
features of
. For
instance,
wheel-cylinder
designs.
However,
all
all use cup-type seals. Some have
share common
features. For
instance,
seals
with internal
springs,
or
all
use cup-type
seals.
have
expanders,
that keep
the Some
seal lips
in
seals with
internal
or
contact
with the
cylindersprings,
walls. With
expanders, that keep the seal lips in
contact with the cylinder walls. With
51
-\
Wheel-Cyl~nderBody
Clever design combats brake fluid sloshing
in main reservoirs. Caps to reservoirs were
modified
to accept
plastic
tube.
Fluid
is fed
Clever design
combats
brake
fluid
sloshing
from
third
reservoir
mounted
high inwere
car.
in main
reservoirs.
Caps
t o reservoirs
There's
air plastic
bubbles
will Fluid
develop
in
modifiedno
to way
accept
tube.
is fed
the
fullyreservoir
filled reservoirs.
fromtwo
third
mounted Any
highsloshing
in car.
and
resulting
air air
bubbles
willwill
be develop
contained
There's
no way
bubbles
in
in third
reservoir.
Modification
inthe
two fully
filled reservoirs.
Any also
sloshing
creases
fluid capacity.
and resulting
air bubbles will be contained
in third reservoir. Modification also increases fluid capacity.
expanders in the cup-type seals, a
residual-pressure valve in the master
expanders
in required.
the cup-type seals, a
cylinder is not
residual-pressure
valve
in thepage
master
Duo-servo drum
brakes,
17,
cylinder
is
not
required.
use a single wheel cylinder with two
Duo-servo
drum cylinder
brakes, page
17,
pistons.
The wheel
has both
use a open
singleand
wheel
two
ends
fluid cylinder
betweenwith
the two
pistons.
wheelbetween
cylinderthehas
both
pistons. The
A spring
pistons
ends
open
and
fluid
between
the
maintains slight pressure against two
the
A spring
the pistons
pistons.This
shoes.
springbetween
also prevents
the
maintains
slight
pressure
the
pistons from
blocking
theagainst
fluid-inlet
shoes.
This
spring
also
prevents
the
port in the wheel cylinder.
pistons
blocking
the fluid-inlet
There from
is usually
a rubber
dust boot
port
wheel end
cylinder.
on in
thetheopen
(s) of a wheel
There isThis
usually
a rubberlining
dust boot
cylinder.
prevents
dust
on
the
open
end(s)
of
a wheel
and moisture from contaminating
the
cylinder.cylinder,
This prevents
dusta
wheel
possibly lining
causing
and moisture
the
sticking
piston.from
Dirtcontaminating
is a major enemy
wheel
possiblyThe
causing
of any cylinder,
brake system.
rubbera
sticking
Dirt
major pistonenemy
boots piston.
also
hold is a the
of
any
brake
system.
The
rubber
to-brake-shoe push rods in position,
boots
also
holdpush the
on
systems
that use
rods. pistonto-brake-shoe
pushrods have
in position,
Some wheel cylinders
a single
on
systems
that
use
pushrods.
piston and a closed end, as shown
Some They
wheel are
cylinders
have
a single
above.
usually
found
on
piston andleading-shoe
a closed end,
as shown
double
brakes-each
above.
Theyis are
usually
on
brake shoe
operated
by afound
separate
double
leading-shoe
bra
kes-each
single-piston wheel cylinder. Similar
brake
is operated
a separate
to
the shoe
dual-piston
type, by
single-piston
single-piston
wheelhave
cylinder.
Similar
wheel cylinders
an internal
to the to
dual-piston
type, single-piston
spring
keep the piston
and push rod
wheel
cylinders
have shoe.
an internal
in
contact
with the brake
spring
to
keep
the
piston
and
pushrod
A wheel cylinder usually
is
in contact with
shoe.
equipped
with the
a brake
bleeder
screw. It
A be
wheel
cylinderat the
usually
is
must
positioned
highest
equipped
with
a
bleeder
screw.
It
point in a wheel cylinder so all trapped
must
be
positioned
at
the
highest
air can be bled off. Usually the posipointofina ableeder
wheel cylinder
so all
trapped
is the only
difference
tion
air can be bled off. Usually the position of a bleeder is the only difference
52
Single-piston wheel cylinder is used on
two-leading-shoe drum brakes. Each shoe
has
its own wheel
spring
Single-piston
wheelcylinder.
cylinderReturn
is used
on
holds piston against
shoe
when brakes
are
two-leading-shoe
drum
brakes.
Each shoe
released.
Drawing
has
its own
wheelcourtesy
cylinder.Bendix
ReturnCorp.
spring
holds piston against shoe when brakes are
released. Drawing courtesy Bendix Corp.
Bleeder screws allows trapped air to be removed from high spots in hydraulic system.
One
is used
at each
spot air
so to
airbe
bubBleeder
screws
allowshigh
trapped
rebles
can
be high
bledspots
off toinprevent
spongy
moved
from
hydraulica system.
pedal.
you at
mount
cylinders,
so air drum
bubOne isIfused
eachmaster
high spot
brakes
calipers
a prevent
differenta position
bles
canorbe
bled offin t o
spongy
from
intended
by thecylinders,
manufacturer,
pedal.that
If you
mount master
drum
bleeder
screws
may in
be a
out
of position.
brakes or
calipers
different
position
from that intended by the manufacturer,
bleeder screws may be out of position.
I
c Cotter Pin
1
Caliper-Support Key
Caliper Housing
Bendix CA floating disc-brake caliper has single piston on inboard side of rotor only. Caliper
housing contains both pads. Not shown is sturdy mounting bracket that bolts to suspension
and
supports
and guides
caliper.caliper
Drawing
Bendix
Bendix
CA floating
disc-brake
hascourtesy
single piston
on Corp.
inboard side of rotor only. Caliper
housing contains both pads. Not shown is sturdy mounting bracket that bolts to suspension
and supports and guides caliper. Drawing courtesy Bendix Corp.
between a right-hand and left-hand
wheel cylinder, so use care not to mix
between
a right-hand
and left-hand
wheel
cylinders
when installing
them.
wheel
cylinder,
so
use
care
mix
Some cars have rubber not
capsto over
wheel
cylinders
whentoinstalling
them.
the bleeder
screws
keep out
dirt
Some
cars have
rubber
caps
and
moisture.
This is
a good
ideaover
for
the bleeder
screwsmost
to keep
out dirt
road
cars because
bleeder-screw
and
moisture.
This
is a goodcaused
idea for
breakage
is from
corrosion
by
road cars because
most bleeder-screw
moisture.
Moisture
reaches the
breakage
is fromseat
corrosion
by
bleeder-screw
and caused
threads
moisture.
Moisture
reaches
the
through the hole in its center. Brake
bleeder-screw
seat in Chapter
and threads
bleeding is discussed
11.
throughWheel
the hole
in its center.
Brake
Note:
cylinders
are usually
11.
bleeding
is
discussed
in
Chapter
made of cast iron or aluminum. Most
Note:
cylindersThese
are usually
pistons Wheel
are aluminum.
metals
made
of and
castcorrode
iron or from
aluminum.
Most
can
rust
moisture
in
pistons are aluminum. These metals
can rust and corrode from moisture in
the system. Wheel cylinders probably
fail more often due to these than any
the system.
Wheel
cylinders
probably
other
reason.
Frequent
bleeding
of
fail
more
often
due
to
these
than
any
brakes protects against rust and
other reason. Frequent bleeding of
corrosion.
brakes protects against rust
corrosion.
DISC-BRAKE CALIPER
and
Disc-brake calipers have one or
DISC-BRAKE
CALIPER
more
pistons. They
perform the same
Disc-brake
calipers
have one
or
function as the wheel-cylinder
pistons
more
pistons.
They
perform
the
same
in a drum brake. The caliper piston (s)
function
as the
pistons
is moved
by wheel-cylinder
hydraulic fluid
and
in
a drum
caliper
pushes
thebrake.
pads The
against
the piston(s)
rotor. As
is movedpressure
by hydraulic
and
hydraulic
increases,fluid
the pads
pushes
the
pads
against
the
rotor.
As
are pushed harder against the rotor.
hydraulic
pressure
increases,
theequal
pads
The
caliper
is designed
to apply
are pushed harder against the rotor.
The caliper is designed to apply equal
AP Racing/Lockheed caliper has one large
piston on each side of rotor. Caliper body
is Racing/Lockheed
bolted rigidly to caliper
suspension.
AP
has one Fixed
large
calipers,
this,
are used
on most
piston on such
each as
side
of rotor.
Caliper
body
race
cars; road
cars
use floating
is bolted
rigidly
totypically
suspension.
Fixed
calipers.
AP Racing.
calipers, Photo
such courtesy
as this, are
used on most
race cars; road cars typically use floating
calipers.
courtesy
AP Racing.
pressurePhoto
to the
pads. This
is done ·with
one or more pistons on each side of
pressure
thewith
pads.piston(s)
This is done'with
the rotor,to or
on one
one and
or more
pistons
on each side of
side
a moving
caliper.
theDisc-brake-caliper
rotor, or with piston(s)
one
cylindersondiffer
side
a moving caliper.
fromand
drum-brake
wheel cylinders in
Disc-brake-caliper
cylinders
differ
several
ways. First, caliper
pistons
are
from drum-brake
in
larger
in diameterwheel
than cylinders
drum-brake
several ways. First,
caliperThe
pistons
are
wheel-cylinder
pistons.
reason
larger
thanrequire
drum-brake
for
thisin isdiameter
disc brakes
more
wheel-cylinder
pistons.
The
force because they have no reason
servo
for this is disc brakes require more
action.
force
because
they have
no servo
Another
difference
between
discaction.
and drum-brake cylinders is the type
discof Another
seals useddifference
with the between
pistons. Cupand
cylinders
is the type
type drum-brake
seals are used
in drum-brake
of sealscylinders;
used with
the pistons.
wheel
usually,
O-ring Cuptype
type
seals
are
used
in
drum-brake
seals are used in disc brakes. The
wheel
O-ring cylinders;
m ay haveusually,
a roundO-ring
or squtype
are
seals are used in disc brakes. The
cross-section.
O-ring
may have
a round
or square
The O-ring
seal on
most calipers
recross-section.
tracts the piston and brake pad from
O-ring
on most
calipers
theThe
rotor,
just seal
as return
springs
do inre-a
tracts brake.
the piston
and brake
pad from
drum
The amount
of retraction
the
rotor, just by
as return
springs
do in a
is controlled
seal and
seal-groove
drum
brake.
The
amount
of
retraction
design. Movement is slight in a disc
is controlled
sealrubber
and seal-groove
brake
becausebythe
parts only
design.
Movement
is slight
in a disc
flex a small
amount,
compared
to
brake
because
the springs.
rubber parts
only
brake-shoe
return
However,
flex
small amount,
a littlea motion
is all that compared
is required to
to
brake-shoe
return
springs.
release a disc brake. And, it However,
is desired
atolittle
required
to
keepmotion
the padisveall
ry that
closeis to
the rotor
release
disc brake.isAnd,
is desired
so
fluid amovement
slightit when
the
to keep are
the applied.
pad very Otherwise,
close to the pedal
rotor
brakes
so
fluid
movement
is
slight
when
the
travel would be e xcessive due to the
brakesdisc-brake
are applied.
Otherwise, pedal
larger
piston.
travel
be excessive
duemountto the
Somewould
calipers
have springs
larger
disc-brake
piston.
ed behind the pistons that hold the
Some
mountpads
verycalipers
close have
to thesprings
rotor surface.
ed behind
the add
pistons
thatforce
hold supthe
These
springs
to the
pads
the rotor surface.
plied very
by close
the tohydraulic
system.
These
springs
add to seal
the provides
force sup-a
However,
the piston
plied
by
the
hydraulic
system.
greater force; thus , the piston
is
However, the piston seal provides a
greater force; thus, the piston is
If brake balance is wrong for wet weather driving, you could be in trouble. Photo taken at
Goodyear proving ground near San Angelo, Texas shows how car behaves when wheels
lock
up during
braking
. Here
testingdriving,
difference
tires
in wet
condiIf brake
balance
is wrong
forthey
wetare
weather
you between
could be various
in trouble.
Photo
taken
at
tions
near limit
of adhesion.
Photo
courtesy
Goodyear.
Goodyear
proving
ground near
San
Angelo,
Texas shows how car behaves when wheels
lock up during braking. Here they are testing difference between various tires in wet conditions near limit of adhesion. Photo courtesy Goodyear.
pulled back from the rotor.
Like drum-brake wheel cylinders ,
pulleddisc-brake
back from calipers
the rotor.have bleeder
most
Like
drum-brake
cylinders,
screws. The bleeder wheel
screw must
also
most
disc-brake
calipers
have
bleeder
be located on top of the caliper
so
screws.
trapped The
air bleeder
can be screw
bled must
from also
the
be located
on top
the caliper
so
system.
Rightand of
left-hand
calipers
trapped
air
can
be
bled
from
the
often differ only by location of the
system.
Right- because
and left-hand
bleeder screw
of this,calipers
so be
often differ
the
careful
not toonly
get by
the location
calipers of
mixed
bleeder
screw
because
of
this,
so
up. Otherwise, you won ' t be able be
to
careful
to get
the calipers mixed
bleed thenot
brakes
properly.
up. Otherwise, you won't be able to
bleed the brakes
properly.
METERING
VALVES
In a brake system with discs on the
METERING
VALVES
front and drums
on the rear, there i~
In a the
brake
system
discs on
the
often
need
for with
a metering
valve.
front and
drums
on thea rear,
there of
is
This
device
prevents
pplication
often
the
need
for
a
metering
valve.
the front brakes below a preset presThis
device
of
sure in
the prevents
hydraulic application
system. The
the front
brakes
a preset
presfront
brakes
arebelow
applied
at about
sure in psi,
the depending
hydraulic onsystem.
The
75-135
the system.
front
brakes
are
applied
at
about
The reason for a metering valve is
75-135
depending
on the system.
the forcepsi,and
fluid movement
reThe reason
for a metering
valve is
quired
to overcome
drum-brake
the force
and Also
fluid, disc-brake
movement pads
rereturn
springs.
quired
to
overcome
drum-brake
lightly touch the rotor when not
return springs.
Also,less
disc-brake
applied,
so it takes
pressure pads
and
lightly
touch the
rotor contact
when with
not
fluid movement
to make
applied,
it takesbrakes
less pressure
and
the rotor.so Drum
take much
fluid
make contact
with
more movement
force and to
movement
to bring
the
rotor.
Drum
brakes
take
much
their friction material into contact
more the
force
and movement
to valve
bring
with
drums.
The metering
their
friction
material
into
contact
balances these requirements and
with thethedrums.
valve
allows
front The
and metering
rear brakes
to
balances
work
more these
evenly. requirements and
allows
the afront
and valve
rear ,brakes
to
Without
metering
the front
work
more
evenly.
brakes do all the braking in an easy
Without
valve, thesefront
stop
with aa metering
disc/drum-brake
tup .
brakesaccelerates
do all thefront-pad
braking wear.
in an Also
easy,
This
stop
with I-drive
a disc/drum-brake
setup.
rear-whee
cars without meterThis
accelerates
front-pad
wear.
ing valves tend to lock the Also,
front
rear-wheel-drive
cars on
without
meterwheels when stopping
snow or
ice .
ing valves tend to lock the front
wheels when stopping on snow or ice.
Metering valves allow pressure to be apI
plied
to rear brakes before front brakes. I
Because
may
be combined
Metering they
valves
allow
pressure with
to beother
apbrake-system
components,
not
plied to rear brakes
before you
frontmay
brakes.
recognize
them.
If your
car has awith
metering
Because they
may
be combined
other
valve,
you maycomponents,
have to push
or may
pull the
brake-system
you
not
stem
during
See
shop
recognize
them.bleeding.
If your car
has your
a metering
manual
for may
specifics.
valves
valve, you
have Metering
to push or
pull are
the
used
on roadbleeding.
cars with
stem during
See combination
your shop
drum/disc
brakes. Metering
Drawing valves
courtesy
manual for specifics.
are
Bendix on
Corp.
used
road cars with combination
drum/disc
brakes.
Bendix Corp.
Drawing
Not
with
Not
setups.
metering valves
disc/drum-brake
ametering
metering valves
valve
all cars use
production
all
carshave
use
Some
courtesy
with production discldrum-brake
setups. Some have a metering valve
53
Front vs. Rear Fluid Pressure Relationships
For Maximum Decleration at Various
Traction
Front vs. Conditions
Rear Fluid Pressure Relationships
For Maximum Decleration atBrake
Various
System
Traction Conditions
Without Proportioning
-.-
1.2g
Ideal Relationship
al x
&.
E
c2
(/J
OJ
>-
~(/)
(/J OJ
(/J.:.t:.
OJ
ro
Changeover
Pressure In FrontBrake System (psi)
Pressure in Front-Brake System (psi)
Upper curve represents
ratio
of front-to-rear
brake
Pressure
in Front-Brake
System
(psi)pressures in
system not using a proportioning valve. Pressure ratio is built into
master
cylinder
or balance
Ideal pressure
relationship
Upper curve
represents
ratiobar.
of front-to-rear
brake
pressuresfor
in
maximum
regardless
of surface,
is ratio
shown
in lower
system notdeceleration,
using a proportioning
valve.
Pressure
is built
into
curve.
would bar.
look ldeal
like this
if brake
system could
masterPressure
cylinder curve
or balance
pressure
relationship
for
automatically
proportionregardless
pressures ofto surface,
make front
and rear
tires
maximum deceleration,
is shown
in lower
reach
a system
proportioning
curve. traction-limits
Pressure curvesimultaneously.
would look likeThe
this closer
if brake
could
valve
comes toproportion
this ideal curve,
the faster
a carfront
will stop
any
automatically
pressures
t o make
and under
rear tires
condition.
reach traction-limits simultaneously. The closer a proportioning
Pressure In Front-
Ideal pressure curve
plotted
with
curve from proportioning valve :
Brake
System
(psi)
At pressures above changeover pressure A , proportioning valve
ldeal pressure
curve
with
curve Notice
from proportioning
valve:
reduces
pressure
riseplotted
to rear
brakes.
that proportioning
valve
does notabove
reproduce
ideal curve,
but itA,comes
close . Without
At pressures
changeover
pressure
proportioning
valve
a
proportioning
valve
pressure
at pOint
pressure to
reduces
pressure
risemodifying
to rear brakes.
Notice
thatA,proportioning
rear brakes
would
continue
to curve,
rise in but
direct
proportion
frontvalve
does not
reproduce
ideal
i t comes
close.toWithout
brake
pressure. valve modifying pressure at point A, pressure to
a
proportioning
rear brakes would continue t o rise in direct proportion to frontbrakepressure.
valve comes t o this ideal curve, the faster a car will
stop under
inside
theany combination
condition.
This proportioning valve looks like a brake
fitting. It contains a spring-loaded valve
that
changes pressure-rise
rear
This proportioning
valve looksrate
like atobrake
brakes. IValves
sucha as
this are found
in
fitting.
t contains
spring-loaded
valve
many changes
production
cars with disc
brakes
on
that
pressure-rise
rate
to rear
front
andValves
drums such
on rear.
brakes.
as Drawing
this are courtesy
in
Bendixproduction
Corp.
many
cars with disc brakes on
front and drums on rear. Drawing courtesy
Bendix Corp.
Kelsey- Hayes adjustable proportioning
valve was used on 1965-'68 Corvettes
and some Ford products. It has been used
Kelsey-Hayes adjustable proportioning
for
adjusting
brake
on many
race
valve
was used
on balance
1965-'68
Corvettes
cars.
ValveFord
is adjusted
loosening
jam
and some
products,by has
been used
nut and
turningbrake
threaded
shaft.
for
adjusting
balance
on many race
cars. Valve is adjusted by loosening jam
nut and turning threaded shaft.
54
Relationship With
Proportioning Valve
ldeal Relationship
For Maximum Deceleration
0.2g
O~----~--~----~----~----~-
/
:?:u~~
0: cO
O.4g
Without Proportioning
Valve
Relationship
With
(~rOportioning Valve
ro~
'-
/ /
/
(/J
~o.
Ideal Relationship
1.0g
/
,
Valve
Relationship
Without Proportioning
Valve
Relationship
valve.
Therefore, don't be concerned if you
inside find the
combination
can't
a metering
valve on valve.
your
Therefore,
don't
be
concerned
if you
car as a sepa rate unit. Metering valves
can't
find a used
metering
valve
on even
your
are seldom
on race
cars,
car
a separate unit. Metering
valves
withasdisc/drum-brake
setups because
are seldom
on very
race hard,
cars, and
evena
race
braking used
is done
with
disc/drum-brake
setups
because
metering valve isn't needed in hard
race
braking is done very hard, and a
braking.
metering
valve isn't
hard
The metering
valve needed
operatesin much
braking.
like a residual-pressure valve. A
The meteringpoppet
valve valve
operates
much
spring-loaded
is seated
like
a
residual-pressure
valve.
A
with a precise amount of spring forc~.
spring-loaded
poppet
valve
is seated
When
hydraulic
pressure
exerts
suffiwith aforce
precise
of spring
force.
cient
on amount
the poppet,
the spring
When
hydraulic
pressure
exerts
suffiforce is overcome and the poppet
cient
force
on
the
poppet,
the
spring
opens to aJlow fluid flow. Another
force is allows
overcome
the through
poppet
passage
fluid and
return
opens
to
allow
fluid
flow.
Another
the valve when the brake(s) is
passage
allows fluid return through
re
leased.
the
valve when the brake(s) is
BRAKE BALANCE
As discussed in Chapter 1, a car unBRAKE BALANCE
dergoes
weight
transfer
during
a carfront
unAs discussed
braking.
WeightinisChapter
added to1, the
dergoes
transfer
during
wheels as itweight
is removed
from the
rear
braking.inWeight
is amount.
added toThe
the probfront
wheels
the same
it
is
removed
from
the
wheels
as
lem is that braking force should berear
apwheels
the same
The probwheelamount.
in proportion
to
plied toineach
lem weight
is that braking
force weight,
should be
apthe
on it-more
more
plied
to and
eachvice
wheel
in proportion to
braking,
versa.
theWeight
weighttransfer
on it-more
weight,
more
depends
on vehicle
braking, and vice
versa. deceleratio n
deceleration.
Maximum
Weight mostly
transferondepends
vehicle
depends
frictiononbetween
deceleration.
Maximum
deceleration
the tires and road surface. If the fricdepends
mostly of
on the
friction
tion coefficient
tires between
is high ,
the tires and road
surface.
fricdeceleration
is high,
as Ifis the
weight
tion coefficient
of surface
the tireswith
is ahigh,
transfer.
On a slick
low
deceleration
is high,
is weight
friction
coefficient,
bothasdeceleration
transfer.
Ontransfer
a slick are
surface
and
weight
low . with a low
friction coefficient, both deceleration
and weight transfer are low.
Correct brake balance means that
front-to-rear braking forces are proCorrect so
brake
balance
means
that
portioned
neither
front
nor rear
front-to-rear
braking
forces
are
prowheels lock first. Pu t another way, the
portioned
so neither
front
norsimulrear
front
and rear
brakes wiJl
lock
wheels lock iffirst.
Put another
way, the
taneously
correctly
balanced.
If
front
andwas
rearadjusted
brakes will
lock
simulbraking
to be
equal
on
taneously
if correctly
balanced.
If
both the front
and rear wheels
, a hard
braking
adjusted
be equal
on
stop
withwas
high
weight to
transfe
r would
both the
and rear
wheels,
a hard
cause
the front
rear wheel
to lock
up first.
If
stop
with
high
weight
transfer
the brakes were proportioned onwould
thi s
cause
rearbraking
wheel tooccurred
lock up on
first.the
If
car
so the
more
yropot.tiot?ed
on
this
the
brakes
were
front, the car could stop quicker.
car
so more
braking occurred
the
Greatest
deceleration
occurs onwhen
front,
the
car
could
stop
quicker.
both front and rear tires reach their
Greatest
deceleration
occurs
traction limit
at the same
time . when
Tires
both frontmaximum
and rear grip
tires ju
reach
their
develop
st before
traction
at the same
time.
Tires
they
slid.limit
Remember,
slatic
friction
is
develop
maximum
grip just before
higher than
sliding/riction.
they slid. Remember, static.fr.iction is
Correct slidingfriction.
brake balance is different
higherthan
for high deceleration than for low .
Correct
brake for
balance
is different
Brakes
balanced
dry pavement
will
for
deceleration
thanpavement.
for low.
not high
be balanced
for wet
Brakes
balanced
for dry
will
For examp
le , a hard
stoppavement
on wet pavenot
be
balanced
for
wet
pavement.
ment will give less deceleration than
For example, a hard stop on wet pavefo r dry pavement; less weight transfer
ment will
less wheels
deceleration
than
occurs
and give
the front
lock up.
forAdry
pavement;
less
weight
transfer
system that corrects the various
occurs and
the front iswheels
lockProporup.
traction
conditions
needed.
A
system
that
corrects
the
various
tioning valves are designed to do this.
traction
conditions issystem
needed,
hasPt.opor.a cerA hydraulic-brake
tionirig
valves
are
designed
to
do this.
tain ratio between front and
rear
A hydraulic-brake
a cerbrake
pressures. A system
tandemhas
mastertain ratio between front and rear
cylinder brake system with equal
brake
pressures. A tandem masterpiston diameters has the same prescylinder
brake system with equal
sures front and rear. This means that
piston
diameters
thewith
same
presif you push on thehas
pedal
enough
sures
front and rear. This means that
force to produce 100 psi in the front
if
YOU lines
push , on
pedal
withlines
enough
brake
thethe
rear
brake
will
forcehave
to produce
100them.
psi inIf the
also
100 psi in
you front
step
brake lines, the rear brake lines will
also have 100 psi in them. If you step
down harder and raise the pressure to
400 psi, both front and rear brakes
down
harder
and raise
the pressure
to
will have
400-psi
pressure.
This is not
400ideal
psi, situation
both front
rear brakes
an
for and
maximum
stopwill
pressure. This is not
pinghave
on all400-psi
surfaces.
anLet's
ideal assume
situation that
for maximum
we have astopcar
ping
all surfaces.disc brakes . Disc
with on
four-wheel
Let's have
assume
that we
havesoa that
car
no servo
action,
brakes
with
four-wheel
disc
brakes.
Disc
simplifies this example. Let 's also
brakes have
action, are
so that
assume
that no
all servo
four brakes
the
simplifies thisdiameter
example.andLet's
also
same-rotor
caliperassume
thatare
all the
four
brakes
the
piston sizes
same.
Thisare
means
same-rotor
diameter
and
caliperthat the torque output of the brakes is
piston
sizesfront
are the
means
the same
and same.
rear ifThis
front
and
that
the torquepressures
output ofare
thethebrakes
rear hydraulic
same.is
theWesame
frontassume
and rear
front
will also
thatif the
car and
has
rear
hydraulic
pressures
are
the
same.of
a 50/50 weight distribution-50%
will also
assume
that wheels
the car and
has
theWe
weight
is on
the front
a50%
50/50
distribution-50%
of
is onweight
the rear.
If we make a panic
the
weight
is
on
the
front
wheels
and
stop on a slick surface , weight transfer
50%
is onzero.
the rear.
we maketorque
a panic
is
nearly
EqualIf braking
is
stop on a from
slick surface,
weightand
transfer
desired
both front
rear
is
nearlyIfzero.
Equal
braking
torque
we are
trying
to stop
in is
a
brakes.
desired
from
both
front
and
rear
hurry on ice, the condition of hard
brakes.
we are
to stop
in a
brak ing Ifwith
lowtrying
weight
transfer
hurry
on ice, exist.
the condition of hard
might actually
braking
Now lewith
t's trylowto weight
design atransfer
brake
might
actually
exist.
system
that
gives
maximum
Now let's regardless
try to design
brake
deceleration,
of thea coeffisystemof friction
that between
gives themaximum
tires and
cient
deceleration,
regardless
of the coeffithe road. This
brake system
would
cient
of
friction
between
tires and
have to adjust the ratio the
of pressures
the
road.thThis
brake
would
between
e front
and system
rear brakes
to
have to adjust
ratio of in
pressures
account
for thethe
difference
weight
between the
and brake
rear brakes
to
transfer.
Thefront
ideal
system
account for the difference in weight
transfer. The ideal brake system
flects high deceleration rates obtained
with high tire grip and the resulting
flects
deceleration rates obtained
weighthigh
transfer.
would be designed to lock all four
wheels at once, regardless of weight
would
transfer.be designed to lock all four
wheels
once, onregardless
weight
In theatgraph
page 54, ofI plotted
transfer.
the relationship between front- and
In the graph
on page
plotted
rear-brake
pressures
for 54,
our Iexample
the
relationship
between frontcar. If
master-cylinder-piston
sizes and
are
rear-brake
our example
equal
, therepressures
is alwaysforequal
pressure
car.
If master-cylinder-piston
sizes are
in the
front- and rear-brake systems.
equal,
there
is
always
equal
This is the straight line in thepressure
graph .
in
the the
frontand rear-brake
systems.
When
pressure
in the front-brake
This
is the
in the
system
is straight
doubled,linethe
reargraph.
also
When
the
pressure
in
the
front-brake
doubles. This is not ideal for maxisystem
is doubled,
thevarious
rear tracalso
mum deceleration
under
doubles.
This is not ideal for maxition conditions.
mum
under various
tracWithdeceleration
a high-traction
surface,
tion
conditions.
weight transfer increases. This reWithlessa pressure
high-traction
quires
at the rearsurface,
brakes
weight
transfer
increases.
This the
reand more at the front because
quires
pressure
at the
reartires
brakes
verticalless
force
on the
front
is
and more
thethe
front
because
the
greater
thanat on
rears.
A brake
vertical with
forceequal
on brake
the front
tiresand
is
system
pressure
greater
than
on
the
rears.
A
brake
equal brake torque will lock the rear
system
equal
wheels with
before
the brake
fronts.pressure
This is and
not
equal
brake
will lock
the rear
desirable
fortorque
maximum
deceleration
wheels
beforeA the
This is rear
not
or stability.
car fronts.
with locked
desirable
for
maximum
deceleration
wheels and rolling front wheels will
or
spinstability.
easily. A car with locked rear
wheels
and rolling
front the
wheels
The lower
curve shows
ratio will
bespin
easily.
tween front-and rear- brake pressures
The lower curve
shows
ratio beautomatically
changed
to the
account
for
tween frontandItrear-brake
weight
transfer.
shows thepressures
need to
automatically
changed
account for
the to
percentage
of
gradually reduce
weight
transfer.
It
shows
the
needrear
to
brake pressure going to the
gradually
reduce increased.
the percentage
of
brakes as traction
This re-
with high tire grip and the resulting
weight
transfer.
PROPORTIONING VALVE
Now that we have an ideal frontPROPORTIONING
to-rear
brake-pressureVALVE
curve for this
an the
idealstraightfrontcar,Now
howthat
can we
we have
modify
to-rear
brake-pressure
curve
forclose
this
line pressure
relationship
to get
car,
how
can
we
modify
the
straightto the ideal curve? Answer: It is done
line
relationship
with pressure
a proportioning
valve. to get close
to Atheproportioning
ideal curve? Answer:
It is done
valve reduces
the
with a proportioning
pressure
increase tovalve.
the rear brakes.
A does
proportioning
reduces the
This
not meanvalve
that pressure
to
pressnre
increase
to
the
rear
the rear brakes is preven tedbrakes.
from
This
does merely
not mean
to
rising-it
risesthat
at apressure
lower rate
the rear
brakes ispressure
prevented
froma
than
front-brake
when
rising-it merely
riseschangeover
at a lower presrate
specified
pressurethan
front-brake
pressure
when
sure-is reached. Th e curve of front-a
specified
pressurecharigeover
presto-rear- brake
pressure
with a proporstlre-is valve
reached.
Therear
curve
of line
fronttioning
in the
brake
is
to-rear-brake
pressure
with
plotted in the graph,
page
54 . a proportioning
valve in the rear
brake curves
line is
The accompanying
pressure
plotted
the graph,
pageaxes
54. because
do
not in
have
numbered
Thevary
accompanying
pressure
they
with each car.
Exactcurves
presdo
not
have
numbered
axes
because
sures in a brake system vary
with
they
vary with each
car. Exact brake
preshydraulic-cylinder
dimensions,
sures
a brake
systemweight
vary with
location,
and
design,in CG
hydraulic-cylinder
brake
wheelbase
of the dimensions,
car. The curve
design, has
CGthelocation,
weightin and
always
shapes shown
the
wheelbase
of
the
car.
The curve
two figures, but the numbers
vary
always
the shapes shown in the
from carhas
to car.
twoMost
figures,
but the numbers
proportioning
valves vary
are
from
car
to
car.
preset at the factory . They cannot be
Most orproportioning
are
adjusted
serviced later. valves
Each valve
brake pressure going to the rear
brakes as traction increased. This re1100
5
AP Racing Adjustable
Proportioning Valve
CP
2611-3 Adjustable
AP Racing
900
900
preset at the factory. They cannot be
adjusted or serviced later. Each valve
ProportioningValve
4
Nominal Performance
4
3
CP 261 1-3
Nominal
Performance
Graph
-
700
.-
E- 700 -
3
2
-::;aIn
2
C/J
.::;
Q.
500
0
1
3
0 300
100
Tilton Engineering offers this AP Racing adjustable proportioning
valve. Lever has five positions, each with a different changeover
pressure.
Valve is ideal
road
occasionally
raced
on racing
Tilton Engineering
offersfor
this
APcar
Racing
adjustable
proportioning
tires.
weight each
transfer
racing tires
means
valve. Improved
Lever hasgrip
fiveand
positions,
withwith
a different
changeover
less
pressure
should
go to
Photo
courtesy AP
Racing.
pressure.
Valve
is ideal
forbrakes.
road car
occasionally
raced
on racing
tires. Improved grip and weight transfer with racing tires means
less pressure should go to brakes. Photo courtesy AP Racing.
1
100
300
1
I
-
900
500
700
900
1100
Graph shows AP RaCing adjustable
proportioning-valve pressure
Input (psi)
100
300
500
700
1
I nput
(psi) I
changes to rear brakes. With valve at setting 2, pressure rises as
if thereshows
were no
until
200-psi proportioning-valve
changeover point is pressure
reached.
Graph
APvalve,
Racing
adjustable
Pressure tothen
at With
a lesser
This effectively
changes
rearrises
brakes.
valverate.
at setting
2, pressure reduces
rises as
pressure-rise
rate
to rear
delays orpoint
prevents
rearif there were no
valve,
until brakes
200-psiand
changeover
is reached.
wheel lockup.
Tiltonrate.
Engineering,
Inc.
Pressure
thenGraph
risescourtesy
at a lesser
This effectively
reduces
pressure-rise rate to rear brakes and delays or prevents rearwheel lockup. Graph courtesy Tilton Engineering, Inc.
55
is suitable for use only on the car for
which it was adjusted. This is unfortuis suitable
for you
use may
only like
o n the
car for
nate
because
an adjustwhich
it was adjusted.
This
unfortuable proportioning
valve
as ais means
of
nate
because
youhigh-performance
may like an adjustbalancing
your
or
able
proportioning
valve as a means
of
race-car
brakes. Fortunately,
some
balancing
yourvalves
high-performance
or
proportioning
allow an external
race-car brakes.
some
adjustment.
Some Fortunately,
of these are shown
proportioning
valves photos.
allow an external
in
the accompanying
adjustment.
S o m e of these
are shown
Porsche, Chrysler,
Chevrolet
and
in
the
accompanying
photos.
Ford have adjustable proportioning
Porsche,
Chrysler, Chevrolet
and
valves
for high-performance
use. The
Ford have
proportioning
Porsche
914 adjustable
uses an adjustable
val ve
valvescanForbehigh-performance
use. T h ea
that
changed by loosening
Porsche
914
uses
an
adjustable
valve
lock nut and turning a screw. Turning
that screw
can beinward
changed
by loosening
the
on this
valve putsa
lock
and turning
a screw.
morenut
pressure
on the
rear Turning
brakes
the
screw
inward
o
n
this
valve puts
during a hard stop. Adjusting
the
more ispressure
o n the rear
brakes
valve
a trial-and-error
process,
as
during a inhard
stop.10.Adjusting the
described
Chapter
valve
a trial-and-error
as
The isChevrolet
Corvetteprocess,
adjustable
described
in
Chapter
10.
proportioning valve, 3878944, is
T h e Chevrolet
Corvette
adjustable
available
both from
Chevrolet
and
proportioning
valve, specializing
3878944, in
is
from
racing shops
available
both fromChrysler's
Chevroletvalve,
and
brake components.
from
racingis available
shops specializing
in
P4120999,
through their
brake
components.
Chrysler's
valve,
performance-parts division, Direct
P4120999, is available
their
Connection.
Ford's through
proportioning
performance-parts
division, through
Direct
valve, M-2328-A is available
Connection.
Ford's dealers.
proportioning
Ford
Motorsport
These
valve, M-2328-A
valves
work muchis available
the samethrough
as the
Ford
dealers. begins
These
PorscheMotorsport
valve. Proportioning
valves
work
much
t
h
e
same
as
the
between 100 and 1000 psi, depending
Porsche
valve.
Proportioning
begins
where adjustment is set.
between
100 and
1000 psi, depending
Another
proportioning
val ve,
where adjustment
is set.
which
operates like
the Porsche and
Anothervalves,
proportioning
Corvette
is available valve,
from
which
operates
like
and
Alston Industries the
of Porsche
Sacramento,
Corvette valves,
available
from
California.
This oneis was
designed
by
Alston Airheart
Industries
Sacramento,
Frank
to goof with
his highCalifornia.
o n e was
designed
by
performanceThis
dual,
tandem
master
Frank Airheart to go with his highcylinder.
performance
dual,valve
tandem
master
A proportioning
is installed
in
cylinder.
line between the master cylinder and
valve
in
theA proportioning
rear brakes. It
willis installed
work with
line between
cylindercylinand
either
a singlet hore amaster
dual master
the inrear
will work
with
der
the brakes.
system, Itbecause
all it does
either
a
single
or
a
dual
master
cylinis affect the maximum pressure at the
der in
t h e system, because all it does
rear
brakes.
is An
affect
t h e maximum
pressure valve,
at the
adjustable
proportioning
rear
brakes.is sold by Tilton EngineerCP2611-3,
proportioning
ingA n ofadjustable
Buellton,
California. valve,
This
CP2611-3,
is
sold
by
Tilton
Engineerdevice can be mounted
in the
cockpit
inga race
of car
Buellton,
Thisit
of
so the driCalifornia.
ver can adjust
device can
be mounted
in the acockpit
during
a race.
He can move
lever
of a anyone
race car so
the driver
canpositions
adjust it
into
of five
different
during
a
race.
H
e
can
move
as brake or track conditions, aorlever
the
into anydistribution
o n e of five of
different
weight
the carpositions
changes
as brake
o r track conditions, or the
during
a race.
weight
distribution
the car changes
Curves of inlet ofpressure
versus
during
a
race.
outlet pressure for this valve are
Curves
of inlet
pressure
versus
shown
on page
55. Note
that pressure
outlet
for this
are
rises in pressure
a one-to-one
ratio valve
until the
shown o n page 55. Note that pressure
rises in a one-to-one ratio until the
56
Inlet and Outlet
,-------- Ports are 7/1624
Thread
for 3/16Inlet
and Outlet
or
1 /4-in.-OD
Ports
are 7/16-Tubing
24 Thread for 3/16or 1/4-in.-OD Tubing
Q)
:;
if>
if>
Q)
~ ~ ~~~--~v--+--~~-+~~
Q)
'"ro
"?
~
Adjusting
Knob
400
t--+-;H---~.rc---t---+­
a:
Mounting
Holes
0.351 -0.342 dia.
0.351 -0.342 dia.
800
,
1000
1200
BW
,DX)
1m
-
2000
Front-Brake Pressure (psi)
lMO
Kelsey-Hayes adjustable proportioning valve is available from
Kelsey
Products
Division
Front-Brake
Pressure
(PSI)
and many U.S. automobile dealers through their high-performance catalogs. Valve functions
the
same as APadjustable
RaCing valve
except it'svalve
infinitely
adjustable
between
and 1000
psi.
Kelsey-Hayes
proportioning
is available
from
Kelsey100
Products
Division
Adjustments
are
made withdealers
thumbscrew.
courtesy Kelsey-Hayes
Corp.
automobile
throughDrawing
their high-performance
catalogs.
Valve functions
and many U.S.
the same as AP Racing valve except it's infinitely adjustable between 100 and 1000 psi.
Adjustments are made with thumbscrew. Drawing courtesy Kelsey-Hayes Corp.
600
.(/J
Q.
-600
500
.-E
-E -500
OJ
(j)
>(fJ
a,
-
Ideal Front vs. Rear Fluid Pressure
Relationships For Different Weight Distributions
ldeal Front vs. Rear Fluid Pressure
Relationships For Different Weight Distributions
Car A
Car weight, wheelbase, and CG height are
Tail-Heavy Car
the same for all three cars. Only
With
front-to-rear
weight distribution
varies.are
Car A40/60 Weight
Car
weight, wheelbase,
and CG height
DistributionCar
Tail-Heavy
the same for all three cars. Only
With 40/60 Weight
front-to-rear weight distribution varies.
Distribution
Car B
OJ
OJ
~
?
50/50 Weight
Distribution
50/50
1.2g Weight
Distribution
,
c -300
m
CarC
V)
.Y
,X
~
(J)
-400
a,
Y
m
0:
a,
u~:::J
I
1.2g
Nose-Heavy
Car With -.
60/40
Weight
Nose-Heavy
Distribution
Car
With
60/40 Weight
1000
900
Distribution
(/J
(/J
~
0...
Pressure I n Front-Brake System (psi)
Pressure
In Front-Brake
System
(psi) cars with different weight
Ideal front-to-rear brake-system
pressures
for three
different
distributions: Nose-heavy car has less pressure to rear wheels; tail-heavy car has more.
Ideal front-to-rear brake-system pressures for three different cars with different weight
distributions: Nose-heavy car has less pressure to rear wheels; tail-heavy car has more.
changeover pressure is reached. For
position 5, pressure rises as if the prochangeover
pressure
For
portioning valve
is notis inreached.
the system
position
5,
pressure
rises
as
if
the
prountil about 950 psi is reached. At that
portioning
valve is not inpoppet
the system
point,
the spring-loaded
valve
until about
950 psi is reached.
that
inside
the proportioning
valve At
opens,
point,
the
spring-loaded
poppet
valve
and output-pressure increase is reinside with
the proportioning
valve
opens,
duced
increasing input
pressure.
and output-pressure
increase
is reMeanwhile,
front-brake
pressure
is
duced
with increasing
not affected.
It increasesinput
as it pressure.
did withMeanwhile,
front-brake
out a proportioning
valve. pressure is
notMost
affected.
increases
as it did withroad Itcars
have proportioning
out a proportioning
valve.
valves
that give approximate
correct
Mostbalance
road cars
brake
withhave
an proportioning
average load
valves that give approximate correct
brake balance with an average load
using street tires. If the car is set up
for racing, its total weight, weight
using street and
tires.tire
If grip
the car
set up
distribution
are islikely
to
for
racing,
its
total
weight,
weight
change from the average values the
distribution
and tire
arebrake
likelybalto
car
was designed
for. grip
Thus,
change
the average
valueseven
the
ance
mayfrom
be incorrect
for racing,
car
was designed
for. Thus, brake
balthough
it has a proportioning
valve.
ance
may
be
incorrect
for
racing,
even
Remember, a proportioning valve
thoughtheit approximate
has a proportioning
gives
correct valve.
brake
Remember,
proportioning
balance
over aa limited
range of valve
tracgives
the approximate correct brake
tion conditions.
balance
range
of tracIf you over
drivea a limited
car on the
street
and
tion conditions.
race
it on occasion, you may want to
youadjustable
drive a car
o n the streetvalve
and
useIf an
proportioning
race it o n occasion, you may want to
use a n adjustable proportioning valve
1
to change brake balance. For street
driving, the car should be correct as
to For
change
brake
balance.
street
is.
racing,
brake
balanceFor
probably
driving,
should be tocorrect
as
havethe
to car
be readjusted
provide
will
is.
For
racing,
brake
balance
probably
more braking force on the front-less
will
haverear.
to be
readjusted
to provide
on the
Racing
tires have
more
more than
braking
forcetires;
on the
front-less
grip
street
thus,
weight
on
the rear.
Racing under
tires have
more
transfer
is greater
maximum
grip
than
street
tires;
thus,
weight
braking .
transfer
is greater
maximum
Let's say
you haveunder
a sports
car that
braking.
you drive to work and slalom on the
Let's say With
you have
a sports car that
weekends.
the quick-adjustable
you
drive
to
work
and
on the
Tilton valve, you don't slalom
even have
to
weekends.
With
the
quick-adjustable
get your hands dirty. In the example
Tilton
valve,
yourun
don't
to
given, you
might
the even
valve have
at posiget
In drop
the example
tion your
5 for hands
street dirty.
use and
to posigiven,
the valve
at posi4 reduces
tion 4 you
for might
racing run
. Position
tion
5
for
street
use
and
drop
to
posirear-wheel braking, starting at a lower
tion
4 forthan
racing.
Position
4 reduces
pressure
position
5. This
comrear-wheel
starting
at a translower
pensates forbraking,
the greater
weight
pressure
than
position
5.
This
fer when braking on racing comtires.
pensates
for setting
the greater
weightbalance
transMore about
up brake
fer
when 10.
braking on racing tires.
in Chapter
More
about
setting up
balance
One disadvantage
of brake
proportioning
in
Chapter
10.
valves is that they increase pedal
One without
disadvantage
of proportioning
effort
reducing
displacement
valves high-deceleration
is that they increase
during
stops. pedal
effort
without
reducing
displacement
If you wish to add a proportioning
during
stops.
valve tohigh-deceleration
a car that doesn't
have one,
If you
to does
add anot
proportioning
make
surewish
the car
have a diagvalve to
a car
thatsystem
doesn't
have rearone,
brake
. Some
onally
split
not
have
a
diagmake
sure
the
car
does
wheel-drive cars and most frontonally split brake
system.
Somesorearwheel-drive
cars are
designed
the
wheel-drive
and most
left-front andcars
right-rear
brakesfrontare
wheel-drive
carssame
are designed
so the
operated by the
half of a tandem
left-front
and right-rear
brakes
are
master cylinder;
right-front
and leftoperated
by
the
same
half
of
a
tandem
rear brakes are operated by the other
master
cylinder;
and alefthalf of the
masterright-front
cylinder. With
direar brakes
arebrake
operated
by the
other
agonally
split
system,
a single
half of the master
cylinder. valve
With awill
diadjustable
proportioning
agonally split brake system, a single
adjustable proportioning valve will
Proportioning-
=
V)
1.2g
V",. S.II'09 2 ~_
Proportioning-
Q
-
1.29
E
a,
V)
$
a,
Y
ProportioningValve Setting 1
2
CP
ProportioningValve Setting 1
L
/.
40/60 Weight Distribution
1.0g
--
50/50 Weight
Distribution
m
K
-C
Ideal-Pressure Relationship
a,
L
3
Actual-Pressure Relationship
V)
V)
Ideal-Pressure Relationship
2
a
Pressure In Front-Brake System (psi)
In different
Front-Brake
System
(psi)
Two ideal pressure curves Pressure
for cars of
weight
distributions
show how one proportioning valve can be adjusted to work with either.
Two ideal pressure curves for cars of different weight distributions show how one proportioning valve can be adjusted t o work with either.
not work. It only works where both
rear brakes are fed by a single hydraunotline.
work.
I t only
works
where both
lic
I cover
adding
a proportioning
rear
brakes
are
fed
by
a
single
hydrauvalve to an existing car in Chapter
12.
lic line. I cover adding a proportioning
valve
to an existing car in Chapter
12.
PRESSURE-LIMITING
VALVES
A pressure-limiting valve is used on
PRESSURE-LIMITING
VALVES
some
cars with disc brakes
on the
A
pressure-limiting
valve
is used
on
front and drums on the rear.
It persome
with function
disc brakes
on the
forms cars
a similar
as a proporfront
drums
on pressure-limiting
the rear. It pertioningandvalve.
The
forms
a
similar
function
as ata the
proporvalve prevents the pressure
rear
tioning
valve.
The
pressure-limiting
brakes from exceeding a preset value.
valvedifference
prevents the
pressure
at the rear
The
between
a proportionbrakes
from
exceeding
a
preset
value.
ing valve and a pressure-limiting
The difference between a proportioning valve and a pressure-limiting
-.L g
valve can be seen by comparing the accompanying graphs.
valve
be seen by between
comparingpressure
the acThecan
relationship
companying
graphs.
in the front-brake system and rearThe system
relationship
between
brake
is shown
in thepressure
graph ,
in
the Note
front-brake
and rearhow thesystem
pressure-limiting
below.
brake system
shown
in the graph,
valve
differs isfrom
a proportioning
below.
Note
how
the
pressure-limiting
valve . Remember, a proportioning
valve
differs the
from
a proportioning
valve allows
pressure
in the rear
valve.
proportioning
system Remember,
to rise if thea driver
pushes
valve
pressure
rear
harderallows
on thethe
pedalbut atina the
reduced
system
to
rise
if
the
driver
pushes
rate. However, a pressure-limiting
harder
the pedal-but
reduced
valve on
limits
pressure toat athe
rear
rate. However, a pressure-limiting
brakes.
valve
pressure
rear
Whenlimits
this preset
valueto is the
reached,
brakes.
When this preset value is reached,
~
_ _ _ _ _ _ _ _ _ Maximum
Pressure
Maximum
Pressure
m,
EC 2
-0
;$
V)
In
a
Y
2 Lm
a m
Pressure In Front-Brake System (psi)
Pressure In Front-Brake System (psi)
t
Honda Civic has diagonally split braking system with two proportioning valves. Valves are shown at bottom. One adjustable proportioning
cannot besplit
used
with system
diagonally
braking
Honda Civicvalve
has diagonally
braking
withsplit
two proporsystem.valves.
Two proportioning
valves at
willbottom.
work, but
tioning
Valves are shown
Oneadjustment
adjustable must
probe synchronized.
Portioning
valve cannot be used with diagonally split braking
Relationship between front- and rear-brake system pressure of
pressure-limiting valve : Compare curve to that of ideal pressure
curve
on pagebetween
54. Withfronta proportioning
valve, system
pressure
continues
Relationship
and rear-brake
pressure
of
to rise in rear-brake
system
beyond
changeover
With
pressure-limiting
valve:
Compare
curve
to that of pressure.
ideal pressure
pressure-limiting
changeover
pressure
is continues
reached,
curve
on page 54.valve,
With aonce
proportioning
valve,
pressure
that's
as it gets.
For a high-performance
car,pressure.
use a proporto
riseasinhigh
rear-brake
system
beyond changeover
With
tioning
valve, not avalve,
pressure-limiting
valve-unless
car is extremepressure-limiting
once changeover
pressure
reached,
ly nose-heavy.
that's
as high as i t gets. For a high-performance car, use a propor-
system. Two proportioning valves will work, but adjustment must
be synchronized.
tioning valve, not a pressure-limiting valve-unless car is extremely nose-heavy.
57
Both proportioning valves are adjusted by spring between rear axle and proportioning-valve lever. Valve adjustment changes with rearsuspension travel from weight on rear wheels. Rear-axle movement moves lever and changes valve setting. As weight on rear wheels
increases,
so doesvalves
rear-wheel-brake
pressure.
Cars that
suchproportioning-valve
large weight-distribution
changes,
such changes
as this with
Plymouth
Both
proportioning
are adjusted by
spring between
rearhave
axle and
lever. Valve
adjustment
rearVoyager/Dodge
Caravan
(left) or
stationRear-axle
wagon (right),
will benefit
from
a height-sensing
proportioning
suspension
travel
from weight
onPeugeot
rear wheels.
movement
moves
lever
and changes valve
setting. valve.
As weight on rear wheels
increases, so does rear-wheel-brake pressure. Cars that have such large weight-distribution changes, such as this Plymouth
Voyager/Dodge Caravan (left) or Peugeot station wagon (right), will benefit from a height-sensing proportioning valve.
pressure to the rear brakes cannot
increase, regardless of how hard the
pressure
to the on
rear the
brakes
cannot
driver pushes
pedal.
A
increase,
regardlessvalve
of how
hard well
the
pressure-limiting
works
driver
on the
pedal.
A
only on pushes
an extremely
nose-h
eavy car,
pressure-limiting
valve workssedan.
well
such as a front-wheel-drive
only
an extremely nose-heavy
car,
pressure-limiting
valves usually
Also,on
such
as
a
front-wheel-drive
sedan.
are not useful for race cars because
Also,
pressure-limiting
most are
not nose heavy.valves usually
are not useful for race cars because
most
are not nose
heavy.
ANTI-SKID
SYSTEM
A nti-skid systems are designed to
ANTI-SKID
prevent wheelSYSTEM
lockup, no matter how
Anti-skid
sysrenls
are designed to
the brakes
are applied.
hard
prevent
wheel
lockup,
how
Many manufacturersno clmatter
aim their
hard the brakes
applied. properties.
systems
have are
anti-skid
Manytheymanufacturers
claim their
What
real ly do is prevent
one
systems
havefrom
anti-skid
pair of wheels
locking properties.
before the
What
they
reallya good
do is propo
prevent
one
other. In
a sense,
rtioning
pair ofiswheels
from locking
the
valve
an anti-skid
device;before
it keeps
other.
In awheels
sense, from
a goodlocking
proportioning
the rear
before
valve
is an In
anti-skid
device; I itdiscuss
keeps
the fronts.
this section,
the
rear
wheels
from
locking
before
systems other than.!7xedproportioning
thepressure-limiting
fronts. In this section,
valves. I discuss
or
systems
than.fixedproportioning
Some other
anti-skid
devices amount to
or pressure-limiting
valves. propornothing
more than adjustable
Some
anti-skid
devices
to
some extioning valves controlled byamount
nothingmeans.
more The
thanvalve
adjustable
proporternal
is adjusted
by
tioning valves controlled
by some
rear-suspension
movement
or exby
ternal
means.
The
valve
is
adjusted
by
sensing the actual decelera tion of the
rear-suspension
movement
or
by
car. The type that operates from rearsensing the actual
deceleration
of the
suspension
movement
compensates
car. The
that operates
rearfor
bothtype
deceleration
andfrom
vehicle
suspension
movement
compensates
weight. This is particularly important
fora both
deceleration
and vehicle
in
truck or
a station wagon,
where
weight.
is particularly
the
CG This
can move
a great important
deal with
in a truck
or a instation
wagon,
changes
in load
the cargo
area. where
the
CG
can
move
a
great
with
The anti-skid valve thatdeal
senses
changes
in
load
in
the
cargo
area.
deceleration uses the bal/-and-ramp
The anti-skid
valve
that senses
prinCiple.
The valve
is positioned
so
deceleration
theup,ball-and-ramp
that
the rampuses
angles
toward the
principle.
Thevehicle.
valve isThe
positioned
so
front
of the
valve conthat the ramp angles up, toward the
front of the vehicle. The valve con58
tains a conventional proportioning
valve and a bypass.
At low
tains
a conventional
proportioning
deceleration,
brake fluid
passes the
valve
a bypass.
At low
ball andand
bypasses
the proportioning
deceleration,
brake
fluid passes
the
valve, regardless
of pressure.
At a preball
and bypasses
the proportioning
determined
transition
decelerationvalve,
of pressure.
about regardless
0 .3 g-the
ball rollsAtupa prethe
determined
transition
ramp, closes the bypass,decelerationand proporabout
g-the ball rolls up the
starts.
tioning 0.3
ramp,
and proporThis closes
valve the
canbypass,
compensate
for a
tioning
starts.
changing CG location . As weight at
compensate
theThis
rear valve
of thecan
vehicle
increases,forthea
changing
C G location.
As weight
at
rear suspension
compresses
and the
the rear
of the
vehicle This
increases,
the
ramp
angle
increases.
increases
rear
the
the suspension
transition compresses
decelerationand and,
ramp
angle
increases.
This
increases
therefore, rear-brake pressure at
the transition
deceleration
and,transition.
Thus, the
rear brakes share
rear-brake
pressure at
atherefore,
larger portion
of the braking.
transition.
the rear
brakessenses
share
A true Thus,
anti-skid
system
awhen
largera wheel
portionstarts
of thetobraking.
lock . It closes a
A true
senses
line to system
that wheel
to
valve
in theanti-skid
when a wheel
starts to It
lock.
It closes
reduce
the pressure.
then
sensesa
valvewheel
in the
line toup that
to
the
speeding
and wheel
reapplies
reduce
the
pressure.
It
then
senses
pressure. A typical system uses
the wheel sensors
speeding to
up sense
and reapplies
magnetic
wheel
pressure. A typical system uses
speed.
magnetic
sensors
to are
sense
Wheel-speed
signals
sent wheel
to an
speed.
electronic module, or computer,
Wheel-speed
sent to an
which
computessignals
wheelare
deceleration
electronic
module,
computer,
and
slip values
for eachor
wheel.
Decelwhich
computes
wheel
deceleration
eration and slip values for that wheel
and slip
values for
each
wheel.for
Decelare
compared
with
values
the
erationwheels
and slip
for that
wheel
other
andvalues
with fixed
thresholds
are
compared
for are
the
(preset
values) . with
Whenvalues
thresholds
other
wheels
and
with
fixed
thresholds
exceeded, the module sends a signal
(preset
values).
When thresholds
the proper
controller.
The valveare
is
to
exceeded,
module
a signal
and the
pressure
to sends
that wheel
is
closed
to the proper
controller.
valve is
reduced.
When
wheel The
deceleration
closed
pressure
to thatlevels,
wheeltheis
and
slipand
go below
threshold
reduced.
When
wheel
deceleration
module signals the controller to inand slippressure
go below
threshold
levels,hapthe
. All
this shuttling
crease
module
signals
the hard
controller
to inpens
rapidly
during
applications,
crease pressure. All this shuttling happens rapidly during hard applications,
ATE skid-control front-wheel sensor,
introduced on '85 Lincoln Mark VII, is ilATE
skid-control
front-wheel
sensor,
lustrated
on display model
with sectioned
introduced
'85 Lincoln
VII,speed
is ilfront-wheel onrotor/hub.
As Mark
wheel
lustratedrapidly
on display
sectioned
changes
whenmodel
brake with
lockup
begins,
front-wheel
rotor/hub.
wheel
speed
brakes are rapidly
cycled As
on and
off to
prechanges
rapidly
when
brake
lockup begins,
vent lockup.
Photo
by Tom
Monroe.
brakes are rapidly cycled on and off to prevent
lockup.
Photo
Monroe.
so the
wheel
(s)by Tom
never
completely
lock.
so theControllers
wheel($ require
never an
completely
Note:
external
lock.
power source, which can be hydraulic,
Note: Controllers
electric
or vacuum. require an external
power
source, which
can behave
hydraulic,
Skid-control
systems
been
electric
or
vacuum.
used on large aircraft since the '50s.
Skid-control
systems have
been
The
first vacuum-powered
road-car
used on developed
large aircraftby since
the '50s.
systems
Kelsey-Hayes
The Delco
first were
vacuum-powered
and
introduced in road-car
the late
systems
developed
by Chrysler.
Kelsey-Hayes
'60s by Ford, GM and
The
and Delco
were systems
introduced
in the late
Ford
and GM
operated
on
'60s rear
by Ford,
andChrysler
Chrysler.had
Thea
the
wheelsG M
only;
Ford and Gsystem.
M systems
operated
on
four-wheel
Porsche
experithe
rear
wheels
only;
Chrysler
had
mented with mo re sophisticated sys-a
four-wheel
system.
experitems
in the early
'7 0s Porsche
on 911 and
917
mented
race
cars.with more sophisticated systems
in the
early
'70s car
on manufactur911 and 917
most
major
Today,
race
cars.
ers
are
developing
four-wheel
Today, 1984
most Porsche
major carand
manufactursystems.
Mercedes
ers are
developing
models
use Bosch
anti-skidfour-wheel
systems,
systems.and
1984
Porsche and
Honda
Mitsubishi
haveMercedes
systems
models
use Bosch
anti-skid
systems.
in
production,
Ford
introduced
a
Honda and Mitsubishi have systems
in production. Ford introduced a
Safety Braker is fancy cylinder mounted in
brake line from nearest master cylinder. It
damps Braker
pressure
pulses
in brake
fluid,
Safety
is fancy
cylinder
mounted
in
giving
more
consistent
brakingcylinder.
and less
brake line
from
nearest master
It
pedal pulsation.
is slightly
difficult
damps
pressureIt pulses
in more
brake
fluid,
to
lock more
one wheel
with a braking
Safety Braker
in
giving
consistent
and less
the
device
is an
pedal system.
pulsation. Because
It is slightly
more difficult
accumulator,
it displaces
fluid Braker
and into lock one wheel
with a Safety
in
creases
pedal travel
slightly.
Safety isBrakthe
system.
Because
device
an
ers are no longer
made. fluid and inaccumulator,
it being
displaces
Three different types of mechanical stoplight switches each have plunger to operate
electrical switch. Usually, switch is operated by movement of brake pedal. Drawing courtesy Bendix
Corp. types of mechanical stoplight switches each have plunger to operate
Three
different
electrical switch. Usually, switch is operated by movement of brake pedal. Drawing courtesy Bendix Corp.
creases pedal travel slightly. Safety Brakers are no longer being made.
system developed by ATE for the
1985 Mark VII. GM released systems
system
developed
by and
ATE ATE
for the
developed
by Bosch
for
1985
Mark
VII.
G
M
released
systems
1986 models. These systems are
developed but
by they
Bosch
and much
ATE imfor
expensive,
provide
1986 models.
systems
are
proved
directionalThese
stability,
steerabiliexpensive,
but they provide
much
imty and deceleration
in critical
braking
proved
directional
stability,
steerabilimaneuvers on all road surfaces.
ty Anti-skid
and deceleration
in critical
braking
systems
can provide
maneuvers
all road surfaces.
these
same on
advantages
in racing, plus
Anti-skid
systems
provide
they
can eliminate
tire can
flat spotting.
these
same
advantages
in
racing,
plus
To date, an ti-skid systems have been
they
can
eliminate
tire
flat
spotting.
used little because of their weight and
To
date, anti-skid
systems have
been
questionable
reliability.
However,
used
little
because
of
their
weight
and
recent advancements in technology
questionable
reliability.
However,
should change that. Many highrecent
advancements
in technology
powered,
exotic road-racing
cars will
should
Many
highprobably change
be using that.
anti-skid
devices
by
powered,
road-racing
will
1990. But exotic
for now,
a skilledcars
racingprobably feel
be using
anti-skid devices
by
driver's
is considered
to be the
1990.
But
for
now,
a
skilled
racingmost effective anti-skid device.
driver's feel is considered to be the
most effective anti-skid
device.
STOP-LIGHT
SWITCHES
Stop-light switches are either meSTOP-LIGHT
SWITCHES
chanical
or hydraulic.
Both are conStop-light
are either
menected
to theswitches
electric circuit
and turn
chanical
or
hydraulic.
Both
are
conon the brakelights when activated.
nected
to the electric
circuit
and turn
The
hydraulic
switch is
designed
as a
on
the
brakelights
when
activated.
hydraulic fitting and is operated by
The
hydraulic pressure.
switch is The
designed
as a
brake-system
mechanihydraulic
fitting
and
is
operated
by
cal type is operated directly by brakebrake-system
pressure.
The
mechanipedal-linkage motion. Most newer
cal type
is operated
directly
by brakecars
use the
mechanical
switch.
pedal-linkage
motion.
newer
With both switch
types,Most
the electricars
use
the
mechanical
switch.
cal circuit is open until the brakes are
With both
switch
types, the
electriapplied.
When
the switch
closes,
the
cal circuit
open until the
brakes the
are
stop
lightsis illuminate.
Usually,
applied.
When
theisswitch
closes,
the
mechanical
switch
designed
to close
stop lights illuminate. Usually, the
mechanical switch is designed to close
Hydraulic stoplight switches screw into a fitting in hydraulic system. Fluid pressure operates switch. Although easier to install, mechanical switches are better for racing. HydrauliC
switch
takes
a smallswitches
amount of
fluid into
movement
to in
operate
it, and
a mechanical
switch operdoes
Hydraulic
stoplight
screw
a fitting
hydraulic
system.
Fluid pressure
not. Also,
hydraulic
switches
leak. Drawing
courtesy
Bendix
ates
switch.
Although
easier can
to install,
mechanical
switches
are Corp.
better for racing. Hydraulic
switch takes a small amount of fluid movement to operate it, and a mechanical switch does
not. Also, hydraulic switches can leak. Drawing courtesy Bendix Corp.
when the brake pedal has been moved
about 112 in. The hydraulic switch is
when the tobrake
beenpressure
moved
designed
closepedal
with has
a small
112
in.
The
hydraulic
switch
is
about
buildup in the system . The exact
designed
to
close
with
a
small
pressure
point at which the switch closes is not
buildupbecause
in the any
system.
exact
critical
modestThe
brake
appoint
at which
theclose
switchthe
closes
is not
plication
should
electrical
critical
because any modest brake apcontacts.
plication
close the
electrical
If you should
are selecting
a stop-light
contacts.
swi
tch for a race car, use a mechanical
If . you
are selecting
stop-light
type
Although
more adifficult
to
switch
for
a
race
car,
use
a
mechanical
install, a mechanical switch will not
type. the
Although
moreif itdifficult
to
affect
brake system
fails. A hyinstall, switch
a mechanical
switch will
not
draulic
is just another
possible
affect
the brake
system
it fails. A hyleak. Also,
slight
fluid ifmovement
is
draulic
switch
is
just
another
necessary for operation. Everypossible
possileak.
Also, must
slightbefluid
movement
ble failure
eliminated
from isa
necessary
race
car. for operation. Every possible failure must be eliminated from a
race
car. WARNING-LIGHT
BRAKE
SWITCHES
BRAKE
Brake WARNING-LIGHT
warning-light switches have
SWITCHES
been in use since tandem master cylinBrake
ders
werewarning-light
introduced in switches
the '60s. have
This
been
in
use
since
tandem
master
cylinpressure switch illuminates
a warning
ders
introduced
in the
'60s.which
This
light were
on the
instrument
panel,
pressure switch illuminates a warning
light on the instrument panel, which
indicates a problem with the brake
system. The switch senses any
indicates a problem
with the
brake
hydraulic-pressure
imbalance
between
system.
The
switch
senses
any
the front and rear brake systems.
hydraulic-pressure
imbalance between
And,
the light · illuminates
when a
the
and-rear
brake systems.
presetfront
pressure
imbalance
occurs.
And, will
thewarn
lighttheilluminates
when a
driver of problems
This
preset as
pressure
occurs.
such
fluid imbalance
leaks,
masterThis
will warn tlie
driver
in the
cylinder-fluid
bypass
or ofairproblems
such
leaks, mastersystem. as fluid
cylinder-fluid
air in the
A typical bypass
brake orwarning-light
system.
switch is shown on the following page.
warning-light
AtAthe typical
center of brake
the switch,
a piston is
switch
following
page.
located isbeshown
tween on
twothe
spri
ngs. Pressure
At
the
center
of
the
switch,
a
piston
is
from the front brakes is on one side of
located
between
two
springs.
Pressure
the piston and rear-brake pressure is
from
frontDifferences
brakes is oninone
of
on
thethe
other.
theside
force
thethe
piston
and rear-brake
pressure
is
of
two springs
compensa
te for the
on the other. pressure
Differences
in the force
designed-in
differential
of
of
two springs
compensate
the
thethefront
and rear
systems. for
When
designed-in
pressure
differential
severe pressure differential occ ursof,
the
front and
rear toward
systems.theWhen
the piston
is moved
lowsevere
pressure
differential
pressure side . This closes the occurs,
switch
the turns
pistononisthe
moved
toward
and
warning
light.the lowpressure
side.
This
closes
the of
switch
There are many variations
this
and turns
on the
warning
light.
simple
switch
. Some
have
centering
There are many variations of this
simple switch. Some have centering
59
Brake WarningLight Switch
Brake WarningPiston Off-Center
Stem
houlder of Piston
Touching Terminal
Brake warning-light switch is indicating hydraulic-system malfunction. Piston between two
centering springs is pushed to left by higher pressure in right chamber. Piston contact with
electrical
terminal turns
on instrument-panel
warning light. malfunction.
Drawing courtesy
Corp.
Brake warning-light
switch
is indicating hydraulic-system
PistonBendix
between
two
centering springs is pushed t o left by higher pressure in right chamber. Piston contact with
electrical terminal turns on instrument-panel warning light. Drawing courtesy Bendix Corp.
springs; some even have two pistons.
The switch type used varies with the
springs;
even
have
two pistons.
design ofsome
car and
brake
system.
near the master cylinder so lines to
the front and rear brakes can be easily
near the master
cylinder so lines to
connected
to the valve.
In recent years, car manufacturers
COMBINATION
VALVE
have
combined the
function of the
In recentvalve,
years,proportioning
car manufacturers
metering
valve
havebrake
combined
the function
and
warning-light
switch of
intothea
metering
valve, proportioning
valve
single
combination
valve. Some manuand
brakecombine
warning-light
switch
into a
facturers
the brake
warningsingle
combination
valve. Some
manulight switch
with either
the proporfacturers
combine
the
brake
warningtioning valve or the metering valve.
light switch
with either the
Some
front-wheel-drive
carsproporwith
tioning valve orsystems
the metering
valve.
combine
two
diagonally-split
Some
front-wheel-drive
with
proportioning
valves with cars
the brake
diagonally-split
systems
combine
two
warning-light switch.
Because
external
proportioning
valves
with
the
brake
appearances of these valves are
warning-light
similar, be switch.
careful Because
when external
moving
appearances
of
these
are
brake-system componentsvalves
from one
similar,
be
careful
when
moving
car to another. Check part numbers
brake-system
components
from one
and
car shop manuals
to be sure.
carCombination
to another. valves
Check are
partfound
numbers
only
and
car
shop
manuals
to
be
sure.
in brake systems using a tandem
Combination
are found
master
cylinder.valves
Usually,
they only
are
in brake
systems
usingdisca and
tandem
found
on cars
with front
rear
master brakes.
cylinder. Most
Usually,
they are
drum
combination
found
on
cars
with
front
disc
and rear
valves cannot be disassembled
for
drum
brakes.
Most
combination
service or adjustment. If defective, a
valves
cannot
be disassembled for
be replaced.
valve must
service
or adjustment.
If defective,
Combination
valves work
similar toa
valve
must
be
replaced.
the individual valves they replace. By
Combination
work similar
to
combining
in avalves
common
housing,
the individual
valves
replace. By
fewer
fittings are
used.they
Consequently,
combining
a common
the valve isinsimpler,
costs housing,
less and
fewer
fittings
are
used.
Consequently,
leak possibilities are reduced.
thePictured
valve isis simpler,
less and
a typical costs
three-function
leak possibilities
are reduced.
combination
valve.
The metering
Pictured
is a the
typical
three-function
valve
operates
front
system and
combination
valve.
The
the proportioning valve themetering
rear. A
valve operates
the must
front be
system
and
combination
valve
mounted
A fluid-level indicator consists of a
FLUID-LEVEL
INDICATOR
device
in the fluid
reservoir and a
A
fluid-level
indicator
brake warning light. It consists
switchesofona
device
in
the
fluid
reservoir
and aa
when reservoir fluid drops below
brake
warning level.
light. This
It switches
on
predetermined
indicating
when reservoir
fluid
drops
device
consists of
a float
andbelow
a me-a
predetermined
level. This indicating
chanically
or magnetically
actuated
device
consists
of a float and a meswitch.
chanically
or magnetically
actuated
Like
the
brake
warning-light
switch.
switch, low fluid-level indicator warns
brakeleakswarning-light
theLike
driverthe
of fluid
or masterswitch,
low
fluid-level
indicator
cylinder bypass. It can
also warns
signal
the
of fluid
leaksbutornot
masterworndriver
disc-brake
linings,
air in
cylinder
bypass.
It can
the system.
Usually,
twoalso
are signal
used
worn
linings,cylinders.
but not airBein
with disc-brake
tandem master
the
system.
Usually,
two
are
used
cause fluid-level indicators perform
with
master
cylinders.
Bemany tandem
of the same
functions
as brake
cause fluid-level
indicators
perform
warning-light
switches,
they are
rarely
many
of the same functions as brake
used together.
The switch type used varies with the
design of car and brake
system.
COMBINATION
VALVE
the proportioning valve the rear. A
combination
valve must be mounted
60
Three-function combination valve combines metering valve, proportioning valve
and brake warning-light
switch
Three-function
combination
valve into
com-a
single metering
unit. Metering
is at leftvalve
end
bines
valve, valve
proportioning
and proportioning
valve is under
brake warning-light
switchlarge
intonut
a
on
bottom.
courtesy
Bendix
Corp.
single
unit.Drawing
Metering
valve is
at left
end
and proportioning valve is under large nut
on bottom. Drawing courtesy Bendix Corp.
the front and rear brakes can be easily
connected
to the valve.
FLUID-LEVEL
INDICATOR
warning-light switches, they are rarely
used
together.
HOSES
Hydraulic fluid is carried to the cali-
HOSES
pers or wheel cylinders by flexible
Hydraulic
is carried
to the calihoses.
Thesefluid
hoses
allow suspension
perssteering
or wheel
cylinders by flexible
and
motion.
hoses.
suspension
In theThese
early hoses
days ofallow
the automobile,
and
steering
motion.
high-pressure flexible hoses did not
In the
early days ofitthe
exist.
Consequently,
wasautomobile,
difficult to
high-pressure
get hydraulic flexible
fluid to hoses
brakesdid
at not
the
exist.
it was difficult
to
wheels.Consequently,
It was amazing
that early
get
hydraulic
fluid
to
brakes
at
the
hydraulic-brake systems worked at
wheels.
amazing
that
Fluid Itwaswas
routed
through
axleearly
and
all.
hydraulic-brake
workedThis
at
suspension
links systems
to the brakes.
all. Fluid
was routed
through
axlefront
and
was
particularly
difficult
on the
suspension
links seals
to thewere
brakes.
wheels.
Sliding
usedThis
to
was
particularly
difficult
on
the
front
allow
steering
and
suspension
wheels. Sliding seals were used to
allow steering and suspension
Although old, cracked brake hose stills
holds pressure; it should be replaced. Condition of outSide
rubber is
the only
to
Although
old, cracked
brake
hoseway
stills
judge
condition of
a brake
It's better
holds pressure;
it should
behose.
replaced.
Conto
replace
a cracked
hose
than
to way
risk to
a
dition
of outs~de
rubber
is the
only
suddencondition
brake failure.
judge
of a brake hose. It's better
to replace a cracked hose than to risk a
sudden brake failure.
motion . To contrast this, the modern
brake hose is simple and reliable.
motion.
To contrast
this,from
the multiple
modern
Brake hoses
are made
brake
hose
is
simple
and
reliable.
layers of fabric impregnated with
Brake hoses
areThey
made are
from
multiple
synthetic
rubber.
tough
and
layers
of years,
fabricbutimpregnated
with
last
many
are still the weaksynthetic
They are
tough Itand
est
link inrubber.
the hydraulic
system.
is
last
many
years,
but
are
still
thecontact
weakeasy to damage a hose through
est
the hydraulic
It is
withlinka in wheel,
tire , system.
suspension
easy
to damage
a hose
through
contact
member,
exhaust
or road
debris.
Or
with
a wheel,
tire, can
suspension
an overzealous
mechanic
damage
exhaust
or road
debris. Or
amember,
brake hose
during
installation.
A
an
overzealous
mechanic
can
brake hose can fail if twisted damage
or imaproperly
brake installed
hose during
installation. A
.
brake
hose
can
fail
if
imBrake hoses expand twisted
slightly or
under
properly
installed.
high internal pressure. This swelling
Brake additional
hoses expand
under
requires
fluid slightly
movement
to
high internalfor
pressure.
This swelling
compensate
the increased
hose
requires The
additional
movement
to
volume.
driver fluid
senses
hose swellcompensate
for
the
increased
hose
ing or expansion as a soft or spongy
volume.
The driver
sensesand
hose swellbrake pedal.
Racing
high-
ing or expansion as a soft or spongy
brake pedal. Racing and high-
Imperial tube bender is available from good
tool stores. Neats bends can be made without risk of
crimping
Beforefrom
youI good
bend
Imperial
tube
bendertube.
is available
brake
lines, Neats
invest bends
in a good
bender.
withtool
stores.
cantube
be made
"Ultimate" brake hoses are steel-braided
teflon. Because exterior is braided stainless steel, hoses
more
resistant
to me"Ultimate"
brake are
hoses
are
steel-braided
chanicalBecause
damage
than is
ordinary
teflon.
exterior
braided rubber
stainhoses.
Steel-braided
hoses
areto mealso
less
steel,
hoses are more
resistant
stiffer, giving
a firmer
pedal.
chanical
damage
than
ordinary rubber
hoses. Steel-braided hoses
stiffer, giving a firmer pedal.
are
also
Don't use high-pressure plastic tubing for
a brake hose! After repeated flexing,
tubing
cracks
at fittings. I've
seentubing
this failDon't use
high-pressure
plastic
for
urebrake
on several
cars.repeated
Plastic tubing
is
a
hose!race
After
flexing,
also easily
damaged
by heat
mechanical
tubing
cracks
at fittings.
I've or
seen
this failcontact.
Although
tubingtubing
can be
ure
on several
raceplastic
cars. Plastic
is
usedeasily
if rigidly
mounted
to frame,
weight
also
damaged
by heat
or mechanical
saved isn't
worth risking
brake
failure.
contact.
Although
plastic
tubing
can be
out risk of crimping tube. Before you bend
brake lines, invest in a good tube bendler.
used if rigidly mounted to frame, weight
saved isn't worth risking brake failure.
performance brake systems require
that rubber brake hoses be replaced
performance
with somethingbrake
better.systems require
that
rubber
brake
hoses be replaced
High-pressure stainless-steelbraidwith
something
ed brake
hoses, better.
developed for aircraft
High-pressure
and
military use,stainless-steel-braidare available from
ed
brake
hoses,. Suppliers
developedare
forlisted
aircraft
specialty shops
at
and
military
use,
are
available
from
the back of the book. Steel-braided
specialty
Suppliers
are listed
at
hoses areshops.
available
in custom
lengths
the
of the
book.to Steel-braided
with back
adapter
fittings
suit special
hoses are available
custom
applications.
These inhoses
are lengths
Teflon
with
adapter
fittings
to
suit
lined and externally reinforcedspecial
with
applications. These
are almost
Teflon
stainless-steel
braid. hoses
They are
lined
and externally
reinforced
with
"bulletproof'
and resist
expansion
stainless-steel
braid.
They
are
almost
under pressure.
"bulletproof'
and resistTeflon-lined
expansion
Aeroquip 6600-series
under
pressure.
hose with
Super Gem fittings is a type
Aeroquipused
6600-series
Teflon-lined
commonly
on race cars.
I highly
hose
with
Super
G
e
m
fittings
is a hose
type
recommend this flexible brake
I
highly
commonly
used
on
race
cars.
to make the brake pedal firmer, and
recommend
this flexible
brake hose
for overall safety.
Remember,
use
to make hose
the brake
flexible
only pedal
wherefirmer,
thereand
is
for
overall
safety.components
Remember,being
use
motion
between
flexible hoseEven
onlythewhere
is
connected.
best there
flexible
motion
between
components
being
hose expands
more
under pressure
connected.
Even the
best flexible
than steel hydraulic
tubing.
hose
expands
more
under
Some race cars use plastic pressure
hose for
than
hydraulic
tubing.
both steel
the brake
tubing
and the flexible
Somehoses.
race cars
plastic
hose
for
brake
Thisuse
tubing
may
work
bothsome
the brake
tubing andapplications,
the flexible
for
low-pressure
brakeit ishoses.
This tubing
mayflexible
work
but
dangerous
to use as
for
some
low-pressure
applications,
brake hose. Plastic tends to crack
but it isthe
dangerous
to usethe
as flexible
where
tube enters
fitting.
brake repeated
hose. Plastic
After
flexing,tends
even to
thecrack
spewhere
the developed
tube enters
cial
fittings
for the
this fitting.
tubing
Afternotrepeated
spe-a
will
preventflexing,
failure. even
If youthe
have
cial fittings
for this
tubing
race
car withdeveloped
plastic brake
hoses,
rewill not
prevent
If you Teflon
have a
place
them
with failure.
steel-braided
race car with plastic brake hoses, replace them with steel-braided Teflon
hoses. Failure of the plastic hose will
occur without warning and cause
hoses. Failure
the plastic hose will
sudden
brakingof
loss.
occur without warning and cause
sudden
braking loss.
HYDRAULIC
TUBING
Most cars use tubing manufactured
HYDRAULIC
TUBING
from
steel for the
brake system. ComMost
cars
use
tubing
manufactured
monly called brake
lubing,
it is availafrom
steel
for
the
brake
system.
Comble in diameters from 1/8
in . through
monly
is availa3/8 in.called
Mostbrake
of tubing,
today ' sit cars
use
ble
in diameters
118 in,
through
3/16-in.
tubing ;from
1I4-in.
tubing
is
318 in.onMost
today's
use
found
most ofolder
cars. cars
Smaller
3116-in.
tubing;and114-in.
tubing
is
tubing is stiffer
lighter and
easier
found
most tubing
older has
cars.less
Smaller
to bend.onLarger
resistubing
stiffermovement
and lighterand
and iseasier
tance tois fluid
less
to
bend.
Larger
tubing
has
resis-.
prone to damage during less
handling
tance3/16-in
to fluid
movement
less
The
.-diameter
tubeand
is aiscomprone
damage atduring
promiseto arrived
after handling.
years of
The
3116-in.-diameter
tube is a using
comexperience.
I recommend
promise
arrived
at
after
years
of
3/16-in . hydraulic tubing for all brake
experience.
I
recommend
using
systems.
3116-in.
for all brake
Copperhydraulic
tubing ortubing
any tubing
of an
systems.
unknown material should never be
Copper
tubingtubing
or any
tubing isofsoft
an
used
for brake
. Copper
unknown
material
should
never
be
and prone to cracking. Ordinary steel
used formay
brake
Copper isbut
soft
tubing
be tubing.
strong enough,
it
and pronemeet
to cracking.
doesn't
the rigidOrdinary
quality steel
and
tubing may
be strong
but it
design
standards
of enough,
brake tubing.
doesn't
meet
the
rigid
quality
and
Tubing manufactured for brake sysdesignby standards
of brake
tubing.
tems
Bendix is made
of soft-steel
Tubingsheathed
manufactured
for brakeThese
sysstrips
with copper.
tems
by
Bendix
is
made
of
soft-steel
strips are then rolled into a doublestripstube
sheathed
with at copper.
These
wall
and bonded
high temperastrips in
area then
rolled
a doubletures
furnace
. Theinto
tu be
is then
wall tube and
at highresistance.
temperatin-coated
forbonded
corrosion
tures
in
a
furnace.
The
tube
is then
Ordinary steel tube is only single
wall
tin-coated
for corrosion
resistance.
and
not copperor tin-plated.
It could
Ordinary
steela few
tubeyears
is only
wall
rust
out after
andsingle
suddenly
and not copper- or tin-plated. It could
rust out after a few years and suddenly
Automotive brake-tubing flares : Doubleflare used on most American cars is at left;
at right is iso-flare
used on
some Doubleforeign
Automotive
brake-tubing
flares:
cars. used
Flares
match fittings
toat
which
flare
on must
most American
cars is
left;
they
attach,
otherwise
a leak
or failure
will
at
right
is iso-flare
used
on some
foreign
result.Flares must match fittings t o which
cars.
they attach, otherwise a leak or failure will
result.
Making double flare: Flaring tool comes
with dies needed to do both forming
operations.
Tool flare:
and tubing
aretool
set comes
up to
Making double
Flaring
do
second
with
dies forming
neededoperation.
to do both forming
operations. Tool and tubing are set up to
do second forming operation.
61
Flaring tool folds tube end back on itself to
finish double-flaring operation. Drawing
courtesy
Chrysler
Corporation.
Flaring tool
folds tube
end back on itself to
finish double-flaring operation. Drawing
courtesy Chrysler Corporation.
Fittings used with steel-braided hose are different than standard automotive brake fittings.
High-pressure steel-braided-hose fittings meet aircraft standards, not automotive
standards.
Special
adapter fittings
aircraft-type
fittings
to automotive
brakes.
Fittings used
with steel-braided
hose attach
are different
than standard
automotive
brake fittings.
Photo courtesy C
& D Engineering Supply
Ltd. meet aircraft standards, not automotive
High-pressure
steel-braided-hose
fittings
standards. Special adapter fittings attach aircraft-type fittings to automotive brakes.
threads.
Accompanying
Photo
courtesy
C & D ~ n ~ i nphotos
eerin
supply
g show
Ltd. seat for the flare they mate to.
Race cars often require fittings not normally found in auto-parts stores. Bulkhead fitting
handy
mounting
lines
Race is
cars
often for
require
fittings brake
not normalwhere
they
pass through
a panel
such fitas
ly found
in auto-parts
stores.
Bulkhead
this fire
wall. Two
nuts support
ting
is handy
for jam
mounting
brake fitting
lines
at
hole they
in panel.
where
pass through a panel such as
this fire wall. Two jam nuts support fitting
at hole in panel.
burst. Always use proper-quality
brake-tubing material, available from
burst. Always
auto-parts
stores. use proper-quality
brake-tubing
material,tubing
available
from
Double Flare-Brake
is availaauto-parts
stores.
ble in several standard lengths with
Doublefittings
Flare-Brake
is availamale
at each tubing
end. Common
ble
in several
standard
lengths
are 8, 12,
20, 30lengths
, 40, 50 with
and
male
at each
end. diameters
Common
60
in . fittings
Commonly
available
lengths
40, 50 cars
and
are
3/16are
or 8,
11412,
in. 20,
for 30,
American
60
in.
Commonly
available
diameters
and 3/16 in. or 4.762mm for imported
114 isin.doubleIlared-tube
for American cars
are 3/16
cars.
Eachorend
and
3/16
in.
or
4.762mm
for imported
is doubled over on itself-in
a convex
cars.
Each
end
is
double7/lared-tube
or concave shape. American and imis doubled
itself-in flares
a convex
ported
carsover
useondifferent
and
or concave shape. American and imported
cars use different flares and
62
some of these differences.
threads.
photosforshow
DoubleAccompanying
flares are important
the
some
of these
differences.
strength
and safety
of a brake system.
Doublewith
flares
are important
for can
the
Anyone
a cheap
flaring tool
strength
and
safety
of
a
brake
system.
make single flares. NEVER singleAnyone
with
a cheap
brake
lines.
If youflaring
don't tool
wantcan
to
flare
make
single
flares.double-flaring
NEVER singleinvest in
a special
tool,
flare
lines.brake
If you tudon't
to
buy brake
preflared
bes want
or pay
invest
in
a
special
double-flaring
tool,
someone to custom-make double
buy preflared
brake are
tubes
or will
pay
flares.
Single flares
weak,
someone
custom-make
doublea
eventually to
fatigue,
crack and cause
flares.
Single
flaressystem.
are weak, will
leak in the
hydraulic
eventually
fatigue,
crack
cause toa
Armor-Brake tubing is and
exposed
leak
in
the
hydraulic
system.
harsh conditions under a car. It gets
Armor-Brake
tubing
is isexposed
to
blasted by dirt and
debris,
immersed
harsh
conditions
under
a car.continue
It gets
in water
and salt, but
should
blasted
by dirt
debris,
is immersed
to
function
forand
years
without
failure.
in
water
and
salt,
but
should
Anytime you are under your continue
car, look
to function
for years
without
for
brake-line
damage
. A failure.
rusty,
Anytime
you are
look
kinked, nicked
or under
leakingyour
line car,
must
be
for
brake-line
damage.
A
rusty,
replaced. If you want extra protection
kinked,
leaking
must be
with
newnicked
brakeortubing
, itline
is available
replaced. with
If you
want
extra This
protection
wrapped
a coil
spring.
armor
with
new the
brake
tubing,
is available
protects
tube
fromit damage
by
wrapped
with asharp
coil spring.
armor
rocks o r other
objects.This
Armored
protects
the can
tubebe from
by
brake lines
founddamage
in major
rocks
or other
sharp objects. Armored
au
to- parts
stores.
brake lines can be found in major
auto-parts
FITTINGSstores.
Brake lines are connected with steel
FITTINGS
or
brass fittings of various types, such
are connected
steel
as Brake
tees, lines
junction
blocks andwith
unions.
or
brass
fittings
of
various
types,
such
Be careful when selecting brake-line
as
tees, They
junction
blocks
fittings.
must
have and
the unions.
correct
Be careful when selecting brake-line
fittings. They must have the correct
Otherwise, they will leak. Many fit-
seat
for look
the OK
flare
matepropto.
tings that
willthey
not mate
Otherwise,
theytubing.
will leak.
Many
erly
with the
Never
use fittatings
OK will
mate
proppered that
pipelook
threads
in a not
brake
system.
erly with
use taThey
will the
leak tubing.
under Never
high pressure,
pered
pipe
threads
in
a
brake
system.
particularly
if installed
without
They willThey
leak will
underalso
highsplit
pressure,
sealant.
when
particularly if installed without
overtorqued.
sealant.
They will switches
also split
when
Some stop-light
have
taovertorqued.
pered pipe threads. They will seal if
Some tape
stop-light
switches
have you
taTeflon
is used
. However,
pered
pipe
threads.
sealanyif
must be
very
careful They
not towill
allow
Teflon tape
tape to
is extend
used. However,
you
Teflon
past the first
must
be
very
careful
not
to
allow
any
thread. A shred of Teflon tape floating
Teflon
tape
to
extend
past
the
first
around in the brake fluid can plug a
A shred
ofsystem.
Teflon tape
thread. port
critical
in the
The floating
best soaround
in
the
brake
fluid
plug a
lution is avoiding the use can
of tapered
critical
port
in
the
system.
The
best
sopipe threads. Take a tip from the airlutionindustry:
is avoiding
theTeflon-tape
use of tapered
craft
Leave
seapipe
threads.
Takeand
a tippipe
fromfitters.
the airlant to
plumbers
It
craft
industry:
Leave
Teflon-tape
seacan cause many problems in a brake
lant to plumbers and pipe fitters. It
system.
canOncause
in a brake
race many
cars, problems
steel-braided
hoses
system.
are
used to improve reliability and
On race
cars,brakes.
steel-braided
provide
firmer
Fittings hoses
used
are
used
to
improve
reliability
and
with steel-braided hoses are different
provide
firmer
used
than those
usedbrakes.
with Fittings
conventional
with
are different
different
hoses.steel-braided
They have hoses
entirely
than
those
used
with
conventional
specifications for threads, flares and
hoses. dimensions.
They have entirely
other
Adapter different
fittings
specifications
threads,
flaressteeland
must be used for
when
installing
other
dimensions.
Adapter
fittings
braided hoses on vehicles with
must be used when
automotive-type
brakeinstalling
fittings. steelbraided
hoses
on
with
Adapter fittings are vehicles
available from
automotive-type brake fittings.
Adapter fittings are available from
Of
·c
*F
'C
600
'E
500
~
300
Selected High BoilingPoint Glycol Brake
Fluids
elected High Boiling-
300
250
20e
250
oint Glycol Brake
'0
20c
al 300
150
2o0o!----'---!;2-~3-~--!--....::::6100
Weight % Water
1
Brake tube in fitting fractured during a
race, causing complete brake failure.
Driver
but luckily
Brake was
tube without
in fittingbrakes,
fractured
during ita
happened
where complete
he could recover
race,
causing
brake without
failure.
crashing.
Failure
occurred
because
fittingDriver was
without
brakes,
but luckily
it
mounting
was
installed.
happened bolt
where
henot
could
recoverVibrating
without
fitting
andFailure
hose occurred
was supported
byfittingtube,
crashing.
because
which eventually
failed
fatigue.
Brake
mounting
bolt was
not from
installed.
Vibrating
tubes and
must supported
be securelybymountfitting
andfittings
hose was
tube,
ed
to prevent
suchfailed
failure.
which
eventually
from fatigue. Brake
tubes and fittings must be securely mounted
prevent such
theto sources
thatfailure.
supply the hoses,
such as e & D Engineering Supply
the
that supply
the hoses,
Ltd., sources
or WREP
Industries.
Some
such asoffer
C &brake-hose
D Engineering
Supply
shops
kits that
inWREP
Industries.
Some
Ltd., or
clude
ada pter
fittings
and correctshops
that inlength offer
hoses.brake-hose
Don't mixkits
automotive
cludeaircraft
adapter
fittings
correctand
fittings.
This and
will result
in
length hoses.
Don'tleaks
mix automotive
damaged
threads,
or cracked
and
aircraft
Thisrecognize
will resultthe
in
fittings.
If fittings.
you can't
damaged
threads,
leaks
or
cracked
difference, ask the adv ice of a shop
fittings.
If you
recognize the
that supplies
thesecan't
fittings.
difference,
ask the
advice
shop
Adapter-fitting
usage
will ofbea minithat
supplies
these
fittings.
mized if a race car is constructed using
usage
will besystem.
miniall Adapter-fitting
aircraft fittings in
the brake
mizedcan
if aberace
carbyis getting
constructed
using
This
done
the proper
all
aircraft
fittings
in
the
brake
system.
fittings from an aircraft hardware
This
can be
done
getting
supplier.
You
maybystill
havethe
toproper
adapt
fittings
fromlineCs)
an aircraft
the brake
to yourhardware
master
supplier. You
still using
have automoto adapt
cylinder(s)
andmay
brakes
the
brake
line(s)
to
your
master
tive flares or fittings.
cylinder(s1
and
brakes
using
automoAircraft flar es are not the same as
tive flares or fittings.
automotive
flares.
They
use
Aircraft flares are notthe
the tubes
same as
ferrules-sleeves-over
to
automotive
They and use
reinforce them. flares.
Aircraft hoses
fitferrules-sleeves-over
tubes AN
to
tings
are
identifiedthe as
reinforce
them. Aircraft
and
fit(Army-Navy)
or
MShoses(Mi
litary
tings
are AN
identified
AN
Standards).
and MSas specI(Army-Navy)
or
M
S
(Military
fications,
written
by
the
U.S.
Standards).
ANstandards
and MS
specigovern
ment , are
recognized
fications,
by Automotive
the U.S.
throughout written
the world.
government,
specifications are
are standards
written byrecognized
the Societhroughout
the world.
Automotive
ty of Automotive
Engineers
(SAE) .
specifications
arealso
written
by the
SAE
standards
have
the Sociesame
ty of Automotive
Engineers
(SAE).
worldwide
recognition
.
SAE standards also have the same
worldwideFLUID
recognition.
BRAKE
Once a brake system is installed, it
BRAKE
must be FLUID
filled with fluid so it can
Once a brake system is installed, it
must be filled with fluid so it can
Brake fluid is lifeblood of any brake
system. For race cars, you must keep fresh
new
fluid
in brake
system atof
all times.
Fluid
Brake
fluid
is lifeblood
any brake
with highest
possible
boiling
is a
system.
For race
cars, you
must point
keep fresh
must
for raCing.
new fluid
in brake system at all times. Fluid
with highest possible boiling point is a
must for racing.
function. Hydraulic fluid for an automotive brake system is simply
function.
Hydraulic
for an aucalled brake
fluid. Thisfluid
distinguishes
it
tomotive
system
simply
from
fluidsbrake
used for
other ishydraulic
This distinguishes
it
called brakefluid.
applications
and systems.
Automotive
from
fluids
used
for
other
hydraulic
brake fluid is designed to work the
applications
Automotive
brake systemand
of asystems.
car. Other
hydraulic
brake have
fluid totally
is designed
to work
the
fluids
diffe rent
chemical
brakephysical
systemproperties.
of a car. Other
hydraulic
and
Always
use aufluids
have
totally
tomotive
brake
fluiddifferent
in a car.chemical
Aircraft
and
physical
properties.
Alwaysand
use aubrake fluid is totally different
will
tomotive
brake
not work in
a car.fluid in a car. Aircraft
brake
fluid
is totally
differentmixture,
and will
Brake
fluid
is a chemical
not
work
in
a
car.
which varies with manufacturer. Each
Brake fluid has
is aa chemical
mixture,
manufacturer
secret formula
dewhich varies
with manufacturer.
signed
to perform
a "better job ."Each
All
manufacturer has
a secret
formulatheir
demanufacturers
must
formulate
signed
to perform
a "better
brake fluid
so it m ee
ts rigid job."
SAE, All
inmanufacturers
must
formulate
their
dustry and government standards.
In
brake
fluid
it meets rigid
SAE, inthe
U.S.
, thesoDepartment
ofTranspordustry
and government
standards. In
tation (DOT)
sets the standards.
theHydraulic
U.S., the brake
Department
of Transporfluid used
in racing
tation
(DOT)
sets
the
standards.
and road cars is mostly a Polyalkylene
Hydraulic
brakemixture-commonly
fluid used in racing
Glycol
Ether
and
road
cars
is
mostly
a Polyalkylene
called glycol. This type of
fluid can be
Glycol
Ether
mixture-commonly
found in any auto-parts store and is
called glycol.with
Thisthetype
fluid can inbe
compatible
fluidoforiginally
found in
store type
and of
is
stalled
in any
yourauto-parts
car. A newer
compatible
fluid
originally
brake fluid with
has the
a si
licone
base . inIts
stalled in
A newer
type of
properti
es your
differcar.from
glycol-based
brake
fluid
has
a
silicone
base.
fluids . Silicone-based brake fluid Its
is
propertieslater
differ
from
glycol-based
discussed
in this
chapter.
fluids.
Silicone-based
brakemust
fluid
is
Glycol-based
brak e fluid
have
discussed
later
in
this
chapter.
the following properties to work corGlycol-based
brake fluid must have
rectly
in an automobile:
the
following
properties
to work
• Must
not boil
at tempera
tures corenrectly
in
an
automobile:
countered during severe braking
Must not
conditions
. boil at temperatures en-
countered during
conditions.
severe
braking
2
3
4
5
I00
6
Weight
% Water
Graph shows how
boiling
point of glycolbased brake fluid drops with exposure to
moisture.
Notice
how
brakepoint
fluid with
highGraph shows
how
boiling
of glycolest
boiling
when with
new exposure
is affected
based
brakepoint
fluid drops
to
most
by Notice
water how
content.
courtesy
moisture.
brakeGraph
fluid with
highYankee
Silicones,
est
boiling
point Inc.
when new is affected
most by water content. Graph courtesy
Yankee Silicones, Inc.
• Must not freeze or thicken in cold
temperatures.
Must not
not compress.
freeze or thicken in cold
• Must
temperatures.
• Must flow through system passages
Must
not compress.
minimal
no res istance.
with
Must
passages
not through
corrode system
or react
with
• Must flow
with
minimal no
resistance.
brake-system
materials.
not corrode
or sliding
react parts
with
Must lubricate
internal
• Must
brake-system
materials.
of brake system.
Must lubricate
sliding parts
• Must
not alter internal
its properties
after
of
brake
system.for extended periods.
being
in system
its properties
after
Must not
be alter
compatible
with other
• Must
being
in
system
for
extended
periods.
glycol-based brake fluids .
Must not
be decompose,
compatible orwith
form other
gum
• Must
glycol-based
brake
fluids.
or sludge at any
temperature.
Must Boiling-The
not decompose,most
or formcritical
gum
Fluid
or
sludge
at
any
temperature.
property of brake fluid is its resistance
Fluid
Boiling-The
most critical
to
boiling
at high temperature.
When
property
of
brake
fluid
is
its resistance
brake fluid boils , small bubbles
form.
to boiling
at high
temperature.
When
These
bubbles
collect
and are trapped
brake
boils,Because
small bubbles
form.
in
the fluid
system.
gas bubbles
These
bubbles
collect
and
are
trapped
are compressible, this results in a
in the brake
system.
Because gas bubbles
spongy
pedal.
areBoiling
compressible,
this
results
in a
generally is
caused
by water
spongy
brake
pedal.
vapor being absorbed by the brake
Boiling
is caused
by water
fluid
. Thegenerally
mo re water
brake
fluid
vapor
being
absorbed
by
the
brake
contains, the lower its boiling point.
fluid.
more water high-quality
brake fluid
New,The
uncontaminated,
contains,
lower
its boiling
point.
brake fluidthe
boils
at 550F
(288e)
~ pure
New,
uncontaminated,
high-quality
water boils at 212F (lOOe). A mixture
brake
fluidfluid
boilsand
at 550F
pure
of
brake
water(288C);
boils somewater
at 212Fthese
(100C).
A mixture
where boils
between
temperatures.
of brake
fluidpoints
and water
boils someTwo
boiling
are referred
to in
where
between
these
temperatures.
brake-fluid specifications: dry boiling
Two
boiling
points paint.
are referred
in
wet bailing
Withouttogetpoil1l and
brake-fluid
specifications:
dry boiling
of the specifications,
ting into details
and wet should
boilingpoint.
Without
getpoint
the meaning
be clear.
Dry boilting
into
details
of
the
specifications,
ing point refers to fresh fluid out of a
the meaning should be clear. Dry boiling point refers to fresh fluid out of63a
,B RAKE-FLUID SPECIFICATIONS
The
print on brake-fluid
cans is
8RAKE-FLUID
SPECIFICATIONS
confusing. Even worse, specifica- ,
The
on constantly,
brake-fluidsocans
is
tions print
change
an old
confusing.
worse,
specif icacan
of fluid Even
may say
something
diftions
constantly,
an old
ferent change
than a new
can . Theso
following
can
may say something
difis of
an fluid
explanation
' of current
ferent
than a new can. The following
specifications.
is Allan
explanation
of current
brake
fluids must meet
federal
standard 116. Under this standard
are three Department of Transportastandard
Under thisfor
standard
tion
(DOT)116.
specifications
brakeare
Department
of Transportafluidthree
performance
: DOT
3, DOT 4
tion
(DOT)
and DOT
5. specifications
All brake fluidsfor
arebrakesuitafluid
DOT
3, or
DOT
4
ble forperformance:
use in either
drum
disc
and
DOTBoiling
5. All brake
are suitabrakes.
pointfluids
for the
three
ble
forof use
either
drum or disc
types
flu,i dsinare
as follows:
specifications.
All brake fluids must meet federal
brakes. Boiling point for the three
types of fluids are as follows:
Dry Boiling Point
Degrees F
, Degrees C
Dry Boiling Point
Degrees F
Wet Boiling Point
Degrees F
Degrees C
Degrees C
Wet Boiling Point
Degrees F
Degrees C
DOT3
DOT 4
DOTS
401
DOT 3
205
446
DOT 4
230
500
DOT 5
260
40 1
284
205
140
284
140
446
311
230
155
31 1
155
500
356
260
180
356
180
it.
I
~
I
e
a
ap:!
:-
[ s~
RACinG
550
Racing
5 5PlUld
0
BtaWl
"k
I"IGt contents 1 hre
us
Brake
338 us II", id
""""""""~,
Iqtl81101
rkatr*nlmlm
U Sr "
e-':I l ••
1" 5
1 1 H U S Ilrv
1 , 18
~ t t , ~
, . I
..
700
~
'we
~ 600
~,
!j'"9 m u
500
'"
o
5~
503400
~
::l
300
y
,~
Typical Glyco l-Based
{Brake Fluid
Typical Glycol-Based
g
200 L----'-----'1'-2---':18---'---'
Months in Service ,
I
I
I
I
200
6
24
Curve shows
what 'I2
happens18 to boiling
Months inbrake
Service
point of glycol-based
fluid in
typical
road-car
use. , toWeather
Curve shows
what happens
boiling
changes
point of curve'-boiling
glycol-based point
brakegradually
fluid in
drops in extremely
climates.
Sili,typical
road-cardamp,
use.
Weather
cone
brake
fluid is not point
susceptible
to
changes
curve-boiling
gradually
moisture
as it· damp
doesn't
pick Siliup
drops
in extremely
climates.
moisture.
Consequently,
silicone
cone
brake fluid
is not susceptible
to
Ibrake-fluid
~ boiling
remains
moisture as
it' point
doesn't
pick high
up
moisture.
silicone
after long Consequently,
use. Graphcoi!rtesy
brake-fhid
boilingInc.
point remains high
Yankee Silicones,
after long use. Graph courtesy
Yankee
Silicones,
of
a fluid
is by lnc.
its DOT number. A
UC-,~
AP 550 Racing Brake Fluid is used ~. in
,most-severe racing applications. Its
dry 550
boiling
pointBrake
of 550F
AP
Racing
Fluid(288C)
is used is
h '
highest for a glycol-based
fluid, Photo
most-severe
racing applications.
Its
courtesy
APpoint
Racing.
dry
boiling
of 550F (288C) is
highest
for a glycol-based
Old brake
fluid meetsfluid.
DOTPhoto
2 or
courtesy
AP Racing.
, SAE
J1703
or 70R3 specifications.
Old brake
fluidrequirements
meets DOT refer
2 or
These
obsolete
SAE
31 703
specifications.
to
, fluid
withora 70R3
dry boiling
paint of
These
obsolete
requirements
374F (190C).
If you
have any ofrefer
th is
to
a dryit. boiling
point
of
old fluid
fluid,with
discard
Don't use
any374F (190C).
If you
have
this
thing
less than
DOT
3 any
fluidof in
a
old
fluid,
discard
it. Don't
anybrake
system
. Prior
to theuse
DOT
2
thing
less thanthere
DOT was
3 fluid
in a
specifications,
a 70Rlbrake
system.brake
2
Prior fluid
to the
DOTfor
specification
meant
specifications,
there
was this
a 70R1drum
brakes only.
Throw
away
specification
for
too
if you find brake
any. Itfluid
has ameant
dry boildrum
brakes
only.
Throw
this away
ing paint
of only
302F
(150C).
tooSpecified
if you find boiling
any. It has
a dry boilpoints
are
ing point of only
302F
(150C).
minimums.
Many
brake
fluids have
Specified
points
are
higher
boiling boiling
points, as
indicated
minimums.
Many brake
fluids
have
on
their containers.
As for
what
to
highera dry
boiling
points,
asover
indicated
use,
bailing
point
500F
on
theiris containers.
for what to
(260C)
best for hardAs
driving.
use,
a 3dryand
boiling
over 500F
DOT
DOT point
4 specifications
(260C)
is best for hard
driving.
are
for glycol-based
brake
fluid and
DOT
and
DOT 4You
specifications
DOT
5 is3 for
silicone.
can tell imare
for glycol-based
brakechemistry
fluid and
mediately
what the basic
DOT 5 is for silicone. You can tell immediately what the basic chemistry
64
glycol-based
brake
fluid
with , a
of
a fluid is bydry
its boiling
DOT number.
A
500F(260C)
point is
glycol-based
tested
to DOT 3brake
or DOT fluid
4, not with
DOT 5.a
500F
(260C) dry
boilingpoint
point is
Sometimes
boiling
tested
to to
DOT
3 o r DOTon
4, not
OT5
referred
asERBP
the DbrakeSometimes
point
is
fluid
can. This boiling
means' equilibrium
referred
to aspoint,
ERBPwhich
on the
brakeisanothreflux boiling
fluid
can.
This means
equilibrium
er way
of saying
wet boiling
point.
reflux boiling
whichin is
anothERBP
refers topoint,
a method
the
speer
way offor
saying
wet is
boiling
point.
cification
how fluid
exposed
to
ERBP
refers
a method
in. the spemoisture
and to
tested
.
cification
forfluid
howboiling
fluid isp~oint
exposed
to '
Note that
drops
moisture
tested.to water. Glycolafter
it isand
exposed
Notebrake
that fluid
boiling
point
drops
based
fluids
absorb
moisture.
after resulting
it is exposed
to water.
GlycolThe
mixture
of brake
fluid
based
brake
fluids in
absorb
moisture.
and
water
results
a boiling~point
The
of brakewater
fluid
drop.resulting
Fluids mixture
that · absorb
and water
in' a hydrostopic.
boiling-point '
easily
areresults
called
drop. Fluids
that absorb
water
Water
in brake-fluid
also causes
easily
hydroscopic.
corrosionare
and called
impurities
to accumuWater
in hydraulic
brake-fluid
also causes
late in the
system.
corrosion and impurities to accumulate in the hydraulic system.
sealed can ; wet boiling point refers to
fluid that has been exposed to moissealed
can; wet
boiling
point refers
to
ture under
specific
conditions
. Both
fluid
that
has
been
exposed
to
moisboiling points should be of concern to
ture, under
conditions.
you
but thespecific
most important
oneBoth
will
boiling
points
should
be
of
concern
Lo
de pend on how you use your car.
you,
but
the
most
important
one
will
Dry boiling point is important for
depend
you usethat
youracar.
racing . on
It ishow
assumed
properly
Dry boiling
i s important
for
m aintained
racepoint
car will
always have
racing.
I
t
is
assumed
that
a
properly
fresh brake fluid, For best permaintained
race
car must
will always
have
form
ance, the
fluid
be changed
fresh
brakeduring
fluid.a racing
For best
many times
seasonperto
formance,
the boiling
fluid must
changed
avoid a lower
point.beCh
anging
many
timesis during
a racing season
the fluid
an inexpensive
way to
to
avoid
a
lower
boiling
point.
Changing
ensure the brakes work bes t at temthe fluid encountered
is an inexpensive
to
peratures
in racingway
.
ensure
the brakes
best
at temWet boiling
pointwork
is most
important
peratures
n racing.
for
street encountered
use , Brake ifluid
in streetWet
boiling
point
is
most
driven cars is not changed important
often-if
for
Brake
fluid
i n streetever.street
If youuse.
could
bleed
your
brakes
driven week
cars isornot
often-if
every
so ,changed
the brake
fluid
ever. I fhave
you could
bleedsimilar
your brakes
would
properties
to a
every
week
or who
so, can
thetake
brake
race car's.
But,
the fluid
time
would
have their
properties
similar
to a
to bleed
brakes
weekly?
race car's. But,
canmust
take function
the time
Normally,
the who
brakes
to
bleed
their
brakes
weekly?
with moisture in the brake fluid
over
Normally,
the
brakes
must
function
long periods of driving during all
with
the brake fluid over
types moisture
of weathe irnconditions.
long
periods
o f driving
during
all
Brake
fluids with
a high wet
boiling
types
o
f
weather
conditions.
point do not necessarily ha ve the highfluids with
boiling
estBrake
dry boiling
point.a high
Mostwet
racers
use
do not necessarily
have
the ahighapoint
glycol-based
brake fluid
with
dry
est
dry boiling
Most(288C)
racers use
bo iling
point point.
of 550F
for
a
glycol-based
brakehigh-performance
fluid with a dry
racing.
A common
boiling
point
(288C)is AP
for
brake fluid
usedo fin 550F
road racing
A common
high-performance
racing.
Racing 550
. This fluid
exceeds DOT 4
brake fluid used
roadboiling
racing point,
is AP
specifications
fori ndry
Racing
550.
This
fluid
exceeds
DOT
and meets DOT 3 specifications for4
specifications
for dry
boiling point,
wet boiling point.
To maintain
your
and
meets Dsystem
O T 3 specifications
racing-brake
properly, it isfora
wet boiling
good
choice . point. To maintain your
racing-brake
properly,
s a
For street system
use, you
shouldi t iuse
good
choice.
brake fluid that meets DOT 4 specifiFor street
you point.
shouldIf use
cations
for wetuse,
boiling
the
brake meets
fluid that
meets
DOT 4 specififluid
DOT
4 specifications,
it
I f the
cations
for all
wet
boiling
point.
also
meets
parts
of DOT
4, includfluid
meets
D Opoint.
T 4 specifications,
boiling
Your choice of ita
ing wet
partsshould
o f DOT
includalso
meets all
brake-fluid
brand
be 4,based
on
ing
boiling
point. Your choice of a
the wet
following
requirements:
brake-fluid
brand
should
on
• Use a fluid
that
your be
carbased
m anuthe following requirements:
facturer recommends.
fluid
that of
your
car manuDon ' a
t mix
brands
fluids.
• Use
facturer recommends.
Violate either of these rules, and
Don't mix brands o f fluids.
long-term harm may occur to your
Violate
either For
of these
rules,some
and
brake
system.
instance,
long-term
your
brake
fluidsharm
maymay
reactoccur
with torubber
brake insystem.
instance,
seals
a brake For
system.
Over asome
long
brake
fluids
may
react
with
rubber
period of time , this may cause swelling
sealsleakage.
i n a brake
a long
or
Thissystem.
occurs Over
commonly
period
o f.S.-manufactured
time, this may cause
swelling
when U
brake
fluid
or
leakage.
is used
in anThis
olderoccurs
foreigncommonly
car with
when
U.S.-manufactured
fluid
natural-rubber
seals . The brake
seals swell
is
used
i
n
an
older
foreign
car
and have to be replaced eventuwith
ally.
natural-rubber seals. The seals swell
and have to be replaced eventually.
You wouldn't dare do this with ordinary
glycol-based brake fluid; it would remove
the
There's
to paint
with
You paint.
wouldn't
darenododanger
this with
ordinary
silicone
fluid. Silicone
fluiditiswould
ideal for
cars
glycol-based
brake fluid;
remove
that
have There's
problems
with brake-system
no danger
to paint with
the paint.
contamination
and corrosion.
courtesilicone fluid. Silicone
fluid isPhoto
ideal for
cars
sy Yankee
that
have Silicones,
problemsInc.
with brake-system
contamination and corrosion. Photo courtesy Yankee Silicones, Inc.
Consult the factory shop manual or
your dealer for brake-fluid recomConsult
t h e factory shop manual or
mendations.
your
dealer
brake-fluid
Brake-fluid for
brands
contain recomblends
mendations.
of
chemicals, so their properties
Brake-fluid
change
when brands
mixed. contain
If you blends
must
of
chemicals,
s
o
their
properties
change brands, flush out the
brake
change and
when
mixed.
If you
system
replace
all brake
fluid.must
See
change brands,
flush
out the brake
brake
Chapter
11 for tips
on changing
system
fluid. and replace a l l brake fluid. See
for the
tips highest
on changing
brake
Chapter
If you 11
want
wet boiling
fluid.
point and a different combination of
If you want
highest
wet changboili~~g
properties,
youthe
might
consider
point
and
a
different
combination
of
ing to silicone-based brake fluid. Siliproperties,
you
might
consider
changcone fluid is required to meet DOT 5
ing to silicone-based
specifications.
This brake
fluid fluid.
does Silinot
cone fluid
is required
DOT 5
absorb
moisture
like toa meet
glycol-based.
specifications.
Thisits fluid
does not
fluid.
Therefore,
wet boiling
is
absorb
moisture
like
a
glycol-based
much higher. Also, silicone fluid will
fluid.
Therefore,
its wet
boiling
not damage
the paint
on your
car is
if
much higher.
Also, silicone
fluidfluid
will
brake
spilled.
But glycol-based
not
damage
h e paint
o n your
car if
makes
good tpaint
remover
on some
spilled.
But
glycol-based
brake
fluid
finishes.
makes good paint remover on s o m e
finishes.
A good application for silicone
brake fluid is in antique and collector
A Brakes
good in
application
silicone
cars.
these typesforof cars
are
brake fluid
is in to
antique
and collector
never
subjected
high temperatures
cars.
Brakes in
types oftemperacars are
encountered
in these
racing-high
never
subjected
to
high
temperatures
tures that can cause si licone fl uid to
encountered
in protection
racing-highof the
temperacompress'
And
intertures
that can
silicone isfluid
to
nal parts
fromcause
corrosion
most
compress!
And
protection
of
the
interimportant. Silicone brake nuid serves
nal
parts from
corrosion
is most
this purpose
beautifully,
because
the
important.ofSilicone
brake
serves
absence
moisture
in fluid
the system
this
purposeeliminates
beautifully,
practically
thebecause
chance the
of
absence
of
moisture
in
the
system
dreaded internal corrosion. However,
practically
chance of
for
racing, eliminates
use only atheglycol-based
dreaded
internal
racing brake
fluid. corrosion. However,
forSilicone
racing, fluid
use only
glycol-based
has abeen
tried in
racing
brake
fluid.
raci ng, bu tit has a tendency to gi ve a
Silicone
fluid
been tried
in
spongy
pedal
afterhasexposure
to high
racing, but it has
tendency
to give
temperatures.
Thisa is
due to the
slighta
spongy pedal after
exposure
to fluid
high
compressibility
of silicone
brake
temperatures.
This
is
d
u
e
to
t
h
e
slight
at high temperature. For ordinary
compressibility
of silicone
brake but
fluida
street
driving, this
is not critical,
at
high temperature, For ordinary
racer needs all the brake-system stiffstreethedriving,
ness
can get.this is not critical, but a
racer
needs
the brake-system
stiffSwitching toallSilicone-If
you change
ness
h e can brake
get. fluid, you must first
to silicone
Switching
to the
Silicone-If
change
clean
all of
old fluidyou
from
the
to
silicone
brake
fluid,
you
must
first
brake system to get the maximum
clean
of the
fluid from
the
benefitall of
the oldsilicone
fluid's
brake system
maximum
properties.
The to
bestget
waythe
to accomplish
benefit
of brake-system
the siliconeoverhaul.
fluid's
this
is during
properties.
T
h
e
best
way
to
accomplish
Totally drain and clean out the old
this isIfduring
brake-system
overhaul.
you merely
bleed out
and influid.
Totally
cleanhave
outa mixture
the old
stall
newdrain
fluid, and
you will
fluid.
you
merely
out and
of
the Iftwo
fluids.
Thisbleed
will work,
butinit
stall
new
fluid,
you
will
have
a
mixture
won't be as good as it could be.
of
the two
This will work, but
Keep
Outfluids.
Contaminants-If
youit
won't
as good
as it could
don't be
use
silicone
brake be.
fluid, do
Keep O u t possible
Contaminants-If
everything
to keep water you
out
don't
use
silicone
brake fluid,
do
of the brake fluid. Although
it's more
everything
possible
to
keep
water
out
expensive, always buy brake fluid in
of t h e brake
more
small
cans. fluid.
KeepAlthough
the cansit'sclosed
expensive,
always
buy opened,
brake fluid
in
before using.
Once
don't
small
cans.
Keep
t
h
e
cans
closed
keep an old can of brake fluid around
before
using.
Once opened,
don'tit
long. Use
it immediately
or throw
keep an
old can of bleed
brake some
fluid around
of the
away.
Periodically
long.fluid.
Use This
i t immediately
or throw it
old
removes contaminated
away.
Periodically
bleed
s
o
m e ofreuse
the
fluid from the system. Never
old
fluid.
This
removes
contaminated
dra ined/hi id.
fluid from the system. Never reiise
hained,fluid.
Howe master cylinder has rubber diaphragm built into lid. This keeps air from
contacting
and cylinder
contaminating
brake fluid.
Howe master
has rubber
diaUnfortunately,
caplid.must
removed
to
phragm
built into
This be
keeps
air from
check fluid level,
partially defeating
advancontacting
and contaminating
brake
fluid.
tage
of rubber diaphragm.
unfortunately,
cap must b e removed to
check fluid level, partially defeating advantage Of rubber diaphragm.
If you have a choice, always use a
master cylinder with a rubber diaIf you inhave
choice,
always
phragm
the acap
to seal
the use
fluid.a
master
cylinder
withfrom
a rubber
This
keeps
the fluid
exposurediato
phragm
the cap to
fluid.
air.
Mostin moisture
in seal
brakethefluid
is
This
keeps
the fluid
from
exposure
to
picked
up from
air on
damp
days. All
air.
Most
moisture
brake fluid
is
master
cylinders
andinreservoirs
must
picked
up
from
air
o
n
damp
days.
All
be vented to atmosphere, so don't
master
cylinders
plug vent
holes. and reservoirs must
be Invented
to toatmosphere,
so don't
addition
moisture, brake
fluid
plug
can vent
be holes.
contaminated by other
In addition
moisture,
brake
fluid
materials.
Dirtto can
enter the
system
can
be
contaminated
by
other
when nuid is added to the reservoir. It
materials.
can enter
system
is critical Dirt
to keep
dirt the
from
the
when fluid
added
to the reservoir.
It
system,
so isuse
extreme
care when
is
critical
to
keep
dirt
from
the
working on your brakes. Usual consystem,
s o isuse
when
tamination
by extreme
petroleumcare
products
working
o
n
your
brakes.
Usual
consuch as oil, grease or solvents. Petrotamination
is bymix
petroleum
products
leum
solvents
with brake
fluid
such can
as oil,
gre'aserubber
or solvents.
Petroand
damage
seals in
the
leum
solvents
mix
with
brake
fluid
system. Never clean brake-system
and
can damage
rubber Use
sealsalcohol,
in the
components
with solvent.
system.
cleat7 brake-systet77
brake fluidNever
or brake-system
cleaners.
cot7~ponenfs
alcohol,
Solvents
are with
too solvenf.
difficult Use
to wash
off,
brake
fluid
or
brake-system
cleaners.
and will contaminate brake fluid.
Solvents are too difficult to wash off,
and will contaminate brake fluid.
65
Brake Pedals & Linkages
Brake Pedals 8 Linkages
Bird's-eye view of foot-box area of formula car shows pedals, linkages and brake and
clutch master cylinders. Dual brake master cylinders with remotely adjustable balance bar
is
used. Note
bumper
protecting
master
cylinders
head-on
impact.
Bird's-eye
view
of foot-box
area
of formula
carfrom
shows
pedals,
linkages and brake and
clutch master cylinders. Dual brake master cylinders with remotely adjustable balance bar
is used. Note bumper protecting master cylinders from head-on impact.
Most road-car pedals are hanging-pivots
are above pedal pad-and pedal bracket
doubles
as a pedals
steering-column
bracket.
Most road-car
are hanging-pivots
Device
nearpedal
top of
brake pedal
a meare above
pad-and
pedalisbracket
chanical
switch.
doubles brakelight
as a steering-column
bracket.
Device near top of brake pedal is a mechanical brakelight switch.
66
The brake pedal and linkage transmil force and movement from the
The brake
driver's
footpedal
to and
the linkage
mastertranscymit
force
and
movement
from the
linder(s). Design and construction
of
driver's
to affect
the how
master
cythese partsfoot
greatly
a brake
l i n d e r ( ~operates
) Design
.
and how
construction
system
and
it feels of
to
these
parts
greatly
affect
how
a brake
the driver. The brake pedal must
be
system
operates
andpart
howofit afeels
to
the most
reliable
brake
the driver.
The brake
system
because
failurepedal
can must
mean bea
the most loss
reliable
part .ofThe
a result
brake
complete
of braking
system
because
failure
can
mean
a
can be catastrophic.
complete
loss
of
braking.
The
result
When building a car, you may want
can
be catastrophic.
to design
and fabricate the brake pedal
When
building
a car,
want
and linkage.
These
partsyou
aremay
some
of
to
design
and
fabricate
the
brake
pedal
the components that can be fabricated
and
linkage.
parts This
are some
of
by the
home These
craftsman.
chapter
the components
that can
fabricated
describes
how pedals
and be
linkages
are
by the home
chapter
designed
and craftsman.
fabricated This
for safe
and
describes
how
pedals
and
linkages
are
reliable brake operation. The pedal
designed
and
fabricated
for
safe
and
and linkage are normally designed as a
reliable
operation.
The pedal
part
of a brake
comp lete
brake system.
This
and
linkage
are
normally
designed
as a
is discussed in Chapter 9.
part of a complete brake system. This
is
discussed
in Chapter 9.
BRAKE
PEDAL
A
brake
pedal
BRAKE PEDAL
A brake pedal
is
familiar
to
is familiar
to
&
everyone who has driven a motor
vehicle. Take a good look at the pedal
everyone
has important
driven a design
motor
in a car. who
It has
vehicle.
Take
a
good
look
at
the
pedal
features . Good brake pedals have
the
in
a
car.
It
has
important
design
following characteristics:
features.
Goodbreak
brake or
pedals
have the
• Must not
permanently
following
characteristics:
bend under
the greatest load a driver
Must
can
apply.not break or permanently
bend
under
the greatest
driver
• Must
be stiff
and notload
flexa during
can
apply.
hard braking.
befree
stiffofand
not flex
during
• Must
Must be
excessive
friction
.
hard
braking.
• Must provide proper leverage at
Mustcylinder.
be free of excessive friction.
master
Must
provide
proper leverage
at
• Must match
requirements
of driver
master
cylinder.cylinder, linkage and
and master
Must match requirements of driver
system.
andA brake
masterpedal
cylinder,
and
consistslinkage
of the arm,
system.
pad and pivot attachments. The pedal
brake pedal
consists This
of the
arm,
is A
connected
to a linkage.
linkage
pad
and
pivot
attachments.
The
pedal
transmits force and movement to the
is
connected
to aThe
linkage.
Thiscan
linkage
master
cylinder.
linkage
be as
transmits
force
and
movement
the
simple as a straight pushrod, ortomore
master
cylinder. The linkage can be as
complex.
simple
as a straight
pushrod, to
or bendmore
The pedal
arm is subjected
complex.
ing loads from the driver 's foot. It is
The pedal
arm is subjected
to bendusually
constructed
of steel plate.
The
ing loads
driver's
is
arm
may from
havethe
holes
in itfoot.
for Itthe
usually
constructed
of
steel
plate.
The
pivots. Often pivot bushings are conit for the
arm
have steel
holes intubes-pivot
tainedmay in
pivots.
Often pivot
bushings
housings-that
are inserted
in are
the conarm
tained
in in place
steel . A tubes-pivot
and welded
good pedal
housings-that
inserted
in the arm
design
will not are
have
welds completely
and
welded
in
place.
A
good
across the arm, particularly atpedal
the
design
have iswelds
pivots. will
A not
weld
a completely
source of
across
the arm, riser-at
particularlya critical
at the
weakness-stress
pivots.
A
weld
is
a
source
of
area of the arm.
weakness-stress
riser-at
a
critical
A pedal arm is usually straight
- the driver's seat. If
area
the arm.
whenofviewed
from
is usually
straight
it A
has pedal
bends arm
or curves
in it , the
arm
when
viewed
from
the
driver's
seat. If
tends to twist when the pedal
is
it
has bends
or curves
it, arm
the arm
pushed
. Twisting
in the in
pedal
can
tends movement
to twist when
is
create
at thethepadpedal
, giving
pushed.
Twisting
the pedal armAlso,
can
the driver
feel ofin sponginess.
create movement
giving
stresses
in a pedal at
willthe
be pad,
higher
due
the
driver
feel
of
sponginess.
to twisting forces. To overcome Also,
these
stresses
in pedals
a pedalwith
will be
higher
due
problems,
bends,
offsets
to twisting
forces.
overcome
these
or
curves must
be To
fabricated
of heavproblems,
ier
material.pedals with bends, offsets
or Acurves
fabricated
good must
pedalbearm
should ofbeheavdeier
material.
signed to take side loads and forward
A good
be deloads.
Side pedal
loads arm
on a should
pedal arm
are
signed
to
take
side
loads
and
forward
most likely to cause failure , because
loads.arms
Side are
loads
on alaterally.
pedal arm
are
most
weaker
Pedals
most
likely
to
cause
failure,
because
shou ld be installed so they won't be
most
weaker
loadedarms
fromarethe
side. laterally.
A brake Pedals
pedal
should
be
installed
so
won'tleg.be
should be in line with thethey
driver's
loaded
the side.
brake
pedal
Pedalsfrom
in most
road A
cars
are made
should
be
in
line
with
the
driver's
leg.
of steel. This gives a pedal the highest
Pedals in most road cars are made
of steel. This gives a pedal the highest
Pedal Bracket
Pedal Bracket
Pivot Housing
Master-Cylinder
Pushrod
Master-Cylinder
Pushrod
Pad
Hanging pecial has pivot housing at top of arm. On many pedals, pivot housing is a steel tube
welded into a hole in pedal arm. Pivot bushing is inside pivot housing. For rear-mounted
master
master-cylinder-pushrod
pivotOn
installs
pivot,
70. is a steel tube
Hangingcylinder,
pecial has
pivot housing at top of arm.
manyabove
pedals,
pivotpage
housing
welded into a hole in pedal arm. Pivot bushing is inside pivot housing. For rear-mounted
master cylinder, master-cylinder-pushrod pivot installs above pivot, page 70.
stiffness and strength of any low-cost
material. Older cars often used steel
stiffness
strengthbut
of modern
any low-cost
forgings and
for pedals,
cars
material.
Older
cars
often
used steel
steel
use parts cut or stamped from
forgings
for cars
pedals,
but modern
cars
plate. Race
sometimes
use lightuse
parts
cut
or
stamped
from
steel
weight materials such as aluminum or
plate. Race cars
sometimes use
lighttitanium.
Consequently,
race-car
weight
materials
such
as
aluminum
or
pedals are expensive when compared
titanium.
Consequently,
race-car
to those for road cars. However, steel
pedals
arethe
expensive
whenItscompared
will offer
best results.
stiffness
to
for road
cars.
However,
is as
high assteel
any
for those
a given
weight
will
the bestand
results.
stiffness
it isItseasier
to
otheroffer
material,
for
a givenDesigning
weight is as
as any
fabricate.
an high
aluminum
other
material,
and itbecause
is easier
to
be difficult
of its
pedal can
fabricate.
Designing an aluminum
low
stiffness.
pedal
difficult
because
its
be of
rigid.
A can
pedalbe arm
must
low
stiffness.
Therefore, it usually has a deep cross
A pedal
must has
be arigid.
section.
A roadarm
car usually
flatTherefore,
has a deep cross
cross
plate or itanusually
open-channel
section. Abutroad
car usually
has ause
flat-a
section,
a race
cars often
plate
or
an
open-channel
cross
tube. Tubular pedals are lighter for a
section,
but a race
cars often
useex-a
given stiffness.
However,
they are
tube.
Tubular
pedals toaremass
lighter
for a
pensive
and difficult
produce.
given
stiffness.
However,
they
are
exWith a tubular pedal, a thin-wall tube
pensive
and
difficult
to
mass
produce.
can be used and still have enough
With a tubular pedal, a thin-wall tube
stiffness.
canA be
used
stillbehave
enough
pad and
should
shaped
to fit
pedal
stiffness.
the foot. A tiny pad is hard to push
A pedal
padand
should
to off
fit
with
comfort
your be
footshaped
can slip
A tiny
padpad
is hard
to push
the foot.
is about
shoe
easily.
A good
pedal
with comfort
and
yourallows.
foot can
off
width;
wider if
space
A slip
rubber
easily.
A
good
pedal
pad
is
about
shoe
pad is used on road cars for aesthetics,
A rubber
width; wider
if space
comfort
and grip.
Forallows.
race cars,
a texpad
used on
cars for
is used
for aesthetics,
maximum
turedis metal
padroad
comfort
andisgrip.
For race
cars, a texespecially
important
in
grip.
This
tured metal pad is used for maximum
grip. This is especially important in
Small pedal pads are in a Formula Ford
road-racing car. These little single-seat
racers
have pads
barelyare
enough
room for Ford
the
Small pedal
in a Formula
driver's
feet,car.
making
small
pedal
pads a
road-racing
These
little
single-seat
must.
surfaces
are made
racersNonskid
have barely
enough
roomfrom
for exthe
panded
pads.pedal pads a
driver's metal
feet, welded
makingtosmall
must. Nonskid surfaces are made from expanded metal welded t o pads.
open race cars that run in the rain.
Some race-car pedals have an adopen racepad,
cars that
run in the
justable
adjustable
to rain.
suit the
Some
race-car
pedals
have
an adare
driver. Seats in many race cars
justable
pad, adjustable
adjustable pedal
to suit pads
the
fixed, so
driver.
Seats
teo in many race cars are
com
pensa
fixed,
so
adjustable
pedal
With adjustable
pads, you
can pads
vary
compensate.
the distance between the steering
Withand
adjustable
pads,This
youwill
canaffect
vary
wheel
brake pedal.
the
distance
between
the
steering
arm position when the driver is seated
wheel
This adjustable
will affect
in the and
car. brake
A racepedal.
car with
arm
position
when
the
driver
is seated
pedal pads and seat can be made
to
in the
A race
carperfectly.
with adjustable
sui
t thecar.
driver
nearly
pedal pads and seat can be made to
suit the driver nearly perfectly.
Room and weight are not a problem in this
racing stock car, allowing big and sturdy
pedal
Such pedals
not fit
in a
Room pads.
and weight
are not would
a problem
in this
cramped
Grand
Prix-car
cockpit.
racing stock
car,
allowing
big and sturdy
pedal pads. Such pedals would not fit in a
cramped Grand ~ r i x - c acockpit.
r
Pedal pad is adjusted by releasing jam nut
and screwing pad in and out. Pad is welded
to
a bolt,
threads
a tapped
Pedal
padwhich
is adjusted
byinto
releasing
jamtube
nut
at top
of pedalpad
arm.
Moreout.
than
l-in.
of adand
screwing
in and
Pad
is welded
justment
movinginto
driver's
seat. tube
to a bolt, requires
which threads
a tapped
at top of pedal arm. More than 1 -in. of ad-
justment
requires moving
driver's
If heel-and-roe
brakeandseat.
accel-
erator-pedal operation is desired, the
heel-and-toe
and acceltwoIf pedals
should brakebe positioned
no
erator-pedal
is desired,
the
I-I/2-in. apa
rt laterally.
more than operation
two pedals
should
be positioned
be adjus ted no
so
Also,
the pedals
should
more
than
1-112-in.
apart
laterally.
that during hard braking , the
brake
Also,
pedals
adjusted
so
to should
about be
1/4-in.
above
pedal the
travels
that
during hard
braking, the brake
the accelerator
pedal.
pedal travels to about 1/4-in. above
the
accelerator
pedal.
PEDAL
FORCES
The two forces a pedal designer
PEDAL
FORCES
must
consider
are:
twoforce
forces
n everdesigner
be ap• The
Highest
thata capedal
must consider are:
Highest force that can ever be ap67
ti-*hh,
b*
4
Once wheels are locked, driver's strength is the only thing limiting brake-pedal force. As
fear increases, the harder he pushes. This condition represents the maximum force that
. Once
can bewheels
appliedare
to a
brake driver's
system. strength
Brake-pedal
force
maximum-deceleration,
conlocked,
is the
onlyduring
thing alimiting
brake-pedal force.
As
trolled
stop is much
fear
increases,
the lower.
harder he pushes. This condition represents the maximum force that
can be applied to a brake system. Brake-pedal force during a maximum-deceleration, controlled stop is much lower.
plied to a pedal.
• Force normally applied in a hard
pliedattomaximum
a pedal. deceleration.
stop
Force
hard
These normally
two forcesapplied
are not inthea same.
stop
at maximum
Maximum
forcedeceleration.
is considerably
Thesethan
twothe
forces
not theapplied
same.
higher
force are
normally
Maximum
force
is
considerably
during a hard stop. To keep the terms
higher thanthetheforce
forcenormally
normally applied
applied
separate,
during aahard
To iskeep
the terms
during
hardstop.
stop
called
pedal
separate,
normally
applied
effort. Thistheis force
the force
applied
to a
during
hard
stopwhen
is called
pedal
pedal bya the
driver
he tries
to
is the force
applied In
to aa
efforl. atThis
stop
maximum
deceleration.
pedal
by pedal
the driver
he tries
to
race car,
effort when
is applied
by the
stop at almost
maximum
In a
driver
everydeceleration.
time he brakes
race
car,This
pedalis effort
applied
by thea
the car.
rarelyisthe
case with
driver
almost
every
time
he
brakes
road car.
theDuring
car. This
rarely the case
an isemergency,
the with
drivera
road car.stop the car at maximum decelshould
During
an the
emergency,
theverge
driver
eration
with
tires on the
of
should
stop
the
car
at
maximum
decellockup. Often, though, a driver
in
eration
theabout
tires on
the vergethe
of
trouble with
forgets
controlling
lockup.
Often,he though,
a driver
in
car.
Instead,
panics and
jams on
trouble
forgets
about
controlling
the
the brakes as hard as he can and locks
car.
Instead,Often
he panics
and
jams and
on
the wheels.
he loses
control
the brakes
hard
as heiscan
and maxilocks
skids.
This as
type
of stop
where
the
losesoccurs.
control The
and
mumwheels.
force Often
on a he
pedal
skids.
This
type
of
stop
is
where
maxipedal and linkage must be designed
on ora pedal
occurs. bend
The
mum
not toforce
break
permanently
pedal
and condition.
linkage must be designed
under this
not
break or permanently
bend
Pedalto Effort-A
high-performance
under
this
condition.
brake system usually is designed for
Pedal 75-lb
Effortpedal
-A effort
high-performance
about
at maximum
brake system This
usually
is designed
for
deceleration.
feels
OK to most
about
pedal effort
maximum
people.75-lb
Anyone
personat can
easily
deceleration.
This his
feels
apply
75 lb with
leg.OK
If to
youmost
are
people.
Any
one
person
can
designing a truck or race car, youeasily
may
Ib with
his leg.
you are
apply
wish to75use
a higher
pedalIf effort.
A
designing
a truck
you may
100-lb pedal
effortoris race
still car,
manageable,
wish
use like
a higher
A
but it tofeels
a hardpedal
push.effort.
I don't
100-lb
pedal
effort
is
still
manageable,
recommend usin!1 more than 100 lb.
I don't
but it there
feels would
like a hard
Then
not bepush.
any reserve
recommend using more than 100 lb.
Then there would not be any reserve
68
force left for brake fade or other
system failures .
force
for brake
other
Mostleftpassenger
carsfade
haveor powersystem
failures.
assisted brakes. With power assist,
Most
passenger
powerpedal
effort
is usuallycars
less have
than 50
lb.
assisted
brakes.
With
power
Maximum Pedal Force-A assist,
heavy
pedal
usuallypush
less with
than 50
Ib.
personeffort
can iseasily
a force
Maximum
Pedal
Force-A
heavy
greater than his weight-about 300 Ib
person
canman.
easilyIf push
with aquickly
force
for
a large
he stomps
greater
than
his
weight-about
300
Ib
on the pedal, the effect of the sudden
for
a large
man.
If he stomps
force
further
increases
stress quickly
on the
on
the Engineers
pedal, the know
effectthat
of the
pedal.
if asudden
load is
force
further
increases
stress
applied quickly, stress on a on
partthe
is
pedal. Engineers
know pedals
that if aare
loaddeis
doubled.
Most brake
applied toquickly,
stressthe
on maximum
a part is
signed
take twice
doubled.
brake
pedals
areI use
de;
force
that Most
a strong
leg can
apply.
twice
the
maximum
signed
to
take
600 Ib for designing pedals.
force
a strong legpedal
can apply.
I use
Safetythat
Factor-The
should
be
600
Ib for designing
pedals.
designed
to withstand
a force much
Safety than
Factor-The
pedal force
should
be
higher
the maximum
. The
designed
to
withstand
a
force
much
ratio of the force required to break a
higher
the maximum
force.
The
part
to than
the maximum
applied
load
is
ratio ofthe
thesafety
forcefactor.
required
to abreak
called
I use
safetya
part toofthe
maximum
applied
load
factor
3 on
critical parts
such
as isa
safe@
factor.
I
use
a
safety
called
the
brake pedal. This means the part is defactor of
on critical
parts
suchthree
as a
signed
to 3break
at a load
at least
brake pedal.
This means
the applied
part is detimes
the maximum
force
to
signed
to break
at a loadthe
at least
three
the part.
Therefore,
breaking
times theformaximum
forceshould
applied
strength
a brake pedal
be to
at
the
part.
Therefore,
the
breaking
least 1800 lb, or 3 X 600 lb .
strength
a braketo pedal
be at
If you for
wanted
test should
your brakeleast
1800
Ib,
or
3
X
600
Ib.
pedal design, apply an 1800-lb force
youpadwanted
to test your
onIfthe
in a direction
in linebrakewith
pedalforce
design,
the
that apply
wouldanbe 1800-lb
applied force
by a
on
the padfoot.
in a Ifdirection
in line
with
person's
the pedal
doesn't
the
force
would
be applied
by a
break,
thethat
safety
factor
is adequate.
person's
foot.
If
the
pedal
doesn't
You may bend the pedal doing such a
break,never
the safety
factor inis aadequate.
testuse a pedal
car after
You
may
the strength
pedal doing
such a
testing
its bend
breaking
.
test-never
use
a
pedal
in
a
car
after
The master-cylinder pushrod must
testing
its
breaking
strength.
withstand the maximum pedal force
The master-cylinder pushrod must
withstand the maximum pedal force
Bird's-eye view of formula-car pedal box:
Note that pedal pad is not centered on
pedal
arm. view
This oftwists
pedal pedal
arm when
Bird's-eye
formula-car
box:
driver
pushes
on pad.
tubular arm
Note that
pedal
pad Although
is not centered
on
can withstand
thistwists
twisting
load,arm
pedal
aspedal
arm. This
pedal
when
semblypushes
would on
be pad.
stronger
if padtubular
and pedal
driver
Although
arm
arm were
centered.
can
withstand
this twisting load, pedal as-
sembly would be stronger if pad and pedal
times
thecentered.
pedal ratio. Pedal ratio can be
arm
were
obtained by dividing pedal travel at
times
the pad
pedalbyratio.
Pedaltravel.
ratio can
be
the
foot
pushrod
Pedal
obtained
by
dividing
pedal
travel
at
ratio is discussed in more detail on the
the foot padpage
by .pushrod
Pedal
following
Also, travel.
a push
rod
ratio is discussed
more detail
should
always be in
straight.
One on
thatthe
is
following
page.
Also,
a
pushrod
straight is many times stronger than a
should
be straight. One that is
bent or always
offset rod.
straight
is many totimes
stronger
In addition
normal
load,than
thea
bent
offset
pedalormust
berod.
able to resist some side
In addition
normal
load,
the
load.
A driver'sto foot
is not
always
pedal
must
be
able
to
resist
some
side
aligned with the pedal pad. The worst
load. occurs
A driver's
not always
case
wherefoot
the isdriver's
foot
aligned
with the
pad.This
The puts
worsta
hangs halfway
offpedal
the pad.
case force
occurs
the arm.
driver's
foot
side
intowhere
the pedal
I recomhangs
halfway
off
the
pad.
This
puts
mend using a side load of 200 lb ona
side
force pad
intointhe
pedal arm.
I recomthe pedal
addition
to the
600-lb
mend using
side
of 200
Ib on
forward
load.a If
youload
apply
the safety
the
pedal
pad
in
addition
to
the
600-lb
factor of of 3, the pedal should not
forward
load. Ifwith
youa apply
break if tested
600-lbthe
sidesafety
load
factortheof pad.
of 3, Note:
the pedal
not
on
The should
side load
break ifbetested
withat athe
600-lb
load
should
applied
sameside
time
as
othe
n forward
the pad.
Note: The side load
load.
should
be applied
the same
timeyou
as
All this
suggestsat that
perhaps
the forward
should
leaveload.
brake-pedal design to an
All this Ifsuggests
engineer.
you arethat
notperhaps
trainedyou
in
should
leave
brake-pedal
design
to an
stress analysis, a mistake here could
engineer.
If option
you areis not
trained
in
be fatal. An
to use
a pedal
stress
analysis,
a mistake
could
that fits
from another
car. here
All pedals
be fatal.
An using
optionsimilar
is to use
a pedal
are
designed
techniques.
that
fits
from
another
car.
All
Safety factors may vary, but the pedals
maxiare
designed
techniques.
mum
force ausing
pedalsimilar
can withstand
is
Safety the
factors
may
but the
maxiabout
same
forvary,
all cars.
Be aware
mum
force from
a pedal
cancarwithstand
is
that a pedal
a road
will probaabout
the
same
for
all
cars.
Be
aware
bly be stronger than a race-car pedal.
that a pedal
fromdesigners
a road cartry
willtoprobaMany
race-car
save
bly be stronger than a race-car pedal.
Many race-car designers try to save
Bad pedal design on homemade race car
has pedal arm off-center to pad and pivot
housing.
pushed
on, twistrace
of arm
Bad pedalWhen
design
on homemade
car
causes
excessive
flexibility
and
has pedal
arm off-center
to pad
andhigher
pivot
stresses.
If arm were
moved
right,ofpedal
housing. When
pushed
on, to
twist
arm
would beexcessive
stiffer and stronger.
causes
flexibility and higher
stresses. If arm were moved to right, pedal
would be stiffer and stronger.
weight at the expense of strength.
If you insist on designing your own
weight
at the follow
expense
of strength.
brake pedal,
these
rules:
on designing
Doyou
not insist
weld across
a pedal your
arm. own
• If
brake
pedal,
rules: when
• Make
the follow
pedal these
arm straight
D o not
weldtheacross
a pedal
viewed
from
driver's
seat.arm.
Make
the
pedal
arm
straight
when
• Use steel, not aluminum or other
viewedalloys.
from the
driver's
light
Steel
givesseat.
maximum
Use steel,
not of
aluminum
or Weldother
stiffness
and ease
fabrication.
light
alloys.
Steel
gives
maximum
ing drastically weakens aluminum.
stiffness
andtheease
of fabrication.
Weld• Position
pedal
arm in the center
ingthe
drastically
aluminum.
of
pad - notweakens
off to one
side.
Position the pedal arm in the center
of
the pad-not
off to one side.
PEDAL
PIVOTS
Pivots in brake pedals should have
PEDAL
plastic orPIVOTS
bronze bushings to reduce
Pivots in
brake bushings
pedals should
have
friction.
Plastic
are often
plastic
or road
bronzecars
bushings
to reduce
used on
to reduce
cost;
friction.
Plastic bushings
often
bronze bushings
are found are
on some
used
on
road
cars
to
reduce
race cars. The best pedal pivots cost;
have
bronze
bushings
are found
o n plastic
some
provision
for lubrication.
Most
race cars.are
T hdesigned
e best pedal
pivots withhave
bushings
to operate
provision
for
lubrication.
Most
plastic
out lubrication, but this does not
bushings
aremaximum
designed durability.
to operate withalways
give
outAvoid
lubrication.
but that
this use
doesunlunot
pedal pivots
always
maximum
durability.
bricatedgive
clevis
pins or
bolts. Some
Avoid
pedalhave
pivots
unlubrake
pedals
beenthat
so use
designed.
bricated
clevis
pins
or
bolts.
S
o mofe
They work for a while, but the lack
brake pedals
havearea
been
designed.
adequate
bearing
andsolubrication
They
for athe
while,
buttothe
lackout
of
usuallywork
causes
pivot
wear
adequate
bearing
area
and
lubrication
rapidly. Then the pedal gets loose and
usually causes
theextra
pivot pedal
to wear
out
sloppy,
requiring
moverapidly.
h e n up
thethe
pedal
loose
and
ment
to Ttake
slop.gets
Pedal
movesloppy,
ment is requiring
a valuable extra
item. pedal
Don't movewaste
ment
to
take
up
the
slop.
Pedal moveit with potentially sloppy pivots.
ment is a valuable item. Don't waste
it with potentially sloppy pivots.
Spherical bearings on master-cylinder pushrods minimize friction and wear. Neal Products
pedal uses a balance bar with special spherical bearing at each end. Balls in spherical bearings are pinned
to on
allow
motion in onlypushrods
one direction.
Ordinary
would
Spherical
bearings
master-cylinder
minimize
frictionspherical
and wear.bearings
Neal Products
allow
ends
to cock,
with
potentially
disastrous
results.
pedal rod
uses
a balance
bar
with
special spherical
bearing
at each end. Balls in spherical bearings are pinned to allow motion in only one direction. Ordinary spherical bearings would
allow rod ends to cock, with potentially disastrous results.
If you have a car with sloppy or unbushed pedal pivots, consider modifyyou have
a car have
with sloppy
or un-a
If you
to enlarge
ingIf them.
bushed
pedal
pivots,
consider
modifyhole to install a bushing, make sure
ing them.
you have
to enlarge
a
you
don't If
weaken
a critical
area. If
hole are
to install
a bushing,
you
uncertain,
leave it make
alone.sure
Or,
you
weakendoa acritical
area. If
have don't
an engineer
stress analysis
you
are
uncertain,
leave
it
alone.
Or,
of the modification. If you don't bush
havepivots,
an engineer
a stress them
analysis
the
at leastdolubricate
at
of the modification.
If youwear.
don't bush
regular
intervals to reduce
the pivots, at least lubricate them at
regular
PEDALintervals
RATIO to reduce wear.
The force required on the masterPEDAL piston
RATIOis usually much higher
cylinder
T
h
e
force
required
o n the masterthan the pedal
effort supplied
by the
cylinder
piston
is
usually
muchact
higher
driver. Thus, the pedal must
as a
than
pedal effort
supplied
by the
the force
supplied
by
lever the
to increase
driver.
Thus, The
the pedal
must act
the driver.
leverage
of as
thea
lever
to increase
the force
pedal-pedal
rario-is
alsosupplied
known by
as
the
driver.
T
h
e
leverage
of the
mechanical advantage. Pedal ratio
for
pedal-pedal
as
manual
brakesratio-is
is aboutalso
5 toknown
1; power
mechanical
advantage.
Pedal
pedal
ratios are
about 3 to
1. ratio for
1; powera
manual
is about
If youbrakes
plan to
design 5 orto modify
3
to
1.
pedal
ratios
are
about
brake system, you need to determine
you plan
design
modify
theIf pedal
ratio.toThere
areorthree
waysa
brake
you need
determine
to
do system,
this. Choose
the to
method
that
the pedal
There
works
best ratio.
for you.
Theyare
are:three ways
to
do this. forces.
Choose the method that
• Measure
works
best
for
you. They are:
• Measure movements.
Measure
forces.
• Measure brake pedal and linkage
Measure movements.
geometry.
MeasureForces-If
brake pedal
and measure
linkage
Measure
you can
geometry.
the force on the pedal pad and the
M e a s u r e Forces-If
simultaneous
force you
on can
the measure
masterthe
force
o
n
the
pedal
pad
cylinder piston, the pedal ratioand
can the
be
simultaneous force o n the mastercylinder piston, the pedal ratio can be
Typical road-car pedal design; pivot bolt
and bushing are removed. Plastic bushings
last longer
if greased
occasionally.
Typical
road-car
pedal
design; pivot bolt
and bushing are removed. Plastic bushings
last longer if greased occasionally.
calculated from this simple formula:
calculated from
F this simple formula:
~
Fpp
F M
FMC
Force
on~ master cylinder in
Pedal=ratio
=pounds
FPP
FMc= =Force
Force
on master
Fpp
on pedal
pad in cylinder
pounds in
Pedal ratio
=
pounds
Forces
are measured
in inpounds;
Fpp= Force
on pedal pad
pounds the
pedal ratio is just a number. If you
Forcespush
are on
measured
pounds;
could
the pedalinwith
a scalethe
or
pedal
ratio isto just
a number.
you
instrument
measure
force,If you
could pushsimultaneously
o n the pedal with ameasure
scale or
could
instrument
to
measure
force,
you
hydraulic-system pressure. If you
could
measure
know the simultaneously
master-cylinder-piston
area,
hydraulic-system
pressure.into
If force
you
pressure
can be converted
know
the
master-cylinder-piston
area,
on the piston.
pressure can be converted into force
o n the piston.
69
FMc*q
~ ~ ~~ Master-Cylinder
i
-
<+-:/,
..;---'
~
I
-"1- ____ .1
I
Position
Master-Cy linder
Position
Pedal Bracket
FMC = Force on Master Cylinder
F pp = Force on Peda I Pad
FMc = Force on
Master Cylinder
FMC
Fpp =Ratio
Force=
on-Pedal
Pad
Pedal
-
Pedal Ratio =-
Fpp
Fpp
F~~
FPP
I V
Pedal ratio can be found by simultaneously measuring forces at pedal pad and master
cylinder. Small spring scales may be used for this. Disconnect master-cylinder pushrod so
it
doesn't
readings.
sure one scale
lines up with
pushrod
and other
scale
with
Pedal
ratioaffect
can be
found Make
by simultaneously
measuring
forces
at pedal
pad and
master
line-of-action
driver's
leg. may
See be
drawing
at right.
Pushrod force
divided by pedal
force so
is
-cylinder.
Smallofspring
scales
used for
this. Disconnect
master-cylinder
pushrod
pedal
ratio.affect readings. Make sure one scale lines up with pushrod and other scale with
i t doesn't
Steel tape is used to measure pedal-pad
movement. Measure movement of mastercylinder
piston
at same
time. Pedal
travel
Steel tape
is used
to measure
pedal-pad
divided by pushrod
travel
is pedalofratio.
movement.
Measure
movement
master-
cylinder piston at same time. Pedal travel
divided by pushrod travel is pedal ratio.
line-of-action of driver's leg. See drawing at right. Pushrod force divided by pedal force is
pedal ratio.
)~- - ---J
L MasterCylinder
Position
Pedal ratio is equal to AlB. Pedal pivot is at point P. Force F, applied by driver, is multiplied
by pedal ratio to produce a larger force at master cylinder. If driver applies 50 Ib and pedal
ratio
4, force
at to
master
cylinder
is is200
lb. Trick
in measuring
A multiplied
and B is
Pedalis
ratio
is equal
A/B. Pedal
pivot
at point
P. Force
F, applieddistances
by driver, is
measuring
them
to line-of-action
of forces
. If driver applies 50 Ib and pedal
by
pedal ratio
t operpendicular
produce a larger
force at master
cylinder.
ratio is 4, force at master cylinder is 200 Ib. Trick in measuring distances A and B is
measuring them perpendicular to line-of-action of forces.
The force method requires special
measuring equipment. So skip this
The force
method
requires
method,
unless
you have
the special
equipmeasuring
equipment.
So
skip and
this
ment that will measure force
method, unless you have the equippressure.
ment
that Movements-Pedal
will measure force ratio
and
Measure
pressure.
can be found by measuring movement
Measure
Pedal ratio
at
the pedalMovementspad and master-cylinder
can
be found
by measuring
piston.
Don't
include movement
movement
at
the pedal
pad up
andclearance
master-cylinder
needed
to take
or free
piston.
play.
The Don't
formula include
for pedal movement
ratio using
needed to take
movements
is: up clearance or free
play. The formula for pedal ratio using
Pedal ratio = is:
~pp
movements
MC
M
Pedal
ratio = 2
Mpp = Movement
of pedal pad in
MMC
inches
Mpp == Movement
pad of
in
MMC
MovementOf in inches
inches
master-cylinder
piston for a single or a
MMc =
Movement
of
tandem
master
cylinder, inor inches
movement
master-cvlinder
tonbalance
for a sinale
or aa
center pivot ofist
the
bar for
of
tandem
master
cylinder,
or mo;ement
car
with dual
master
cylinders.
of center pivot of the balance bar for a
car with dual master cylinders.
70
To use this formula , you must be
careful to get the direction of moveTo use
this formula,
must be
ment
right.
Pedal-pad you
movement
careful
to
get
the
direction
of
moveshould be measured through the
full
ment
right.
Pedal-pad
movement
stroke of the pedal. You will have to
should
be measured
through
thefrom
full
open a bleeder
or drain
the fluid
stroke
of the system
pedal. You
have
to
the hydraulic
to dowill
this
. Start
open
a
bleeder
or
drain
the
fluid
from
the measurement from the point
the hydraulic
system are
to do
this.out
Start
where
all clearances
taken
of
the linkage
measurement
from the
the
and the pushrod
just point
starts
where
all the
clearances
are taken piston
out of.
to move
master-cylinder
the
linkage
and
the
pushrod
just
To hold the pedal in this position,starts
put
move between
the master-cylinder
piston.
ato spacer
the pedal stop
and
To
hold the pedal in this position, put
pedal.
a spacer
thepoint,
pedal move
stop and
Startingbetween
from this
the
pedal.
pedal all the way to the floor. Measure
Starting
from this
point, full
move
the
piston
movement
through
travel
pedal
the way
to thethe
floor.
Measure
of
the all
pedal.
Indicate
starting
and
piston
movement
fullpad
travel
stopping
points ofthrough
the pedal
by
of
the
pedal.
Indicate
the
starting
and
placing a piece of plywood or cardstopping
points of
pad by
board alongside
thethe
padpedal
and making
placing a piece of plywood or cardboard alongside the pad and making
' M
Pedal Ratio =--EE..
MMC
Mpp = Pedal-Pad Movement
MMC = Master-CylinderPiston Movement
Mpp = Pedal-Pad
Movement
MMC= Master-C.ylinderPedal ratio
can Movement
be determined from simulPiston
taneous
pedal-pad
and
mastercylinder-piston
Measure
Pedal ratio can bemovements:
determined from
simullarge movements
to keep measuring
errors
taneous
pedal-pad
and
mastersmall. Measure movements
as shown.
cylinder-piston
movements:
Measure
large movements t o keep measuring errors
small. Measure movements as shown.
marks on it. Total movement of the
pedal pad between the starting and
marks onpoints
it. Total
of the
stopping
is Mmovement
pp , or the number
pedal
the starting
and
to usepad inbetween
the formula.
MasterM,,,or the
stopping points is
cylinder-piston
movement
is number
how far
to
the formula.
the use
pistonin moved
down theMasterbore.
cylinder-piston
movement
is howis far
How to measure this movement
ilthe
piston
moved down the bore.
lustrated
above.
How
to measure
this ratio
movement
is ilFinding
the pedal
by measurlustrated
above.
ing movements gives an average pedal
Finding
ratio
measurratio
for thethe
fullpedal
stroke.
It isbynot
a very
ing movements
givesThe
an average
pedal
accurate
number.
problem
is
ratio
for
the
full
stroke.
It
is
not
a
very
pedal ratio changes as the pedal
accurate
Theaccurate
problem
is
moves. Tonumber.
get a more
pedal
pedal
ratio
changes
as
the
pedal
ratio, use the method described
moves. To get a more accurate pedal
ratio, use the method described
below. This uses the geometry of the
pedal and linkage. It can give instantabelow. pedal
This uses
the
neous
ratio the
at geometry
any point of
along
pedal
and
linkage.
It
can
give
instantathe pedal movement.
neous pedal
ratio at any point along
Pedal
Geometry-Dimensions
of a
the pedal
movement.
pedal
determine
its ratio. Formulas to
Pedal
use
for Geometry-Dimensions
various pedal mountingsofarea
pedal
determine
its ratio.
Formulas
to
given in the drawing
at left.
Use the
use
for
various
pedal
mountings
are
formula that matches your pedal
given. in
Use the
setup
In the
eachdrawing
formulaatis left.
a distance
A
formula
that
matches
your
pedal
and B. Measuring these distances
acsetup. Iniseach
is a distance
curately
the formula
only problem.
To do A
it
and
Measuring
these
distances
acright,B. you
need to
know
the linecurately
only problem.
To do it
of-action is
of the
the forces
on the pedal.
right,
you
need
to
know
the
lineThe line-of-action is drawn from
of-action
of
the
forces
on
the
pedal.
the driver's hip to the ball of his foot.
The line
line-of-action
drawn from
This
changes, is
depending
on
the driver's
hip to
his foot.
where
the pedal
padthe
is ball
in itsoftravel.
To
This
linematters,
changes,
on
simplify
pick depending
a spot in the
where
the
pedal
pad
is
in
its
travel.
To
movement of the brake pedal to measimplify
matters, pick a stick
spot toinit.the
sure
lines-of-action-and
movement
of the brake
to meaThe line-of-action
for pedal
a pushrod
is
sure
lines-of-action-and
stick
to it.
always a straight line joining the
ends
for pushrods
a pushrodare
is
of The
the line-of-action
pushrod. Bra ke
always
a
straight
line
joining
the
ends
usually straight, so it is easy to
of the pushrod.
pushrods
determine.
If yourBrake
pushrod
makes are
an
usually
straight,
so
it
is
angle with the pedal arm, be easy
sure to
to
determine.
If yourBpushrod
measure distance
at a 90°makes
angle an
to
angle
with the
pedal
arm, be nearby.
sure to
the pushrod.
This
is illustrated
measure
distance B at a 90" angle to
If the brake-pedal linkage has an inthe
pushrod.
This is illustrated nearby.
termediate mechanism, such as a
If
the
brake-pedal
linkage
an beinbellcrank, determining
pedalhas
ratio
termediate
mechanism,
such
as
comes more complicated. The pedala
bellcrank,
determining
ratio
beratio
for the
pedal itselfpedal
can be
meascomes
more complicated.
pedal
ured using
the methodsThealready
ratio for the
pedalyou
itselfmust
can be
discussed
. Then
findmeasthe
ured
using
the
methods
already
leverage of the rest of the linkage.
discussed.
Then youthemust
Call
that leverage
ratiofind
of the
the
leverage Pretend
of the rest
the into
linkage.
linkage.
the of
force
the
Call
thatis leverage
ratio
of the
linkage
the force the
from
a driver's
linkage.
Pretend
the force
leg , and treat
the linkage
the into
samethe
as
linkage
is
the
force
from
a
driver's
you would a pedal. When you find
the
leg, and" treat
linkage
the, multiply
same as
"pedal
ratio the
of the
linkage
you
a pedal.
When
youto find
it bywould
the ratio
for the
pedal
get the
the
"pedal"
ratio
of
the
linkage,
multiply
total brake-pedal ratio. The accomipanying
t by thedrawing
ratio forshows
the pedal
get the
how atocomplex
total brake-pedal
The accomsystem
is analyzedratio.
for overall
pedal
panying
drawing shows how a complex
ratio.
system
analyzed
for overall
pedal
and linkage
geomet
ry,
Using ispedal
ratio.
pedal ratio can be found for a particupedal
linkageYou
geometry,
larUsing
position
of and
the pedal.
should
pedal ratiopedal
can be
found
for a particumeasure
ratio
at several
posilar
position
the pedal.
You how
should
tions
of theof pedal
to see
it
measure Itpedal
ratiotoatdraw
several
posichanges.
is useful
a graph
of
tions
of the
pedal
to see pos
how
pedal ratio
versus
pedal-pad
ition.it
changes.
is useful
to draw
graph
of
This
givesIt you
a picture
of ahow
your
pedal
ratio
versus
pedal-pad
position.
brake system works. You want a pedal
This
you aa picture
how your
that gives
avoids
radical ofpedal-ratio
brake system
works. as
Youthewant
a pedal
change
, particularly
pedal
gets
that toavoids
a radical pedal-ratio
close
the floor.
change,
particularly
as the
pedal
Choosing
the correct
pedal
ratiogets
on
close
to
the
floor.
a special car is a compromise because
Choosing the correct pedal ratio on
a special car is a compromise because
PUSHROD LlNE-OF -ACTION
PUSHROD LINE-0F.ACTION
PUSHROD
LEG LlNE-OF-ACTION
FOOT -TO-PEDAL
CONTACT POINT
E G LINE-OF-ACTIO
FOOT.TO-PEDAL
CONTACT P O I N T
Line-ot-action ot leg is between pedal pad and driver's hip. Measure distance A perpendicular to this line. Distance B is measured perpendicular to line-ot-action of mastercylinder
pushrod,
Pushrods
shouldpedal
not be
shown,
but
if one is,
its line-of-action
Line-of-action
of leg
is between
padbent
and as
driver's
hip.
Measure
distance
A perpenwould
pushrod
ends.BDrawing
by Tomperpendicular
Monroe.
dicularbetothrough
this line.
Distance
is measured
t o line-of-action of mastercylinder pushrod. Pushrods should not be bent as shown, but if one is, its line-of-action
would be through pushrod ends. Drawing by Tom Monroe.
Master Cylinder
Q
8
C;
a:
8
7 -g
<ii
poor-",,/
um
nrOJ
67 -0..3
---u
a,
6-a
5r4
5
Pedal Ratio
Linkage
Ratio =
=
Overall Ratio =
J
Force From
Driver's Leg
~L
~
L
X
~~
-
A
AL
Overall Ratio = - X
If pedal operates
a bellcrank,
B through
BL
rocker or other linkage, pedal ratio alone is
not
the final
answer. through
Overall ratio
between
If pedal
operates
a bellcrank,
driver's
foot
andlinkage,
master cylinder
is required
rocker or
other
pedal ratio
alone is
for
calculations.
Once
pedal
not brake-system
the final answer.
Overall ratio
between
ratio is foot
determined,
ratio
of intermediate
driver's
and master
cylinder
is required
linkage
is determined,
When determining
for
brake-system
calculations.
Once pedal
linkage
force from
is the same
ratio is ratio,
determined,
ratiopedal
of intermediate
as
force isfrom
driver's foot.
Note
that linklinkage
determined.
When
determining
age
pictured
has afrom
ratio
lessis than
1.0.
linkage
ratio, force
pedal
the same
Force
from
pedal
is reduced
by linkage
beas
force
from
driver's
foot. Note
that linkcausepictured
AL is smaller
B L , less than 1.0.
age
has than
a ratio
Force from pedal is reduced by linkage because A, is smaller than B,.
of conflicts between high and low
pedal ratios. A low pedal ratio inof conflicts
between high
and and
low
creases
pedal-linkage
stiffness
pedal
inreducesratios.
forcesAonlow
the pedal
pivots.ratio
A high
creases
pedal-linkage
stiffness
pedal ratio
reduces pedal
effort and
and
reducesa forces
on the pivots.
high
allows
large-diameter
masterAcylinpedal
ratio
reduces
pedal
effort
and
der to be used . I detail these trade-offs
allows
a large-diameter
in Chapter
9. Total travelmaster
at the cylinpedal
der
used. by
I detail
these 'strade-offs
pad to
is be
limited
the driver
leg. His
in
Chapter
9.
Total
travel
the pedal
anatomy determines the at
distance
he
pad move
is limited
by the
driver's
leg.floor
His
can
his foot
back
from the
anatomy
determines
he
or accelerator
pedal the
to distance
the brake
can
move
his
foot
back
from
the
floor
pedal. If he has to stop quickly, he
or accelerator
pedal histofoot
theverybrake
doesn't
want to move
far.
pedal. If he has to stop quickly, he
doesn't want to move his foot very far.
-
/
--;r-/
./
-----
-- --
Good ---""
A
Good
3
2 -
4
3
2
-
-
1
Retracted
o
1I
On Floor
2I
3I
4I
5I
Pedal-Pad Movement (in.)On Floor
Retracted
0 shows
1
2 curves
3 of 4
5
Graph
two
pedal-pad
Pedal-Pad Movement (in.)
movement versus pedal ratio. Solid line is
for a good
changes
Graph
showsdesign-pedal
two curves ratio
of pedal-pad
little with pedal
movement;
dotted
movement
versus
pedal ratio.
Solidcurve
line is
is
poor-pedal
ratio - changes ratio
considerably,
for a good design-pedal
changes
Angle
changes
pedal ordotted
linkagecurve
movelittle with
pedalwith
movement;
is
ment
determines
curve
shape. considerably.
poor-pedal
ratio.
changes
Angle changes with pedal or linkage movement determines curve shape.
Pedal Movement-Another consideration is how far the brake pedal moves
Pedal Movement-Another
considerduring
brake application. Most
brake
ation
how far
the the
brake
pedal moves
pedalsjs move
from
retracted
posiduring
application.
tion to brake
the floor
in less Most
than brake
6 in.
pedals
move
from
retracted
posimeasured
at the
pad.the
Pedal
movement
tion
to
the
floor
in
less
than
6
in.
must be less than this for safety and
measured When
at the pad.
Pedal movement
comfort.
designing
a special
must
less than
for movement
safety and
brake be
system,
keepthis
pedal
comfort.
When
designing
special
during normal braking as ashort
as
brake
system,
keep
pedal
movement
possible.
during
as shortThe
as
Let's normal
review braking
some basics:
possible.
brake pedal must supply movement
some movement
basics: The
as Let's
well asreview
force. Pedal
inbrake
pedal
must
supply
cludes all slop and clearancemovement
takeup in
as
as system
force. Pedal
movement
inthewell
brake
, movement
of friccludes
all slop and
in
tion material,
and clearance
combinedtakeup
deflecthe
brake
system,
movement
of
friction of all parts in the system . In
tion material, and combined deflection of all parts in the system. In
71
Tilton Engineering pedal-and-bracket assembly mounts dual master cylinders to
rear. Assembly
is used
with hanging-pedal
Tilton
Engineering
pedal-and-bracket
asmount. Stock
cars
withmaster
clearance
problems
sembly
mounts
dual
cylinders
to
in engine
compartment
benefit
from this
rear.
Assembly
is used with
hanging-pedal
setup. Stock
Mastercars
cylinders
install inproblems
driver's
mount.
with clearance
compartment,
away from benefit
engine heat.
in
engine compartment
from this
setup. Master cylinders install in driver's
compartment, away from engine heat.
Neal Products offers a complete line of pedals, brackets and other brake-system hardware
for special cars. Neal pedals and brackets accept various master cylinders. Dual units
shown
include offers
balance
bar and are
up for brackets
floor mounting
. Pedal
and cylinders
can be
Neal
Products
a complete
line set
of pedals,
and other
brake-system
hardware
changed
for cars.
hanging-pedal
installation.
for
special
Neal pedals
and brackets accept various master cylinders. Dual units
shown include balance bar and are set up for floor mounting. Pedal and cylinders can be
addition, extra movement must be
available at the pedal pad in case there
addition,
extra lining
movement
must be
is fade , non-flat
wear, hot-lining
available
at
the
pedal
pad
in
case
there
compression, or air in the brake fluid.
is
fade,
non-flat
lining
wear,
hot-lining
Normal brake-pedal movement must
compression,
air in the
be as short asorpossible
to brake
allow fluid.
extra
Normal
brake-pedal
movement
must
movement for these emergencies
or
be
as
short
as
possible
to
allow
extra
failures in a brake system . There 's
movement
emergencies
or
more if youfor
' re these
working
with a dualfailures
in a orbrake
brake system
d rum system.
brakes. There's
more
you're orworking
with a dualIn a iftandem
dual master-cylinder
brake
system
or
drum
brakes.
system , extra pedal movement must
a tandem
dual
master-cylinder
be Inprovided
in or
case
one
brake system
system,
extrahave
pedal
movement
must
fails. It must
enough
pedal travel
be provided
in case
available
to lock
up one
two brake
wheelssystem
when
fails.
It must
travel
the brakes
arehave
hot enough
and one pedal
system
has
available
to
lock
up
two
wheels
when
failed .
theInbrakes
are hot overheating
and one system
has
addition,
drum
failed.
brakes can
cause extra
pedal
In addition,
movement.
When overheating
the drums getdrum
hot,
brakes
can
cause
pedal
they expand away fromextra
the shoes.
movement. When
drums
getmust
hot,
Consequently,
the the
brake
shoes
they
expand
away
from
the
shoes.
move farther. If the pedal hits the
Consequently,
the be
brake
floor,
you may not
able shoes
to stopmust
the
move
farther.
If
the
pedal
hits disc
the
car. This is not a problem with
floor,
brakes.you may not be able to stop the
car.If you
Thiscannot
is not achieve
a problem
withtravel
disc
a pedal
brakes.
less than the 6-in. maximum , possible
If you
pedal assists
travel
cures
are cannot
bigger achieve
brakes, apower
lessother
than the
6-in.changes.
maximum,
possible9
or
design
Chapter
cures are bigger
brakes, . power
discusses
this problem
Beforeassists
you
or
other
design
changes.
Chapter
panic , though , minimize each
contri-9
discusses
this pedal
problem.
Before Start
you
bution to total
movement.
panic,some
though,
minimize
eachand
contriwith
careful
measuring
testbution
to total
movement.
ing
to find
whatpedal
is causing
most ofStart
the
with
some
careful
measuring
and testpedal movement.
ing to find what is causing most of the
pedal movement.
72
changed for hanging-pedal
SPECIAL
PEDALS installation.
PEDAL BRACKETS
If you'd rather not design the brake
SPECIAL
PEDALS
pedal, excellent
aftermarket pedal asIf you'd are
rather
not design
brake
semblies
available
fromtheseveral
pedal,
excellent
aftermarket
pedal
assources. Neal Products of San Diego,
semblies
are
available
from
several
California offers a complete line of
sources.
Products
San Diego,
pedals, Neal
linkages
and of
other
brakeCalifornia
offers A
a Neal
complete
of
system hardware.
ped al line
assempedals,
linkages
and
other
brakebly can be purch ased with its own inteNeal pedal assemsystem
hardware.
gral
bracket
, Aincluding
master
bly can be. purchased
with its own
inte- .
cylinders
This assembly
is easily
gral
bracket,
including
mounted
on a special
car. Neal master
pedals·
cylinders.
This sizes
assembly
is easily
come in various
and mounting
mounted
on
a
special
car.
Neal
configurations to suit most pedals
applicome
various sizes
and mounting
cations.in Winters
Performance
Prodconfigurations
to suit most
appliucts of York, Pennsylvania
also offers
cations.
Winters Performance Prodsimilar pedal-and-master-cylinder
asucts
of
York,
also offers
semblies with Pennsylvania
integral brackets.
similar
pedal-and-master-cylinder
A special
brake-pedal assembly asis
semblies
with
integral
brackets. They
offered by
Tilton
Engineering.
A special
is
offer
a racing brake-pedal
brake-pedal-assembly
and- bracket
offered
by
Tilton
Engineering.
They
assembly that positions the master
offer a racing
brake-pedal-and-bracket
cylinders
toward
the rear of the car
assembly
positions
master
rather thanthat
the front.
This the
installation
cylinders
toward
the
rear
of
the
car
is designed for stock-car and GT
rather
than
the
front.
This
installation
racing, where having the master cylinis designed
for stock-car
and can
GT
ders
in the engine
compartment
racing, where
havingWith
the master
cylincause
problems.
rear-facing
ders in cylinders,
the enginethecompartment
can
master
master cylinders
cause
problems.
With
rear-facing
are not subject to heat from the
master cylinders,
thenot
master
cylinders
engine,
and they do
interfere
with
are
subject
to heat fromvalve
the
parts notsuch
as carburetors,
engine,
and
they
do
not
interfere
with
covers or headers, or with sparkplug
parts such
as , the
carburetors,
valve
removal.
Instead
master cylinders
covers
headers,
or with sparkplug
end
up or
under
the instrument
panel or
removal.
thedisadvantage
master cylinders
front
cowl.Instead,
The one
with
end
up
under
the
instrument
or
this setup may be servicing thepanel
master
front
cowl.
The
one
disadvantage
with
cylinders.
The strength of a brake-pedal brackPEDAL
et
shouldBRACKETS
match that of a properly deThe strength
of a brake-pedal
bracksigned
brake pedal.
It is essential
to
et
should
match
that
of
a
properly
demount a brake pedal on a strong and
signed
brake pedal.
It is essential
to
rigid bracket.
In addition,
the master
mount
a
brake
pedal
on
a
strong
and
cylinder should be part of the brakerigid
addition,
the master
pedal bracket.
mount toInreduce
the relative
decylinder
should
be
part
of
the. Forces
brakeflection of the two assemblies
pedal
to reduce
the relative
deon themount
brake-pedal
bracket
can ex ceed
flection
of
the
two
assemblies.
Forces
2000 lb, so it must be rigid .
on
the brake-pedal
bracket
exceed
Otherwise
, the bracket
may can
be danger2000
Ib,
so
it
must
be
rigid.
ous and can cause a spongy feel to
the
Otherwise,
the
bracket
may
be
dangerbrake pedal.
ous
and can
causeand
a spongy
feel to
the
Neal,
Tilton
Winters
brake
brake
pedals pedal.
come witb their own bracket,
Neal,links
Tilton
and Winters
which
the pedal
directly tobrake
the
pedals
come
with
their
bracket,
master cylinder. This isown
important.
whichbracket
links isthemounted
pedal directly
to but
the
The
to the car,
master oncylinder.
This mounting
is important.
forces
the bracket
are
The
is mounted
the car, butl
lowerbracket
than forces
on theto brake-peda
forces
on the
bracket
mounting
are
pivot and
master
cylinder
or the
lower
than
forces
on
the
brake-pedal
pushrod . Still , the mounting of the
pivot
and master
cylinder
or This
the
pedal bracket
to the car
is cri tical.
pushrod.
Still,
the
mounting
of
mounting should also be rigid sothe
it
pedal
bracket the
to the
car of
is critical.
This
will support
force
the driver
's
mounting
shoulddon't
also mount
be rigid
so it
Therefore,
a brake
foot.
will
force of the
pedalsupport
on a flatthe
sheet-metal
firedriver's
wall or
foot.
Therefore,
don't mount
a brake
unreinforced
floorboard
. Mount
the
pedal
on
a
flat
sheet-metal
fire
or
pedal in a corner or on a boxedwall
beam
unreinforced
floorboard.
Mount
the
so there won't be excessive deflection .
pedal
in aroad
corner
on a boxed
beam
Many
carsor have
brake-pedal
so
there
won't
be
excessive
deflection.
brackets that can be adapted to other
Many
road
have
brake-pedal
cars.
Some
havecars
small
compact
brackbrackets
that
can
be
adapted
to other
ets that can be purchased with
the
cars.alsSome
small compact
ped
for have
a reasonable
price. brackIt is
ets
thatbetter
can beto purchased
the
much
adapt an with
existing
pedals
for
a
reasonable
price.
It
is
bracket-and- pedal assem bly to a car
this setup may be servicing the master
cylinders.
much better to adapt an existing
bracket-and-pedal assembly to a car
Pedal bracket on homemade sports car is
built into frame structure. It pays to work in
pedal-bracket
design
with frame
ro"Pedal bracket on
homemade
sportsorcar
is
cage
design.
Save
time, weight
and
built into
frame
structure.
I t pays
t o cost
workby
in
planning
ahead. design with frame or rollpedal-bracket
cage design. Save time, weight and cost by
planning ahead.
than to design and build one yourself.
It's a lot less expensive , too , to buy an
than to design
existing
unit. and build one yourself.
It'sMany
a lot less
expensive,
too, tobrackets
buy an
race-car
brake-pedal
existing
unit.
are integrated into the frame
Many race-car
brake-pedal
brackets
structure.
This approach
is excellent
if
are
integrated
intoentire
thecar. frame
designing the
Most
you are
structure.
This approach
is excellent
if
race-car frames
have tubes
or rigid
you
are
designing
the
entire
car.
Most
bulkheads that make excellent strucrace-car
have pedals.
tubes or
rigida
tures forframes
mounting
With
bulkheads
that makestructure
excellent like
struc-a
sheet-metal
large
tures
for mounting
With a
passenger-car
fire wall,pedals.
the mounting
large
sheet-metal
likethea
requires
a special structure
bracket for
passenger-car fire wall, the mounting
pedals.
requires
a special
bracket
fortypes
the
Pedal Location
- There
are two
pedals.
of brake-pedal mounts: floor-mounted
Pedalhanging.
Location-There
are two
and
Both are used
and types
both
of
brake-pedal
mounts:
have
advantages.
Most floor-mounted
modern road
and use
hanging.
Bothpedals.
are used
andis both
There
a lot
cars
hanging
have
advantages.
Most
modern
road
of room under the dash for brackets,
cars often
use hanging
pedals.column
There is
lot
and
the steering
is asupof
roombyunder
the structure.
dash for brackets,
ported
the same
andHanging
often the
steering
suppedals
alsocolumn
can beislong,
ported
same
are
ou tby
ofthe
sight
andstructure.
the pivots are less
Hanging pedals
also can
be floorlong,
than
susceptible
to corrosion
are
out
of
sight
and
the
pivots
are
mounted pedals. Additionally, less
the
susceptible
to corrosion
than infloormaster
cylinder
ends up high
the
mounted
pedals. Additionally,
the
engine
compartment,
where it is easy
master
cylinder
endsadvantage
up high of
in this
the
Another
to service.
engine
compartment,
where
it
is
easy
is air bubbles rise to the master
to service.then
Another
advantage
of this
cylinder,
into the
fluid reservoir.
is air the
bubbles
rise istoself-bleeding,
the master
Thus,
system
cylinder,
theat fluid
reservoir.
except
forthen
a fewinto
spots
the wheels.
Thus,
the
system
is
self-bleeding,
On low-profile race cars, floorexcept
for apedals
few spots
the wheels.
mounted
areat more
popular.
On
low-profile
race
Race-car design demandscars,
a lowfloorCG,
mounted
pedals
popular.
so
it's best
to are
keepmore
components
Race-car as
design
demands
low CG,
mounted
low as
possible.a Also,
the
so
it's ofbest
to keep
components
height
the body
nose of
a rear- or
mounted as low as
Also,
the
midship-engine
carpossible.
is often
deter-
height of the body nose of a rear- or
midship-engine car is often deter-
Eagle Indy Car has large hole in pedal box for easy pedal access. Balance bar has remote
brake-balance adjuster, so frequent access to the brake pedal is not required. Cable
balance-bar
adjuster
(arrow)
to knob
panel.
Eagle lndy Car
has large
holegoes
in pedal
boxon
forinstrument
easy pedal
access. Balance bar has remote
brake-balance adjuster, so frequent access t o the brake pedal is not required. Cable
balance-bar adjuster (arrow) goes to knob on instrument panel.
Sturdy universal bracket mounts dual
master-cylinder-and-bracket assembly to
frame
roll cage. bracket
Photo courtesy
Sturdy oruniversal
mounts Tilton
dual
Engineering.
master-cylinder-and-bracket assembly t o
Hanging pedal-and-bracket assembly is
ready to mount in car. Unit includes pivot
bushings,
return spring and assembly
pedal stop
Hanging pedal-and-bracket
is
(arrow)t o
. . Such
assemready
mountbracket-and-pedal
in car. Unit includes
pivot
blies can return
be found
in junkyards
a
bushings,
spring
and pedal for
stop
modest
(arrow). price.
.Such bracket-and-pedal assem-
frame or roll cage. Photo courtesy Tilton
Engineering.
blies can be found in junkyards for a
modest price.
mined by the height of the driver's
feet inside the cockpit. If hanging
mined
by used,
the height
of theheight
driver's
pedals are
the added
refeet
inside
the
cockpit.
If
hanging
quired above the driver's feet raises
pedals
are used,
added
height re-a
the height
of thethe
nose.
Therefore,
quired
abovecar
theor driver's
feetusually
raises
formula car
racing sports
the floor-mounted
height of the nose.
has
pedals.Therefore, a
racing
sportscylinders
car or formula
car usually
Master
with
floorhas
floor-mounted
pedals.
mounted pedals are difficult to
Masterunless
cylinders
floorservice,
they are inwith
front of
the
mounted
pedals
are
difficult
front suspension. The balance bar to
is
service.
unless
areWorst
in front
of , the
also
difficult
to they
adjust.
of all
air
L s ~ e n stends
i o n to end up at
barthe
is
in the ssystem
also
difficult
to adjust.
all, air
wheels
rather
than Worst
the of master
in the systemandtends
to end (s).
up atConthe
cylinder(s)
reservoirs
wheels rather than the master
cylinder(s) and reservoirs(s) . Con-
Hanging pedals are neat and package we"
in most large cars. Such a setup with dual
Inangins
pedals are
and package
wel:
master cylinders
canneat
be difficult
to adjust,
particularly
when
a hurry-just
inmost large
cars. you're
such ainsetup
with dual
the
place
for a remote
adjuster.
master
cylinders
can be
difficult to adjust,
particularly when you're in a hurry-just
the place
a
adjuster.
73
BALANCE BARS VS.
ADJUSTABLE
BALANCE
BARS VS.
PROPORTIONING
VALVES
ADJUSTABLE
Both a balance bar and an adjustPROPORTIONING
able proportioning VALVES
valve can be
Stock car uses tandem master cylinder
and adjustable proportioning valve mounted in cockpit.
drivermaster
simplycylinder
moves
Stock
car usesThe
tandem
leveradjustable
on valve to
adjust brake
balance.
It
and
proportioning
valve
mountwould've
been difficult
to use
dual master
ed
in cockpit.
The driver
simply
moves
cylinders
with to
a balance
bar because
lever
on valve
adjust brake
balance. of
It
frame-tube
interference.
would've
been
difficult to use dual master
cylinders with a balance bar because of
frame-tube
sequently, interference.
floor-mounted pedals usu-
ally are more sensitive to air buildup
sequently,
floor-mounted
pedals
usuin the system.
As a result they
require
ally
are
more
sensitive
to
air
buildup
more frequent bleeding.
in Brake-fluid
the system. As
a result they
reservoirs
for arequire
floormore
frequent
mounted
pedalbleeding.
often must be remote
Brake-fluid
reservoirs
a floorfrom
the master
cylinders.forThis
adds
mounted
pedal
often
must
be
remote
complexity to the brake system
. In
from
the dirt
master
cylinders.
Thisshoes
adds
addition,
from
the driver's
complexity
the pedal
brake linkage
system.and
In
can get intoto the
addition,
dirt
from
the
driver's
shoes
cause problems; hanging pedal lincan
the pedal
kagesget
stayinto
relatively
clean. linkage and
cause
problems; use
hanging
pedalpedal
linTo summarize,
a hanging
kages
mountstay
if relatively
possible. clean.
If not, a floorTo summarize,
a hanging
pedal
mounted
setup wi lluse
work
even though
mount
if
possible.
If
not,
a
floorit has disadvantages.
mounted setup will work even though
BALANCE
BARS
it has disadvantages.
Bath
bar relationship
and an adjustused ato balance
change the
beable
valve can;;l$F
tween proportioning
front- and rear-brake
hydrauused
to change and,
the.rqlatians.hip.boL'
lic pressure
consequently,
tween
andHowever,
tBar-brake
hydraubrake fronfbalance.
they
work
lic
pressure
and, consequenlly,
in different
ways.
brake
balance.
However,
work
A balance
bar
divides they
the pedal
In
dllferenl
ways.
force
between
two separate master
A balance
divides ratio.
the pedal
cylinders
in bar
a preset
This
force between
two be
aparate
master
ratio can
adjusted
by
cylinders
a p rpivot
e e f .ratio.
moving theIncenter
of the This
balcan ha
adjusted
by
force
tatio closer
ance bar
to one
mastermoving
centerorpivot
of thethus,
balcylinderthe
pushrod
the other,
ance
bar closer
increasing
pressureto inone
one rnastersystem
cylinder
pushrod
the other,
ano reducing
it in w
another.
On thus,
most
jncreaslng
in mecylinder
$yslem
road cars, aprMaure
tandem master
and
reducilig
another.
most
is used,
whichit in
cannot
be On
changed
road
cars,brake
a tandem
master cylirlder
to adjust
balance.
is used, which cannot be changed
to adjust brake balance.
-
An adjustable proportioning valve
varies the ratio of front-to-rear
An adjustable
v.qlve
brake
pressure proportioning
in the direction
of
varies
thebrakes
ratio above
of front-lo-liar'
the front
a preset
brake
pressure
in the The
direction
changeover
pressure.
valve of
is
the
frontplaced
brakesin above
a preset
usually
the rear
brake
mangeover
pressu:t?~~~Tfi~~FBlve
@'i
system to compensate
for weight
udually
.in
' rear-wheel
w r brafit
transfer placed
to prevent
sysfehn
t~ mrnperigete
tor weight
lockup under
hard braking.
transfer
to prevent
A proportioning
valveroar-wheel
gives a
lockup
under hard
braking.hydraulicfront-to-rear
brake
A propbrtloning
valve
a
pressure
relationship
that gives
approxifront-to-rear
brake
hydraulicmates the ideal relationship
for varipressure
thet
approxlous valuesrelationship
of tire grip. A
balance
bar
mates
theautomatically
Ideal relationship
br varldoes not
compensate
ous
values ofintire
for variation
tiregrip.
grip.A balance bar
dm6
not aaubrnatlcallyproportioning
-comprnsate
Nonadjustable
tr3r
variation
tire grip.
valves
are in
used
on most modern
Wonad]ustabie
praportionlng
road
cars . An adjustable
proportionvalves
are
on most
ing valve
canused
be easily
addedmodwn
to any
road
An adjustable
proportionbrakecars.
system
to make the
balance
Ing
valve can
be easily
added
to any
adjustable
within
a limited
range.
brdce system to maka t k belance
.N€i
adjustable within a llmited range.
Rear-Brake Master Cylinder
A balance bar is used to adjust the
BALANCE
BARS
brake balance
for only one value of
A
balance
bar isnot
used
to adjust the
tire grip. It does
compensate
for
brake
balance
for
only
one
value
changing traction conditions the
wayofa
tire grip. It does
not compensate
for
proportioning
valve
does. For this
changing
traction bars
conditions
reason , balance
usuallythe
areway
nota
proportioning
valve does. For this
used on a road car.
reason,
balance
bars
usually
are race
not
Balance bars are
used
on most
used with
on a road
cars
dual car.
master cylinders. The
Balancebar
barsproportions
are used on the
mostforce
race
balance
cars
with
dual
master
cylinders.
from the brake pedal to the The
two
balance
bar proportions
the force
master cylinders.
Most balance
bars
fromadjustable
the braketo pedal
two
are
vary to
the the
braking
mastergoing
cylinders.
Most
balance
force
to the
front
and bars
rear
are adjustable
theand
braking
cylinders,
thus tothevary
front
rear
force
going
to
the
front
and
rear
brakes. The most-exotic balance bars
cylinders,
thus bythe
can
be adjusted
the front
driver and
from rear
the
brakes. The most-exotic balance bars
cockpit.
canThe
be adjusted
the driver
the
simplest by
balance
bar isfrom
a cross
cockpit.
link, or beam. The brake pedal pushes
simplest
balance
cross
onThe
a pivot
near the
centerbar
of isthea cross
beam.then
The pushes
brake pedal
pushes
link, or
link,
which
on the
two
on a pivot near the
center of that
the cross
master-cylinder
pushrods
are
link, which
pushes
two.
mounted
to then
the ends
of on
thethe
beam
master-cylinder
pushrods
that
are
Where
the brake-pedal
pivot is
in relamounted
themaster-cylinder
ends of the beam.
tion
to thetotwo
pushWhere the brake-pedal pivot is in relation to the two master-cylinder push74
Pedal Pushrod
Pedal
Pushrod
Force From
Pedal
Simplest balance bar is a link with three holes. Ratio between front and rear brake pressure
is determined by proximity of center hole to outer holes. To adjust this type of balance bar,
it must bebalance
replacedbar
with
newwith
bar with
in between
a different
place.
Simplest
is aa link
threecenter
holes.hole
Ratio
front
and rear brake pressure
is determined by proximity of center hole to outer holes. To adjust this type of balance bar,
it must be replaced with a new bar with center hole in a different place.
rods determines front-to-rear brake
balance. Some balance bars can be
rods determines
front-to-rear
adjusted;
some cannot.
A simplebrake
balbalance.
Some
balance
ance
bar is
shown
above .bars
This can
type be
is
adjusted;
someascannot.
A simple balnot adjustable
is.
ance
bar are
is shown
above. balance
This type
is
There
other simple
bars
not
adjustable
as
is.
that are adjustable, but not easily.
Thereorare
other simple
balance
Shims
washers
must be
movedbars
to
that arebrake
adjustable,
not can
easily.
change
balance. but
Balance
be
Shims or washers
be , moved
to
determined
throughmust
testing
and once
change
brake
balance.
Balance
can
be
set, it never gets changed again.
determined
testing,
For racing,through
a balance
bar and
mustonce
be
set, it neveraccording
gets changed
adjusted
to again.
track conFor racing,
a balanceif bar
ditions.
For instance,
the must
track be
is
adjusted the
according
to should
track beconslippery,
balance bar
additions.toFor
thethe
track
is
justed
giveinstance,
less forceif on
front
slippery, the balance bar should be adjusted to give less force on the front
brakes . Less forward weight transfer
with a slick track means the front
brakes. must
Less forward
wheels
do less weight
braking.transfer
If the
with
slickgood
tracktraction,
means the
the front
track ahas
front
wheels
less more
braking.braking.
If the
brakes must
shoulddo do
track has good
traction,would
the front
Balance-bar
adjustment
then
brakes
should
do
more
braking.
be made to give more front-braking
Balance-bar
adjustment
would then
force.
Normally,
the balance
bar
be made
give more
front-braking
would
be toadjusted
during
a prerace
force. Normally,
thethebalance
bar
practice
session. Once
race starts,
would
be
adjusted
during
a
prerace
the bar is left alone .
practice
session.inOnce
the race equipstarts,
The ultimate
sophisticated
the
bar
is
left
alone.
ment is a balance bar that can be adThe ultimate
in sophisticated
equipjusted
by the driver
during a race
. If
ment
is a balance
thator can
adthe driver
desires bar
more
lessbefront
justed
the driver
duringchange,
a race. he
If
brakes by
as track
conditions
the driver desires more or less front
brakes as track conditions change, he
eR
Simple Link
FL
Simple Link
Pedal Arm MasterCylinder
Pushrod
Homemade balance bar is not good because it is weak and hard to adjust. Threaded
rods are not
strongbar
in bending-a
failure
Homemade
balance
is not good
becould
Correctly
engineered
cause be
it isdisastrous.
weak and hard
t o adjust.
Threadbalance
barsnot
are
large in
atbending-a
the center failure
where
ed
rods are
strong
stresses
are highest.Correctly
Also, balance
bar
could
be disastrous.
engineered
probably
would
if one
master-cylinder
balance bars
arebind
large
at the
center where
pushrod moved
much Also,
more balance
than other
stresses
are highest.
bar
pushrod. would bind if one master-cylinder
probably
pushrod moved much more than other
pushrod.
Neal Products' adjustable balance bar :
Center ball slides in tubular housing
welded
into pedal
arm. Turning
threaded
Neal Products'
adjustable
balance
bar:
bar
moves
right housing
or left
Center
ball center
slides bearing
in tubular
inside pedal
housing.
welded
into pedal
arm. Special
Turning spherical
threaded
bearings
have
threads
inside bore
bar
moves
center
bearing
right and
or pins
left
(arrows)pedal
to restrict
ball Special
movement
to only
inside
housing.
spherical
pivoting
one threads
direction.
bearingsinhave
inside bore and pins
(arrows) to restrict ball movement to only
pivoting in one direction.
Fs
Adjustable Balance Bars
FBBalance-Bar Center Pivot
Fs = Force on
Adjustable Balance Bars
FL = Force on Left Master
Force on (Ib)
Balance-Bar Center Pivot
FB = Cylinder
FL =
FR
= Force
Force on
on Left
RightMaster
Master
Cylinder
Cylinder (Ib)
(lb)
Force on From
Right Center
Master Pivot to
FR== Distance
d
l
Cylinder
(Ib) (in.)
Pushrod
Left
dL =
Distance
Distance From
From Center
Center Pivot
Pivot to
to
d
R = Left
Pushrod(in.)
(in.)
RightPushrod
dR = Distance From Center Pivot to
Right Pushrod (in.)
FL =
qdSR)
+
FB = FL FR
Compute forces on master cylinders with
formulas given above. If center bearing
(F L) is moved
toward
front-brake
pushrod,
Compute
forces
on master
cylinders
with
front brakes
getabove.
more hydraulic
formulas
given
If centerpressure
bearing
and
versa.toward
Note that
sphericalpushrod,
bearing
(F,) vice
is moved
front-brake
in bottom
drawing
is off-center
pedalfront
brakes
get more
hydraulic in
pressure
arm vice
housing.
It Note
slidesthat
sideways
when
adand
versa.
spherical
bearing
justing
screw
is turned.
Distances
from
in bottom
drawing
is off-center
in pedalspherical-bearing
center
to pushrod
arm
housing. It slides
sideways
whenbearadings determines
balance-not
distances
justing
screw is turned.
Distances
from
from center of pedal
arm. to pushrod bearspherical-bearing
center
ings determines balance-not
from center of pedal arm.
distances
can make the change. For example, if
it rains, and traction suddenly drops, a
can
make brake-balance
the change. For
example, isif
adjustment
rearward
it
rains, and
required.
It traction
takes asuddenly
skilled drops,
race-cara
rearward
adjustment is
driver
to brake-balance
know when a brake-balance
required.
It takes a skilled race-car
change
is needed.
driver
to
know
when a brake-balance
In-cockpit adjustable
balance bars
change
are
usedisinneeded.
Grand Prix cars and similar
In-cockpitmachines,
adjustablewhere
balance
bars
high-priced
the drivare
used
in
Grand
Prix
cars
and
similar
ers are sufficiently skilled to make use
high-priced
where the drivof
the featuremachines,
.
ersThe
are sufficiently
skilled to
make use
most popular
balance-bar
of the feature.
The most
.popular
balance-bar
Neal pedal assembly is fitted with remote adjuster that can be operated by driver. Handle is
mounted so adjustments can be made while racing. Driver must be able to sense need for
brake-balance
changes
beforewith
he can
use adjuster that
effectively.
Neal pedal assembly
is fitted
remote
can be operated by driver. Handle is
mounted so adjustments can be made while racing. Driver must be able t o sense need for
brake-balance
before
use adjusterSetting
effectively.
up a balance bar can be
design
is one changes
where the
barhe
is can
mount-I
difficult. First , choose master-cylinder
ed in the pedal arm . A spherical bearSetting
up
a
balance
bar becan
design
is
one
where
the
bar
is
mountsize(s) so the balance
bar can
set be
in
ing rides inside a tube welded into a
difficult.
First, choose
master-cylinder
ed
pedal
arm. A spherical
the
center
for
average
track
holein inthethe
brake-pedal
arm . Thebearbalsize(s)
so the
be setnot
in
ing rides
a tube welded
into a
conditions.
A balance
balance bar
barcan
should
ance
bar isinside
a high-strength
rod mountthe
center
for
average
track
hole
in
the
brake-pedal
arm.
The
balbe used to compensate for the wrong
ed firmly inside the bore of the sphericonditions.
A balance
bar (s).
should
not
ance
bar is a high-strength
master-cylinder
diameter
If you
cal bearing.
A clevis to rod
eachmountbrake
be
used
compensate
forbar
the awrong
ed
firmlyisinside
the bore
of the
need
to to
vary
the balance
great
pushrod
mounted
at each
endspheriof the
. If youto
master-cylinder
clevisistothreaded
each brake
cal
deal from the diameter
center (s)
position
rod. bearing.
Each endA fitting
so a
need
to
vary
the
balance
bar
a great
pushrod
is
mounted
at
each
end
of
the
obtain proper brake balance, a change
turn of the rod will move the spherical
deal
from the center
position
to
rod.
Each
endorfitting
is threaded
so a
in a master-cylinder
diameter
would
bearing
right
left inside
the pedal
obtain
proper
balance,
a change
turn of
theforce
rod will
move
the spherical
be better.
The brake
balance-bar
adjustment
arm.
The
on the
bearing
is then
in
a master-cylinder
diameter
would
bearingtoright
or left
pedal
range
should be sufficient
to compencloser
one end
of inside
the rod,themaking
be
better.
T
h
e
balance-bar
adjustment
arm.
The
force
on
the
bearing
is
then
sate
for
conditions
encountered
at the
that master cylinder share more of the
range
closer
one and
endthe
of other
the rod,
track. should be sufficient to compenbrakingtoforce
less.making
sate
formotion
conditions
the
that
master
cylindercars
share
of the
Most
road-racing
usemore
adjustable
The
of aencountered
balance bar atmust
track.
braking
force
and
the
other
less.
balance bars. You can adapt one of
allow one master cylinder to operate
Mostto road-racing
carscan
usepurchase
adjustablea
The the
motion
of aone
balance
bar must
when
other
bottoms.
The
these
your car. You
allow one
masterbecylinder
to operate
balance
adapt
one of
balance bars.
bar You
from can
Neal
Products,
system
should
designed
so the
when
the not
other
The
these toEngineering,
your car. You
can purchase
Tilton
Winters
Perform-a
pedal does
run one
au t ofbottoms.
travel before
system
should
be
designed
so
the
balance
bar
from
Neal
Products,
both master cylinders bottom. Someance Products or other racingpedal
notoverlook
run out this
of travel
before
Tilton
Engineering,
times does
people
, so difficulcomponent
outlets. Winters Perform-
ance Products or
component outlets.
other
racing-
both master cylinders bottom. Sometimes people overlook this, so difficul75
Handle in upper left corner of Indy Car instrument panel adjusts
balance bar. Slots in handle mount provide positive setting and
lock
handle
in position.
Handle
in upper
left corner of lndy Car instrument panel adjusts
balance bar. Slots in handle mount provide positive setting and
lock handle in position.
Hanging pedals operate reverse-mounted master cylinders installed above pedal box. Setup gets master cylinders out of
engine
As shown,
balance bar must
be cylinders
able to operHangingcompartment.
pedals operate
reverse-mounted
master
inate
at extreme
one Setup
hydraulic
system
fails.cylinders out of
stalled
above angles
pedal if
box.
gets
master
engine compartment. As shown, balance bar must be able to operat extreme
angles if positive-return
one hydraulic system
fails.built into the
stops
deal.ateThis
potential
stroke a great
movement should be checked using
stroke a great
deal. during
This potential
accurate
drawings
design.
movement
should be
checked
using
should
be
Actual balance-bar
action
accurate ondrawings
during adesign.
checked
the car by opening
bleedActual
balance-bar
actionandshould
be
er
on one
brake system
stroking
checked
on
the
car
by
opening
a
bleedthe pedal. This forces the balance bar
er
on one
brake
system
and stroking
to move
into
extreme
angles.
Upper end of production road-car hanging
pedal is equipped with return spring, pedal
stop
pushrod.
Pedal stop
is rubber
pad
Upperand
end
of production
road-car
hanging
at
endisofequipped
arm to right-it's
not
adjustable.
pedal
with return
spring,
pedal
Hairpin-type
return
spring
around
stop
and pushrod.
Pedal
stopwraps
is rubber
pad
pivot
housing.
at
end
of arm to right-it's not adjustable.
Hairpin-type return spring wraps around
pivot housing.
Stop for Piston
Adjustable Pushrod
(Too Long)
Adjustable Pushrod
If piston can't return to its retracted
position, seal covers compensating port
and
brakescan't
won't
fully torelease.
Adjust
If piston
return
its retracted
pedal
stopseal
or pushrod
move piston back
position,
covers tocompensating
port
in its brakes
bore. If pedal
or pushrod
be
and
won'tstop
fully
release. can't
Adjust
adjusted,
master cylinder
pedal stopshim
or pushrod
to moveforward.
piston back
in its bore. If pedal stop or pushrod can't be
ties ariseshim
in emergency
situations.
adjusted,
master cylinder
forward.
A balance bar must not bind when
ties arise inatemergency
situations.
operating
extreme angles
possible
A
balance
bar
must
not bindstrokes
when
when one master cylinder
operating
at extreme
angles
possible
much
more
than the
other.
For
when
oneboiling
master
strokes
example,
fluidcylinder
or a slow
leak
muchrequire
more one
thanmaster
the cylinder
other. For
may
to
example, boiling fluid or a slow leak
may require one master cylinder to
76
the pedal. This forces the balance bar
to move into
extreme angles.
RETURN
SPRINGS
&
PEDAL STOPS
RETURN
SPRINGS
&
There must
be a return
spring to
PEDAL
STOPS
push a brake pedal back to its retracted
There when
must the
be brakes
a return
to
position
are spring
released.
push areturn
brake pedal
retracted
The
springback
thatto its
pushes
the
position
when thepiston
brakesback
are released.
master-cylinder
can also
The
spring
thatpedal
pushes
the
returnreturn
the pedal,
if the
is light,
master-cylinder
piston
back
can
also
the pedal is mounted vertically, and
return
the have
pedal,low
if friction.
the pedalOn
is some
light,
the pivots
the pedal
mountedreturn
vertically,
road
cars, is
a separate
springand
is
the pivotson
have
friction.
Onsure
some
mounted
the low
pedal
to make
it
road
cars,Ona separate
return
is
returns.
race cars,
the spring
mastermountedreturn
on thespring
pedal (s)
to make
it
cylinder
usuallysure
does
returns.
thejob. On race cars, the mastercylinder
return
usually
does
A brake
pedalspring(s)
must have
a positive
the
job.
stop in the retracted position. This poA brake
have
a positive
sition
must pedal
alwaysmust
be the
same
so the
stop incan
the find
retracted
position.
This podriver
the pedal
immediately.
sitionpositive
must always
thepushrod
same sousuthe
The
stop orbethe
driver
can
find
the
pedal
immediately.
ally is adjustable to make sure the
The
positive stoppiston
or the returns
pushrod fully.
usumaster-cylinder
allytheispiston
adjustable
to make
sure
the
If
is prevented
from
reachmaster-cylinder
piston
returns
fully.
ing its retracted position, the ports in
If
pistoncylinder
is prevented
fromopen
reachthethe
master
may not
as
ing itsshould
retracted
the pressure
ports in
andposition,
hydraulic
they
the build,
mastercausing
cylinder
may brake
not open
will
severe
drag. as
they
should
and
hydraulic
pressure
With the pedal in the retracted posiwill
severe
drag.
tion build,
againstcausing
its stop,
therebrake
should
be a
Withamount
the pedalofin the
small
free retracted
play in posithe
tion against its stop,
thereThis
should
be a
master-cylinder
pushrod.
ensures
small
of free piston
play in
the
that theamount
master-cylinder
is fully
master-cylinder
pushrod.
This
ensures
retracted. Most road cars have
that the master-cylinder piston is fully
retracted. Most road cars have
master cylinder or brake booster. If
positive-return
stops built
the
your
car has an external
stop,into
see the
master cylinder
brake adjustment
booster. If
shop
manual or for
your car has an external stop, see the
instructions.
shop
for
adjustment
If youmanual
are designing
your own
instructions.
system, be careful not to use a sepaIf return
you are
designing
your ifown
rate
spring
on the pedal
the
system,
not from
to useits asocket
sepapushrod be
cancareful
be pulled
rate
return
spring on thepiston.
pedal ifMost
the
in the
master-cylinder
pushrod
can
be
pulled
from
its
socket
pushrods are retained in the piston,
in the
master-cylinder
Most
but
some
are loose. If a piston.
return spring
pushrods
retained
in thethan
piston,
the are
pedal
back faster
the
forces
but some are loose.
If a return
spring
master-cylinder
piston,
the pushrod
forces
than
can
fall the
out pedal
unlessback
it is faster
retained
in the
the
master-cylinder
piston. Therefore,piston,
use onlythe
the pushrod
mastercan fall out unless
it isspring
retained
in the
cylinder-piston
return
to retract
piston.
Therefore,
use
only
the
masterthe pedal if the master-cylinder pushcylinder-piston
return
spring
to retract
rod is not retained
to the
piston.
theAllpedal
if theand
master-cylinder
pushtandem
most single master
rod is not retained
to the
piston.so that
cylinders
are strong
enough
tandem
mostmaster-cylinder
single master
theAll
closed
endand
of the
cylinders
are
strong
enough
that
bore can be used as the forwardsopedal
the closed
master-cylinder
stop.
If youend
are of
notthe
sure
about this or
bore can
be used
as the forward
pedal
don't
want
to bottom
the masterstop.
If
you
are
not
sure
about
this
or
cylinder piston for fear of damage, indon't
want
to
bottom
the
masterstall a forward pedal stop. Many cars
cylinder
piston for fear
of damage,
inuse the floorboard
as the
stop. If you
stall
forward
pedal
stop.
Manyin cars
use aa stop,
allow
some
stroke
the
use the cylinder
floorboard
as the
you
master
with
the stop.
pedalIf hard
use
a
stop,
allow
some
stroke
in
the
against the floorboard.
master
cylinder
withpedal
the pedal
hard
Test the
forward
stop when
against
thethe
floorboard.
you
bleed
brakes. With the bleeder
Test
the
pedal
when
screws open,forward
push the
pedalstop
gently
all
you
bleed
the
brakes.
With
the
bleeder
the way down. Make sure it is hard
screws
push
the floor
pedalbefore
gently the
all
against open,
the stop
or the
the way down. Make
it is hard
master-cylinder
piston sure
bottoms.
The
against
the stophave
or the
floor1/16
before
piston should
about
in. the
of
master-cylinder
piston
bottoms.
travel left before it bottoms. If The
the
piston hits
should
about
1/16sure
in. of
pedal
thehave
floor,
make
it
travel left
If the
cannot
get before
jammedit inbottoms.
the carpet
or
pedalother
hitsobject.
the floor, make sure i t
any
cannot get jammed in the carpet or
any other object.
Power Assist
7
Girlock LSC 50 vacuum booster and tandem master cylinder has threaded rods passing through booster from master-cylinder mounting
flange. Rods transmit forces on master-cylinder mounting flange directly to booster mounting bracket . Because booster chamber is not
loaded
forces
from master
cylinder,
booster master
is lightercylinder
than it would
otherwise
be.passing
Boosterthrough
weighs only
4 lb.from
Photo
courtesy Girlock
Ltd.
Girlockby
LSC
50 vacuum
booster
and tandem
has threaded
rods
booster
master-cylinder
mounting
flange. Rods transmit forces on master-cylinder mounting flange directly to booster mounting bracket. Because booster chamber is not
loaded
by road
forcescars
fromand
master
cylinder,
lighter than
it wouldthe
otherwise
Booster weighs
Photo courtesy
Most
a few
large booster
race ismounted
withGirlock
less Ltd.
servo
canonlybe4 Ib.designed
behind
master be.
cylinder.
cars use power assist-boosters-to
Most braking
road carseffort.
and a A
fewcar
large
racea
reduce
with
cars
use
power
assist-boosters-to
power assist is said to have power
reduce
braking
effort. the
A brakes
car with
brakes. To
the driver,
feela
power
assist
said stopping
to have power;
power
like they
haveismore
brakes. Toit's
thejust
driver,
thepedal
brakes
feel
however,
lower
effort.
like
they
have
more
stopping
power;
Most power-brake systems are dehowever,
it'sa just
effort.
signed
with
lowerlower
pedal pedal
ratio so
the
Most
power-brake
systems
are
dedriver also senses less pedal travel.
signed
with
a
lower
pedal
ratio
so
Power brakes can fade the same the
as
driver also brakes.
senses less
pedal travel.
standard
Luckily,
power
Power
can fade
sameperas
brakes brakes
are reliable
and the
usually
standard
brakes.
Luckily,
form
well for
the life of
the car. power
brakes
are reliable
andbrakes
usuallycomes
perThe power
in power
form
well
for
the
life
of
the
car.
from a uni t called a brake booster. It is
The power
in power
comes
usually
mounted
on thebrakes
fire wall
befrom
a
unit
called
a
brake
booster.
is
tween the brake- pedal linkage and Itthe
usually
mounted
on
the
fire
wall
bemaster cylinder. The brake booster
tween like
the abrake-pedal
andtype
the
looks
large tank, linkage
if it is the
master
The vacuum.
brake booster
operatedcylinder.
by engine
Some
looksuse
likea ahydraulic-powered
large tank, if it is the
type
cars
booster
operated
by
engine
vacuum.
Some
that looks like a complex valve
cars use a hydraulic-powered booster
that looks like a complex valve
Whatever the design of the booster,
mounted
the master
cylinder.
they all dobehind
the same
thing-add
extra
Whatever
the
design
of
the
booster,
force to the master cylinder when
the
they allpushes
do theon
same
driver
the thing-add
brake pedal.extra
The
force
the driver
master pushes,
cylinder the
whenmore
the
harderto the
driver the
pushes
on the
brake
force
booster
adds.
Thepedal.
effectThe
to
harder
theis driver
the more
the driver
reducedpushes,
pedal effort.
force
the brakes
booster are
adds.
Theoneffect
to
Power
used
heavy
the driver
pedaldisc
effort.
cars
and is
onreduced
cars with
brakes.
Powerassist
brakeswasareused
used before
on heavy
Power
the
cars
and
on
cars
with
disc
switch was made from drums tobrakes.
discs.
Power most
assist large
was used
beforepower
the
Now,
cars use
switch
madesmall
fromcars
drums
to discs.
brakes. was
M any
using
disc
Now,
largepower
cars assist.
use Power
power
brakes most
also have
brakes.
Many
small
cars
using
disc
assist makes the job of designing
brakes
have
assist.thePower
brakes also
easier.
Forpower
example,
disc
assist
jobaction
of designing
brake'smakes
lack ofthe
servo
requires
brakes
For example, theforce
disc
more easier.
master-cylinder-piston
brake's
lack
of
servo
action
requires
than a drum brake . If a drum brake is
more master-cylinder-piston
force
designed
with a large servo action,
it
than
a
drum
brake.
If
a
drum
brake
is
can stop a heavy car without power
designed
with
a large
servo
action,
it
assist.
With
power
assist,
drum
brakes
can stop a heavy car without power
assist. With power assist, drum brakes
action. That makes them less affected
can
be designed
with
less shoes
servo
by changes
in friction
between
action.
That
makes
them
less
affected
and drum. Thus, a car can have drum
by
changes
in friction
between
shoes
brakes
that are
more fade
resistant
by
and
usingdrum.
powerThus,
assist.a car can have drum
brakes
are more
fade resistant
by
Manythat
early
power-brake
systems
using too
power
assist. The power assist
were
sensitive.
Many
early
systems
was
so great
thatpower-brake
the slightest push
on
were
too
sensitive.
The
power
assist
the brake pedal locked the wheels.
was
so great
the from
slightest
on,
Nothing
was that
gained
this push
design
the the
brakebrakes
pedalwere
locked
the wheels.
and
dangerous
. In a
Nothing
was gainedwith
from overassisted
this design,
panic situation
and
the
brakes
were
dangerous.
In a
brakes, it is nearly impossible to avoid
panic
situation
with
overassisted
locking the wheels and losing control.
brakes, it is nearly
avoid
Fortunately,
mostimpossible
modern topowerlocking
the wheels
losing control.
brake systems
are and
designed
to feel
Fortunately,
most
modern system.
powermore like an
unboosted
brake systems
are designed
to feel
Therefore,
a driver
should have
few
more
likewith
an aunboosted
system.
problems
later power-brake
Therefore,
a driver
have with
few
system. Power
assistshould
combined
problems
with
a
later
power-brake
the consistency of disc brakes gives
system.
Power
assist combined
the modern
car excellent
brakes. with
the consistency of disc brakes gives
the modern car excellent brakes. 77
1_--- Fire Wall
SaO-psi Hydraulic Pressure
500-psi Hydraulic Pressure
Master Cylinder - - - _ ' l l
~SOO-Ib
Master Cylinder
Force
b1 - 005 -&r >
Vacuum Hose
Intake Manifol
-Brake
Pedal
Valve Rod
Force
Piston Area = 1 sq in .
Hydraulic-Cylinder Force & Pressure
Piston Area = 1 sq in.
\:' 10-psi Vacuum
Hydraulic-Cylinder
Force & Pressure
BoosterSaO-lb.
\
Diaphragm
Force
Area
=
BoosterAddedb.to
500-1
Diaphragm
50
sq in.
Master
I
Force
Area =
Cylinder
' I
Added
to
50 sq in.
JjjT
_--__..... ~II
Typical vacuum-booster setup : Intake manifold supplies vacuum to booster. Brake pedal
pushes directly on booster-valve rod, which controls force booster applies to master
cylinder.
If vacuum supply
dropsIntake
to zero
or booster
fails,vacuum
a mechanical
linkage
operates
Typical vacuum-booster
setup:
manifold
supplies
to booster.
Brake
pedal
master-cylinder
by pushing harder
on pedal.
Effort
increases
pushes directly piston
on booster-valve
rod, which
controls
force
boostersignificantly
applies t o without
master
boost. Drawing
courtesy
Bendix
Corporation.
cylinder.
If vacuum
supply
drops
to zero or booster fails, a mechanical linkage operates
master-cylinder piston by pushing harder on pedal. Effort increases significantly without
boost. Drawing courtesy Bendix Corporation.
Diaphragm
Booster Housing
~_ _
Vacuum Line
OpenTo
Atmosphere
1O-psi Vacuum
Zero-psi Atmospheric
Pressure
Zero-psi Atmospheric
Piston F
=
Force on Master Cylinder Piston
Pressure on diaphragm is difference
between
vacuum
and atmospheric
pressures. Because
F = Force
on Master
Cylinder
Piston
vacuum is below atmospheric pressure, it is given a minus value. In this example -10 psi is
in
vacuumonside
of chamber
and 0 pSi-atmospheric
in other
side. Vacuum
of
Pressure
diaphragm
is difference
between vacuumpressure-is
and atmospheric
pressures.
Because
-10 psi
is
vacuum
below
atmospheric
i t is given
a minus
value. Inbut
thisresulting
exampleforce
-10
psi is
gives
same
force as 1pressure,
O-psi pressure
above
atmospheric,
is in
oPPosite
in vacuumdirection.
side of chamber and 0 psi-atmospheric pressure-is in other side. Vacuum of
-10 psi gives same force as 10-psi pressure above atmospheric, but resulting force is in
opposite direction.
VACUUM-BOOSTER TYPES
Most power-brake systems use a
VACUUM-BOOSTER
TYPES
booster
operated by vacuum
from the
Most
power-brake
systems
use a
intake manifold of a naturally aspiratbooster
operated
by
vacuum
from
the
ed engine. Because manifold vacuum
intake
manifold of a naturally
aspiratis
highest-pressure
is lowest-when
ed
Because
manifold
vacuum
the engine.
driver lifts
his foot
off the throttle,
is
highestpressure
is
lowest-when
vacuum in the booster is maximum as
the driver
liftsare
his foot
off theThis,
throttle,
the
brakes
applied.
of
vacuum isindifferent
the booster
maximum as
course,
for ais supercharged
the brakes
applied.
This,usuof
engine,
whereare
manifold
pressure
course,
is
different
for
a
supercharged
ally is greater than ambient air
engine,
pressure.where manifold pressure usually
greater
air
Theis extra
forcethan
on ambient
the masterpressure.
cylinder piston is provided by a large
The inside
extra the
force
on booster.
the masterpiston
power
In a
cylinder
piston isthis
provided
a largea
vacuum booster,
piston by
is called
piston
inside
theseepower
booster.ofInthea
diaphragm.
You
the outside
vacuum
booster,
this
piston
is called
cylinder-chamber- when you
looka
diaphragm. You see the outside of the
cylinder-chamberwhen you look
78
at a vacuum booster. It's the large,
round object that looks like a tank.
at Vacuum
a vacuumboosters
booster. have
It's thea large,
large
round
object
that looks
like a tank.
diameter
because
vacuum
exerts a
Vacuum
boosters have
a large
Actually,
the
very
low "pressure."
diameter
because
vacuum
exerts
outside air exerts pressure; vacuuma
very low it."pressure."
the
removes
Ambient Actually,
air pressure
outside
air
exerts
pressure;
vacuum
(14.7 psi) is one one side of the diaremoves
it. engine
Ambient
air pressure
phragm and
manifold
vacuum
(14.7
psi)
is
one
one
side
of the diathe other. Air pressure is reduced
on
phragm
and side
engine
manifold
vacuum
the vacuum
by engine
vacuum.
A
the
other.
Air pressure
is reduced
on
perfect
vacuum
on one side
of the dithe vacuum
side abymaximum
engine vacuum.
A
aphragm
allows
pressure
perfect
vacuum
on
one
side
of
the
diof only 14.7 psi. This is a pelfec!
aphragm allows
maximum
pressure
vacuum.
In real alife,
it is never
that
of
only
14.7
psi.
This
is
a
pellfect
high. Compared to about lOOO-psi
vacuum.
real life,
is never
that
maximumInpressure
in ait brake
hydrauhigh.
Compared
to about pressure
1000-psi
lic system,
the vacuum-boost
maximum
a brake
hydrauis
about 10 pressure
psi. The in
result
is the
large-
lic system, the vacuum-boost pressure
is about 10 psi. The result is the large-
Master
Cylinder
I,ll
II
II
---
Vacuum- Booster Force & Pressure
VacuumBooster operates
Force & Pressure
Master
cylinder
at about
1 OOO-psi maximum hydraulic pressure. Because
at
Master vacuum
cylinderdiaphragm
operates operates
at about
about
10-psi
maximum
pressure,
booster
1000-psi
maximum
hydraulic
pressure.
Bediaphragm
is 5 to
10 times operates
diameter of
cause
vacuum
diaphragm
at
master-cylinder
piston pressure,
to give required
about 10-psi maximum
booster
area.
diaphragm
is 5 to 1 0 times diameter of
master-cylinder piston t o give required
diameter
cylinder. Remember, total
area.
force equals pressure multiplied by
diameter
Remember,
total
the area ofcylinder.
the piston
- diaphragm
in
force
equals pressure
multiplied
by
the pressure
is hythis case-whether
the areaorof
the piston-diaphragm
in
draulic
a vacuum
.
this
casewhether
the
pressure
is
hyThe pedal linkage is connected to a
draulic
or a vacuum.
mechanical
linkage that pushes on the
The pedal
linkage
connected
to a
master
cylinder.
The isdriver
can push
mechanical-linkage
that
pushes
on
the master cylinder the same as inthea
master
The driver
can push
normal cylinder.
brake system.
However,
the
the
the same
asfrom
in a
pedalmaster
effort cylinder
is high without
assist
normal
brakeThe
system.
the
the booster.
boosterHowever,
merely adds
pedal
effort
is
high
without
assist
from
force to the master-cylinder pushrod
the booster.
The pushes
boosteron
merely
adds
when
the driver
the pedal.
forcetotal
to the
master-cylinder
pushrod
The
force
on the master-cylinder
when
driver
on pedal
the pedal.
piston the
is the
forcepushes
from the
plus
The
total
force
on
the
master-cylinder
the booster force.
piston
the force
fromlook
the pedal
plusa
Let'sis take
a closer
at how
the booster
force.works . To restate, a
vacuum
boost
Let's take
a closer
look atforce
how bya
booster
diaphragm
supplies
vacuum
boost
works.
To
restate,
having a vacuum on one side of the di-a
booster
supplies
force on
by
aphragm diaphragm
and atmospheric
pressure
having
a vacuum
on one
sidewhenever
of the dithe other.
A vacuum
exists
aphragm
on
pressure and
in atmospheric
a gas falls pressure
below atthe
other.
A
vacuum
exists
whenever
mospheric pressure. Most pressure
pressure
a ingasthefalls
below , atgages
read inzero
atmosphere
so
mospheric
pressure.
vacuum
gagesMost
are pressure
used to
special
gages
read zero
in the atmosphere,
so
measure
pressure
below
one
special
vacuum
gages
are
used
atmosphere. If most of the air to
is
measure
one
pumped out pressure
of a cylinder,below
atmospheric
atmosphere.
the on
air the
is
pressure
triesIfto most
push of
inward
pumped
out
of
a
cylinder,
atmospheric
outside of the cylinder. There is a
pressure
tries to push inward on the
lower pressure-vacuum-inside
the
outside of
themain
cylinder.
There
is a
cylinder.
The
parts of
a simple
lower
the
vacuumpressure-vacuum-inside
booster are the power chamber
cylinder. The main parts of a simple
vacuum booster are the power chamber
ber is the diaphragm and its housing.
They supply the force. The control
valve lets air or vacuum into the
power chamber.
and the control valve. The power chamAir-Suspended
Boosters
early
ber is the diaphragm
and itsAll
housing.
boosters
operated
under
no
load
with
They supply the force. The control
air on lets
both air
sidesor ofvacuum
the diaphragm
at
valve
into the
one
atmosphere
pressure.
When
the
power chamber.
brakes were applied, a valve between
Air-Suspended Boosters - All early
the booster and intake manifold was
boosters operated under no load with
opened. Air was pumped from one
air on both sides of the diaphragm at
side of the diaphragm. This type of
one atmosphere pressure. When the
booster is called an air-suspended
brakes were applied, a valve between
booster. That means there is air on
the booster and intake manifold was
both sides of the diaphragm when it
opened . Air was pumped from one
has no force on it.
side of the diaphragm . This type of
Vacuum-Suspended
Booster-The
booster is cailed an air-suspended
more modern type of vacuum booster
booster. That means there is air on
is called vacuum suspended. It has a
both sides of the diaphragm when it
vacuum on both sides of the diahas no force on it.
phragm when there is no force on it.
Vacuum-Suspended
Booster-The
Atmospheric air is let into the power
more modern type of vacuum booster
chamber on one side of the diaphragm
is called vacuum suspended. It has a
when the brakes are applied. It is
vacuum on both sides of the diaeasier to let air into a vacuum than it
phragm when there is no force on it.
is to pump air out-particularly when
Atmospheric air is let into the power
it must be done quickly. Because
chamber on one side of the diaphragm
vacuum is an absence of ail; air naturalwhen the brakes are applied. It is
ly flows into the vacuum when the
easier to let air into a vacuum than it
valve is opened. Also, the vacuumis to pump air out-particularly when
suspended booster is more fail-safe
it must be done quickly. Because
than an air-suspended booster. That's
vacuum is an absence of ail; air naturalanother reason it is popular today.
ly flows into the vacuum when the
Tandem Booster-Most
vacuum
valve is opened. Also, the vacuumboosters have one diaphragm in the
suspended booster is more fail-safe
power chamber. If a large force is rethan an air-suspended booster. That's
quired
from the booster, cylinder
another reason it is popular today.
diameter must be large. To make a
Tandem
Booster-Most
more compact
booster, some vacuum
use two
boosters have one diaphragm in the
diaphragms. This type of booster is
power chamber. If a large force is recalled a tandem booster: The diaquired from the booster, cylinder
phragms are mounted in front of each
diameter must be large. To make a
other in the power chamber, as are
more compact booster, some use two
the pistons in a tandem master
diaphragms. This type of booster is
cylinder. They each provide part of
called a tandem booster. The diathe booster force.
phragms are mounted in front of each
Brake-Booster Operation-There are
other in the power chamber, as are
three basic vacuum-booster operating
the pistons in a tandem master
conditions:
cylinder. They each provide part of
Brakes released.
the booster force.
Brake being applied.
Brake- Booster Operation - There are
Brakes holding at constant force.
three basic vacuum-booster operating
The
control valve is operating difconditions:
ferently
each of these conditions.
• Brakes for
released.
operation is shown in
•Control-valve
Brake being applied.
drawing,
pageat80.
•the
Brakes
holding
constant force.
The power chamber of a vacuumThe control valve is operating difsuspended booster is divided into a
ferently for each of these conditions.
front chamber and a rear chamber by
Control-valve operation is shown in
the diaphragm. There is always
the drawing, page 80.
vacuum applied to the front chamber.
The power chamber of a vacuumThe
vacuum line contains a check
suspended booster is divided into a
front chamber and a rear chamber by
the diaphragm. There is always
vacuum applied to the front chamber.
The vacuum line contains a check
Vacuum In Front of Diaphragm
Air to Rear
Hydraulic
Hydraulic Pistons Move Forwar
I
I
Pushrod
Typical vacuum-suspended
booster: Diaphragm acts like a piston. When brakes are
r: ":; -:·.1 Vacuum
applied, air is admitted t o chamber behind diaphragm, applying force to master-cylinder
".'·:·'1
Air Corporation.
pushrod. Drawing courtesy
Bendix
I
Typical vacuum-suspended booster: Diaphragm acts like a piston. When brakes are
applied, air is admitted to chamber behind diaphragm, applying force to master-cylinder
.agrns and
pushrod. Drawing courtesy Bendix Corporation.
Move Forw
Diaphragms and
Plates Move Forward
~ l i Pistons
c
Move Forward
Vacuum
Air
I
I
Vacuum in Front of Each Diaphragm-Air to Rear of Each Diaphragm
1::::;...::1Vacuum
Bendix tandem-diaphragm Master-Vac booster in applied position: Vacuum acts on each of
[':::-;:::-:1Airbooster force. Unit is used where high force is required and
t w o diaphragms, doubling
space is limited. Drawing courtesy Bendix Corporation.
Vacuum in Front of Each Diaphragm-Air to Rear of Each Diaphragm
-
Bendix tandem-diaphragm Master-Vac
booster
Vacuum acts on each of
Front Shell
3vRear in applied position: Shell
two diaphragms, doubling booster force. Unit is used where high force is required and
Vacuum
Check
Valve Bendix Corporation.
space is limited
. Drawing
courtesy
Reaction Disc
Vacuum Check Valve - - - 1
/
W
V
V
-
\
Control
Vallie
Rod
Val
Hydraulic Pushrod
.agm Return Spring
Diaphr
Master Cylinder
Power Section
~rJtJJ Plate
\
Valve Rod
I
I
Cross-section of Master-Vac booster with working parts indicated. Control valve admits
Diaphragm Plate
air into chamber behind diaphragm. Valve rod is moved when driver pushes on brake pedal.
Drawing courtesy Bendix Corporation.
Cross-section of Master- Vac booster with working parts indicated. Control valve admits
air into chamber behind diaphragm. Valve rod is moved when driver pushes on brake pedal.
Drawing courtesy Bendix Corporation.
79
I
I
Atmospheric Port closed
'i-
Atmospheric
Air
Valve
Rod
(Retracted)
(Retracted)
Diaphragm 3
(Retracted)
L ~ e aShell
l
Vacuum
Released Position
Atmospheric Port Open
Atomspheric
Air
Valve
Rod
Rod
(Forward)
(Forward)
-
\
Diaphragm--'
(Forward)
~.
~
lI'lf-'fl,,·'1l
Rear Shell
-vacuum
port closed
Atmospheric Air
Applied Position
Atmospheric Port Closed
Atmospheric
Valve
Rod
(Forward)
Diaphragm
(Forward)
(Forward)
\
'vacuum Port Closed
Atmospheric Air (Trapped)
Holding Position
Vacuum-booster control-valve operation shown in simplified form: Rear shellencloses rear
chamber of booster and mounts booster-and-master-cylinder assembly to fire wall.
wall, Parts
move relative to each other. Valve rod
rod moves when driver steps on pedal.
pedal. Diaphragm
Diaphragm moves
moves
when acted on by atmospheric air pressure and vacuum.
80
valve to prevent vacuum loss in booster when rnnti~folbklpress~rre
rises above
boosler
pressure-or manifold vacuum
booster presslrre-or
drops below booster vacuum. A check
valve opens to allow air to flow
flow from
bu t closes when ai
airr tries to
booster, but
flow into the booster.
booster,
With bbrakes
r a k e s released, control
valve opens a vacuum port that connects front and rear cham
bel's. Preschambers.
sure on
o n both sides of the diaphragm is
ized with the brakes released.
equalized
Both chambers contain a vacuum as
running.
long as the engine is running.
With brakes applied, control valve
moves forward. This shuts the
vacuum port between front
frolit and rear
chambers and opens the atmospheric
port. Air flows into rear chamber
through the
t h e atmospheric port, raising
The
pressure against the diaphragm. T
he
diaphragm is pushed forward by the
air pressure on
o n its rear side. The
T h e diaphragm then pushes on
o n tthe
h e mastercylinder pushrod and adds to the force
ver.
being supplied by the
t h e dri
driver.
If the brake pedal is applied without
moving, forces
forces on
o n the control valve
shut both the atmospheric port and
vacuum port. This maintains a constant force on
o n the master-cylinder
pushrod. IIff tthe
h e brake pedal is pushed
harder, atmospheric port is opened
again and additional force is applied
by the booster. Wirh
With brakes /.elensed,
vacuum port is opened: Booster force
and assist disappear,
disappear.
Booster Spring-Boosters
Spring-Boosters often are
fitted with springs to give the driver
the
t h e correct amount of feel.
feel. It is important that pedal effort not be too low.
low.
This makes the brakes too sensitive_
sensitive.
For the correct amount of feel, pedal
effort should increase with pedal
travel. As the spring is compressed,
pedal effort increases.
HYDRAULIC B O O S T E R
Some
S o m e brake boosters use hydraulics
rather than vacuum. Fluid is pressurized by the
t h e ppump
u m p that also supplies
the power-steering system.
A hydraulic brake booster is used
on
o n cars that have a poor source of
vacuum from the
manifold,
t h e intake manifold.
Not only does a su
supercharged engine
eliminate the
t h e manifold as a source of
vacuum, many newer cars are
are
equipped with emission controls and
vacuum-operated accessories that
reduce manifold vacuum,
vacuum. On such
cars, hydraulic boosters are more
practical, particularly if the car is also
-
Accumulator Port
(j)
-
E- 1500
Pedal Rod
Accumulator Port
.~
(I]
Pressure Port
:::J
(j)
_a
1500(j)
With power Ass'lst
?
OJ
tl: 1000
,g0F
:::J
C1l 1000.-0
V)
;
Booster-Runout
with power A s Point
s i s t
f32
500
Booster-Runout Point
2
500-
u
/Output
Pushrod
/
0~~--2~0--~~40~--~6~0----~8~0-----1~0~0----1~20
0
20
40
Pedal60
Effort (lb)
80
100
Output
Pushrod
120
Pedalon
Effort
(Ib)effort. Runout pOint
Curves show effect of power assist
pedal
is where power booster supplies maximum possible force. If pedal
effort isshow
higher
thanof50
Ib, brake-fluid
pressure
the
Curves
effect
power
assist on pedal
effort.increases
Runout point
same
as itpower
wouldbooster
withoutsupplies
power assist-curve
with power
is
is where
maximum possible
force.assist
If pedal
parallel
non-power-assist
past runout
point.increases
Runout point
effort istohigher
than 50 Ib, curve
brake-fluid
pressure
the
variesas
according
to eachpower
car. Boost
force is with
limited
by available
same
it would without
assist-curve
power
assist is
vacuum tor
power-steering-pump
pressure.
parallel
o non-power-assist
curve
past runout point. Runout point
varies according t o each car. Boost force is limited by available
vacuum
or power-steering-pump
pressure.
equipped
with power steering.
And,
Power-Steering Gear
there's the advantage of fitting the
equipped hydraulic
with powerbooster
steering.into
And,a
smaller
there's
the
advantage
of
fitting
the
crowded engine compartment.
smaller
hydraulic
booster
into
a
Like the vacuum booster, hydraulic
crowded
compartment.
booster isengine
located
between the brakeLike linkage
the vacuum
pedal
and booster,
master hydraulic
cylinder.
booster
is
located
between
the brakeThe boost piston has hydraulic
prespedal behind
linkageit and
master
sure
to add
forcecylinder.
to the
The
boost pistonpushrod.
has hydraulic
presmaster-cylinder
In the event
sure
behind
it to the
adddriver
forcecantopush
the
of
booster
failure,
master-cylinder
pushrod.
In
the
event
on t he master-cylinder piston just like
driverHowever,
can push
aof booster
normal failure,
brake the
system.
on
theeffort
master-cylinder
piston
justto like
pedal
is much higher
due
the
alownormal
brake system. However,
pedal ratio.
pedal
effort
is much
higherparts
dueare:
to the
Basic
hydraulicbooster
low
pedal
ratio.
• Boost piston.
Basic hydraulic-booster
parts
are:
• Sliding
spool valve, which
regulates
Boost pressure.
piston.
braking
valve,
regulates
• Sliding
Lever spool
system
to which
operate
spool
braking
valve. pressure.
system tosystem.
operate spool
• Lever
Reserve-pressure
valve.
The boost piston operates much
Reserve-pressure
like
any hydraulic system.
piston. Because
The
boost piston
operates
much
power-steering
hydraulic
pressure
is
like any
hydraulic
Because
much
higher
than piston.
the "pressure"
power-steering
hydraulicthe
pressure
available
from vacuum,
piston is
is
much
higher
than
the
"pressure"
much smaller than a vacuum-booster
available from
the ispiston
is
diaphragm.
The vacuum,
boost piston
located
much
smaller
than
a vacuum-booster
between
the rod
from
the brake pedal
diaphragm.
The boost piston ispushrod.
located
and
the master-cylinder
between
the
rod
from
the
brake
When the brakes are applied,pedal
the
and
thethemaster-cylinder
pushrod.
lever on
input rod slides the
valve
When
the brakes
are high-pressure
applied, the
to
a position
that allows
lever
on
the
input
rod
slides
valve
hydraulic fluid to enter the the
chamber
to
a
position
that
allows
high-pressure
behind the piston. This applies force
hydraulic
fluid to enter the chamber
to
the master-cylinderpushrod.
behind
the pressure
piston. This
Reserve
is applies
stored force
in a
to
the
master-cylinder
,pushrod.
cylinder called an accumulator. There
pressure
stored
in a
is Reserve
a very heavy
spring is
inside
the accuThere
cylinder called an accurn~~lato~:
is a very heavy spring inside the accu-
Return
Port
Return
Port
Power
Section
Power
Section
Linkage Bracket
Bendix Hydro- Boost hydraulic brake booster mounts between
master cylinder and brake pedal. High-pressure hydraulic fluid
allows
to be much
smaller brake
than vacuum
Bendix unit
Hydro-Boost
hydraulic
boosterbooster.
mounts Hydraulic
between
pressure
is supplied
power-steering
pump. Drawing
courtesy
master cylinder
and by
brake
pedal. High-pressure
hydraulic
fluid
Bendix unit
Corporation.
allows
to be much smaller than vacuum booster. Hydraulic
pressure is supplied by power-steering pump. Drawing courtesy
Bendix Corporation.
f
Accumulator
,-----\
I
Power-Steering Gear
f
Accumulator
Spool Spool
t
t
Master Hydro-Boost
Cylinder
Power-Steering D
Pump
C
Return Lines
High-Pressure Lines
-
With Bendix Hydro-Boost power section in
Pump
~7
High-Pressure Lines
released position, most fluid from pump is.
routed
through
power
section
powerWith Bendix Hydro-Boost
powerto
section
in
steering gear.
Some
fluid
returns
pump
released
position,
most
fluid
from to
pump
is.
reservoir
throughpower
return section
port. Spring
accurouted through
to powermulator
sufficient
under
pressteering stores
gear. Some
fluid fluid
returns
to pump
sure to through
provide return
two port.
or three
reservoir
Springpoweraccuassisted stores
brake sufficient
applications
case presfluid
mulator
fluidinunder
flow from
power-steering
sure
t o provide
two or pump
three ceases.
powerAccumulator
is applications
charged within fluid
assisted brake
case when
fluid
steering
is turned or
brakes
are
flow
fromwheel
power-steering
pump
ceases.
applied.
Drawing
courtesy
Accumulator
is charged
with fluidBendix
when
Corporation.
steering
wheel is turned or brakes are
applied.
Drawing
mulator
that
appliescourtesy
a force Bendix
to a
Corporation.
piston. Hydraulic fluid contained be-
mulator
applies
a force
tween thethat
piston
and the
end oftothea
piston. Hydraulic
fluid by
contained
becylinder
is pressurized
the spring.
tween
pistonis and
of the
If
the the
engine
shutthe
off,end
pressure
cylinder
pressurized bypump
the ceases.
spring.
from the is
power-steering
If
the
engine
is
shut
off,
pressure
The pressurized fluid stored in the acfrom the power-steering
pump
ceases.
cumulator
is enough to
apply
the
The
pressurized
fluid stored
in the
acbrakes
several times
with the
engine
cumulator
is
enough
to
apply
the
shut off. This safety feature allows the
brakes
times
the stalls
engine
car
to beseveral
stopped
if thewith
engine
or
shut
off.
safety
allows
the car
is This
rolling
with feature
the engine
off.the
car to be stopped if the engine stalls or
the car is rolling with
the engine off.
ADJUSTABLE
PUSHRODS
Most boosters are designed with adADJUSTABLE
PUSHRODS
justable
master-cylinder
push rods.
Most
are touch
designed
adThis
rodboosters
should just
the with
masterjustable
master-cylinder
pushrods.
cylinder piston with the brakes
This rod should just touch the mastercylinder piston with the brakes
Hydro- Boost in released position (above)
and applied position (below): With brake
pedal
depressed,
input position
rod and (above)
piston
Hydro-Boost
in released
moveapplied
forward
slightly.
LeverWith
assembly
and
position
(below):
brake
moves
sleeve forward,
four
pedal depressed,
input clOSing
rod andoffpiston
holes
center
of spool.
Formove leading
forwardto open
slightly.
Lever
assembly
ward
of spool closing
allows additional
movesmovement
sleeve forward,
off four
hydraulic
fluidt to
entercenter
cavity of
behind
holes leading
o open
spool.boosForter piston
to pressurize
This
moves
ward
movement
of spool area.
allows
additional
piston
and
rod
forward
hydraulic
fluidoutput
t o enter
cavity
behindagainst
boosmaster-cylinder
pistons area.
to apply
ter piston to pressurize
This brakes.
moves
Drawingand
courtesy
Bendix
piston
output
rod Corporation.
forward against
master-cylinder pistons to apply brakes.
Drawing
Spool courtesy
Moved Bendix Corporation.
Forward
Spool Moved
Piston , Pushrod and End
Moved Forward
Piston, Pushrod and End
long rod will leave
Moved Forward
released. A
the
master-cylinder compensating port
released.and
A cause
long rod
leave
the
covered
brakewill
drag.
A short
master-cylinder
compensating
port
rod will add slop or excess pedal travel
covered
and cause
brake
A short
to the system.
See
yourdrag.
car's
shop
rod
will add
or excesson
pedal
travel
manual
for slop
instructions
adjusting
to
system. Seepushrod.
your car's shop
the the
master-cylinder
manual for instructions on adjusting
the master-cylinder pushrod.
81
Other Types of Brakes
8
Outlawed by most racing organizations, movable air brakes, such as one at rear of this 1955 300SLR Mercedes, are extremely effective at
over 100 mph. Frontal area and drag coefficient are increased dramatically when air brake is activated. Photo courtesy Mercedes-Benz .
Outlawed by most racing organizations, movable air brakes, such as one at rear of this 1955 300SLR Mercedes, are extremely effective at
over 1 0 0 mph. Frontal area and drag coefficient are increased dramatically when air brake is activated. Photo courtesy Mercedes-Benz.
In this chapter, I briefly describe
brakes other than the traditional
In this
chapter,
I briefly
describe
drum
or disc
brakes.
Also, there
are
brakes
other
than
the
traditional
several differeht ways to operate
drum
disc there
brakes.areAlso,
brakes.orAnd,
otherthere
waysare
of
several
ways than
to operate
stopping different
a vehicle other
friction
brakes.
thereAlthough
are other ways
of
at
the And,
tires.
briefly
stopping
a
vehicle
other
than
friction
discussed, I don't go into details on
at the
Although
briefly
other
braketires.
systems.
The subject
is
discussed,
I
don't
go
into
details
on
too extensive for this book.
FF = Force on Front Tires
FA = Force on Rear Tires
FF = Force on Front Tires
We = Car Weight
FR= Force on Rear Tires
FD = Aerodynam ic Drag
Wc = Car Weight
RD = Rolling Drag
FD= Aerodynamic Drag
FT = Forward Thrust
RD= Rolling Drag
FA = Aerodynamic Downforce
FT = Forward Thrust
FA = Aerodynamic Downforce
other brake systems. The subject is
too
extensive for thisDRAG
book.
AERODYNAMIC
&
FA
v-
Drag acts to slow a moving car.
AERODYNAMIC
DRAG
Drag forces act toward
the rear of the
Drag
acts
to
slow
moving
car.
car when it is moving aforward
. Drag
0
FR
FT
Forces on moving car: Vertical forces on the tires, FF and F R, are determined by car's
weight and aerodynamic forces. Aerodynamic-drag force, F o' acts on car near center of
body
cross
section,car:
viewed
from forces
the front.
Downforce,
any,F
actdetermined
anywhere on
Forces
on moving
Vertical
on the
tires, FFifand
,, canare
by body.
car's
With
thisand
car,aerodynamic
downforce isforces.
mostly Aerodynamic-drag
on rear wing.
weight
force, F, acts on car near center of
body cross section, viewed from the front. Downforce, if any, can act anywhere on body,
With this car, downforce is mostly on rear wing.
82
Drag forces
act toward
theaerodynamrear of the
consists
of rolling
drag and
car
when
it is moving
forward.
Drag
ic drag.
Rolling
drag is caused
by resisrolling
drag
and
aerodynarnconsists
of
tance of the tires to rolling, friction in
ic drag.
Rolling
drag is caused
the
wheel
bearings,
and allby resisother
tance
of
the
tires
to
rolling,
drive-train friction forces. friction in
theRolling
wheel drag
bearings,
and allexists
other
or resistance,
at
drive-train
friction
forces.
all speeds, but increases with speed.
Rolling
drag or resistance,
at
You
can experience
rolling exists
drag by
all
speeds,
but on
increases
pushing
a car
a level with
road.speed.
You
You
drag will
by
must can
keepexperience
pushing or rolling
rolling drag
pushing
a
car
on
a
level
road.
You
stop the car. The force you use to
drag
must
pushing O r
stop the car. The force you use to
maintain speed equals rolling drag.
Aerodynamic drag is caused by air
maintain around
speed equals
rolling
drag.The
flowing
the car
body.
Aerodynamic
drag
is
caused
by air
force on the car is zero when air speed
flowing
around
the
car
body.
is zero. It increases with the squareThe
of
forceaironspeed.
the carThis
is zero
whenthat
air speed
the
means
aerois zero. It increases
with the square
of
dynamic
drag quadruples
if you
the
air
speed.
This
means
that
aerodouble car speed. If a car has 100 lb of
dynamic drag
will
aerodynamic
dragquadruples
at 30 mph ,if it you
double
carlbspeed.
a carIfhas
100islbinof
have 400
at 60 If
mph.
speed
aerodynamic
drag
at
30
mph,
it
will
creased to 90 mph, aerodynamic drag
have
400 Ib atto 60900
mph.
If speed
inis
increased
Ib-9
timesis the
creased to 90 mph,
aerodynamic
drag aerodynamic
at 30 mph. drag
At
is increased
900 lb-9 force
times onthea
racing
speeds,toaerodynamic
aerodynamic
dragtheatcar's
30 weight.
mph. On
At
car
can approach
racing
speeds,
aerodynamic
force
on
the very powerful land-speed-recorda
car can
the car's weight.
On
cars
runapproach
at the Bonneville
Salt Flats,
the
very
powerful
land-speed-record
aerodynamic drag gets so high the
cars run
theatBonneville
Flats,
to
tires
can at
spin
high speedSalt
trying
aerodynamic
drag
gets
so
high
the
overcome it!
tires
can spin atdrag
highisspeed
trying by
to
Aerodynamic
determined
overcome
it!
maximum cross-section size and the
Aerodynamic
dragThe
is determined
by
of the car.
cross-section
shape
maximum
cross-section
size
and
the
size is called /rontal area. Frontal area
shape
of the car,
cross-section
is approximately
theThe
height
of the car
size
is
called
frontal
area.
Frontal
area
is nearly
times its width . Frontal area
is
a
~
~
r
o
x
i
m
a
t
e
l
the
v
height
of
the
the same for most road cars, as it is car
for
most race cars in a given class. Shape
the
same
for most
cars,one
as itcar
is foi
var ies
a great
dealroad
from
to
most
race
cars
in
a
given
class.
Shape
another. Reducing drag by improving
varies
great streamlining.
deal from one
car to
A streamshape isa called
another.
Reducing
by improving
aerodynamic
drag
lined shape
has lowdrag
shape
is called streamlining. A streamfor its size.
lined
aerodynsmic
Theshape
shapehas
of low
the car
compared drag
to a
for
its
size.
standard flat shape is described by a
The shape
the drag
car compared
a
coefficient.to A
number
calledof the
standard
shape is means
described
by a
high dragflat
coefficient
a highnumber
calledA the
A
lowdrag
dragcoefficient.
coefficient
drag shape.
high
drag
coefficient
means
a
highmeans a streamlined shape. The worst
drag
shape.have
A low
drag
coefficient
of
car shapes
a drag
coefficient
means
a
streamlined
shape.
The worst
nearly 1.0. The most streamlined
cars
car
a drag coefficient
of
haveshapes
a draghave
coefficient
of about 0.2.
nearly
1
.O.
The
most
streamlined
cars
Aerodynamic drag on a car varies
have
a drag
of about 0.2.
directly
with coefficient
its drag coefficient.
For
Aerodynamic
drag
on
a car
varies
example, a car with a drag
coefficient
directly
with
its the
dragaerodynamic
coefficient. drag
For
of 0.6 has
twice
example,
car with
a drag
coefficient
as the
same-size
car
at a givena speed
of
0.6a drag
has twice
the aerodynamic
drag
of 0.3.
with
coefficient
at When
a giventhespeed
the his
same-size
driveraslifts
foot off car
the
with
a
drag
coefficient
of
0.3.
throttle at high speed, drag on the car
When
the driver
foot off the
will
rapidly
slow lifts
it. hisDeceleration
throttle
at
high
speed,
drag
on the car
by
equals the total drag force divided
will
rapidly
slow
it.
Deceleration
car weight. Above 60 mph, most drag
equals
the total drag
force divided
is aerodynamic.
If a 2000-lb
car hasbya
car
Above
drag
500 lb60, itmph,
will most
decelerate
dragweight.
force of
is
aerodynamic.
If
a
2000-lb
car
has
a
at 0.25 g when not under power. Bedrag
force
of
500
Ib,
it
will
decelerate
cause aerodynamic drag drops as
at
0.25drops,
g when
not under drops
power.asBespeed
deceleration
car
cause aerodynamic drag drops as
speed drops, deceleration drops as car
Except for lights atop body, custom Camaro pace car has improved streamlining on an already excellent body shape. Note smooth-flowing lines with a minimum of projections or
corners.
Except for lights atop body, Custom Camar0 pace car has improved streamlining on an al-
ready excellent body shape. Note smooth-flowing lines with a minimum of projections or
corners.
Old sports cars are unstreamlined. Body shapes are rough, angular and have lots of parts
sticking into airflow. Streamlining of cars refers to shape, not size of body. An unstreamlinedsports
car has
a higher
drag force on itBody
than shapes
a streamlined
car ofangular
the same
. lots of parts
Old
cars
are unstreamlined.
are rough,
andsize
have
sticking into airflow. Streamlining of cars refers to shape, not size of body. An unstreamlined
has a higher
drag force on drag
it than is
a streamlined
car of of
theobject
same size.
W = Weight
in pounds
speedcar drops.
Aerodynamic
very low at low speeds.
speed
drops.is Aerodynamic
is
the formula fordrag
the acFollowing
very
low
at
low
speeds.
celeration of an object in g's. RememFollowing
is the formulais fornegative
the acber
that deceleration
celeration
of
an
object
in
g's.
Rememacceleration.
ber that deceleration is negative
Acceleration = ~
acceleration.
F force on object in
F = Unbalanced
Acceleration
=
pounds
F = Unbalanced force on object in
pounds
w
that ifin the
unbalanced
W Remember
= Weight of object
pounds
force acts in a direction to slow the
Remember
thathasif athe
unbalanced
object,
that force
negative
value.
force
acts inforce
a direction
to slow
the
A negative
makes the
acceleraobject,
thatobject
force negative.
has a negative value.
tion of the
A If
negative
force
makes
to the
be a acceleraspeeding
an object
happens
tion
of
the
object
negative.
car and the driver lifts off the throttle,
object hamens
a speedinn
force.
theIf an
unbalanced
forcetoisbedrag
car and t h k drive; lifts off the throttle,
the unbalanced force is drag force.
83
HOW TO CALCULATE
AERODYNAMIC-DRAG FORCE
HOWformula
TO CALCULATE
The
for aerodynamic-drag
AERODYNAMIC-DRAG
FORCE
force
is simple:
The formula for aerodynamic-drag
Aerodynamic drag
force is simple:
= 0.00256AFCoS2 in pounds
Aerodynamic
AF = Frontal drag
area of car in square
= 0.00256A,CDS2 in pounds
feet
Frontal
area Of ofcar
in 'quare
CD == Drag
coefficient
body
shape
feet
S == car speed in miles per hour
D
' TheDrag
'OeffiCient
Of body
frontal
area is
the shape
crossS = car speed in miles per hour
sect·ional area of a car as viewed
frontfrom
front. area
If you isdraw
Thethefrontal
the a crosssectional
area
of a
viewed
outline
of the
carcar
on as
a sheet
of
view
from the
front.
You draw
a frontandIf count
the squares
graph
paper
view
of that
the Car
a sheet of
will on
approximate
insideoutline
outline,
graph
Raper
andarea.
COunt
the squares
the car's
frontal
H each
square
inside outline, that will approximate
the car's frontal area. If each square
-
on the paper is scaled at 1 inch on a
side,the frontal area will come out
on
the paper
is scaled
at 1divide
inch on
a
inches.
If you
the
in square
side,
theoffrontal
area
will come
out
number
square
inches
by 144,
in square
inches.
you
get square
feet.If you divide the
square
number
has inches
nothingbyto144,
do
Frontalofarea
you get
with
thesquare
shapefeet.
of the front ofa car.
Frontal
area has cross-sectional
nothing to do
Only
the maximum
front of Shape
a car.
with
thethe
shape
size of
car of
is the
important.
Only the
cross-sectional
affects
themaximum
drag coefficient,
not the
size of the
is important.
Shape
frontal
area.carTypical
drag coeffiaffects
theproduction
drag coefficient,
notfrom
the
cients for
cars vary
frontal
Typical
coeffia low of area.
0.30 to
a high drag
of 0.60.
The '
cientscoefficients
for production
cars vary
for many
carsfrom
are
drag
a low in
of magazine
0.30 to a articles
high of 0.60.
The
and road
given
drag
for article
many cars
are
tests.coefficients
Find such an
for your
given
in magazine
and road
car
to determine
its articles
drag coefficient.
tests. Find such an article for your
car to determine its drag coefficient.
1500
Cd = Drag Coefficient
1500
Frontal Area = 25.4 sq It
Cd = Drag Coefficient
Frontal Area = 25.4 sq f t
Cd = 0.6
1000
Air
Drag
1000 -
,/
/'
(Ib)
Air
Drag
(I b)
/
500
500
/"
- C d =0.3
./
-
/
- --
/
/
oL---~~~~--+-----~------+-----~----80
160
200
40
120
0
40
80
Car SpeedI (mph)
120
I
I
160
200
I
Graph shows how aerodynamic drag varies with
car speed
and drag coefficient. Solid line is
Car Speed
(rnph)
for unstreamlined car with a 0 .6 drag coefficient. Dotted curve is for streamlined car with
the
same
frontal
but half the
drag,
or 0.3
coefficient.
Drag
figures areSolid
typical
Graph
shows
howarea,
aerodynamic
drag
varies
withdrag
car speed
and drag
coefficient.
linefor
is
a large
sedan.
for
unstreamlined
car with a 0.6 drag coefficient. Dotted curve is for streamlined car with
the same frontal area, but half the drag, or 0.3 drag coefficient. Drag figures are typical for
a large sedan.
The formu la for dece leration can be
written another way:
The formula for deceleration can be
.
written
another
way: FD
Deceleration of a car = WFDc
Fa = Drag force
of aoncarcar=in
-- pounds
Deceleration
W,LJpounds
Wc = Weight of the car in
F, = Drag force on car in pounds
W, = Weight of the car in pounds
In this formul a, deceleration is In
g's. If you know the drag forc e on a
thiscan
formula,
deceleration
is In.
calculate
its deceleration
car,Inyou
g's.
If you know
dragway,
forceif on
Approaching
it anthe
o ther
youa
car,
you
can
calculate
its
deceleration.
could measure deceleration , you
Approaching
another
you
could
calculateitdrag
force .way,
This if
is how
could
measure
you
vehicle drag
can bedeceleration,
determined withcould
calculate
drag
force.
This
is
how
out using a wind tunnel.
vehicle drag can be determined without
using a wind tunnel.
AERODYNAMIC
BRAKING
If a car is streamlined and suddenly
AERODYNAMIC BRAKING
If a car is streamlined and suddenly
84
increases its drag coefficient for braking while at high speed, it can slow
increases This
its dragis coefficient
for brakquicker.
how aerodynamic
ing
whileworks.
at high
speed,
slow
braking
Added
dragit iscan
created
quicker.
This
is
how
aerodynamic
by changing the shape or size of the
braking
Added dragchange
is created
car.
Theworks.
drag-coefficient
has
by
changing
or size of
the
to be
large tothe
getshape
a significant
effect
car.
drag-coefficient
fromThe
aerodynamic
braking.change
Also, has
the
to be must
large be
to high.
get a Itsignificant
speed
also helps effect
if the
from
aerodynamic
braking.
Also, the
car is light because deceleration
speed
mustonbe weight.
high. It also
helps aeroif the
depends
Finally,
car
is
light
because
deceleration
dynamic braking is worthwhile only
depends
weight.
Finally,
on
a race on
car that
brakes
at very aerohigh
dynamic
braking is worthwhile only
speed
.
onAerodynamic
a race car thatbraking
brakes atis very
high
efficient
speed.
because there is no heat to dissipate in
braking
is efficient
theAerodynamic
brake system.
Instead,
aerono heat
dissipate in
because there
dynamic
drag isheats
thetosurrounding
the asbrake
Instead, it. aeroair
the carsystem.
passes through
The
dynamic drag heats the surrounding
air as the car passes through it. The
wheel brakes can be applied along
with aerodynamic braking for even
wheel
can be applied
along
higher brakes
deceleration.
Deceleration
with
aerodynamic
brakingoperating
for even
with both
brake systems
is
higher than
deceleration.
greater
either systemDeceleration
can achieve
with both brake systems operating is
Singularly!
greater
than either system
can achieve
If aerodynamic
braking
is so
singularly!why is it used infrequently
efficient,
braking
is so
or If
onlyaerodynamic
on a few specialized
race cars?
efficient,
why
is
it
used
infrequently
• The braking force is useful only at
or only
onspeeds-near
a few specialized
very
high
200 race
mph.cars?
braking force
is useful
at
• The
Aerodynamic
braking
will notonly
bring
very
high
speeds-near
200
mph.
a car to a dead stop. The braking force
Aerodynamic
not nears
bring
approaches
zerobraking
as ca r will
speed
a car. to a dead stop. The braking force
zero
approaches
zero brakes
as car add
speedweight,
nears
• Aerodynamic
zero.
complexity and cost.
Aerodynamic
brakesareaadd
weight,
• Because
car frontal
should
incomplexity
and cost.
crease
for aerodynamic
braking to be
Because the
car frontal
should
ineffective,
car willarea
occupy
more
crease
for
aerodynamic
braking
to
be
space on the road with the brakes
effective,This
themay
car mwill
more
applied.
a ke occupy
it difficult
to
space near
on other
the road
drive
cars. with the brakes
applied.
Thisracing
may make
it difficult
to
• In most
classes,
movable
drive
near
other
cars.
aerodynamic devices are illegal.
In
most racingbrakes
classes,have
movable
Aerodynamic
been
aerodynamic
illegal.
tried in roaddevices
racing,are
such
as on the
Aerodynamic
brakes
have
Mercedes
sports cars
of the
mid-been
' 50s
tried
in
road
racing,
such
as
on the
and early winged Can-Am Chaparral
Mercedes sports cars of the mid-'50s
racers.
and
early winged
Chaparral
Mercedes
used aCan-Am
flap-mounted
flat
racers.
on the tail of their 300SLR. This fl ap
Mercedes
used a flap-mounted
flata
was
raised hydraulically
by operating
on the tail
of their
300SLR.
flap
control
valve
in the
cockpitThis
, nearly
was
raisedthe
hydraulically
doubling
frontal areabyofoperating
the car. Ita
control
valve
in
the
cockpit,
nearly
also made the airflow more turbulent.
doubling
the
frontal
area
of
the
car.tal
It
The combination of the larger fron
also
made
the airflow
more
and air
turbulence
more
thanturbulent.
doubled
The
combination
the larger
frontal
aerodynamic
drag .of
Because
this car
exand
air
turbulence
more
than
doubled
ceeded 180 mph on the 3-mile
aerodynamic drag.
Becauseand
this car
straightaway
at LeMans,
had exto
ceeded
mph hairpin
on theturn,
3-mile
slow for 180
a 30-mph
the
straightaway
LeMans,
hadload
to
aerodynamic at
brake
took a and
lot of
slow
for
a
30-mph
hairpin
turn,
the
off the wheel brakes. Competing drivaerodynamic
brake
a lot ofprobload
ers
complained
abouttook
a visibility
off
wheel
Competing
drivlemthe
when
thebrakes.
Mercedes
aerodynamic
ers
complained
about
a visibility
brake
was raised.
This,
however,probwas
lem
when
the
Mercedes
aerodynamic
probably due to the superiority
of the
brake was raised.
was
Mercedes
rather This,
than ahowever,
"visibility"
probably
hazard. due to the superiority of the
Mercedes
rather ran
than
a "visibility"
The Chaparral
a large
wing over
hazard.
the rear wheels, which could be
The Chaparral
large wing
over
varied
in its angleran
of aattack.
The wing
the
rear
wheels,
which
could
be
ran at low angles when the car was
varied
in
its
angle
of
attack.
The
wing
accelerating, to give some downforce
ran at
anglesdrag
when
the car
and
to low
minimize
created
by was
the
accelerating,
to give some
downforce
wing. When braking,
the driver
could
and
to minimize
drag created
by the
tip the
wing to maximize
downforce
wing.
When
braking,
the
driver
could
and drag . The downforce increase
on
tip
to maximize
downforce
the the
rear wing
tires allowed
more rear-wheel
and
drag.Because
The downforce
on
braking.
this car increase
was highly
the
rear
tires
allowed
more
rear-wheel
successful, the racing rules were
braking. Because
car was highly
changed,
banningthismovable
aerosuccessful,
the racing rules were
dynamic devices.
changed, banning
dynamic devices.
movable
aero-
High-Drag
Position
High-Drag
Position
Aerodynamic brake on the Chaparral Can-Am car was similar to
this. Wing in low-drag position supplied downforce to rear tires for
improved high-speed
cornering.
When
flipped
to high-drag
Aerodynamic
brake on the
Chaparral
Can-Am
car was
similar to
position,
aerodynamic
increased
deceleration
. Movathis.
Wingadded
in low-drag
positiondrag
supplied
downforce
to rear tires
for
ble wings are
illegal in road
racing today.
improved
high-speed
cornering.
When flipped to high-drag
Aerodynamic braking has been used for years in drag racing.
Racing chutes stop funny cars much quicker than ordinary brakes.
Cars are traveling
near has
250 been
mph atused
finishfor
line.
After in
each
run,racing.
paraAerodynamic
braking
years
drag
chute ischutes
repacked.
would
work
for cars
brakes
are
Racing
stopThis
funny
cars not
much
quicker
thanwhere
ordinary
brakes.
applied
than once
during
a race.
mph
at finish line. After each run, paraCars
aremore
traveling
near 250
position, added aerodynamic drag increased deceleration. MovableAerodynamic
wings are illegalbraking
in road racing
has today.
found a
chute is repacked. This would not work for cars where brakes are
applied more than once during a race.
home in drag racing. All the really fast
Aerodynamic
braking
has found
drag
cars, such as
top fuelers
, funnya
homeand
in drag
racing. All
really fast
cars
pro stockers,
usethe
a parachu
te
drag
cars,
such asBecause
top fuelers,
funny
to assist
stopping.
a parachute
cars
pro stockers,
use a parachute
reliesandon
aerodynamic
drag for
to
assist
stopping.
Because
a parachute
effectiveness, it is true aerodynamic
relies
aerodynamic
dragwon't
for
braking. on
Obviously,
a parachute
effectiveness,
it is ortrue
aerodynamic
work in road racing
on the
street bebraking.
Obviously,
a parachute
cause
it has
to be repacked
afterwon't
each
work
in
road
racing
or
on
the
streetis beapplication. In a drag race, this
no
cause
it has
to be repacked
after each
problem
because
the car makes
one
application.
a drag
this is no
stop
per run.InThe
chuterace,
is repacked
by
problem
because
the
car
makes
the pit crew prior to the next run . one
stop
per drag
run. The
is repacked
by
Some
cars chute
reach or
exceed 250
the pitand
crew
the next
run. , the
mph
areprior
veryto light.
If large
Someapplies
drag cars
reachmore
or exceed
250
chute
much
stopping
mph
and
are
very
light.
If
large,
force than the wheel brakes, thusthe
is
chute
applies
muchin more
stopping
extremely
effective
reducing
speed
force
than100themph
wheel
thus is
to under
in a brakes,
short distance.
extremely
In fact, theeffective
only limitintoreducing
how fastspeed
a car
to under
mphwith
in a ashort
distance.
could
be 100
slowed
chute
is the
In
fact,force
the only
to how
fastwitha car
inertia
that limit
the driver
must
could when
be slowed
withopens.
a chute is the
stand
the chute
inertia
force that
The critical
partthe
of driver
settingmust
up a withdragstand
opens.
racingwhen
chutetheischute
where
and how the
Themounts
critical part
of setting
a dragchute
to the
frame. up
If mountracing
chute is
where
and the
howchute
the
ed
off-center,
when
opened
chute
mounts
to
the
frame.
If
mountwill cause the car to swerve. Ideally,
ed
when opened
the off-center,
mount should
be near the
thechute
CG
will
cause
car to swerve.
Ideally,
height,
andthe
centered.
The maximum
the mount
should bemount
near is
themany
CG
force
on a parachute
height,
and
centered.
The
maximum
tons, so mount strength is critical.
force
on a mounts
parachutehave
mount
is many
Parachute
ripped
off
tons, leav
so ing
mount
strength
cars,
the driver
only isthecritical.
wheel
Parachute
haveThe
ripped
off
brakes
to mounts
stop with.
mount
cars, leaving
the driver
theseveral
wheel
should
be strong
enoughonly
to lift
brakes
stop
with. who
Thesellmount
race
cars to
from
it. Those
dragshould
be
strong
enough
to
several
race parachutes, such as liftSimpson
race cars
from it. Those
who
sell dragSafety
Equipment
Co., can
provide
inrace parachutes,
such and
as setting
Simpson
structions
on mounting
up
Safety
Equipment Co., can provide inthe
system.
structions on mounting and setting up
the system.
Compressed air moves brake shoes by
means of an actuating chamber mounted
on
axle housing.
chamber
rotates
Compressed
airActuating
moves brake
shoes
by
tube
(arrow)
pushrod
and mounted
lever to
means
of an through
actuating
chamber
move
brake
shoes
against chamber
drum. Note
lack
on
axle
housing.
Actuating
rotates
of backing
plate
on these
truck and
brakes.
tube
(arrow)
through
pushrod
lever to
move brake shoes against drum. Note lack
of backing plate on these truck brakes.
PNEUMATIC BRAKES
Pneumatic brakes, commonly called
PNEUMATIC
BRAKES
air brakes, refer
to the actuating
Pneumatic
brakes,
commonly
system. Pneumatic brakes
use called
comair brakes,
to the
the brakes
actuating
pressed
air torefer
operate
insystem.
Pneumatic This
brakes
comstead
of hydraulics.
typeuse
of brake
pressed isair
to primarily
operate the
brakes
insystem
used
for large
comstead
of
hydraulics.
This
type
of
brake
mercial vehicles. A truck usually uses
system is used
primarily
for large
pneumatic
brakes
because
therecomare
mercial vehicles.
usuallybrake
uses
advantages
over Aa truck
hydraulic
pneumatic brakes because there are
system.
advantages
a hydraulic
brake
Pneumaticover
brakes
are actuated
by
system.
compressed
air supplied by an enginePneumatic
brakes areThe
actuated
by
driven
air compressor.
comprescompressed
air
supplied
by
an
enginesor supplies high-pressure air to a stordriven
compressor.
The compresage
tankair
, which
is big enough
to mainsor supplies
high-pressure
to a stortain
pressure
when the air
brakes
are
age tank, which is big enough to mainapplied.
tain
pressure air
when
theto brakes
are
Compressed
is fed
the brakeapplied. system by valves controlled
actuating
is fedIfto the
the brakeby Compressed
the brake air
pedal.
driver
actuating system by valves controlled
by the brake pedal. If the driver
Pneumatic truck brakes are actuated by
compressed air supplied by engine-driven
air
compressor.
reservoir
emergenPneumatic
truckAirbrakes
arehas
actuated
by
cy supply of air
brakes by
won't
fail if comcompressed
air so
supplied
engine-driven
pressor
belts break.
air compressor.
Air reservoir has emergen-
cy supply of air so brakes won't fail if compressor belts break.
pushes harder on the brake pedal,
more air pressure is applied to the
pushes
on the
brake
pedal,
brakes. harder
The driver
is not
supplying
more
air
pressure
is
applied
to
the force or air movement, so the
his
brakes. The
driver
is not supplying
strength
doesn't
matter.
theBecause
force ortrucks
air movement,
his
are very so
heavy
strength
doesn't
matter.
under full load, power-assisted hyBecause
trucks
very heavy
draulic
brakes
wouldare
be necessary.
A
under
full load, ofpower-assisted
hymajor advantage
pneumatic brakes
draulic
necessary.
A
is
they brakes
have would
built-inbe power
assist.
major
advantage
of
pneumatic
brakes
Another advantage is pneumatic
is theyarehave
built-in by
power
brakes
not affected
smallassist.
leaks
Another
advantage
is pneumatic
in the system.
Air is supplied
continubrakes by
arethe
not compressor,
affected by small
leaks
ously
so unless
in
the
system.
Air
is
supplied
continuthere is a huge hole in the system,
ously by
the compressor,
unless
there
is never
a loss of so
pressure.
there is athe
hugeairhole
in the system,
Instead,
compressor
must
there harder
is never
a loss ofpressure
pressure.
work
to maintain
in
Instead,
the
storagethe
tank.air compressor must
work
to maintain
pressure
in
The harder
pneumatic
system does
not use
the
storage
tank.
hydraulic fluid, so it is not affected by
The pneumatic system does not use
hydraulic fluid, so it is not affected by
85
Aircraft multi-disc brake: Brake, which is
buried in wheel, is good for one stop after
landing.
Brake must
cool Brake,
before which
another
Aircraft multi-disc
brake:
is
landing in
can
be made.
buried
wheel,
is good for one stop after
landing. Brake must cool before another
landing can be made.
the reduced boiling point of old, contaminated fluid. Thus, the system can
the much
reducedlonger
boilingbetween
point of servicing.
old, congo
taminated
fluid. Thus,
the system
can
This
is important
on long-haul
trucks.
goThe
much
longer
between
servicing.
disadvantages of a pneumatic
This
important
n long-haul
trucks.
brakeissystem
are osize,
complexity
and
T h eAlso,
disadvantages
of a pneumatic
cost.
it takes engine
power to
brakethe
system
are size, complexity
and
run
air compressor.
System prescost.
Also,
it
takes
engine
power
to
sure is much lower than that of a hyrun the system.
air compressor.
System
presdraulic
Thus, the
diameters
sureallis much
than that of a and
hyof
the lower
cylinders-master
draulic
system.
T
h
u
s
,
the
diameters
wheel- are much larger. Trucks have
of
the cylinders-master
and
lots all
of room,
so there's no problem
wheel-are
larger.
Trucks
havea
fitting
large much
cylinders.
But
size has
lots of room,
so there's
no problem
definite
disadvantage:
It takes
time to
fitting
large
cylinders.
But
size has a
build up pressure at the brakes.
definite
It takes
timethe
to
There disadvantage:
is a small delay
between
build the
up pressure
at the
time
driver hits
thebrakes.
pedal and the
Thereactually
is a small
delayEngineers
between can
the
brakes
apply.
time
the
driver
hits
the
pedal
and
the
design a system to reduce, but not
brakes
actually
apply.
Engineers
can
eliminate, this time lag.
design
a system
reduce,
but not
Compressor
costtomakes
a pneumateliminate,
this time
lag.expensive than
ic brake system
more
Compressor
cost makes
a pneumata hydraulic
system.
However,
because
ic brakecommercial
system morevehicles
expensive
than
many
require
a hydraulic system.
However,
because
compressed
air to run
other systems
many
vehicles
on
the commercial
vehicle, the cost
of therequire
comcompressed
air
to
run
other
systems
pressor is justified, considering
its
o n the vehicle,
the cost of the comdouble-duty
function.
pressor
consideringin itsa
There isarejustified,
other complexities
double-duty
function.
pneumatic brake system. The comThere must
are other
in a
pressor
have complexities
a pressure-relief
pneumatic
brake over
system.
T h e comvalve
to prevent
pressurizing
the
pressor must
a pressure-relief
system.
Also, have
there's
a pressurevalve to prevent
overpressurizing
controlled
unloader
that takes the
the
system.
Also,
there's
a pressureload off the compressor once
storagecontrol
led unloader
the
reaches that
abouttakes
100 psi.
tank pressure
load
off
the
compressor
once
storageThere are also one-way valves to
tank pressure
reaches pressure
about 100if psi.
maintain
storage-tank
the
There
are
also
one-way
valves to
compressor fails.
maintain
storage-tank introduce
pressure ifboth
the
Air compressors
compressor
fails.
water and oil into a brake system.
Air compressors introduce both
water and oil into a brake system.
86
HPBooks' very "slippery" Monza at Bonneville Salt Flats. To illustrate effect aerodynamic drag
has on speed, Tom Monroe set C/Production record in car at 217.849 mph. Power was by
fuel-injected
370-cubic
inch
small-block
Chevy. Salt
AlProduction
record iseffect
219.334
mph, set in drag
a '67
HPBooks' very
"slippery"
Monza
at Bonneville
Flats. To illustrate
aerodynamic
Camaro
powered
by Monroe
a 510-cubic
inch big-block-Chevy-37%
displacement
andwas
0.68%
has on speed,
Tom
set ClProduction
record in car atmore
217.849
mph. Power
by
faster!
This is
a good-news/bad-news
when it comes
to is
braking.
two set
cars
fuel-injected
370-cubic
inch small-block situation
Chevy. NProduction
record
219.334 Ifmph,
in awith
'67
different
drag coefficients
are traveling
at the same speed and more
stop at
the same deceleration
Camaro powered
by a 510-cubic
inch big-block-Chevy-37%
displacement
and 0.68%
rate, carThis
withisthe
lower Cd will require the
higherwhen
braking
force. Photo
by BillIf Fisher.
faster!
a good-newslbad-news
situation
it comes
to braking.
two cars with
different drag coefficients are traveling at the same speed and stop at the same deceleration
rate, car with the lower C, will require the higher braking force. Photo by Bill Fisher.
These liquids are removed to prevent
the pneumatic system from being
These
liquids
removed
prevent
damaged.
Not are
only
can the toparts
corthe
systembutfrom
rode pneumatic
due to moisture,
they being
could
damaged.
only brake
can the
parts corfreeze andNot
cause
failure.
The
rode d u e to moisture,
they could
fluid-removal
system but
is similar
to
freezetraps
and in
cause
brake
failure. T h e
compressed-air
fluid
a shop
fluid-removal system is similar to
system.
fluid
traps in brakes
a shoparecompressed-air
Pneumatic
actuated by a
system.
diaphragm inside a housing, rather
Pneumatic
actuatedThese
by a
than
a pistonbrakes
in a are
cylinder.
diaphragm
inside
a
housing,
rather
units are the brake chambers. You can
thanthem
a piston
in aoncylinder.
see
mounted
the rearThese
axles
units
are trucks
the brake
You can
of
large
and chambers.
trailers. They
are
see
n the rear
too them
big to mounted
fit insideo wheels,
so axles
they
of large the
trucks
andthrough
trailers.a They
are
operate
brakes
shaft and
too
big
to
fit
inside
wheels,
so
they
mechanical linkage. A return spring
operatethe
t h e chamber
brakes through
a shaft
and
inside
returns
the diamechanical
A position
return spring
phragm to itslinkage.
retracted
when
inside
the are
chamber
returns the diathe
brakes
released.
phragm
to its
retracted
position
when
On some
large
off-road
commercial
the brakes
are as
released.
vehicles
such
earth movers, graders
O n road
s o m e large
off-road
commercial
and
rollers,
a combination
vehicles
such
as
earth
movers,
hydraulic/pneumatic system isgraders
used.
and
road to rollers,
a combination
Referred
as an air-aver-hydraulic
hydraulic/pneumatic
is used.
system, the brakes aresystem
operated
by a
Referred
to
as
an
air-over-hydraulic
hydraulic system, but the hydraulic
system, the
brakes are
by a
system
is applied
by operated
a pneumatic
hydraulicbetween
system,thebutbrake
the pedal
hydraulic
system
and
system
is applied
a ispneumatic
the hydraulic
system.byThis
a type of
system assist
between
brake
and
power
thattheuses
air pedal
pressure
the
hydraulic
system.
This
is
a
type
of
rather than vacuum.
power assist that uses air pressure
rather
than vacuum.
MULTIDISC
BRAKES
A multi disc brake works like a mul-
MULTIDISC BRAKES
A multidisc brake works like a mul-
tidisc clutch. There are a number of
driven and statianalY discs in a stack.
tidisc clutch.
There
are a number
of
Friction
material
is between
the discs.
drivendriven
and stationary
discs inwith
a stack.
The
discs rotate
the
FrictionWhen
material
between
discs.
wheel.
theisbrakes
arethe
applied,
T
h
e
driven
discs
rotate
with
the
the stack is clamped together. The stawheel.
h e n thebecause
brakes are
tionary Wdiscs,
theyapplied,
can't
the stack
is clamped
together.discs
T h e starota
te, slow
the rotating
by
tionary
discs,
because
they
can't
friction.
rotate,
slowbrakes
the rotating
by
Multidisc
are small discs
and light
friction.
compared to other types of brakes
Multidisc
small and
light
that
absorbbrakes
the are same
energy.
compared
to
other
types
of
brakes
However, because the rubbing surthat are
absorb
the same
energy.
faces
all "buried"
inside the
unit,
However,
becausecool
theslowly.
rubbing
sur-a
multidisc brakes
Thus,
faces are all
"buried"
inside
the unit,
multidisc
brake
is good
for only
one
multidisc
cool slowly.
Thus,
hard
stop. brakes
Considerable
cooling
timea
multidisc
is good
for only
is needed brake
before
the next
stopone
is
hard
made.stop. Considerable cooling time
is The
needed
before theof next
stop is
compactness
a multidisc
made.
brake makes it desirable for aircraft
T h An
e compactness
of a wheels
multidisc
use.
airplane has small
to
brakespace,
makesmaking
it desirable
aircraft
save
a tight for
fit for
any
use.
hasstops
small
wheels
to
brake.A nA airplane
plane only
hard
once as
save
space,
making
a
tight
fit
for
any
it lands, and has a great deal of cooling
brake.before
A plane
only stops
hardand
once
as
time
another
landing
stop.
it lands,
has a great
of cooling
And,
theand
extremely
highdeal
temperatures
time beforein another
landingdictate
and stop.
generated
aircraft brakes
the
And,
the
extremely
high
temperatures
use of sintered-metallic or graphitegenerated in
aircraft
brakes dictate the
composite
friction
materials.
useAircraft-type
of sintered-metallic
or graphitemultidisc
brakes
composite
friction
materials.
might work well on dragsters or landAircraft-typecars, multidisc
brakes
speed-record
but to my knowlmightthey
workhave
wellyet
o ntodragsters
edge
be used or
on landsuch
speed-record
cars, but to my knowlvehicles.
edge they have yet to be used o n such
vehicles.
Dragster brake is operated by hand lever. Note pushrod between lever and master cylinder
(arrow). Hand-lever movement can be more than a brake pedal, so higher pedal ratio is
possible
lever-operated
Dragsterwith
brake
is operated bybrakes.
hand lever. Note pushrod between lever and master cylinder
(arrow). Hand-lever movement can be more than a brake pedal, so higher pedal ratio is
possible with lever-operated brakes.
HAND-OPERATED BRAKES
Some specialized cars use a brake
HAND-OPERATED
system
operated by BRAKES
a hand lever
Somethan
specialized
cars use
a brake
rather
a brake pedal.
A dragster
system
by dragster
a hand handLever
is one ofoperated
these. The
rather
than
a
brake
pedal.
A
dragster
lever brake operates identically to a
is one of these.
dragster
foot-pedal
brake,Thebut
with handtwo
lever brake operates identically to a
differences:
foot-pedal
but awith
two
• Maximum brake,
force with
person's
differences:
hand is less than can be applied with a
Maximum force with a person's
foot.
hand
is -lever
less than
can becan
applied
with a
• Hand
stroke
be longer
foot.
than a foot pedal, allowing a higher
Hand-lever
stroke can be longer
ratio
.
than
pedal, allowing
a higher
Likea foot
a foot-brake
pedal, the
hand
ratio. operates a master cylinder
lever
Like aa foot-brake
pedal, the
hand
through
pushrod . Because
dragsters
lever
operates
a
master
cylinder
have rear-wheel brakes only, a single
through
a pushrod.
Because
dragsters
master cylinder
is used.
Most
of the
have rear-wheel
only,
a single
stopping
is donebrakes
by the
parachute.
masterwheel
cylinder
is used.
Most atof low
the
The
brakes
are used
stopping
is
done
by
the
parachute.
speeds, particularly for holding the
The
brakesline.
are used at low
car onwheel
the starting
speeds,
particularly
holding the
Another type offorhand-operated
car
on
the
starting
line.
brake is found on dune buggies.
Another
hand-operated
Known
as a type
CUllingofbrake
or steering
brake
found
dunelevers
buggies.
brake, itis has
one on
or two
with
Known
as
a
cutting
brake
or
two separate master cylinders tosteering
operit hasorone
or two
levers with
brake,
ate
the right
left rear
wheel.
two
separate
master
cylinders
to operCutting brakes are used for steering
ate
rightinorsoft
left sand
rear wheel.
the the
buggy
or tight turns.
Cutting
brakes
are do
used
steering
The
front tires
often
notfor
have
suffithe
buggy
in
soft
sand
or
tight
cient bite for steering control in turns.
these
The front tires
often do
not tires
have suffisituations.
Because
rear
have
cient
steering
these
more bite
bite,forthey
can control
turn thein buggy
situations.
Because
rear is tires
have
quickly
when
one wheel
braked.
A
more bite, they can turn the buggy
quickly when one wheel is braked. A
Ja-Mar cutting-brake assembly is used on
sand buggies for steering control in soft
sand. One
operates one
master
cylinder
Ja-Mar
cutting-brake
assembly
is used
on
when buggies
pulled; other
lever operates
sand
for steering
controlopposite
in soft
cylinder.
Each
master one
cylinder
is designed
sand. One
operates
master
cylinder
to
operate
a single
when
pulled;
other rear
leverbrake.
operates opposite
cylinder. Each master cylinder is designed
t o operate a single rear brake.
Disc-brake caliper can be operated by either hydraulic pressure or separate mechanical
linkage. Used on competition rally cars at the rear wheels and operated by a mechanical
linkage
by a caliper
parking-brake
driver
pull hydraulic
lever to slide
out rear
formechanical
entering a
Disc-brake
can be lever,
operated
bycan
either
pressure
or wheels
separate
turn.
This
allows
ultra-tight turns
to beatnegotiated
quicklyand
in operated
dirt or onbyslick
surfaces.
linkage.
Used
on competition
rally cars
the rear wheels
a mechanical
Courtesy
Racing.
linkage
byAP
a parking-brake
lever, driver can pull lever to slide out rear wheels for entering a
turn. This allows ultra-tight turns t o be negotiated quickly in dirt or on slick surfaces.
conventional
brake pedal is used for
wheel drive. It is handy for the driver
Courtesy
AP Racing.
braking the
buggy during
normal
conventional
brake pedal is used for
operation .
braking
the buggy
during normal
Hand-operated
rear-wheel
brakes
operation.
also
are found on competition rally
Hand-operated
rear-wheel
cars.
Unlike a cutting
brake,brakes
rearalso
are
found
on
competition
rally
wheel rally-car brakes are operated
cars.
Unlike a cutting
rearsimultaneously
with brake,
one
hand
wheel
rally-car
brakesRally
are operated
lever/master
cylinder.
cars run
simultaneously
with
hand
on slick roads and often one
have frontleverlmaster cylinder. Rally cars run
on slick roads and often have front-
to brake only the rear wheels to throw
wheel
handy for skid.
the driver
the cardrive.
into Ita isdeliberate
This
to
brake
the rear
wheels
to throw
helps
to only
negotiate
tight
slippery
turns
the car steering
into a deliberate
where
control skid.
might This
be
helps
to
negotiate
tight
slippery
turns
marginal. Separate from the hydraulic
where steering
control might
be
system,
special mechanical
linkages
marginal.
are often Separate
used forfrom
the the
rearhydraulic
brakes.
system,is special
linkages
This
similarmechanical
to parking-brake
are
often
used
for
the
rear
brakes.
linkage, but is designed for severe
use .
This is similar to parking-brake
linkage, but is designed for severe use.
87
High-Performance Brakes
High-Performance Brakes
9
Design of modern race-ear-brake system is not arrived at through magic. Instead, carefully planned steps are required. Success starts with
a written statement of what brake system must do. This is your design criteria. Don't lose sight of it when you're deep into the design.
Design of modern race-car-brake system is not arrived at through magic. Instead, carefully planned steps are required. Success starts with
a written statement of what brake system must do. This is your design criteria. Don't lose sight of it when you're deep into the design.
If you are designing a special car for
either street or racing use, you'll also
If you
are designing
a special
car
for
have
to design
the brake
system
. It's
either
racing
use, you'llbrake
also
difficultstreet
to or
take
a complete
have to from
designone
thecarbrake
It'sa
system
and system.
use it on
difficult
to
take
a
complete
brake
different one and have it work
system
car andconfiguration
use it on a
Carone
weight,
properly.from
work
different
one andall have
and
performance
affeciit brakeproperly.
Car
weight,
configuration
system design .
and
performance design
all affecr
brakeBy brake-system
I mean
putsystem
design.a group of components
ting together
Bywork
brake-system
mean putthat
properly. design
I'll notI attempt
to
ting
together
a
group
of
components
discuss how to design a brake rotor or
that
work properly.
not attempt
to
proportioning
valve.I'll Instead,
I will
discusshow
how to
brakenecessary
rotor or
show
to design
make a the
proportioning plan
valve.
I will
the Instead,
entire system,
calculations,
show
how
to
make
the
necessary
and select the components to do the
calculations,
plancomponents
the entire system,
job
. The correct
already
and select
the components
to doprobthe
exist,
regardless
of the car. The
job.
The
correct
components
already
lem is selecting the right ones for your
exist, regardless of the car. The probcar.
lem
is selecting
the right
ones forbrakeyour
This
chapter covers
complete
car.
system
design . If you have an existing
covers to
complete
brakeare trying
improve
the
carThis
andchapter
system
design.
If
you
have
an
existing
brakes, read Chapter 12. However, if
car and
are tryingthetocarimprove
the
you
are designing
rather than
brakes,
read
Chapter
12.
However,
if
modifying it, you have more choices.
you are designing the car rather than
modifying it, you have more choices.
88
There are fewer ways you can easily
change an existing car. This is why the
There
fewerbeways
you canplanned
easily
design are
should
carefully
change
an existing
car. This
is why the
before buying
or building
parts.
design
should be
carefully
Brake-system
design
requiresplanned
severbefore
buying
or
building
al steps. There are many parts.
ways to apBrake-system
design
requires
proach
the design
process,
butseverhere
al steps.
There are many ways to apare
my suggestions:
proach
the design
• List design
criteria.process, but here
are
my
suggestions:
• Calculate forces on tires.
List design brake
criteria.torques at maxi• Calculate
Calculate
forces on tires.
mum
deceleration.
braketype
torques
at maxi• Calculate
Choose brake
and mounting
mum
deceleration.
location .
Choose brake
type and
mounting
• Determine
hydraulic
pressure
relocation.
quired.
Determine
hydraulic pressure
pedal-and-linkage
design.re• Choose
quired.
• Calculate master-cylinder diameter
Choose pedal-and-linkage design.
required.
Design restmaster-cylinder
of brake system.diameter
• Calculate
required.
There may be some reason to rearDesign
reststeps.
of brake
range
these
Forsystem.
instance, you
There
mayhave
be some
reasonand
to rearthe pedals
wish
may
already
range
these
steps.
For
instance,
you
to retain them. That'll work fine
may
already
have
the
pedals
and
wish
unless you have to compromise braketo retainperformance
them. That'll
system
to do work
it. But,fine
if
unless you
have to compromise
existing
components
won't givebrakegood
system performance to do it. But, if
existing components won't give good
brake performance, don't use them.
The brakes are too critical to comprobrake
performance,
use them.
mise because
of a few don't
extra dollars.
The brakes are too critical to compromise because
of a few extra dollars.
DESIGN
CRITERIA
The first step in any design process
DESIGN
is listing CRITERIA
the reasons for the design
The
step in any
and
thefirst
objectives.
Thisdesign
writtenprocess
docuis
listing
the reasons
the design
ment
is your
design for
criteria.
For a
and
objectives.
Thissheets
written
brakethe
system,
several
of docupaper
ment
is
your
design
criteria.
For a
should be enough. You are writing
brake
system,
several
the criteria
so you
can sheets
refer toofit paper
later.
should
be enough.
You are
Keep your
design-criteria
list writing
handy
t later.
the criteria
you can
referthe
to idesign
during
and
read itsooften
Keep
your
design-criteria
list
process. Don't lose track of handy
your
and read it often during the design
objectives.
process.
Don't lose criteria
track ofshould
your
A brake-design
objectives.
answer the following questions:
brake-design
criteria will
should
Under
what conditions
the
• A
answer
the following
brake system
have to questions:
operate?
Underlong
what
conditions
the
• How
do you
expect thewill
system
brake
system
have
to
operate?
to last?
How
youfor
expect
thestreet
system
• Is
car long
to bedo
used
rac ing,
or
to
last?
both?
car toperformance
be used for racing,
street or
• Is
What
specifications
both? the brakes meet?
should
What
specifications
• If
you performance
have to compromise
on
should the brakes meet?
If you have to compromise on
Road
will withstand
withstand exRoad cars must have
have brake
brake components
components that will
treme cold.
cold. Corvette master cylinder
cylinder and
and booster
booster are being
being tested
at S8F
58F below
below zero (-SOC).
(-50C). Road-car brake
brake manufacturers
manufacturers must
must
test components
components under extremely severe conditions.
conditions. If designing
designing
a special
special car, you can
can save money by limiting
limiting conditions
conditions car has
has to
operate under.
under. Photo
Photo courtesy Girlock
Girlock Ltd.
Ltd.
)
,
I)
specifications, what is most important? What is least important?
• What are maximum loads imposed
on system?
system? What are normal operatloads?
ing loads?
Conditions-Think twice
Operating Conditions-Think
about this one: It is much harder to
design a brake system to perform
under every possible operating condicondiuse. For
tion than it is to limit its use.
instance, do you want the brake
system to function in the rain? Will it
get used in sand dunes like an off-road
vehicle? Is it used strictly for drag
racing, where there's a long cool-down
racing,
period after each stop?
stop? Will the car be
roads?
used on icy,
icy, salted roads?
specific and practical about the
Be specific
conditions your vehicle will likely
encounter. The more operating condiencounter.
tions you can eliminate or minimize,
the easier and cheaper the job will be.
The most difficult job an engineer has
to do is design a car that will be driven
on the street, in races, off-road and in
weather conditions ranging from the
burning deserts to sub-zero cold.
cold.
With luck, your special car will have
specialized operating conditions for
specialized
the brakes.
brakes. This will eliminate some
extremes.
Life-Every car component
Design Life-Every
or system has a certain life assumed
when the engineer designs it.
it. Most
road-car parts are expected to last at
Easiest
Easiest car to design
design is
is one with a special
special purpose-win
purpose-win sportscar races,
races, in
in this case. If car also
also had
had to transport wife and
and kids
kids to
church
would
church on
on Sunday,
Sunday, and
and still
still win races,
races, race-car designer would
really
really have a tough
tough job. Be
Be realistic,
realistic, but limit
limit functions car must
must
perform-design
will be easier.
perform-design job will
easier.
least 50,000 miles, but often last twice
that.
If every car were designed to last 40
years, the cars would be too expensive
and much heavier. If something is designed for a long life,
more. So
life, it costs more.
restrict long-life items to those that
are safety-related.
safety-related. Because brakes are
safety-related, the structure of the
brake system should be extremely
durable. You choose the miles, time
or number or races. If you are using
passenger-car brake parts and will be
operating them at less than their original design loads, you can expect them
to last a long time.
Some brake-system parts wear out
quicker than the basic system. This includes the linings, seals and,
rotors.
sometimes, the drums and rotors.
Parts that wear should be designed to
don't
manner-so they don't
do so in a safe manner-so
cause a loss of braking. Conventional
brake systems are so designed.
Therefore, if you use conventional
design practice, the brakes will be safe
when parts wear out.
out.
What life do you expect wear-prone
brake parts to have? If the linings you
10,000 miles on a
are using last 10,000
2500-lb sedan, you can expect them
1500-lb
to last at least that long on a 1500-lb
way. Use
sports car driven the same way.
life.
comparisons to predict useful life.
However, if you drive your special car
Always consider the application:
application: If stockcar designer failed to consider
consider that car
might
might compete
compete in
in road
road races with right
right
turns, driver would be
be in
in trouble. It is
is easier
design a car for left turns only.
only. Likewise,
Likewise,
to design
it's easier to design
design brakes
brakes for a short
track with high-banked
high-banked turns than
than one with
long
long straights and
and flat turns.
harder than the sedan that weighs the
same, don't expect the linings to last
the same. More brake-lining area or a
harder lining would be needed to
compensate.
You cannot make an exact predicprediction of brake life.
life. However, write
down what you are expecting and
keep the desired life in mind while
designing the brake system.
system. You must
have a design goal.
goal.
This decision
Racing vs. Street UseUse-This
must be made early in the design
process. Make usage part of your
criteria. The brake system that works
89
Production-sedan designers have the most difficult design job. I wonder if the VW brakedesign engineers visualized Rabbits racing at Riverside on a hot summer day? Brakes get a
severe
workout compared
to their
Production-sedan
designers
haveeveryday
the most highway
difficult service.
design job. I wonder if the VW brake-
design engineers visualized Rabbits racing at Riverside on a hot summer day? Brakes get a
severe workout compared to their everyday highway service.
SAMPLE PERFORMANCE SPECIFICATIONS
Car SPECIFICATIONS
A
Car B
SAMPLE PERFORMANCE
Type of car
Usage
Type
of car
Percent
racing use
Usage
Horsepower
Percent
racing
use
Car
weight
Ob) -average
racing
Horsepower
distribution (front/rear)
Weight
Car weightcar
(Ib)weight
-average
(Ib) racing
Maximum
Weight
distribution
Minimum
car weight(fronthear)
(Ib)
Maximum speed
car weight
(Ib)
Maximum
(mph)
Minimumrace
car weight
(Ib)
Average
speed (mph)
Maximum race
speedduration
(mph) (minutes)
Maximum
Average
race 0-60
speedmph
(mph)
Acceleration
(seconds)
Maximum tire
racegrip-street
duration (minutes)
Maximum
Acceleration
mph (seconds)
Maximum tire0-60
grip-racing
Maximum tire
grip-street
Maximum
deceleration-street
(g's)
Maximum tire
grip-racing
Maximum
deceleration-racing
(g's)
Maximum deceleration-street
(g's)
Downforce
at top speed (Ib)
Maximum deceleration-racing (g's)
Downforce at top speed (Ib)
Sports Car
Car A
Street & slalom
Sports
Car
5% or less
Street
200 8 slalom
5%
or less
2000
200
50/50
2000
2400 (street)
50/50
2000 (racing)
2400
125 (street)
2000 (racing)
60
5125
860
5
0.9
8
1.2
0.9
0.9
1.2
1.2
Race car
Car B
Road racing
Race
100% car
Road
150 racing
100%
1100
150
40/60
1100 (max fuel)
1150
40/60
1050 (min fuel)
1 150 (max fuel)
150
1050 (min fuel)
100
150
60
6100
60
6
1.4
-
0.9
o
1.4 (with wings)
2.0
500
0
500
1.2
2.0 (with wings)
Performance specifications for two imaginary cars: Car A is a sports car designed for both
street use and slaloms; car B is an all-out race car for a small formula-car class. Note how
road-car's
weight
can vary. for
Brake
must
be able
to is
accommodate
all variations,
but
Performance
specifications
twosystem
imaginary
cars:
Car A
a sports car designed
for both
remain
balanced.
street use
and slaloms; car B is an all-out race car for a small formula-car class. Note how
road-car's weight can vary. Brake system must be able to accommodate all variations, but
remain balanced.
best for racing is not the best for the
street and vice versa. Either system
best
bestwhile
for the
will for
workracing
OK isfornota the
little
in
street and
vice versa.
either
application,
but Either
you willsystem
have
will
worksooner
OK for
a little while in
problems
or later.
either
application,
but
youracing,
will have
Remember that while
the
problems
sooner
or
later.
brakes are usually warmed up before a
Remember
the
hard
stop; theythat
are while
not onracing,
the street.
brakes are usually
warmedrequire
up before
Street-driving
conditions
pro-a
hard
stop;
on the street.
tection
fromthey
dirtare
andnot
corrosion;
racing
Street-driving
conditions
require
conditions may not. Some
formsproof
tection from
dirt and
corrosion;
racing
are much
worse
than racing
street
conditions
Some formsand
of
driving
for may
bothnot.
contamination
racing
are
much
worse
than
street
high temperatures.
driving
for both
contamination
The hardest
thing
to design is a and
car
high istemperatures.
that
used for both street driving and
The hardest thing to design is a car
that is used for both street driving and
90
racing . If you attempt this, you must
make design compromises that will
racing.theIf you
this, you
hurt
car'sattempt
performance
in must
both
make design
compromises
situations.
Therefore,
try to that
limit will
the
hurt' s operating
the car's conditions,
performance
both
car
for in
highest
situations.
Therefore,
to limit the
performance
and lowesttry
cost.
car's
operating
conditions,
highest
Performance Specs - List for
specificaperformance
andtolowest
tions you want
meet. cost.
Because each
Performance
-List specificatype of vehicleSpecs
has different
specs, I
tions
you
want
to
meet.
Because
can't give you a list for
your each
car.
type of vehicle
has different
specs, aI
However,
the above
table gives
can't
youfora two
list types
for your
car.
samplegive
listing
of cars.
However,
the weight
above and
tablespeed
givesarea
Note
that car
sample
for two ittypes
cars.
included.listing
Obviously,
takesof more
Note
that
car
weight
and
speed
bra ke to stop a fast, heavy car thanare
it
included.
takes more
does
to stopObviously,
a light, slowitone.
brake to stop a fast, heavy car than it
does to stop a light, slow one.
Maximum loads on car may occur during an
off-road excursion or some other emergency
situation.
Normal
loads
don't
Maximum
loads
on caroperating
may occur
during
an
include unexpected
in other
the rough
stuff,
off-road
excursion ortrips
some
emergenbut
such conditions
be allowed
in
cy situation.
Normalmust
operating
loads for
don't
a
design,unexpected
including driver
include
trips error.
in the rough stuff,
but such conditions must be allowed for in
a design,
including
driverand
error.
Include
car weight
CO location
in the performance specifications.
Include
weight
CG you
location
You
must car
know
theseand
before
can
in
the
performance
specifications.
design the brake system. When startYou
know ,these
youknow
can
ing amust
car design
you before
may not
design
the weight
brake system.
When startthe exact
or CO location.
To
ing a the
car design,
you may
not , know
start
brake-system
design
estithe exact
weightand
or CO
CG location
location.forToa
mate
the weight
start
the
brake-system
design,
esticar such as yours. Then you can begin
mate brake-system
the weight and
C G location
for a
your
design
.
carAfter
such as
can begin
caryours.
and Then
brakeyou
system
are
your
brake-system
design.
designed, go back and do all the calcuAfter again
car and
brake
lations
using
the system
exact are
car
designed,
go CO
back location
and do all
calcuweight and
. Ifthe
you
eslations
using
car
timated again
correctly
the the
first exact
time , few
weight
and C Gchanges
location. should
If you esbrake-design
be
timated .correctly
theit first
time,takes
few
required
However,
usually
brake-design
changes
shouldeffort
be
two or three rounds
of design
required.
However,
it
usually
takes
before an entire car design is
two or three
completed
. rounds of design effort
before an entire car design
completed.
BRAKE-SYSTEM LOADS
is
As already discussed , the two loads
BRAKE-SYSTEM
LOADS
to be concerned with
are maximum
As and
already
discussed,
two Maxiloads
loads
normal
operatingthe
loads.
to
be
concerned
with
are
maximum
mum loads on most brake compoloads and
normal
operating
loads. Maxinents
occur
during
an emergency.
It
mum loads
on most
brake where
compo-a
could
be a panic
situation
nents occur
during
It
crash
may be
aboutan toemergency.
occur. The
could
be
a
panic
situation
where
driver panics and slams his foot on thea
crash
may as
be hard
about
to can,
occur.
The
brake pedal
as he
usually
driver panics
and slams
footresult
on the
locking
the wheels.
Thishis
may
in
brakeofpedal
as hard
he can,
loss
control
or as
worse
. It usually
is the
locking
the wheels. This
may result
in
maximum-loading
condition
for the
loss
of
control
or
worse.
It
is
the
brake pedal and linkage.
maximum-loading
condition
for the
There may be different
maximumbrake
pedal
and
linkage.
load conditions for parts of the brake
There other
may bethan
different
system
the maximumpedal and
load
conditions
for
parts
the brake
linkage. A brake-reservoirofbracket
exsystem
than the
periencesother
maximum
load pedal
when and
the
linkage. A brake-reservoir bracket experiences maximum load when the
MAXIMUM LOADING FOR BRAKE-SYSTEM COMPONENTS
Component
Maximum-Load
Maximum
Load on Component
MAXIMUM LOADING
FOR Condition
BRAKE-SYSTEM
COMPONENTS
Panic
stop-wheels
locked
600
Ib
forward
200
Ib side
Maximum-Load Condition Maximum Load&on
Component
load on pedal pad.
Brake pedal 8
Panic stop-wheels locked
Ib forward
& 200 Ib side
Hydraulic system Panic stop-wheels locked 600
Calculated
hydraulic
linkage
load on pedal
pad. pressure
with 300 Ib on pedal.
Hydraulic
system Panic stop-wheels locked Calculated hydraulic pressure
Brake caliper
Panic stop-wheels locked Calculated hydraulic pressure
with 300 Ib on pedal.
with 300 Ib on pedal.
Brake caliper
Panic stop-wheels
locked Maximum
Calculatedcalculated
hydraulic brake
pressure
Caliper
bracket
Maximum
deceleration
with 300
torque
. Ib on pedal.
Caliper
bracket
Maximum deceleration
Maximum calculated brake
Brake rotor
Maximum deceleration
Maximum calculated brake
torque.
torque.
Brake rotor
Maximum deceleration
Maximum calculated brake
Fluid-reservoir
Maximum bump &
5-g downward load & 2.5-g
torque.
bracket
cornering
side load on reservoir.
Fluid-reservoir
5-g downward load & 2.5-9
Maximum bump 8
bracket
cornering
side load on reservoir.
Brake pedal &
Component
linkage
Formula car ran head-on into barrier with
brakes locked. Forward-projecting master
cylinders
pushed
bulkhead
rearward
and
Formula car
ran head-on
into
barrier with
broke
brake Forward-projecting
pedal due to resistance
of
brakesoff
locked.
master
driver's foot.
Because
of rearward
severe and
leg
cylinders
pushed
bulkhead
injuries,
Indy
Car
prohibited
broke
off '85
brake
pedal
duerules
to resistance
of
forward-mounted
master cylinders.
driver's
foot. Because
of severeLater
leg
rules
prohibit
mounted
of
injuries,
' 8 5 pedals
lndy Car
rules forward
prohibited
front-wheel centermaster
line.
forward-mounted
cylinders. Later
rules prohibit pedals mounted forward of
car hits acenter
bump.
front-wheel
line.Assume that the
driver runs off the road and hi ts a
car
a The
bump.
Assume
that
the
hard hits
bump.
bracket
should
be dedriver for
runs
off the
road and hits
signed
similar
maximum-load
co n-a
hard bump.
The
bracket should
be desuspension
and frame.
dition
as the
signed
for
similar
maximum-load
This maximum-load condition is condifdition than
as the
and frame.
ferent
thesuspension
maximum-load
condiThis
tion maximum-load
for the brake condition
pedal. Seeis difthe
ferent
than
the
maximum-load
sample list of maximum loads condiin the
tion for table.
the brake
See the
above
Writepedal.
down
the
sample
list of maximum
loadsforin the
maximum-load
conditions
all
above parts
table.
Write the
down
system
and calculate
loads.the
maximum-load
conditions
for all
For all parts of the
system receiving
system
partsthe
andbrake
calculate
loads from
fluid,the
theloads.
normal
For all parts
systemmaximumreceiving
operating
load ofisthe
during
loads
from theSlamming
brake fluid,
the foot
normal
deceleration.
your
on
operating
load
is
during
maximumthe pedal and locking the wheels does
deceleration.
Slamming your footInona
1101 give maximum-deceleration.
the
pedal
and
locking the wheels
maximum-deceleration
stop, does
the
not
give
maximum-deceleration.
In a
wheels are not locked, but the brakes
maximum-deceleration
the
develop
maximum torque. stop,
The driver
wheels
but than
the brakes
pushes are
lessnot
on locked,
the pedal
he is
develop of.
maximum
driver
capable
This is atorque.
normalThe
stop
in a
pushes
less
on
the
pedal
than
is
race or a controlled fast stop onhethe
capable
of. This is a normal stop in a
road.
race
a controlled fast
stopmust
on the
All orbrake-system
parts
be
road.
made to operate properly at normal
All brake-system
be
operating
loads. And, parts
they must
must not
made
to operate
properly atload
normal
breakwhile
under maximum
.
operating loads. And, they must not
Maximum Loads-Each car and car
breakwhile under maximum load.
designer will have different requireMaximum
Loads-Each
car
ments for what
loads to usecar
for and
designdesigner
will
have
different
requireing the brake system. I use the followments
fordesigning
what loadsa race
to use
for designcar:
ing when
ing the brake system. I use the follow-
75-lb pedal force at maximum
ing when designing a race car:
deceleration- normal operating
75-lb pedal force at maximum
condition;
decelerationoperating
600-lb
forward normal
and 200-lb
sideways
condition;
maximum force on pedal-panic-stop
600-lb forward and 200-lb sideways
conditions.
maximum force on pedal-panic-stop
conditions.
Exact values and loading conditions will vary from one car to another. Make sure
you select the worst loading condition for each component-that is, the
Exact values
and
loading
conditions
willNotice
vary from
car to condition
another. Make
condition
most
likely
to cause
a failure.
that one
the worst
is notsure
the
you
select
the worst
loading
each component-that
the
same
for each
component
in condition
the brake for
system.
Hydraulic-system is,
components
condition
mosttolikely
to cause
thethan
worst
is not
are designed
withstand
300aIbfailure.
on the Notice
pedal, that
rather
thecondition
600-lb load
thethe
same
each component
in the load
brakeincludes
system.aHydraulic-system
for. The pedal
factor for sudden components
load
pedal for
is designed
are designedwhich
to withstand
Ib on
rather
than the 600-lb load the
application,
does not300
apply
to the
the pedal,
hydraulic
system.
pedal is designed for. The pedal load includes a factor for sudden load
application, which does not apply to the hydraulic system.
Factor of Safety-The maximum
loads discussed in the previous section
Factor
of effects
Safety-The
maximum
incl
ude the
of suddenly
applied
loads discussed
the previous
sectiona
However,inthey
do nol include
forces.
include the
applied
of effects
safety.of suddenly
As previously
factor
do not include
forces. However,
they factor
discussed,
the safety
accountsa
factor
of safety.between
As previously
for the difference
the maxidiscussed,
factor
mum load the
on asafety
part and
its accounts
breaking
between
for
the difference
strength.
Never design
a partthe
to maxibreak
mum
load
on
a
part
and
its
breaking
just as it reaches its maximum load.
strength.
design adesign
part toisbreak
Not evenNever
an airplane
that
just
as it reaches its maximum load.
marginal.
Not
an factor
airplane
design for
is that
Theeven
safety
accounts
unmarginal.
knowns that cannot be calculated.
Theis safety
factor
accounts
unOne
needed
because
parts for
someknowns
that
cannot
calculated.
times have
hidden
flaws,bethey
corrode
One long
is needed
because
parts
someafter
use, and
loads are
often
diftimes tohave
hiddenaccurately.
flaws, they corrode
ficult
calculate
after
long use, and using
loads are
often difI recommend
a factor
of
ficult
to
calculate
accurately.
safety of 3 on critical components.
I recommend
using
a factor
of
This
means that the
breaking
strength
safety
on critical
of the of
part3 should
be atcomponents.
least three
This
that the breaking
strength
timesmeans
the maximum
load on the
part.
of
the
part
should
be
at
least
three
You can test a part to see if it is strong
times theifmaximum
load ontothe
part.
enough,
you can afford
destroy
You
to see if test,
it is strong
one can
part.test
Ina apart
breaking
apply
enough,
if you
afford toload
destroy
three times
thecan
maximum
the
one
part.
In
a
breaking
test,
apply
part was designed for. If it doesn't
three
the amaximum
load But,
the
break, times
you have
good design.
part
wasthedesigned
it and
doesn't
destroy
part afterfor.
theIftest
use
design.
abreak,
brandyou
newhave
one aingood
the car.
The But,
test
destroy
the
part
after
the
test
and Reuse
may have caused damage.
amember,
brand new
in the
Thetimes
test
you one
tested
it tocar.
three
may
have load
caused
Rethe highest
that itdamage.
should ever
member,
you
tested
it
to
three
times
experience.
the highest load that it should ever
experience.
Loads - Brake-system
componen ts
also are lo aded inertiaJly when the car
Loads
-Brake-system
components
is
accelerating
, decelerating,
cornering
alsohitting
are loaded
inertially
the excar
or
bumps.
Inertia when
loads are
is
accelerating,
decelerating,
cornering
pressed in g's. One g is an inertia load
or hitting
bumps.
loads
are exequal
to the
weightInertia
of a part,
assembly
pressed
One equal
g is antoinertia
load
or
car; 2ing g's.
is a load
two times
equal
to the
weight
of aI use
part,the
assembly
the weight
, and
so on.
follow2 gtoisdesign
a load bracke
equal to
two structimes
or
ingcar;
loads
ts and
the
weight,
and
so
on.
I
use
the
followtures that hold parts together:
ing
loads to design
struc• Maximum
bump brackets
load = 5and
g except
turesoff-road
that holdcars
parts
for
or together:
dirt-track racers.
= 5 cars
g except
Maximum
Use
10 g or bump
more load
for race
that
for
off-road
cars
or
dirt-track
racers.
normally hit large bumps.
Use
10 g or cornering
more for race
thatg
• Maximum
load cars
= 2.5
normally
large bumps.
on
a car hit
without
wings or at speeds
2.5 g
Maximum
cornering
below
100 mph.
Cars load
with= wings
on
a
car
without
wings
or
at
speeds
above this speed will have higher
below 100 mph. Cars with wings
loads.
above
this speed
will have
• Maximum
deceleration
= higher
2.5 g
loads.
on a car without wings or at speeds
Maximum
deceleration
= wings
2.5 g
below
100 mph.
Cars with
on a carthiswithout
or at speeds
above
speed wings
will have
higher
below
loads. 100 mph. Cars with wings
above
this speed
will have
higher
acceleration
= 2.0
g on
• Maximum
loads.
all cars except dragsters. Use 5.0 g or
Maximum
acceleration = 2.0 g on
higher
for dragsters.
allOn
carssmall
exceptparts
dragsters.
5.0 g or
such Use
as brackets
higher forother
dragsters.
holding
parts to the frame, viOn small
such as Abrackets
bration
must parts
be considered.
small,
holding
other
parts
to the frame,
vilightweight part is subjected
to higher
A small,
bration must
considered.
vibration
loadbe
s than
a large,
heavy
lightweight
is subjected
higher
part.
The part
amount
of to
vibration
vibration onloads
than
a large,
heavy
depends
engine
design
, suspension
part.
The
amount
of
vibration
stiffness,
engine
mounts ,
road
depends on engine design, suspension
stiffness, engine mounts, road
91
Maximum loads can occur in two directions at once. Here, stockcar driver cuts a close apex. Resulting bump load from going over
curb on right
front
wheel
occurs
same timeatasonce.
maximum
Maximum
loads
can
occur
in twoatdirections
Here,cornerstocking load.
car
driver cuts a close apex. Resulting bump load from going over
curb on right front wheel occurs at same time as maximum cornering load.
surface, and many other factors. If in
doubt , design small parts to withstand
surface,
many other
If in
twice theand
maximum
loadsfactors.
just given.
doubt,
design
small
to withstand
If anything
falls
offparts
the car,
increase
twice
the maximum
its design
load when loads
doing just
the given.
repair.
If
anything
falls
off
the
car,
increase
The only way to measure vibration
its
design
loadexpensive
when doing
the repair.
loads
is with
sophisticated
The
only way
to measure
vibration
equipment,
which
most people
can't
loads
is
with
expensive
sophisticated
afford .
equipment, which most people can't
afford.
CALCULATING TIRE FORCES
To start a brake-system design , first
CALCULATING
determine
forces TIRE
acting FORCES
on the tires
To start aa brake-system
first
during
stop
at design,
maximum
determine forces
onthe
theeffects
tires
deceleration.
This acting
includes
during
a stoptransfer
at and
maximum
of both weight
aerodeceleration.
This
includes
the
effects
dynamic forces on the car. To do
the
of both
transfer
and some
aerojob
right, weight
you need
to know
dynamicfacts
forces
ont the
thecar:
car. To do the
specific
abou
job
right,
you
need
to
driversome
and
• Weight of car includingknow
specific
facts about the car:
other
loads.
of car
including driver and
• Weight
Wheelbase
length.
other
loads.
• CG
height
and
fore-and-aft
Wheelbase
length.
location
.
G
height
fore-and-aft
• C
Maximum
tire gr and
ip.
location.
• Aerodynamic forces on body.
Maximum
grip.
almost completely
A
car has tire
to be
Aerodynamic
on body.
designed
before forces
this information
can
car has to accurately.
be almost completely
be Adetermined
Therefore,
designed
before
this information
all
the above
information
may notcan
be
be
determined
accurately.
Therefore,
available at the time the brake
system
all first
the above
information
may notyou
be
is
designed
. Consequently,
available
at theassumptions-educated
time the brake system
must make
is first designed.
you
guesses.
Start by Consequently,
making the brake
must make
assumptions-educated
system
adjustable
if you don't start
guesses.
Start byinformation.
making the Later,
brake
with
accurate
system car
adjustable
during
testing, if
youyou
candon't
makestart
adwith accurate
information.
justments
to the brake
system . Later,
during carThe
testing,
youof can
make
adWeightweight
a car
greatly
justments
the brake system.
affects thetobrake-system
design. The
Weight-The weight of a car greatly
affects the brake-system design. The
92
Toughest type of vehicle to maintain brake balance under all loading conditions is nose-heavy, front-wheel-drive pickup. Loadsensing proportioning
valve
between brake
body balance
and rear under
axle ofallDodge
Toughest
type of vehicle
to maintain
loadRampage
adjusts
so brake
balance is maintained
under
all
ing
conditions
is brakes
nose-heavy,
front-wheel-drive
pickup.
Loadload conditions.
sensing
proportioning valve between body and rear axle of Dodge
Rampage adjusts brakes so brake balance is maintained under all
load conditions.
car will have to stop in its heaviest
form, traveling at m aximum speed. If
car
will ishave
to stoptheincalculation
its heaviest
the car
for racing,
is
form,
traveling
at
maximum
speed.
If
easy. Most race cars have nearly
a conthe carweight
is for racing,
is
stant
except the
for calculation
fuel weight.
easy.
Most race
cars have
nearly
a conSo
, design
race-car
brakes
assuming
stant
weight
full fuel
load. except for fuel weight.
So,Ondesign
race-car
brakes assuming
a road
car, weight
can vary
full
fuel load. The hardest vehicle to
considerably.
On abrakes
road for
car, isweight
canTrucks
vary
design
a truck.
considerably.
The
hardest
vehicle
to
weigh much more fully loaded than
design
brakes
for
is
a
truck.
Trucks
when empty. In addition , their centers
weigh
much
more
fully when
loaded
than.
of gravity
move
greatly
loaded
when
empty.
In
addition,
their
centers
The design of a brake system for such
gravityshouId
move be
greatly
aofvehicle
basedwhen
on itsloaded.
maxiThe
design
of
a
brake
system
such
mum weight. However, brake for
balance
amust
vehicle
be basedaton the
its maxibeshould
considered
nomum weight. However,
balance
load/full-load
extremes .brake
Unless
the
must has
be anconsidered
at the
notruck
adjustable brake
balance
load/full-load
extremes.
Unless
the
or
a special anti-skid
device
, balance
truck probably
has an adjustable
brake balance
will
be incorrect
when
or a special
balance
empty.
Mostanti-skid
trucks device,
lock the
rear
will
probably
be
incorrect
when
wheels under hard braking if reasonaempty.
Most trucks
lock the
rear
bly well balanced
when loaded
.
wheels
under -CG
hard braking
reasonaCG Location
location ifcan
be esbly
well balanced
whenwith
loaded.
timated
or calculated
reasonable
CG
Location-CG
location
be esaccuracy. Most sedans arecanslightly
timated
or
calculated
with
reasonable
nose-heavy when empty and closer to
accuracy.
Most
sedans are
slightly
50/50
weight
distribution
when
fully
nose-heavy
when
empty
and
closer
to
loaded. This puts the CG at the mid50/50
weight
distribution
when
fully
point of the wheelbase at full load.
loaded.
This puts
the sports
C G at cars
the midThe
majority
of road
also
point 50/50
of theweight
wheelbase
at full Most
load.
have
distribution.
The majority
road sportswith
cars drag
also
race
cars are oftail-heavy,
have
50/50
weight
distribution.
Most
racers being the most tail heavy and
race cars
draga
stock
cars are
the tail-heavy,
least. You with
can get
racersfeel
being
the most
and
good
for weights
andtail
CGheavy
locations
stock
cars
the
least.
You
can
get
from automotive-magazine road tests.a
good
for weights
and CG
locations
CGfeel
height
is harder
to guess
at.
from automotive-magazine
tests.
Most
sports-car CGs areroadslightly
CG height is harder to guess at.
Most sports-car CGs are slightly
above wheel center. A race-car CG is
lower than on a road car. If you know
above
wheel
A race-car
CGare
is
where all
the center.
heavy parts
of the car
lower
than
a road
car. IfCG
you height
know
located,
youoncan
calculate
where
all the heavy
parts ofBut
the, car
are
with reasonable
accuracy.
if you
located,
you
can
calculate
CG
height
don't know where they are, it is probawith
reasonable
you
bly too
soon toaccuracy.
design But,
the ifbrake
don't
where the
theycar
are,design
it is probasystemknow
. Establish
first,
bly
design
brake
then too
comesoon
back to
to the
brake the
system
.
system.
Establish simple
the car chart
designcan
first,
As illustrated,
be
then
back to the
system.
used come
to calculate
CGbrake
location.
Find
illustrated,
simple
can be
theAsweight
of each
majorchart
component
used
to
calculate
CG
location.
Find
of the car and its planned CG location
the
weight from
of each
component
measured
the major
ground
and disof
the from
car and
planned CG
location
tance
theitsfront-axle
center
line.
measured
from
the
ground
and
Multiply the weight times dis-a
tance
from thelong
front-axle
distance-as
as it'scenter
from line.
the
Multiply
the write
weight
times ina
same
point-and
the number
distance-as
longcarasweight
it's seems
from too
the
the chart. If total
same
point-and
write
the
number
in
low , you left out something. Miscellathe
chart.small
If totalitems
car weight
neous
are seems
hard too
to
low, you left
out something.
estimate.
However,
try to Miscellaestimate
neous
small when
items designing
are hard the
to
their weight
estimate.
However,
try toliquids
estimate
brakes. Also,
don't forget
and
their weight
whenof designing
the
people.
The sum
the individual
brakes.
Also,
don't
forget
liquids
and
weights is obviously tota l car weight.
people.
sum
of the
The
sumThe
of the
weight
timesindividual
distance
weights
is obviously
totalweight
car weight.
column divided
by total
gives
The
sum of the weight times distance
CG location.
column
divided by
weight gives
Tire Grip-Tire
griptotal
is important.
It
C G location.maximum deceleration of
determines
Tire
Grip-Tire
grip is important.
It
the car.
On a car without
aerodynamic
determines
maximum
deceleration
of
downforce , maximum deceleration of
the car.
a carmaximum
without aerodynamic
the
car On
equals
tire friction
downforce, On
maximum
deceleration
of
coefficient.
a car with
aerodynamic
the
car
equals
maximum
tire
friction
downforce, deceleration is higher.
coefficient.
a car
with aerodynamic
Tire grip On
varies
considerably.
Road
downforce,
deceleration
higher.
condition is as importantis as
the tires
Tire grip varies
Road
themselves.
Racingconsiderably.
tires on dry pavecondition
as important
the tires
ment can ishave
a grip ofasover
1.0 .
themselves. Racing tires on dry pavement can have a grip of over 1.0.
Component
Engine
Component
Transmission
Engine
Driver
Transmission
Front wheels/tires
Driver
Rear wheels/tires
Front
wheels/tires
Front suspension
Rear wheels/tires
Rear
suspension
Front suspension
Front
brakes
Rear suspension
Rear
brakes
Front
Framebrakes
Rear
Body brakes
Frame
Fuel
tank
Body
Radiator
& water
Fuel
tank
Battery
Radiator
Pedals 8, water
Battery
Seats
W
x
(WX)
y
(WY)
W
X
(WX)
Y
(WY)
Pedals
Seats
Totals
W(total)
-
Totals
W(total)
XCG=:t~t~~tal
-
WX(total)
-
WX(total)
WY (total)
~
~
Y
(WX) total
CG
X~~ == (WY) total
Y
W total
CG
(WY) total
W=
each compoment in
Y~~ =
X = distance
CG
W totalof component CG from
front-wheel
inches
= weight center
of eachincompoment
in pounds
W
'CG
Y=
= distance
height of of
component
CGCG
from
the ground in inches
X
component
from
front-wheel
center in
inches
XCG = CG location
behind
front-wheel center in inches
= height
of component
frominthe
ground in inches
Y
Y CG
= CG location
above CG
ground
inches
XCG= CG location behind front-wheel center in inches
= CG location above ground in inches
,Y
,
we%~~t~~
WY(totail
-
pound~
- -
:
CG
Ground
t
Ground
CG location can be determined by filling out chart and performing calculations. Each
component in a car has its own weight and CG location. List weight and CG location for
each
component
If component
is out
forward
front-wheel
center,
use a negative
CG location
can as
beshown.
determined
by filling
chartof and
performing
calculations.
Each
number for X-in
thishas
case
times
X will
negative.
forlocation
WX, make
component
in a car
its W
own
weight
andbeCG
location.When
List adding
weight totals
and CG
for
sure you
add negative
numbers
correctly orisWX
total will
be too large. center, use a negative
each
component
as shown.
If component
forward
of front-wheel
number for X-in this case W times X will be negative. When adding totals for WX, make
sure you add negative numbers correctly or WX total will be too large.
Road tires seldom exceed 0.8. You'll
have to choose the tires before you
Roadestimate
tires seldom
exceedgrip.
0.8. If
You'll
can
maximum
you
have to
the tires
before
guess
toochoose
high, weight
transfer
willyou
be
can
estimate maximum grip. If you
too high.
guess
too high,Forces-Most
weight transfer
willcars
be
Aerodynamic
race
too high. quickly at high speed bedecelerate
Aerodynamic
Forces-Most
racefrom
cars
cause
of aerodynamic
downforce
decelerate
quickly
at
high
speed
bewings and the shape of the body.
cause
of
aerodynamic
downforce
from
Downforce varies with car design and
wings
the that
shape
of huge
the wings
body.
speed. and
On cars
have
Downforce
withdownforce
car design may
and
or
ground varies
effects,
speed.
On
cars
that
have
huge
wings
exceed the weight of the car!
or
ground effects,
may
Consequently,
you downforce
should know
exceed
weight
of thebefore
car!
somethingtheabout
downforce
Consequently,
brakeshould
system. know
First,
you can design ayou
something
before
the supplier about
of your downforce
wing(s) should
be
you
a brake
system. inforFirst,
able can
to design
give you
downforce
the supplier
of youronwing(s)
should be
mation.
However,
a ground-effects
able
to
give
you
downforce
inforcar, testing in a wind tunnel is usually
mation.
However,
on
a
ground-effects
the only way to get this information.
car, testing
in a wind anything
tunnel is by
usually
You
can't estimate
just
the onlyatway
to get this information.
looking
the car.
You
estimate
anything
by just
At can't
highway
speed,
aerodynamic
looking are
at thesmall.
car. So ignore aeroforces
At highway
speed,
aerodynamic
dynamic
forces on
a road
car unless
forces
are
small.
So
ignore
aeroyou
have accurate information.
dynamic forces on a road car unless
you have accurate information.
Again, be ready to change the brake
system during testing if things don't
Again,as be
to change
the brake
work
youready
estimated
.
system
during totesting
if things
In addition
the amount
of don't
aerowork as you
estimated.
dynamic
force,
you must know where
In force
addition
of aerothis
acts to
on the
the amount
body. The
point
dynamic
force,
you
must
know
where
where the center of all aerodynamic
this force
the body.
point
forces
actsactsis oncalled
the The
center
of
where the
allcenter
aerodynamic
pressure.
Oncenter
a wing of
, the
of presof
forcesis acts
is called
theof center
sure
roughly
a fourth
the way
pressure.
a wing,
center
of wing
pres-.
front the
edge
of the
back fromOnthe
sure
fourthbeofanywhere
the way.
On a is
carroughly
body, ita could
back
from
the
front
edge
of
the
wing.
If you don't have any information,
On
a
car
body,
it
could
be
anywhere.
assume the center of pressure is at the
If
you don't
center
of have
the any
bodyinformation,
- not
the
assume
the
center
of
is at the
wheelbase. Designingpressure
a ground-effects
center
of testing
the tobody-not
the
car without
find the center
wheelbase.
a ground-effects
of pressureDesigning
may cause
big trouble .
car
without
testing
to findonthegroundcenter
Many
handling
problems
of
pressure
may
cause
big
trouble.
effects cars have been caused by a
Many handling
problems
center
of pressure
being inonangroundunexeffects
cars have been caused by a
pected place.
center
pressure
being in anwith
unexAdd Upofthe
Numbers-Now,
all
pected
place.
the estimated weights or loads, calcuAdd tire
Up the
Numbers-Now,
all
simple,
late
forces.
To make life with
the
estimated
weights
or
loads,
calcuassume that friction force on a tire
late tirevertical
forces.force
To make
lifegrip.
simple,
equals
times its
For
assume that friction force on a tire
equals vertical force times its grip. For
a tire with 1000 Ib of vertical force on
it and a grip of 0.8, friction force is
a tirelb.with
1000
Ib were
of vertical
on
800
If the
grip
raisedforce
to 1.1,
i t and
grip ofdeliver
0.8, friction
is
that
tirea could
1100 lb force
of fric800 lb.
If the
were force
raised istowhat
1.1,
Thegrip
friction
tion
force.
that tire
deliver
lb high
of fricstops
thecould
car-it
should1100
be as
as
tion
force.
The
friction
force
is
what
possible.
stops
car-it page
should
as high
as
See the
drawing,
94,bethat
shows
possible.
the forces acting on a car during
See drawing,
94, that
shows
braking.
For this page
calculation,
I assume
the
forces
acting
on
a
car
during
the right and left tires at both ends of
braking.
For loaded
this calculation,
assume
the car are
equally. IThis
asthe right and
left tires
at both
ends
of
sumption
is more
accurate
than
other
the
car
are
loaded
equally.
This
asdata usually used for this calculation.
sumption
is more
accurate
than other
The
formulas
with
the drawing
are
data
usedtire
for forces
this calculation.
used usually
to calculate
. If you are
The
formulas
the drawing
are
assuming
somewith
aerodynamic
lift, put
used
to
calculate
tire
forces.
If
you
are
a negative number into the formula
assuming
some
aerodynamic
lift,
put
for downforce .
a When
negative
numbera car
intoto the
designing
run formula
on varifor downforce.
ous
surfaces or different types of tires,
When the
designing
car to accordingly.
run on varichange
grip avalue
ous
surfaces
or
different
types
of tires,
Then perform a calculation for
each
change
the
grip
value
accordingly.
grip. Grip might be as low as 0.3 for a
Then
performto aperhaps
calculation
for aeach
1.4 for
hot
slick surface
grip.
low .asResulting
0.3 for a
racingGrip
tire might
on a be
dryastrack
slick surface
to the
perhaps
for forces
a hot
answers
will be
range 1.4
of tire
racing
tire
on
a
dry
track.
Resulting
you must deal with.
answers will be the range of tire forces
you
must deal with.BRAKE TORQUE
CALCULATING
Brake torque is the friction force on
CALCULATING
BRAKE
TORQUE
the
tire, multiplied
by the
rolling
Brakeoflorque
is the
friction
on
radius
the tire.
For
designforce
of the
the
tire,
multiplied
by
the
rolling
brake system, always use maximum
radius
the tire.Maximum
For design torque
of the
brake oftorque.
brake when:
system, always use maximum
occurs
brake
torque.
torque
• Vertical
force onMaximum
tire is maximum
.
occurs
when:
• Tire grip is maximum.
Vertical force on
tireare
is maximum.
tires
used.
• Largest-radius
Tire
grip
is
maximum.
• Car is stopped at maximum possible
Largest-radius tires are used.
deceleration.
Car
possible
If a is
carstopped
has a at
nutmaximum
on the center
of
deceleration.
each wheel, you could measure brake
If a car
hasa a large
nut on
the center
of
torque
with
torque
wrench.
each
you on
could
Whilewheel,
pushing
themeasure
brake brake
pedal
torquean with
large torque
with
efforta needed
to givewrench.
maxiWhile
pushing
on
the
pedal
mum deceleration, turn brake
the wheel
with
an effort
give
maxiwith the
torqueneeded
wrenchtoand
measure
mum deceleration,
turnEven
the though
wheel
torque
as the wheel turns.
with
the
torque
wrench
and
measure
this test is done rarely, this example iltorque aswhat
the wheel
Even
though
lustrates
braketurns.
torque
means.
A
ilthis
test
is donemust
rarely,
brake
system
be this
ableexample
to deliver
lustrates
what
braketorque.
torqueOtherwise,
means. A
the needed
brake
brake
system
must
be
able
to
deliver
the driver won't be able to stop
the
the
needed
brake
torque.
Otherwise,
car at maximum deceleration with an
the driver won't
be ableHe
to may
stop not
the
acceptable
pedal effort.
car
maximum
an
haveat the
strengthdeceleration
to achievewith
maxiacceptable
pedal
effort.
He
may
not
mum deceleration'
have
the strength
to achieve
maxiCalculate
maximum
brake torque
mum
using deceleration!
the formulas given . Use the
Calculate
maximum
brake
values
of grip,
car weight
andtorque
aerousing
the
formulas
given.
Use the
dynamic force that give maximum
values offorce
grip,oncarthe
weight
aerofriction
tire. and
Calculate
dynamic force that give maximum
friction force on the tire. Calculate
93
Modern cars with wings and ground effects generate much more
downforce than ordinary cars. Indy Car cornering and braking
loads
arecars
much
higher
than
forground
a modified
roadgenerate
car. You much
must know
Modern
with
wings
and
effects
more
speed
and downforce
to correctly
calculate
loads generated
by
downforce
than ordinary
cars, lndy
Car cornering
and braking
tires.
loads are much higher than for a modified road car. You must know
speed and downforce t o correctly calculate loads generated by
tires.
~---------b--------~·~I
Center of
Design of ground-effects car should be left to experts. Windtunnel testing is the only sure way to determine aerodynamic
loads
Note ground-effects
at rear of
car.
Designonof car.
ground-effects
car shouldexit
be tunnels
left to experts.
WindPhoto by
Tom Monroe.
tunnel
testing
is the only sure way t o determine aerodynamic
loads on car. Note ground-effects exit tunnels at rear of car.
Photo by Tom Monroe.
I
wheelbase of car (in.)
=
We = total weight 01 the car (lb)
F,
vertical force
on (in.)
both front tires (Ib)
I == wheelbase
of car
force of
onthe
both
F,, = =vertical
W
total weight
carrear
(Ib)tires (lb)
FA
= vertical
aerodynamic
downforce
Ff =
force on
both front(lb)
tires (Ib)
f-t
(coeflcient
friction)
tires
F, == grip
vertical
force onofboth
rear of
tires
(Ib)
d
= aerodynamic
maximum deceleration
FA
downforce(g's)
(Ib)
M=
b =
from front
axle to center
p
= distance
grip (coeffcient
of friction)
of tires of pressure (in.)
Xeg
= maximum
distance from
front axle(g's)
to CG (in.)
deceleration
dM =
Y
height offrom
CG above
ground
(in.) of pressure (in.)
b eg
= -distance
front axle
to center
Xcg = distance from front axle to CG (in.)
Ycg - height of CG above ground (in.)
[Xeg f-t Ye~
f.1. YegJ
F, = We~ --1- + -I-J+ FAL
+ --I-
[b
,
2FFR
__-
-I
=
w,[-p + 'j++ F]
FA[-:
_ _ Xcg _ _ _ _...... 1 We
I
I-
I
Fr = W,
.1
+ FA- Ff
I
FF = Friction Force On One Front Tire =~
LIL
FF
=
d M = ~ +FAP
-
wc
f-t F,
Friction Force On One Rear Tire = - -
2
vFf
2
/JFr
FF = Friction Force On One Front Tire =FF =on
Friction
Forcetire
On One
Rear
Tire =forces
- are computed.
If you can estimate or calculate all data shown on drawing, 2you can calculate forces
tires. From
forces,
friction
2
Friction forces are then used to calculate brake torque during maximum deceleration. It is assumed FA is the only aer?dynamic downforce.
If you can estimate or calculate all data shown on drawing, you can calculate forces on tires. From tire forces, friction forces are computed.
Friction forces are then used t o calculate brake torque during maximum deceleration. I t is assumed FAis the only aerodynamic downforce.
both front- and rear-tire forces.
Maximum brake torque is calculatboth
and rear-tire
forces.
ed
byfrontthe following
formulas:
Maximum brake torque is calculatFront-brake torque = FFF r FT in
ed by the following formulas:
i nCh-pou nds
Front-brake
torque
rFTtire
in in
FFF
= Friction
force =
onF,front
inch-pounds
pounds
Frictionradius
force on
front tire
tire inin
FFF
r FT == Rolling
of front
pounds
inches
,r = Rolling radius of front tire in
Rear-brake
torq ue = FFRr RT in
inches
inch-pounds
Rear-brake
torque
in in
FFR
= Friction
force=onFF,rrear tire
inch-pounds
pounds
F
Frictionradius
force on
rear tire
tire inin
r,RT == Rolling
of rear
pounds
inches
,,r = Rolling radius of rear tire in
Rolling Radius - The rolling radius of
inches
a tire is the distance from the center
Rolling
Radius
rolling radills
of
of
the wheel
to -The
the pavement
wilh the
a tire is the distance from the center
of the wheel to the pavement with the
94
lire loaded. You cannot get an accurate
rolling radius by measuring an unloadtire tire.
loaded.
Youtirecannot
get an
accurate
ed
The
deflects
when
suprolling
porting radius
a car. by measuring an unloaded Rolling
tire. The
tire depends
deflects on
when
radius
the supload
porting
a
car.
on the tire, tire size, inflation pressure
radius
the load
andRolling
stiffness
of depends
the tire on
casing.
So
on the tire,
tire size,
inflation
pressure
measure
rolling
radius
with the
car on
and
stiffnessMake
of the
the ground.
suretirecarcasing.
weight So
is
measure
rolling
radius
with
the
on
the same as yours will be. Also car
check
the
ground.pressure;
Make surecorrect
car weight
inflation
it is
if
the
same as yours will be. Also check
necessary.
inflation pressure; correct it if
necessary.
SELECTING
&
POSITIONING BRAKES
SELECTING
&
Take the following
into consideraPOSITIONING
BRAKES
tion before selecting
brakes:
following
• Take
Disc orthe
drum
brakes. into consideration before selecting brakes:
Disc or drum brakes.
• Brake diameter.
• Brake mounting-inboard or outBrake diameter.
board.
Brake
mounting-inboard
outEach decision
must be madeorbefore
board. a brake .
selecting
Each
be made
Theredecision
are a must
number
of before
brake
selecting
a
brake.
sources. Several manufacturers have
Thereforarespecial
a number
of brake
brakes
applications.
Or,
sources.
Several
have
you could
use manufacturers
standard road-car
brakes
for special
applications.
Or,
brakes. Your
choice depends
primarily
you
could
use
standard
road-car
on the intended use. For instance, is
brakes.
choiceuse
depends
primarily
your
carYour
for street
or racing?
If it's
the intended
Fordesigned
instance,for
is
aonrace
car, use use.
brakes
it's
your
for street
or racing?
racing.carBrakes
fromuse
a road
car areIfusua racetoo
car, heavy
use brakes
for
ally
for designed
best racing
racing.
Brakes
from
a
road
car
are
usuperformance. And racing brakes on a
ally too
racing
street
car heavy
may be foran best
unnecessary
performance. And racing brakes on a
expense.
street car may be an unnecessary
expense.
Unloaded Radius
of Tire
Unloaded Radius
Tire at Proper
Inflation Pressure
and
Load
Tire Under
at Proper
Inflation Pressure
and Under Load
--~-----r--~~~~----~--~r---~----~Ground
While most road-car brakes are too heavy,
some are worth considering for highperformance
use. Cast-iron
Corvette
While
most road-car
brakes1984
are too
heavy,
sliding are
caliper
was designed
more
high
some
worth
considering
forforhighperformance
thanCast-iron
low cost.1 9It8 4may
be a
performance use.
Corvette
natural
for road
with 4-wheel
sliding caliper
was car
designed
more for disc
high
brakes. Photo than
courtesy
performance
low Girlock
cost. ItLtd.
may be a
natural for road car with 4-wheel disc
brakes. Photo courtesy Girlock Ltd.
F = Vertical Force on Tire
= Vertical
Force
on Tire from wheel center to ground with car weight on tire. Tire
RollingF radius
of tire
is distance
must be at correct inflation pressure.
Rolling radius of tire is distance from wheel center to ground with car weight on tire. Tire
must be at correct inflation pressure.
Disc Brakes or Drums? - Because
disc brakes are usually superior to
Disc Brakes
Drums?
-Because
drum
brakes, or
most
people
choose
disc
brakes
are
usually
superior
to
discs for high-performance applidrum brakes,
mostthere
people
cations.
For racing,
is nochoose
other
discs for
high-performance
applichoice
if you
want to win. Drum
cations.
For
racing,
there
is
no
brakes have many limitations. other
You
choice
want
to to
win.
will needif a you
special
reason
use Drum
drum
brakes
have
many limitations.
You
brakes for
racing-such
as rules requir-
will
need a special reason to use drum
ingthem.
requirbrakes
racing-such
as rules of
On a for
road
car, a combination
disc
ing
them.
and drum brakes may be best. Drums
Onbe
a road
car, aon
combination
of disc
may
standard
the rear axle
you
and drum
brakesroad
may cars
be best.
mustDrums
have
will
use. Also,
may
be standard
on theare
rearusually
axle you
parking
brakes- drums
set
will
use.
Also,
road
cars
must
up for parking brakes. Although have
disc
parking
brakes-drums
are usually
set
brakes on
the rear are good
for a road
up for
parking
brakes. Although
disc
car,
they
may introduce
added combrakes
rear Aaredisc
good
for athat's
road
plexity on
andthecost.
brake
car,
they mayforintroduce
not designed
a parkingadded
brakecommay
plexity
andtocost.
be
difficult
adapt.A disc brake that's
notNow
designed
for posed
a parking
brake may
that I've
the disc/drumbe
difficult
to
adapt.
brake question, I'll assume you are
Nowdisc
that brakes
I've posed
discldrumusing
on allthefour
wheels.
brake high-performance
question, I'll assume
Most
cars you
are are
so
using
disc
brakes
on
all
four
wheels.
designed. If you choose drum brakes,
Most
high-performance
cars areThe
so
the design
procedure is similar.
designed. Ifis you
brakes,
difference
thatchoose
you'll drum
have to
conthe design
procedure
is similar.
The
sider
the servo
action
of a drum
difference
is
that
you'll
have
to
conbrake. Servo action is discussed in
sider the2. servo action of a drum
Chapter
brake.
Servo action is discussed
in
Brake Diameter-Disc-brake
diameChapter
2. outside diameter of the
ter is the
Brake Choose
Diameter-Disc-brake
diamerotor.
the largest-diameter
ter
is
the
outside
diameter
the
brakes that will fit in the wheels,ofif the
rotor.
Choose
the inlargest-diameter
brakes are
mounted
the wheels, not
brakes that
will98.
fit The
in theonly
wheels,
if the
inboard,
page
exception
brakes are mounted in the wheels, not
inboard, page 98. The only exception
to this is on a very light car or one
with large-diameter wheels. Most
to this is on a very
light
car or from
one
high-performance
cars
benefit
with
large-diameter
the largest
possible rotorwheels.
that will Most
fit.
high-performance
benefit
from
Maximum rotor cars
diameter
is about
the
largest
possible
rotor
that
will
fit.
3-in. smaller than wheel diameter.
Maximum
diameter
is about
For
example, rotor
a IO-in.
rotor should
go
3-in.
than wheel
diameter.
inside smaller
a 13-in. wheel
or a 13-in.
rotor
For
example,
a 10-in.
rotor
should
go
in a 16-in.
wheel.
Caliper
design
deterinside
a
13-in.
wheel
or
a
13-in.
rotor
mines how big a rotor can be used for
a 16-in.
wheel. Caliper design deterwheel.
aingiven
mines
how
big a rotor
canuse
be used
for
For pavement
racing,
a largea given wheel.
diameter
wheel with a low-profile tire
For than
pavement
racing,
rather
a smaller
wheeluse
andaa largehighdiameter
wheel
with
a
low-profile
tire
profile tire. With a given rolling
rather
than
a
smaller
wheel
and
a
highradius, the large wheel allows the use
profile
tire.brake
Withrotor;
a given
of
a larger
and therolling
lowradius,
the corners
large wheel
profile tire
better.allows the use
of
a larger brake
rotor;- and
the lowDisc-Brake
Selection
Rotors
and
profile
tire
corners
better.
calipers should be selected as a
Disc-Brake
and
matched
set. Selection
By using -aRotors
caliper and
calipers
shouldto be
rotor
designed
workselected
together,asyoua
matched
set.to By
usingabout
a caliper
and
don't have
worry
a dimenrotor
designed
to
work
together,
you
sional mismatch between the two. So
don't have
to worry
dimenchoose
the caliper
andabout
rotor aintended
sional
the two.
So
for
themismatch
same roadbetween
car or from
a racechoose
the
caliper
and
rotor
intended
car- brake manufacturer.
forCalipers
the same
car or
from
a raceandroad
rotors
must
meet
the
car-brake requirements:
manufacturer.
following
and be
rotors
mustenough
meet the
• Calipers
Rotor must
massive
to
following
requirements:
absorb heat from at least one stop
Rotor
must be speed
massive
to
from
maximum
at enough
maximum
absorb
heat from at least one stop
vehicle weight.
from
maximum
speed
and caliper
mustatfit maximum
mounting
• Rotor
vehicle
weight.
space on car.
Rotor and
caliperdeliver
must fit maximum
mounting
• Brake
must
space
car. required without excesbrake on
torque
Brake must deliver maximum
brake torque required without exces-
Although fixed, aluminum race-car caliper
appears similar to Corvette caliper in
above photo.
APaluminum
CP2751 race-car
caliper was
deAlthough
fixed,
caliper
Signed forsimilar
IMSA toroad
racers using
appears
Corvette
caliper13in
in.-diameter
above
photo.rotors.
AP C PThese
2 7 5 1 require
caliper minimum
was de14-in.-diameter
inboard
brakes.
signed
for IMSAwheels
road or
racers
using
13Photo courtesy
AP Racing.
in.-diameter
rotors.
These require minimum
14-in.-diameter wheels or inboard brakes.
Photo courtesy AP Racing.
Race cars generally use largest possible
brake diameter. On this Indy Car, caliper
almost
rubs generally
against inside
wheel.possible
Race cars
use of
largest
brake diameter. On this lndy Car, caliper
almost rubs against inside of wheel.
sive tl uid pressure.
One-Stop Temperature Rise Roadsive
pressure. weight must be
Car fluid
Rotors-Rotor
One-Stop
Temperature
Roadhigh enough
to absorb Rise
all kinetic
Car
Rotors-Rotor
weight
must
be
energy stored in the moving car. The
high enough
absorb all
worst
conditiontois stopping
a carkinetic
travenergyatstored
in thewith
moving
car.atThe
eling
top speed
the car
its
worst
condition
is
stopping
a
car
maximum weight. Some road travcars
eling
at top that
speedprobably
with thedon't
car at
its
have brakes
meet
maximum
weight.This
Some
road cars
this
requirement.
is probably
be-
have brakes that probably don't meet
this requirement. This is probably be95
Kinetic energy
Wc S2
=---
W,S2
29.9
Kinetic
energy =in foot-pounds
29.9
We = Weight of car
in pou nds
Sin =foot-pounds
Speed of car in miles per hour
W, = Weight of car in pounds
After
calculating
kinetic
energy
S
= Speed
of car inthe
miles
per hour
of a car, determine how much energy
After
kinetic
goes
to calculating
the front the
brakes
andenergy
how
of
a
car,
determine
how
much
energy
much to the rears. A good guess
is to
goes
to thekinetic
front energy
brakes according
and how
proportion
much
the torques.
rears. A This
goodrelationship
guess is to
to the to
brake
proportion
kinetic energy
is only approximate,
but theaccording
calculato
the
brake
torques.
This
tion for rotor weight does relationship
not have to
is
but the
calculabe only
exact.approximate,
Use the following
formula:
tion for rotor weight does not have to
=
KrTF
K exact.
be
Use the following formula:
F
Exception to the rule: Brake is considerably smaller than wheel allows on front ofI
lu
sprint
car. Demands
on Brake
brakesisofconsideracar raced
Exception
to the rule:
on
are than
muchwheel
less allows
than ifonraced
bly dirt
smaller
front on
of
pavement.
sprint
car. Demands on brakes of car raced
on dirt are much less than if raced on
pavement.
Garage area or pits is best place to look at
and photograph race-car brakes. Take advantage
of oryears
trialGarage area
pits isof
bestexpensive
place to look
at
and-error
development
to select
and
photograph
race-car brakes.
Takerotor
adsizes and of
designs.
the mechanics.
vantage
yearsTalk
of toexpensive
trialIf they have
brake trouble,
their
and-error
development
to consider
select rotor
problems
your
Indy
sizes
and during
designs.
Talkbrake
to thedesign.
mechanics.
Car
brake
wasbrake
photographed
at Phoenix
InIf they
have
trouble, consider
their
ternational
Raceway-one-mile
problems during
your brake design.paved
lndy
track
that was
putsphotographed
high demands
on brakes.
Car brake
at Phoenix
InPhoto by Tom Raceway
Monroe. -one-mile
ternational
paved
track that puts high demands on brakes.
Photo by Tom Monroe.
cause some road-car designers think
it's unreasonable to drive at the top
cause
some
designers
speed of
a carroad-car
at maximum
weightthink
and
it's unreasonable
drive
at thethink
top
suddenly
do a hardtostop.
I don't
speed
of a car at maximum
weightdrivand
it's unreasonable,
even though
suddenly
a hard
think
ing at topdo
speed
is stop.
illegalI don't
and unsafe
it's
unreasonable,
even
though
on the road; but some people do it.drivingFrom
at top
speed 1,
is the
illegal
and energy
unsafe
Chapter
kinetic
on
the
road;
but
some
people
do
it. as
of a moving car is determined
From
Chapter
1,
the
kinetic
energy
follows:
of a moving car is determined as
follows:
96
(T F + T R)
KF = Kinetic energy to front brakes in
foot-pounds
KF =
Kinetic
energy
to front
brakes
Kr
= Total
kinetic
energy
of car
in in
foot-pounds
KT
Total kinetic
energyinofinch-pounds
car in
T
F == Front
brake torque
foot-pounds
T
R = Rear brake torque in inch-pounds
T, = Front brake torque in inch-pounds
= Kr - KF
T , KR
= Rear brake torque in inch-pounds
KR = Kinetic energy to rear brakes in
K,= K T - K,
foot-pounds
K, = Kinetic energy to rear brakes in
The kinetic energy calculated is for
foot-pounds
a pair of brakes-two front and two
TheDivide
kineticthe
energy
calculated
for
rear.
answers
by 2 tois get
pair of
brakes-two
and
two
akinetic
energy
absorbed front
by each
brake.
rear.
Divide
the answers
by 2 to rise
get
Now,
compute
the temperature
kinetic
energy
absorbed
by
each
brake.
of the rotor after one stop using
Now, compute
formula
on page the
11 .temperature
Use weightrise
of
of therotor
rotoror after
stop
using
single
drum one
for W
s' This
is
formula
on temperature
page 11. Use
of
the average
of weight
the entire
single
rotor
drumtemperature.
for W,. This is
rotor, not
theor
surface
theIfaverage
temperature
of the entire
the average
rotor temperature
is+
rotor,
the surface
near not
lOOOF
(538C) temperature.
use a heavier
If the
average
temperature
rotor.
This
meansrotor
a thicker
rotor is
if
near
lOOOF
(538C)
use
a
you have chosen the largestheavier
rotor
rotor.
This
means The
a thicker
rotor
if
diameter
possible.
type of
brake
you
have
the largest
linings
usedchosen
will determine
howrotor
hot
diameter
The still
type have
of brake
the rotor possible.
can be and
the
linings
used
will
determine
how
hot
brakes work.
the rotor Rotors-If
can be andyou
stillarehave
the
Race-Car
designbrakes
work.
ing
a race
car, and the brakes are used
Race-Car
Rotors-If
designmany times
during a you
race,are
a calculaing
a
race
car,
and
the
brakes
are
used
tion for one stop will not mean much.
many times
a race,
a calculaBefore
each during
stop, brake
temperature
tion be
formuch
one stop
willthan
not mean
much.
will
higher
100F (38C).
Before
each
stop,
brake
temperature
For a road racer, assume the rotors
will
much500F
higher(260C)
than 100F
( 3 8the
0.
are be
about
when
For
a road
racer, assume
the rotors
brakes
are applied.
Also, each
brake
are about is500F
(260C)topwhen
application
not from
speed the
to
brakes
are
applied.
Also,
each
brake
full stop as assumed in the previous
application is not from top speed to
calculations.
fullRacers
stop ashave
assumed
in the previous
experimented
with
calculations.
different-size and -weight rotors for
Racers
have experimented
with
years.
Although
some work, others
different-size
-weight
for
can
overheat. and
After
years rotors
of trialyears.
Although
others
and-error,
a brake some
designwork,
has been
decan
overheat.
Afterracing
yearsclass
of trialveloped
for each
that
and-error, a brake design has been developed for each racing class that
works for most cars under normal
conditions. Go to the track and look at
works
for on
most
under
normal
the brakes
carscars
similar
to yours.
If
conditions.
G o selected
to the track
and lookdifat
the rotor you
is greatly
the brakes
on cars
to yours.
If
ferent
in size
andsimilar
weight,
you are
the
rotor
you
selected
is
greatly
difprobably wrong. If in doubt, go larger.
ferent
size and
weight,
you onarea
Use thisinmethod
to select
rotors
probably
wrong.your
If incar
doubt,
go larger.
race car, unless
is unique.
Use
thisword
method
to selectIfrotors
One
of caution:
other on
carsa
race
car,
unless
your
car
is
unique.
in your class are using water-cooled
One word of147
caution:
other have
cars
brakes-page
-they Ifeither
in
your classrotors
are using
water-cooled
undersized
or improper
air
brakes-page
ducting.
Water 147-they
cooling is aeither
crutchhave
and
undersized
or unless
improper
air
should
not rotors
be used
larger
ducting.
Water cooling
is a. crutch
and
brakes cannot
be fitted
In other
should
notthebecompetition
used unlessis larger
words, if
using
brakes
cannot
be
In thicker
other
water cooling, go to afitted.
larger or
words,
if they
the use.
competition is using
rotor than
water
cooling,
to ayou
larger
thicker
While
at the go
track,
canormake
inrotor
than observations
they use.
teresting
about brakes.
at the
canoval
make
inIf While
you are
at atrack,
flat, you
paved
track
teresting
about
brakes.
where
hardobservations
braking is used
going
into
If
youone
areand
at athree,
flat, time
pavedvarious
oval track
turns
cars
where
hard
braking
is
used
going
early in a long race and late in into
the
turns one
time increase
various cars
same
race.and
If three,
lap times
on
early in
longnot
race
latechances
in the
some
carsa and
on and
others,
same
lap times
increase
on
are therace.
cars Ifrunning
slower
near the
some
cars
and
not
on
others,
chances
end are "running out of brakes." See
are
carsvarious
running cars
slowerarenear
the
whatthethe
doing
end
are
"running
out
of
brakes."
See
differently.
what
carslong
arestraights
doing
At a the
road various
course with
differently.
followed by tight turns, such as turn
Atata road
course
withthelong
straights
five
Elkhart
Lake,
importance
followed
by tight
turns, such
turn
of
good brakes
is evident.
Walkasalong
five
at Elkhart
the straight
to Lake,
where the
theimportance
cars start
of
good brakes
is evident.
Walkdeeper
along
braking
and see
how much
the
straight
to
where
the
cars
start
cars with good brakes go. Good
braking
andmean
see ashow
much
brakes can
much
as a deeper
200-ft
cars
with going
goodinto
brakes
Good
advantage
a slowgo.
corner
off
brakes
can
mean
as
much
as
a
200-ft
a fast straight. Imagine how much
advantage
a slowitcorner
horsepowergoing
and into
handling
takes off
to
amake
fastupstraight.
200 feet!Imagine how much
horsepower
and handling
it takescan
to
Race-ear-brake
manufacturers
200
feet!
make
up
be a big help when selecting rotors for
Race-car-brake
can
a race
car. They aremanufacturers
aware of all applibe a big for
helptheir
whenproducts
selecting and
rotorswhat
for
cations
a race car.
aware
of all aware
appliworks
best.They
Theyare
also
are made
cations
for their
their brakes
productsdon't
and work.
what
of it when
works
best.
They
also
are
made
aware
Manufacturers work with race-car deof it when
brakes
signers
to their
develop
the don't
best work.
rotor
Manufacturers
work with
design
for each racing
class.race-car designers
to companies
develop the
rotor
Contact
suchbest
as Hurst,
design
for
each
racing
class.
JFZ, Tilton, Wilwood or their dealers
Contact
suchyour
as special
Hurst,
before
you companies
buy rotors for
JFZ,
Tilton, Wilwood or their dealers
race car.
before Area-Another
you buy rotors for
special
Swept
aid your
in selecting
race
car.
the proper rotor size is the swept area
Swept
aid on
in selecting
of
the Areabrake. Another
The chart
page 28
swept cars.
area
the proper
rotor
sizefor
is the
shows
swept
area
various
of
the
brake.
The
chart
on
page
28
Consider using a swept-area-to-weight
shows
swept
area
for
various
cars.
ratio for a car of nearly the same
Consider
a swept-area-to-weight
power andusing
speed
as yours. If you are
ratio
for aa car
nearly
same
designing
raceofcar,
use the
a swept-
power and speed as yours. If you are
designing a race car, use a swept-
area-to-weight ratio for race cars, not
for road cars. In both cases, if long
area-to-weight
race cars, not
lining life andratio
fadefor resistance
are
for
road
cars.
In
both
cases,
if long
more important than brake weight,
lining
life and
use a higher
sweptfade
area. resistance are
more
important
thanmeans
brakeyou
weight,
Higher
swept area
must
use
swept
area.rotor. This may
use aa higher
larger-di
ameter
Higher
sweptusing
area means
you must
mean
larger-diameter
also
use
a
larger-diameter
rotor.
Thisrotor
may
wheels, if the wheels limit
also
meanIf you
usingsimply
larger-diameter
diameter.
cannot get
wheels,
if the area
wheels
limit ofrotor
enough swept
because
the
If
you
simply
diameter.
wheels, you can reso rt tocannot
using get
inenough
swept page
area 98.
because
of the
board brakes,
An inboard
wheels,
can resort
to using
inbrake isyou
mounted
inboard
on the
board or
brakes,
page transferring
98. An inboard
frame
transaxle,
brakinboard onto the
brake
is through
mounteda driveshaft
the
ing force
frame
or
transaxle,
transferring
brakwheel.
ing force
a driveshaft
the
Vented
or through
Solid Rotors
- When to
lookwheel.
ing at cars like yours, note whether
Vented ororSolid
vented
solidRotors-When
rotors are lookused.
ing at cars
likeweight
yours,and
note
whether
Usually,
rotor
cooling
revented
or solid
rotors ifare vented
used.
quirements
determine
Usually,
weight
and cooling
rerotors arerotor
needed.
Vented
rotors are
quirements
determine
if needed.
vented
rotors are
used where heavier
rotors
needed.
Vented
are
A very are
thick
solid rotor
doesrotors
not cool
used
where
heavier
rotors
are
needed.
adequately. Because of this, it is
A
very thick
solid
cool
unusual
to see
a rotor
solid does
rotor not
thicker
adequately.
than 1/2 in. Because of this, it is
unusual
see needs
a solidverotor
If yourto car
nted thicker
rotors ,
than
112
in.
refer to the rotor section in Chapter 3.
If yourtypes
car of
needs
vented
rotors,
Various
vented
rotors
are
3.
refer
to theYour
rotorbrake
section
in Chapter
available.
supplier
will be
Various
types of
rotors
are
able to compare
thevented
merits of
one type
available.
Your brake
be
versus another.
I supplier
suggest will
using
able
to compare
thecurved
merits vents
of oneiftype
vented
rotors with
you
versus
another.
I suggest
using
can
afford
them. The
cooling advanvented
rotors
with
curved
vents
if
you
tages are worth the expense.
can afford them. The cooling advantages
are worth
expense.
CALIPER
SELthe
ECTION
Caliper
and
rotor
selection
go
CALIPER
SELECTION
together because
they often come
Caliper
and manufacturer.
rotor selection
go
from
the same
He will
together
they works
often with
comea
supply a because
caliper that
from
the same manufacturer.
will
certain-diameter
and -thicknessHerotor.
supply
a
caliper
that
works
with
Make sure the caliper fits in thea
certain-diameter
andcalipers
-thickness
desired area. Some
are rotor.
more
Make
caliper
fits in the
compactsure
thanthe
others.
Pay attention
to
desired
area. You
Somemust
calipers
more
the details.
not are
machine
compact
others.
Pay attention
to
metal off than
a caliper
to provide
clearance
the
details.
You
must
not
machine
to a wheel or suspension member.
metal
offuse
a caliper
to provide
clearance
Also,
a caliper
that will
mount
to a wheel
suspension member.
on
your or suspension
or chassis
Also, use aSome
calipercalipers
that will
components.
aremount
easily
on
your
suspension
or
adapted to existing components.chassis
Concomponents.
calipers are
sult
a brake Some
manufacturer.
He easily
may
adapted
to existing components.
Conoffer a ready-made
caliper mounting
sult
a brake manufacturer. He may
bracket.
offer
a ready-made
caliper mounting
If you
are also designing
a new
bracket.
suspension,
be sure to consider the
If you and
are also
designing
new
caliper
provide
space a large
suspension,
be
sure
to
consider
enough for it. A proper caliperthe
is
caliper bit
and asprovide
spaceas large
every
important
the
enough for it. A proper caliper is
suspension.
every bit as
suspension.
important
as
the
Don ' t buy a caliper that must use a
flimsy mounting bracket. Make sure
buy isa caliper
thatand
muststrong.
use a
theDon't
bracket
very stiff
flimsy
Extra "mounting
beeP ' on bracket.
this partMake
helps sure
the
the
bracket
very stiffbracket
and strong.
braking.
A ismounting
that
Extra
"beef'
onpoor
this brake
part helps
the
twists can
cause
performbraking.
A mounting
ance
and uneven
pad wear.bracket that
twists
cause
poor delivered
brake performThe can
brake
torque
by a
ance
and
uneven
pad
wear.
caliper and rotor must be as great or
The than
brakewhat
torque
delivered
by a
greater
is required
for maxicaliper
and rotor mustThe
be as
great or
mum deceleration.
maximum
greater
what
is required
for by
maxipossiblethan
brake
torque
is limited
the
mum
deceleration.
The
maximum
maximum operating pressure the calipossible
torqueIfisthis
limited
by the
per can brake
withstand.
maximum
maximum
the calipressure isoperating
exceeded,pressure
the caliper
can
per can
withstand.theIf this
flex
excessively,
seals maximum
can leak
pressure
is exceeded,
the caliper
caliper can
can
and,
in severe
cases, the
flex
excessively,
the
seals
can
leak
fail. Never design a brake system that
and, in severe
cases, the caliper
can
exceeds
the manufacturer's
recomfail.
Never
design a brake system
mended
maximum-pressure
rating.that
exceeds
theRotor
manufacturer's
recomCaliper &
Placement-When
mended
maximum-pressure
rating.
fitting brakes to a new car, it's imporRotor
tant to position
theP1aeement-when
caliper in the best
fitting
to a the
new rotor,
car, it'sand
imporpositionbrakes
around
the
tant toand
position
theincaliper
in the
best
rotor
caliper
the best
lateral
position around the rotor, and the
position.
rotor
and
caliper
in the
bestposition
lateral
First,
let's
consider
caliper
position.
aro
und the rotor. Assume you are
First, let's
consider
caliper
position
looking
at the
left-front
wheel
from
around
the
rotor.
Assume
you
are
the outside. Theoretically, the caliper
lookinggoat at
the any
left-front
wheel
from1
could
position
from
the outside.
o'clock
to 12Theoretically,
o'clock. Therethe
arecaliper
many
could
go
at
any
position
things to consider, such as from
existing1
o'clock
to 12
o'clock.bleeding,
There arespindle
many
mounting
bosses,
things to consider,
such as and
existing
deflection,
air-duct location,
susmounting
pension andbosses,
steeringbleeding,
clearances.spindle
deflection,
air-duct
location,
susIf you have
an existing
car,and
mountpension
and
steering
clearances.
ing bosses on the spindles- or
If you have
uprightsmay an existing
dictate car, mountcaliper
ing
bosses
on isthebestspindles-or
at 3 and 9
location.
Bleeding
uprights-may
dictate positioned
caliper
o'clock. Usually, calipers
location.
Bleeding
is
best
at
3
and 9
at 12 and 6 o'clock must be removed,
o'clock.
Usually,
positioned
rotated and
have acalipers
spacer inserted
to
12 .and
6 o'clock
be removed,
at
bleed
Spindle
and must
axle-shaft
deflecrotated
and have
a spacer can
inserted
to
tion during
cornering
cause
bleed.
Spindle
and
axle-shaft
defleccaliper-piston knockback with calipers
tiontheduring
cause
at
12- andcornering
6-0'clock can
positions.
caliper-piston
ktiockback
with calipers
This
should not
be a problem
with
at
the 12- hubs
and or
6-o'clock
positions.
full-floating
sliding calipers.
This
shouldairnot
be aenter
problem
Because
ducts
from with
the
full-floating
hubs or
sliding calipers.
front
of a brake,
3 o'clock
is usually
Because
from can
the
best
for theaircaliducts
per soenter
the ducts
3
o'clock
is
usually
front
of
a
brake,
enter the center of the rotor at 9
best for the
caliper suspension
so the ductsclearcan
o'clock.
Although
enter differ
the center
of tothecar,rotor
ances
from car
thereatare9
o'clock.
Although
suspension
usually ball
joints and
uprights clearat 12
ances
differ
from
car
to
car, arms
there are
are
and 6 o'clock. Steering
usually
ball
joints
and
uprights
at
12
either at 3 or 9 o'clock . Usually, when
and 6 o'clock.
Steering
everything
is considered
, 3 arms
o'clockare
is
either
at 39 or
9 o'clock.
Usually,
when
best and
o'clock
is second
best,
but
everything
considered,
is
any
positionis will
work. It 3allo'clock
depends
best
and
9
o'clock
is
second
best,
but
on what is best for your car.
anyFor
position
work. It all
lateral will
positioning,
thedepends
things
on what is best for your car.
For lateral positioning, the things
Caliper did not fit wheel correctly, so metal
was removed from outboard edge. Don't do
this
to get
a caliper
to fit.
Caliperso
flexing,
Caliper
did not
fit wheel
correctly,
metal
cracking
or other
problems edge.
may Don't
result do
if
was removed
from outboard
excess
metal
is removed.
Instead, flexing,
select
this to get
a caliper
to fit. Caliper
calipers and
wheels
that clear
without
cracking
or other
problems
may result
if
modification.
excess
metal is removed. Instead, select
calipers and wheels that clear without
to consider are eXistIng mounting
bosses, and wheel and suspension
to considerWith
are anexisting
clearances.
existingmounting
car, you
bosses,
and
wheel
and suspension
may be able to use existing
bosses and
clearances.
Withbut
an you
existing
car, you
hole locations,
will probably
may
be
able
to
use
existing
bosses
have to fabric ate an adapter plate.and
It
hole
but I/2-in.
you will
probably
must locations,
be rigid . I like
steel
plate.
have
to fabricate
an adapter
It
Position
each caliper
so itplate.
has at
like 112-in.tosteel
must
be rigid. I clearance
the plate.
wheel
least O.080-in.
it has at
Position
and
114 in.each
to caliper
moving sosuspension
least
0.080-in.
clearance
to
the
parts. Be sure to check the fron wheel
t susand
114with
in. the
to steering
moving atsuspension
pension
full lock,
parts. and
Be sure
to check
front posisusrightleft-turn.
If nothe
caliper
pension
with
the
steering
at
full
lock,
tion can be found that clears at full
rightand left-turn.
If nostops.
caliperExcept
posi'steering
lock, consider
tiondirt
canoval-track
be found cars,
that few
clears
at cars
full
for
race
lock, as
consider
'steeringangle
stops.as Except
need
much steering
a road
for dirt oval-track cars, few race cars
car.
need
much steering
anglecaliper
as a road
RotorasOffset-Once
lateral
pocar.
sition is found, the rotor position is
Rotor Offset-Once
caliper
pofixed.
Determine lateral
rotor-hat
offset
sition
is
found,
the
rotor
position
is
next. Hat offset is the distance from
fixed.
Determine
rotor-hat
offset
the hub mounting surface to the rotor
next. Hat offset
the distance
mounting
surface.is Never
order from
hats
the hubthe
mounting
the rotor
until
calipersurface
and torotor
are
mounting
order
hats
positioned. surface.
Rotor Never
hats with
almost
untiloffset
the cancaliper
and off
rotor
are
any
be supplied
the shelf
positioned.
hats with byalmost
or
machinedRotor
to specification
your
any
offset
canorbe
supplied off the shelf
brake
dealer
manufacturer.
or
machined
to
specification
your,
Rotor-Hat Holes-For some by
reason
brake
dealer
or
manufacturer.
many hats come with large holes
Rotor-Hat
Holes-For
some reason,
around
their
circumference.
These
many
hats
come
with
large holes
holes help air flow to the outboard
suraround
These
face of their
solid circumference.
rotors and ventilated
holes help
air flow
to theairoutboard
surrotors
not using
sealed
ducts. With
face ofducts
solid
rotors
and
ventilated
sealed
, these
holes
allow
cooling
rotors not using sealed air ducts. With
sealed ducts, these holes allow cooling
97
Sprint-car rear axle: Single inboard brake
on solid axle is possible because of exposed axle rear
shaftaxle:
and Single
locked inboard
rear end.
Not
Sprint-car
brake
only
is weight
by because
one-half,ofwhen
on solid
axle isreduced
possible
exone
wheel
a bump,
brake rear
moves
smalposed
axlehits
shaft
and locked
end.
Not
ler distance
than
wheel,byreducing
brake's
only
is weight
reduced
one-half,
when
effective
weight.
Improved
hanone
wheelunsprung
hits a bump,
brake
moves srnaldling
results. than
Photowheel,
by Tomreducing
Monroe. brake's
ler distance
-
Inboard rear brakes are used on this Formula Ford. Brake COOling is excellent, rotor diameter is not limited by wheel size, and handling on rough surfaces is improved . Inboard brakes
are
not rear
usedbrakes
on ground-effects
cars
because
they
reduce
tunnel
width and
resulting
lnboard
are used on this
Formula
Ford.
Brake
cooling
is excellent,
rotor
diamedownforce.
ter
is not limited by wheel size, and handling on rough surfaces is improved. lnboard brakes
-
effective unsprung weight. Improved handling results. Photo by Tom Monroe.
are not used on ground-effects cars because they reduce tunnel width and resulting
downforce.
Caliper mounts to quick-change side-bell and rotor-to-axle adaptor clamps to axle shaft: Actual sprint-car installation is at right. Note
bearing housing- cage-with control-arm brackets at outer end axle. Photo at left courtesy AP Racing; photo at right courtesy Tilton.
Caliper mounts to quick-change side-bell and rotor-to-axle adaptor clamps to axle shaft: Actual sprint-car installation is at right. Note
bearing
housing-cage-with
control-arm
brackets
at outer
axle.allow
Photo at
left courtesy
photo
at right
Tilton.
air to escape
from the center
of the
only
doesend
this
larger
rotors, AP Racing;
such as
those
forcourtesy
an independently
rotor before it flows through the
air
to escape
from the center
the
rotor.
Consequently,
these ofholes
rotor before
it flows
through
the
should
be plugged.
When
ordering
rotor.
Consequently,
holes
new hats,
specify with these
or without
should depending
be plugged.
ordering
holes,
on When
your rotor
and
new
hats,
specify
with
or
without
cooling system. If existing hats
have
holes, and
depending
rotor aluand
you wishon
to your
plug them,
holes
cooling
If existing
hats have
minum system.
tape with
high-temperature
holes andworks
you wish
adhesive
well.to plug them, aluminum
tape
with
high-temperature
Inboard Brakes-For
one reason or
adhesive works
well. want to consider
another,
you might
Inboard Brakes-For
reasonNot
or
mounting
the brakes one
inboard.
another, you might want to consider
mounting the brakes inboard. Not
98
cooling is better because the brakes
only not
doesshrouded
this allowby larger
rotors,
are
the wheels.
cooling
is
better
because
the
Wheel-weight reduction alsobrakes
imare
not handling
shroudedon byrough
the surfaces
wheels.
proves
Wheel-weight
and
brake torquereduction
does not goalso
into imthe
proves
handling
on
rough
surfaces
suspension.
and
brake
torque
doesbrakes
not gomounted
into the
Why
aren't
many
suspension.
inboard? To begin with, they compliWhya aren't
many . brakes
mounted
For example,
cate
car design
inboard?
To
begin
with,
they
mounting provisions must becomplimade
cate
a car
For example,
for the
rotordesign.
and caliper
on the
mounting
provisions
mustand
be joints
made,
chassis.
Then
an axle shaft
for the rotor and caliper on the
chassis. Then an axle shaft and joints,
sprung, driven wheel, must be used.
such
as the
those
for must
an independently
spindle
rotate in the
Finally,
sprung,
driven
wheel,
must
be used.
upright. All this increases
complexity,
Finally,
the
spindle
must
rotate
the
cost and weight. To top it off, inmost
upright. All this increases
complexity,
front-wheel-drive
cars don't
have
cost
top it Race
off, most
roomand
for weight.
inboardTobrakes.
cars
front-wheel-drive
cars
don't
have
using ground effects need the narrowroombody
for possible
inboard brakes.
cars
between Race
the side
est
using ground
thethe
narrowducts;
inboardeffects
brakesneed
make
body
est
the side
andpossible
reduce between
the aerodynamic
widerbody
ducts;
inboard
brakes
make
the
body
downforce on the car. Use inboard
wider
and
reduce
the
aerodynamic
brakes if it makes sense , but keep in
downforce on the car. Use inboard
brakes if it makes sense, but keep in
TOTAL PISTON AREA FOR EACH TYPE OF CALIPER
AT = Total Piston
TOTAL PISTON AREA FOR EACH TYPE OF CALIPER
Type of Caliper
Area (sq in.)
Fixed mount-one piston on each side of rotor
Type
of Caliper
Fixed mount-two pistons on each side of rotor
Fixed
mount-one piston
on on
each
side
of rotor
Fixed mount-three
pistons
each
side
of rotor
Fixed mount-two
pistons
rotor
Floating
mount-one
pistonononeach
onlyside
one of
side
of rotor
Fixed mount-three
of rotor
Floating
mount-twopistons
pistonson
oneach
only side
one side
of rotor
Floating mount-three
mount-one piston
on on
only
oneone
side
of rotor
Floating
pistons
only
side
of rotor
Floating
pistons
on only one side of rotor
Ap
= areamount-two
of one piston
(sq in.)
A, =Total Piston
Area (sq in.)
2AP
4AP
6AP
2AP
4AP
Floating mount-three pistons on only one side of rotor
GAP
A,
= area of one piston (sq in.)
Chart gives total piston area for each type of caliper. Floating-sliding-caliper
has one
piston doing job of two in a fixed caliper. If you don't know the type of caliper, remember
that
calipers
piston(s)
one Floating-sliding-caliper
side. Area Ap of each piston
in
Chartfloating-mount
gives total piston
areahave
for each
typeon
of only
caliper.
has is
one
square doing
inches.
Determine
for your
particular
piston
job
of two inAp
a fixed
caliper.
If youcaliper.
don't know the type of caliper, remember
that floating-mount calipers have piston(s) on only one side. Area A, of each piston is in
square inches. Determine Ap for your particular caliper.
mind the
concept.
disadvantages
of
the
mind the disadvantages of the
concept.
DETERMINE
HYDRAULIC-SYSTEM
DETERMINEPRESSURE
OPERATING
HY
DRAULIC-SY
T E M torque is
Once
required Sbrake
OPERATING
PRESSURE
known and you've made a caliper
Once required
braketo determine
torque is
selection,
it's possible
known
and
you've
made
caliper
fluid pressure. Some brake a catalogs
selection,
it's
possible
to
determine
give the relationship between hydraufluid
pressure.
catalogs
andSome
brakebrake
torque
for a
lic pressure
give thecaliper
relationship
betweenHowever,
hydraugiven
and rotor.
lic
pressure and
for a
remember
that brake
the torque
torque-vergiven
caliper
and
rotor.
However,
sus-pressure relationship depends on
remember
that coefficient.
the torque-verbrake-lining friction
sus-pressure
depends
on
fluid pressure
required
To find therelationship
brake-lining
friction
coefficient.
for your car, you need the following
To find the fluid pressure required
information:
for
your car, you
needcoefficient.
the following
• Brake-lining
friction
information:
• Total piston area for each caliper.
Brake-lining
friction
coefficient.
effective
radius.
• Rotor
Total
piston
area
for
each
caliper.
• Brake torque at maximum
decelerRotor effective radius.
ation.
Brake
at maximum
decelerIf you torque
have the
friction coefficient
ation.
for your linings, use it. Otherwise,
If you it's
have
friction
coefficient
assume
0.3.the
Most
linings
are this
for
your linings,
it. by
Otherwise,
approximate
value.use
Start
calculatassume
it's 0.3. Most
ing caliper-piston
area: linings are this
approximate value. Start by calculatArea of piston = 0.785 Dp2 in square
ing
caliper-piston area:
inches
Area
piston =
in square
Dp = of
Diameter
of0.785
pistonDP2
in inches
inches
Total piston area is the area of one
D p = Diameter of piston in inches
piston multiplied by the number of
Total piston
area is the area
of one
pistons
for a fixed-mount
caliper.
If
pistonhave
multiplied
by caliper,
the number
of
you
a floating
multiply
pistons
fixed-mount
If
the
areafor
of aone
piston by caliper.
twice the
you
have
a
floating
caliper,
multiply
total number of pistons to get total efthe area
of one
mice the
fective
piston
area.piston
This by
is illustrated
total number of pistons to get total efabove.
fective
piston selected
area. Thisa iscaliper
illustrated
If you've
with
above.
non-circular pistons, such as those
If you've
selected a you
caliper
from
Alston Industries,
mustwith
use
non-circular
pistons,
as those
an
effective piston
area insuch
the formulas.
from Alston
Industries,
must
use
piston
area foryou
each
caliper
Effective
eJfective
piston
area
in
the
formulas.
an
is given in the caliper manufacturer's
Effective piston area for each caliper
is given in the caliper manufacturer's
catalog. If you use a formula that requires using piston diameter, you
catalog.
If
you use
formula that
remust
compu
te a effective
piston
quires
diameter.using
This piston
is the diameter'
diameter of a
that has
an area piston
equal
circular
must piston
compute
effective
diameter.
Thisarea
is the
diameter
of a
to
the piston
of the
non-circular
circular
piston
that
has
an
area
equal
caliper. All formulas requiring piston
to the piston
area using
of thethis
non-circular
diameter
will work
method.
caliper.
formulas
requiring
piston
Brake All
effective
radius
is the distance
diameter
will
work
using
this
method.
from the center of the rotor to the
Brakeofeffective
radiuspad.
is the
distance
center
the brake
Once
you
from
center ofradius,
the rotor
to folthe
know the
the effective
use the
center
of the brake
pad. Once
you
to compute
fluid preslowing formula
knowatthe
effectivebrake
radius,
use the folsure
maximum
torque.
lowing formula to compute fluid presT
sure
at maximum
torque.
Maximum
hydraulicbrake
pressure
= __
8_
,uLATrE
in pounds hydraulic
per squarepressure
inch
Maximum
'8
=-
T 8 = Brake torque in inch-pounds
PLAT'E
in Dounds
Der sauare inch of brake
,uL
= Coefficient-of-friction
T,'
=
rake torque in inch-pounds
linings
p
Coefficient-of-friction
of brake
AT, == Total
area of caliper pistons
in
linings inches
square
A,
Total arearadius
of caliper
pistons
in
r E == Effective
of brake
in inches
square inches
r, = Effective radius of brake in inches
Once
maximum
pressure
is
calculated, make sure the caliper can
Once at maximum
is
operate
this pressure .pressure
Usually, the
calculated,
make
sure
the
caliper
can
maximum operati;lg-pressure rating
operate
at thisis pressure.
the
of
the caliper
specified Usually,
by the brake
maximum operatiag-pressure
manufacturer.
It varies from rating
about
of
the tocaliper
specified
by theonbrake
1000
1500 ispsi,
depending
the
manufacturer.
It
varies
caliper. The caliper cannot from
safely about
oper1000continuously
to 1500 psi, above
depending
on the
ate
maximumcaliper.
The
caliper
cannot
safely
operrated pressure because seal or caliperate
continuously
above
maximumbridge fatigue failure may occur.
rated
pressure
because seal
or caliperHowever,
an occasional
locked-wheel
bridgestop
fatigue
panic
is OK. failure may occur.
However,
an occasional
locked-wheel
If calculated
fluid pressure
is too
panic
stop
is
OK.
high for the caliper, the solution is
If calculated
fluiddopressure
simple.
You can
one ofis too
the
high for the caliper, the solution is
following:
simple.
can with
do more
one ofpiston
the
• Use a You
caliper
following:
area - bigger pistons or more of them.
a caliper
withcaliper
more onpiston
• Use
Use more
than one
each
arearotor. bigger pistons or more of them.
Use more
than one
on each
• Use
a larger
rotorcaliper
diameter,
if
rotor.
Use a larger rotor diameter, if
{
\--.-/
Effective radius of disc brake is measured
from center of pad to center of rotor. Make
sure
you have
correct
combiEffective
radius
of discrotor/caliper
brake is measured
nationcenter
to determine
effective
radius.
from
of pad to
center of
rotor. Make
sure you have correct rotor/caliper combination to determine effective radius.
there's space.
• Use a caliper that has a higher
there's space.
operating
pressure.
Use
caliper
that one
has caliper
a higher
If
youause
more than
per
operating
pressure.
rotor, each caliper supplies its rated
If you Thus,
use more
one caliper
per
torque.
twothan
calipers
on each
rotor, doubles
each caliper
suppliesthat
its brake
rated
rotor
the torque
torque.
Thus,
calipers
on fluid
each
can
deliver.
Fortwo
a given
torque,
rotor
doubles
the
torque
that
brake
pressure for a two-caliper disc brake
can be
deliver.
Forfor
a given
torque,
will
half that
a single
caliper;fluid
repressure fluid
for a displacement
two-caliper disc
quired
willbrake
be
will be half that for a single caliper; redouble.
quired
fluid
displacement
will you
be
Operating
Pressure-In
general,
double.
should use an operating pressure
Operating
general, you
that's
wellPressure-In
below maximum-rated
should
operating
pressure use
for aancaliper.
Leaks pressure
and exthat's well
below can
maximum-rated
deflection
result from
cessive
pressurefluid
for apressure.
caliper. Leaks
and exexcess
If maximum
cessive deflection
resulthalf
from
operating
pressure can
is, say,
of
excess fluid pressure.
If maximum
maximum-rated
pressure
for the
operatingthepressure
is, say,
half of
caliper,
extra margin
of safety
in
maximum-rated
pressure
for
the
the brake system is sufficient.
caliper, the extra margin of safety in
the brake&system
is sufficient.
PEDAL
LINKAGE
DESIGN
After selecting and positioning the
PEDAL
& LINKAGE
DESIGN
brakes and
calculating
maximum
After selecting and
positioning
the
hydraulic-system
operating
pressure,
brakes
calculating
maximum
the next and
step is
to design the
pedals
hydraulic-system
operating
pressure,
and
linkage. Various
types of
pedals
the
next
step
is
to
design
the
are discussed in Chapter 6. As pedals
stated
and linkage.
types of
pedals
earlier,
use Various
a hanging
pedal
if
6. As stated
are
discussed
Chapter
possible
. This in
allows
the master
cylinearlier,
a hanging
pedal
ders to beuse
mounted
high in the
car forif
possible.
This
allows
the
master
cylinon
easy servicing. Also, brake balance
ders
to be mounted
in tothe
car for
balance-bar
setups ishigh
easier
adjust.
easy
servicing.
Also, of
brake
balance
on
The
disadvantage
hanging
pedals
balance-bar
setups
is
easier
to
adjust.
is the extra height required. On a lowThe disadvantage
hanging
profile
race car, thereofmay
not bepedals
suffiis the extra
a lowcient
roomheight
for required.
hangingOnpedals.
profile race car, there
not be
Consequently,
you'llmay
have
to suffiuse
cient
room
for
hanging
pedals.
floor-mounted pedals.
Consequently, you'll have to use
floor-mounted pedals.
99
Hurst! Airheart 200X2 caliper is largest
one offered by this manufacturer. Brake
torque
is rated2 0at
brake
Hurst/Airheart
0 x 223,000
caliperin-Ib
is largest
torque
at 1200-psi
hydraulic pressure.
one offered
by this manufacturer.
Brake
Double-piston
caliper
is popularin-lb
for use
on
torque
is rated
at 23,000
brake
racing stock
cars. Photo
courtesy
Hurst
torque
at 1200-psi
hydraulic
pressure.
Performance.
Double-piston caliper is popular for use on
Two calipers on rotor doubles brake torque for a given hydrauliC pressure-an easy and effective means of lowering pedal effort or fluid pressure. Smaller single-piston caliper is
stiffer
than a dual-piston
caliper,
too. torque
Photo by
Monroe.
.TWO
callpars
u r i rudor doubles
brake
TorTom
a ylven
nyaraullc pressure-an easy and ef-
fective means of lowering pedal effort or fluid pressure. Smaller single-piston caliper is
stiffer than a dual-piston caliper, too. Photo by Tom Monroe.
Ideal race-car brake- pedal setup; balance bar with remote adjuster. Remote - adjuster
cable is routed to left of balance bar under clutch pedal. Floor-mounted pedals are necessary
Idealbecause
r,-- .,- of -.low-profile
,., .-,,, body height.
d ; balance bar with remote adjuster.
-r
,.,
.,.,.
,,,,.
cable is routed to left of balance bar under clutch pedal. Floor-mounted pedals are necessary because of low-profile body height.
Decide at this point what type of
brake-balance method to use . There
this point
whatfortype
of
areDecide
severalatchoices
available
a race
brake-balance
method
to
use.
There
car:
are• several
available for a race
Balancechoices
bar.
car:• Adjustable proportioning valve.
Balance bar. of the two.
• Combination
Adjustable
proportioning
Road
cars usually
don't use valve.
balance
thedifficult
two.
to inbars Combination
because theyofare
Road cars
usually
don'tpedals.
use balance
corporate
into
existing
Also ,
bars
are difficult
to inbrakebecause
balance they
for road
use is not
as
corporate
existing
predictableinto
as for
~acing.pedals.
This isAlso,
bebrake road
balance
use istypes
not as
cause
carsfor
runroad
on many
of
predictable as for racing. This is because road cars run on many types of
100
surfaces. And, adjusting a balance bar
while driving on the road is simply not
surfaces.
bar
practical. And,
On a adjusting
race tracka, balance
conditions
while
driving
on
the
road
is
simply
not
are stable or reasonably predictable .
practical.
a race
track, conditions
Also, the On
driver
constantly
uses the
are
stable
reasonably
brakes
hardorand
can sense predictable.
the need to
Also,
the driver constantly uses the
adjust balance.
brakes
hardbars
and are
can used
senseon
therace
needcars
to
Balance
adjust
for twobalance.
m ain reasons:
are pedal
used on
carsa
• Balance
Provides bars
stiffer
fee race
l than
for
two
main
reasons:
proportioning valve .
Provides master
stiffer pedal
feelare
than
cylinders
easya
• Separate
proportioning
to
change to mvalve.
ake large bra ke-balance
Separate master cylinders are easy
to change to make large brake-balance
racing stock cars. Photo courtesy Hurst
Performance.
changes. An adjustable proportioning
valve has limited adjustment.
changes.
An adjustable
If you plan
on using aproportioning
balance bar,
valve has limited
adiustment.
consider
using an
adjustable proporIf youvalve,
plan on
a balance
tioning
toousing
. A balance
bar bar,
can
consider
using
an
adjustable
proporbe adjusted to accomplish the desired
tioning valve, brake
too. Abalance,
balance but
bar can
front-to-rear
the
be adjusted to valve
accomplish
desired
proportioning
does itthe
autom
atifront-to-rear
brake balance,
but the
cally
over a limited
range of tire-grip
proportioning
valve
does
it
automativalues. The disadvantage of using a
cally
over a limited
rangea balance
of tire-grip
proportioning
valve with
bar
values.
The disadvantage
of using a
is
the added
weight , cost, complexity
proportioning
valve with a balance bar
and pedal travel.
is Unless
the added
weight,
cost, complexity
you like climbing
into a raceand
pedal travel.
car cockpit
upside down on your back,
Unless
climbing
make
sureyou
thelike
balance
bar into
can aberaceadcar
cockpit
upside
down
on
your
back,
justed from a convenient position.
makemay
sureaffect
the balance
bar canposition
be adThis
the mounting
justed
fromfora the
convenient
position.
you choose
pedals. But
, pedal
This
may affect the
mounting are
position
and balance-bar
maintenance
critiyou
choose
for
the
pedals.
But,
cal to keeping a. brake system inpedal
top
and
balance-bar
maintenance
are critioperating
condition.
A balance
bar
cal
a. brake system
in and
top
withtoa keeping
remote-adjustment
cable
operating
condition.
A balance bar
knob may be
the solution.
with
a
remote-adjustment
and
Brake-pedal ratio and cable
masterknob
may
be
the
solution.
cylinder size (s) should be selected at
theBrake-pedal
same time.ratio
The and
objectmasteris to
cylinder the
size(s)
shouldoperating
be selected
at
achieve
maximum
presthe
same
time.
The
object
is
to
sure you established with an acceptachieve
the effort
maximum
presable
pedal
usingoperating
the following
sure you established with an acceptsteps:
able
pedal
effort
the following
• Select
pedal
ratiousing
.
steps:
• Select pedal effort at maximum
Select pedal ratio.
deceleration.
pedal
at maximum
• Select
Calculate
forceseffort
on master-cylinder
deceleration.
push rod (s) .
Calculate
forces on master-cylinder
master-cylinder
diameter(s)
• Select
pushrod
(s)
.
that gives proper maximum operating
Select in
master-cylinder
diameterk)
pressure
hydraulic system.
that
gives geometry
proper maximum
operating
• Check
of the pedal
and
pressure
in
hydraulic
system.
linkage at extremes of travel.
of theandpedal
and
• Check
Design geometry
pedal bracket
masterlinkage atmount.
extremes of travel.
cylinder
Design pedal bracket and mastercylinder mount.
MASTER-CYLINDER SIZE VS. PISTON AREA
Making under-dash brake-balance adjustment forces mechanic into this uncomfortable
position. Hanging
brake pedal
with
Making under-dash
brake-balance
adjustbalance
bar and
remote into
adjuster
more
ment
forces
mechanic
this is
uncompractical.position. Hanging brake pedal with
fortable
balance bar and remote adjuster is more
practical.
• Change anything necessary and
start over.
l Change anything
necessary and
Pedal Ratio- There is nothing
Select
start
over.
magic about the pedal ratio. Many
Select Pedal
Ratio-There
is nothing
values
are possible.
However,
if you
magic know
aboutwhat
the to
pedal
don't
use, ratio.
try a Many
pedal
values
possible.
However, if you
ratio
of are
about
5.0.
don't
know
try use
a pedal
If you
buywhat
a settoofuse,
pedals,
the
ratio
about
5.0.into them. Unless the
pedalofratio
built
If you buy
a set of pedals,
use the
resulting
master-cylinder
size(s)
or
pedal
them.
the
linkage movement is incorrect, you
resultinghave
master-cylinder
Size(S)
or
should
a good design.
Don't
linkage amovement
incorrect,
you
design
new pedal isunless
you have
should
a good design.
Don't
to. It is have
time consuming
and difficult
design
a
new
pedal
unless
you
have
to do correctly.
to.Some
It is time
consuming
and
difficult
points to consider when
to do correctly.
selecting
a pedal ratio:
Some a points
given to
pedalconsider
ratio, iswhen
the
• With
selecting
a
pedal
ratio:
master cylinder(s) mounted in a conl With place?
a given pedal ratio, is the
venient
master
cylinder(s)
mounted
in a con• Can you
get master
cylinder(s)
with
venient place?
enough
stroke so the pedal hits the
l Can before
you getthe
master
cylinder(s)
with
floor
master
cylinder(s)
enough
bottoms?stroke so the pedal hits the
floor
master
cylinder(s)
• Doesbefore
the the
pedal
position
feel
bottoms?
comfortable?
D o e s the
feel
Pedal pedal
Effort position
at Maximum
Selecting
comfortable?
Deceleration-Most people can stop a
Selecting
Pedal Effort
Maximum
car
that requires
100-lbatpedal
effort.
Deceleration-Most
stop
for acan
road
car.a
However,
this is highpeople
car
that
requires
100-lb
pedal
effort.
And, it may not allow enough safety
However,forthis
is high
road car.
or
margin
brake
fadefor
fora street
And,
not allowthat
enough
racing.it Imay
recommend
you safety
use a
margin
for brake
street or
75-lb pedal
effortfadeforformaximum
racing.
I
recommend
that
you
deceleration. If you use less use
pedala
75-lb
pedal
effort
for
maximum
effort, the brake pedal will feel less
deceleration.
If you
less pedal
rigid
and will have
moreuse
travel.
effort,
the
brake
pedal
will
feel less
Master-Cylinder Pushrod Force-If
rigid
and
will
have
more
travel.
your car uses a tandem master cylinMaster-Cylinder
Pushrod
Force-If
der
or a single master
cylinder,
the
your car
tandem master
cylinforce
on uses
the apushrod
is found
by
der or a single master cylinder, the
force on the pushrod is found by
Nominal
Diameter
MASTER-CYLINDER
SIZE VS. PISTON AREAArea
Bore Size
In.
Sqln.
Nominal
Diameter
Area
5/8
in.
0.6250
0.3068
Bore Sire
In.
Sq In.
11/16
in.
0.6875
0.3712
5/8
in.
0.6250
0.3068
19mm
0.7480
0.4394
11/18in.
0.6875
0.371 2
3/4in.
0.7500
0.4418
19mm
0.7480
0.4394
20mm
0.7874
0.4869
3/4
in.in.
0.7500
0.4418
13/16
0.8125
0.5185
20mm
0.7874
0.4869
21mm
0.8268
0.5369
13/16 in.
0.8125
D.5185
22mm
0.8661
0.5892
21 mm
0.8268
0.5369
22.2mm
0.8740
0.5999
22mm
0.8661
0.5892
7/8
in.
0.8750
0.6013
22.2mm
0.8740
0.5999
23mm
0.9055
0.6440
7/8 in.in.
0.8750
0.661 3
29/32
0.9063
0.6451
23mm
0.9055
0.6440
15/16in.
0.9375
0.6903
29/32 in.
0.9063
0.6451
24mm
0.9449
0.7012
0.9375
0.6903
15/16 In.
25.4mm
1.0000
0.7854
24mm
0.9449
0.701 2
1 in.
1.0000
0.7854
25.4mm
1,0090
8.7854
1~1/32 in.
1.0313
0.8353
1 in.
1.OOOO
0.7854
26.6mm
1.0472
0.8613
1-1/32 in.
in.
1.0313
0.8353
1-1/16
1.0625
0.8866
26.6mm
1.0472
0.861 3
1-1/8 in.
1.1250
0.9940
0.8866
1-1/16in.
1.0625
28.6mm
1.1260
0.9958
1-1/E3 in.
1.7250
0.9940
1-1/4in.
1.2500
1.2272
28.6mm
1.f26Q
0.9958
31.8mm
1.2520
1.2311
1.2600
1.2272
1I-1/4
~5/16In.
in.
1.3125
1.3530
3?.8rnm
1.2520
1.231 I
1-11/32in.
1.3438
1.4183
1-5/16in.
1 3 125
1.3530
1-1/2in.
1.5000
1.7671
1-1 1/32
1.3438
1,4183
1-3/4
in. in.
1.7500
2.4053
1-1/2 In.
1.5000
1,7671
1.7500
2.4053
1-3/4 in.
Listed are diameters of popular mass-produced master cylinders and their areas. Note that
some metric sizes are close to standard inch sizes. Be careful to get correct sizes when
buying
replacement
Many mass-produced
cylinders have diameters
marked and
on them.
Listed are
diametersparts.
of popular
master cylinders
their areas. Note that
some metric sizes are close to standard inch sizes. Be careful to get correct sizes when
buying replacement parts. Many cylinders have diameters marked on them.
multiplying the pedal ratio by pedal
effort.
multiplying
the if
pedal
For example,
pedalratio
ratiobyis peda!
10.0
effort.
and pedal effort is 75 Ib, force on the
For example, pushrod
if pedal isratio
is 10.0
master-cylinder
750 lb.
and
pedal
effort
is
75
Ib,
force
on the
the
If you are using a balance bar,
master-cylinder
pushrod
is
750
lb.
force just calculated above is the pedal
If you
a balance
bar, Itthe
thatare
actsusing
on the
balance bar.
is
force
force
justbetween
calculated
is the cylinpedal
divided
the above
two master
force
that acts ontothethe
balance
bar. Iton
is
ders according
formulas
divided
between
the
two
master
cylinpage 75.
ders
according to
on
I recommend
thatthe
youformulas
assume the
page 75. bar divides pedal force equally
balance
I recommend
thatmaster
you assume
the
between
the two
cylinders.
balance
bar
divides
pedal
force
equally
This allows the maximum amount of
between
the adjustment
two master incylinders.
balance-bar
either
This
allowsItthe
maximum
amount
of
direction.
also
makes the
design
balance-bar
adjustment
in
either
easier. If you do this, divide equally
direction.
It pushrod
also makes
design
the
resulting
forcethe
found
by
easier. If you
do effort
this, divide
equally
multiplying
pedal
by pedal
ratio.
the resulting
by
This
gives thepushrod
force onforce
eachfound
mastermultiplying
pedal
effort
by
pedal
ratio.
cylinder pushrod. If you do not center
This
gives the
on each
masterthe balance
bar,force
calculate
the force
to
cylinder
pushrod. If you do not center
each
pushrod.
theNow
balance
the on
force
to
that bar,
you calculate
have force
each
each
pushrod.
pushrod, you also have the force apNowto that
have force onpiston.
each
plied
eachyou
master-cylinder
pushrod,
you
also
have
the
force
apThe forces are the same.
plied to each master-cylinder piston.
The forces are the same.
Master-Cylinder Size-Now that
you know the desired maximum
Master-Cylinder
Size-Now
operating
pressure and
force on that
the
you
know
the
desired
master-cylinder piston, it's maximum
simple to
operating the
pressure
and force
on the
the
required
area for
calculate
master-cylinder
piston,
it's
simple
to
master-cylinder piston:
calculate the required area for the
F
master-cylinder piston:
Master-cylinder-piston area
=
~
p
in
square inches
~aster-cylinder-piston
area - F M C
FMC = Force on master-cylinder P
piston
insquare
in
pounds inches
FMc
Force onpressure
master-cylinder
piston
P
= =
Hydraulic
in pounds
per
square
inch
in Pounds
= Hydraulic pressure in pounds per
inch
A list of piston areas for commonly
available master-cylinder diameters is
A listinof piston
areas for commonly
given
the accompanying
table.
available
master-cylinder
diameters is
Most cars use 3/4-1-in.-diameter
given
the accompanying
table.
master in
cylinders.
If your calculated
Most
cars
use
314-1-in.-diameter
area falls between two standard sizes,
master the
cylinders.
If your calculated
choose
master-cylinder
diameter
area
falls
between
two
closest to the required standard
area. Yousizes,
can
choose
the adjustments
master-cylinder
make small
later diameter
with the
closest
balance to
bar.the required area. You can
make
small
adjustments
later witharea
the
If the required
master-cylinder
balance
bar.
is smaller than what's available, go to
the required
master-cylinder
numerical
pedal ratio area
or
a Iflarger
is smaller than what's available, go to
a larger numerical pedal ratio 101
or
Pedal
1
.-
Pedal
Centerline
F-;r;
/J Must Be Less
Than 5° For All
Positions
Pedal
0 Must BeofLess
Than 5" For All
Positions of Pedal
L
Pushrod
Make a drawing to determine
angle between pushrod and mastercylinder centerline. Angle must not be excessive, or binding and
rapid
wear
will result.angle
Limit between
angle to 5°
maximum.
If angle
Makecylinder
a drawing
to determine
pushrod
and masteris too large,
increase
length
pushrod
or shorten
total pedal
cylinder
centerline.
Angle
mustofnot
be excessive,
or binding
and
travel.cylinder
Angle should
be result.
nearly Limit
zero angle
with pedal
in positionIfwhere
angle
rapid
wear will
to 5" maximum.
maximum
deceleration
Onpushrod
most cars
hanging
is too large,
increase occurs.
length of
or with
shorten
totalpedals,
pedal
this occurs
with
pedalbe
at nearly
about 2zero
in. from
travel.
Angle
should
withfloor.
pedal in position where
I
Floor-mounted Neal pedal bracket ties master cylinder to pedal
pivot in one assembly. Only forces on chassis are those delivered
directly
by driver's
on master
cylinder
and
Floor-mounted
Neal foot.
pedalLarger
bracketforces
ties master
cylinder
to pedal
pedal
pivot
taken byOnly
bracket.
pivot in
oneare
assembly.
forces on chassis are those delivered
directly by driver's foot. Larger forces on master cylinder and
pedal pivot are taken by bracket.
maximum deceleration occurs. On most cars with hanging pedals,
power
brakes
However,
this
occurs
with .pedal
at about 2don't
in. fromuse
floor. the pedals and seat. Position them as
power brakes on a race car unless abpower brakes.
However,
use
solutely
necessary.
There don't
are easier
power
brakes
on
a
race
car
unless
abways of avoiding this, unless your
solutely
race car isnecessary.
extremely There
heavy. are easier
ways
of avoiding
unless your
If you
select a this,
5/8-in.-diameter
race
car
is
extremely
heavy.
master cylinder, be aware that you
If you goselect
cannot
to a a 5/8-in.-diameter
smaller size
master
cylinder,
be aware
that Ityou
later-there
are none
available.
is
cannot
go a to
a orsmaller
size
better to use
3/4-in.
larger cylinlater-there
It is
der
so you are
can none
makeavailable.
a change,
if
better
to
use
a
314-in.
or
larger
cylinneeded. For example, if new tires give
der
youthan
canwhat
make
change,for,if
moresogrip
youa allowed
needed.
For
example,
if
new
give
you'll need smaller master tires
cylinders
more
grip
than
what
you
allowed
for,
to keep the same pedal effort for maxiyou'll
need
smaller
master
cylinders
mum deceleration. So, leave yourself
to keeproom
the same
pedalchanges.
effort forTo
maxisome
to make
inmum
deceleration.
So,
leave
yourself
crease the master-cylinder diameter
some
room topedal
make
changes.
inand maintain
effort,
use aTo
larger
crease
the
master-cylinder
diameter
pedal ratio.
and
maintain
pedal effort,
use a larger
Pedal
& Linkage
Geometry-A
pedal ratio.
brake
pedal must be designed to fit
Pedal
& As
Linkage
Geometry-A
the driver.
the driver
pushes the
brake
pedal
must
be
designed
fit
pedal, the ball of his foot shouldtostay
the
driver.
As
the
driver
pushes
the
in contact with the pedal pad. Measure
pedal,foot
the orball
his foot should
stay
your
theofdriver's-if
the sizes
in
contact
with
the
pedal
pad.
Measure
are significantly different-and check
your
or the driver's-if the sizes
pedal foot
positions.
areAlso,
significantly
check
look for different-and
a car with pedals
in
pedal
positions.
the "perfect" position for the driver's
Also,
look forthe
a carrelationship
with pedalsbein
feet.
Measure
the "perfect"
position
driver's
tween
the floor,
ped als for
and[he
seat.
Copy
feet.
Measure
bethe design
of a the
goodrelationship
car if you find
tween
the
floor,
pedals
and
seat.
Copy
one that's suitable. There is no perfect
if you
find
the
of abecause
good car
pedaldesign
design,
each
person's
one
suitable.
There is nodifferent
perfect
bodythat's has
slightly
pedal design,So,
because
person's
dimensions.
designeach
yourdifferent
car to
body
has
slightly
suit the driver.
dimensions.
SO,doubts
design about
your car
to
If you have
pedal
suit
the driver.
position,
make a full-size model of
If you have doubts about pedal
position,
make a full-size model of
102
they will be in the car and see how
the
and seat.
as
theypedals
fit. Now's
the Position
time to them
change
they
will
be
in
the
car
and
see
how
things that are not comfortable.
they fit.theNow's
thethetime
to change
Check
pedal in
extreme
posithings
comfortable.
tions of that
travel.areYounot
should
have no
Check
the pedal
in the
more than
6 in. of
totalextreme
travel atposithe
tions pad.
of travel.
You
should have no
pedal
Try it to
be sure.
of total
travel of
at the
more
than
After
you6 in.
make
a drawing
the
pedal pad.
it to be sure.
and Try
its mounts,
check the linkyouextreme
make apositions.
drawing of
the
ageAfter
at the
There
pedal and
the linkshould
be its
no mounts,
binding.check
Pay particular
age
at thetoextreme
positions.
There
attention
the angle
the pushrod
should
be
no
binding.
Pay
particular
makes with the master cylinder. If the
attention
to the
angleextreme
the pushrod
pushrod goes
through
angles
makes
m ~ master
s t e cylinder.
r cylinder,
If the
to the with
bore the
of the
it
extreme severe
angles
pushrod
goes This causes
can
bind.
the bore of
the t-naster
cylinder, Ait
problems,
including
breakage.
longer bind.
pushrod
may causes
be required
to
Can
This
severe
reduce the misalignment
angle. A
problems,
breakage.
longer
pushrod
may be required
maximum
of 5° misalignment
between
pushrod the
and master
cylinder angle.
is recomreduce
misalignment
A
mended
See
maximumby brake manufacturers.
between
pushrod
and master
Vlinder
recornthe accompanying
drawing
forisan
illusmended
manufacturers. See
tration ofby
thisbrake
pro blem.
for an
the
Pedal-Bracket
&drawing
Master-Cylinder
Mount-On
many cars the pedal
Uation
this problem.
Master-C~linder
bracket and master-cylinder
mount
Mount-On
many
cars the
pedal
are the same. This makes
a strong,
b r x k system
e t and with
master-cylinder
mount
rigid
minimum of overall
are
the Race-car
same. This
a strong,
weight.
pedalmakes
brackets
manurigid
system
with
minimum
of
overall
factured by companies such as Tilton,
weight.
brackets
manuNeal or Race-car
Winters pedal
use this
concept.
A
factured
by colnpanies
as Tilton,
pedal bracket
is difficultsuch
to design,
so
Neal
Winters
use this
concept.
A
buyingor one
of these
sturdy,
lightpedal
bracket
is
difficult
to
design,
So
weight brackets makes sense. These
of these
sturdy,applicalightparts areone
designed
for racing
weight
tions andbrackets
are easy makes
to use. sense. These
are designed
for racing
applicaparts
pedal-bracket
design
in
I discuss
tions
and
are
easy
to
use.
Chapter 6. However, re member this
I discuss pedal-bracket design i n
6 . However, remember this
important point: The bracket must
not deflect an excessive amount when
important
point:
The hard.
bracket
must
the pedal is
pushed
A pedal
not
deflect
an
excessive
amount
when
bracket mounted in the center of a
the
is pushed
thin pedal
sheet-metal
fire hard.
wall A ispedal
1101
bracket mounted
center pedal
of a
satisfactory.
This, in
or the
a flexible
tfor
thin
sheet-metal
fire airwall
is hybracket,
is worse than
in the
satisfactory.
This,
or
a
flexible
pedal
draulic system. With a flexible pedal
bracket,
worse
than pump
air in the
bracket, isyou
cannot
up hythe
draulic
With
a flexible
pedal orsystem.
bleed the
trapped
air to pedal
cure
bracket,
you cannot pump up the
the problem'
pedal
or
bleed
the trapped air
cure
I f you stress-analyze
the to pedal
the
problem!
bracket,
remember to use maximum
If you normal
stress-analyze
load-not
operatingthe
load.pedal
The
bracket,
remember
to
use
maximum
maximum load occurs during a panic
load-not
operating
stop
when normal
the driver
pushesload.
withThe
all
maximum
loadIf occurs
duringis astrong
panic
of
his might.
the bracket
stop when
driver
pushes
withfine
all
enough
forthethis,
it will
work
of
his
might.
If
the
bracket
is
strong
during maximum deceleration.
enough Design
for this,Problem-Following
it will work fine
Sample
during
maximum
deceleration.
is a sample
race
-car brake-design
Sample
Problem-Following
problem. Design
The steps
are in the same
is
a
sample
race-car
brake-design
order presented .
problem.
The
steps
are
in thesystem
same
First select the disc- brake
ordergives
presented.
that
the requi red brake torque at
select
the disc-brake
a First
500-psi
operating
pressure system
at the
that
gives
the
required
brake
at
front brakes and 400-psi
at torque
the rear.
a 500-psi
operating are
pressure
at the
These
calculations
explained
in
front
brakes
the first
part ofand
this400-psi
chapter.at the rear.
These
calculations
explained
in
system
has an
A proven pedal are
the
first part
of this
8.0-to-l
pedal
ratio.chapter.
I wish to design
proven
pedal
has an
forAa pedal
effort
of 75system
lb at maximum
8.0-to-1
pedal
ratio.
I
wish
to
deceleration. The pedal force design
acting
for the
a pedal
effort
lb at maximum
on
balance
barofis 75
calculated:
deceleration. The pedal force acting
Force
balance
= PE Rp in
on
the on
balance
barbar
is calculated:
pounds
PE = Pedal
pounds
on effort inbar
=
R~ i n
pounds
Rp
= Pedal ratio
effortinbarpounds
pE = Pedal
= (75 Ib)(8.0)
Force
on balance
R, = Pedal
ratio bar = 600 lb.
Force
on balance
',
Force on balance bar
Force on balance bar
= (75 lb)(8.0)
= 6 0 0 Ib.
Accident waiting to happen: Steel brake line must be secured to
frame with a bracket where the flexible hose attaches (arrow).
With this waiting
setup, steel
line is subjected
to line
bending
fatigue as
Accident
to happen:
Steel brake
must and
be secured
to
the
suspension
moveswhere
up and
the line
will
frame
with a bracket
the down.
flexibleEventually,
hose attaches
(arrow).
fracture,
brakeline
failure.
With
this causing
setup, steel
is subjected to bending and fatigue as
the suspension moves up and down. Eventually, the line will
fracture, causing brake failure.
Brake-line mounting bracket is simple plate, located near suspension pivots (arrow). This minimizes hose bending and pulling as
wheel
moves.
Line and
hose attaches
bracket
using
an suspenaircraft
Brake-line
mounting
bracket
is simple to
plate,
located
near
bulkhead
fitting.
Jam This
nut clamps
bulkhead
to bracket.
sion
pivots
(arrow).
minimizes
hose fitting
bending
and pulling as
wheel moves. Line and hose attaches to bracket using an aircraft
bulkhead fitting. Jam nut clamps bulkhead fitting to bracket.
Assuming the balance bar divides
pedal force equally between the front
Assuming
the balance
cylinders,barthedivides
force
and
rear master
pedal
force
equally
between
the front
lb.
on each pushrod is 300
andAlthough
rear master
cylinders,
the force
the master
cylinders
have
on eachforces,
pushrod
is 300 lb.
equal
different
size cylinders
cylinders
have
rear brakes.
areAlthough
required the
for master
front and
equal
forces,
different
size
cylinders
This is due to the difference in the
are
requiredpressure
for frontofand
brakes.
operating
therear
front
and
This
is due to the difference in the
rear systems.
operating
of page
the front
From thepressure
formula on
101: and
rear systems. F
~ on page 101:
Piston
Fromarea
the =formula
P
F master-cylinder
M ~
FMC
= Force
piston
Piston
area =on
P
in pounds
Force onpressure
master-cylinder
piston
FMc
P= =
Hydraulic
in pounds
per
in pounds
square
inches
P = Hydraulic pressure in pounds per
For
theinches
front brakes, master-cylinder
square
piston area is:
For
brakes, master-cylinder
. the front 300lb
Piston area
= 500 psi
oiston
area is:
300 Ib
= 0.6 sq in.
Piston
area =
For
the rear-brake master cylinder:
= 0.6 sq in.
.
300lb
Piston
= 400 psi
For
thearea
rear-brake
master cylinder:
= 0.75 sq in. 300 Ib
Piston
area =400 psi
The closest standard-size master
= 0.75 sq in.
cylinder is selected from the table on
The101:closest standard-size master
page
cylinder is selected from the table on
:
page 101
Front
master-cylinder
diameter = 7/8
in. (area = 0.601 sq in.)
Frontmaster-cylinder
master-cylinder diameter
diameter == 7/8
Rear
in.in.(area
sqsqin.)
1
(area==0.601
0.785
in.).
Rear master-cylinder diameter =
1 in.
(area
= 0.785
sq in.).
Note
that
the front
master cylinder
is almost perfect and the rear cylinder
that large.
the front
master
is Note
a bit too
I'll use
the cylinder
balance
is
perfect
and the the
rearsystem.
cylinder
baralmost
in testing
to fine-tune
is Also
a bit note
too large.
the balance
that I'll
the use
smaller
master
bar in testing to fine-tune the system.
Also note that the smaller master
Custom-fabricated reservoirs are secured
with hose clamps and rubber cushions in
between.
Reservoirs
will slipare
if secured
clamps
CUJLUIII-~dbricated
reservoirs
loosens.
with
hose clamps and rubber cushions in
between. Reservoirs will slip if clamps
cylinder is considerably larger than
loosens.
Reduced diameters at centers positively
locate fluid reservoirs in mounting clamps.
Clamps
have toatloosen
considerably
R e u u ~ awould
uularnerers
centers
poslr~vely
before
reservoirs
could in
slip.
locate fluid
reservoirs
mounting clamps.
Clamps would have to loosen considerably
to complete
a could
brake-system
design.
before
reservoirs
slip.
the minimum size. This is good in
cylinder
is considerably
wrong at thelarger
start ofthan
the
case
I guessed
the
minimum
size.
This
is
good in
design. I can easily change hydraulicwrong
the startsmaller
of the
case I guessed
system
pressure
byat using
easilya change
hydraulicdesign. I can
cylinders.
When
problem
occurs,
system
by using
smaller
cylinder
is reusually a pressure
smaller master
cylinders.
When
a
problem
quired to reduce pedal effort. occurs,
usually
smaller master
cylinder is re-I
After a finishing
the calculations,
quireda side
to reduce
draw
view pedal
of theeffort.
pedals to check
After geometry.
finishing the
calculations,
linkage
Because
I selectedI
draw
a
side
view
of
the
pedals
checka
from
a standard pedal design to
I
selected
linkage
geometry.
Because
manufacturer, this step is probably
anot standard
pedal sets
design
required. Pedal
shouldfrom
be de-a
manufacturer,
this
step
is
probably
signed to work without binding.
The major items remaining are:
to
complete
brake-system
• Route
brakealines
on chassis. design.
The
major
items
remaining
are:
• Attach flex hoses to chassis.
Route
brake
lines
on
chassis.
• Locate and mount remote masterAttachfluid
flex reservoir
hoses to chassis.
cylinder
(s) (if used).
Locate
and
mount remote
master• Locate proportioning
valve
(if
cylinder
fluid
reservoir(s1
(if
used).
used) .
Locate mounts
proportioning
valverotors
(if
• Design
for calipers,
used).
and
other brake hardware.
Design mounts
for calipers,
rotors
• Design
cooling-duct
system,
if
and
other
brake
hardware.
required.
Design that
cooling-duct
bleeders aresystem,
accessibleif
• Confirm
required.
and
mounted high.
Confirmthethatcarbleeders
are accessible
After
is completed,
the
and
mounted
high.
brake system must be tested before
After use,
theChapter
car is 10.
completed, the
serious
not required. Pedal sets should be designed to work BRAKE
without binding.
COMPLETE
SYSTEM
There are now other steps required
COMPLETE BRAKE SYSTEM
There are now other steps required
brake system must be tested before
serious use, Chapter 10.
103
78sting
10
...
Testing is required to get maximum performance
n any car, but particularly race cars. This includes brake testing. George B.,..>tti and
Tom Sneva discuss effects of changes to car between practice runs while tire engineer measures tire temperatures. Photo by Tom Monroe.
served brake
while
it George
operates.
BrakeAs any
you car,
now
a great
Testing is required to get maximum performance from
butknow,
particularly
racedeal
cars.of
This includes
testing.
Bignotti
and
dynamometer
testing
done
the brake-system
design
processmeasures
is
Tom Sneva discuss effects of changes to car between
practice runs while
tire engineer
tire temperatures.
Photo is
by usually
Tom Monroe.
Brake dynamometer, designed to run
continuously, is driven by a 289-cu in. Ford
V 8 through a gearbox. Power delivered to
brake is equivalent to a sedan under a hard
stop. Datsun drum brake is being tested.
Brake dynamometer, designed to run
continuously, is driven by a 289-cu in. Ford
V8 through a gearbox. Power delivered to
brake is equivalent to a sedan under a hard
stop. Datsun drum brake is being tested.
based on assumptions. For this
reason, a brake-test program is absolutely necessary. Often, when a new
As car
youisnow
know,and
a great
of
race
designed
built, deal
testing
the
brake-system
design
process
is
is neglected in favor of getting the car
based
on
assumptions.
For
this
to its first race. This is false economy.
reason,
program
absoTesting aatbrake-test
a race takes
a lotis longer
lutely
necessary.
Often
,
when
a
new
than at a planned private test session.
race
car
is
designed
and
built,
testing
I've seen many people use up a whole
isracing
neglected
in favor
of getting
the car
season
to get
a car working
to
its
first
race.
This
is
false
economy.
properly when they could've sorted
at in
a race
takes
longe r
Testing
out the car
one full
day aoflot
testing.
than at a pl anned private test session.
Brake testing falls into two
I' ve seen many people use up a whole
categories: laboratory testing and
racing season to get a car working
track testing. Laboratory testing inwhen they
couldbrake
' ve sorted
properly
volves running
a single
on a
out the car in one full day of testing.
testing machine called a brake
Brake testing
falls on
into
two
See photo
the back
dynamometer.
andto
categories:
laboratory
cover. This type
of testingtesting
is similar
track
Laboratory
intestingtesting
an . engine
on testing
an engine
running
a
single
brake
on
a
volves
dynamometer. Because a brake is out
testing
machine
called
a
brake
in the open, it can be studied and ob-
dynamometer. See photo on the back
cover. This type of testing is similar to
testing an engine on an engine
dynamometer. Because a brake is out
in the open, it can be studied and ob104
by the big brake manufacturers, but if
you are so inclined you can make such
a device for yourself.
served
it operates.
BrakeMost while
brake-testing
time will
be
dynamometer
testing
is
usually
spent on the track. You take the done
car to
by
the bigtest
brake
manufacturers
but if
a private
track
and test the ,brakes.
you
are so inclined
can make such
Measuring
brake you
performance
and
apushing
device for
yourself.
them
to the limit should be a
Most
brake-testing
timethat
will
part
of the
test. Many tests
canbe
be
spent
on
the
track.
You
take
the
car to
done very easily during track testing
awould
privateotherwise
test track and
test the brakes.
be difficult
or imMeasuring
brake
performance
and
possible during a race. Even a practice
pushing
them
to
the
limit
should
be
a
session during a race weekend is not
of
the
test.
Many
tests
that
can
be
part
appropriate for testing. Other cars on
done
very easily
during
the track
prevent
you track
fromtesting
doing
otherwise
be
difficult
would
what is needed for a good test. or impossible during a race. Even a pract ice
during a race weekend is not
session
BRAKE-DYNAMOMETER
appropriate
TESTING for testing. Other cars on
theBrake
track manufacturers
prevent you use
from
doing
brake
dywhat
is
needed
for
a
good
test.
namometers for laboratory testing. A
single brake is mounted o n and driven
BRAKE-DYNAMOMETER
TESTING
Brake manufacturers use brake dynamometers for laboratory testing. A
single brake is mounted on and driven
by the dynamometer. Instruments
measure and record such things as
DY Lne temperature,
uy narnomeler. rpm,
1nsLrumenrs
brake
brake
measure
record such
thingsand
as
pressure
torque, and
hydraulic
brake
temperature,
rpm,
brake
stresses. The dynamometer is powtorque,
and
ered
by anhydraulic
engine or pressure
electric motor.
stresses.
The
dynamometer
is
powUsually, a large high-speed flywheel is
ered
used. by an engine or electric motor.
Usually,
a large high-speed
is
Dynamometer
testing flywheel
involves
used.
revving up the flywheel until there is
testing ofinvolves
a Dynamometer
predetermined amount
energy
revvinginupit. the
is
Theflywheel
driving until
motorthere
is disstored
aconnected
predetermined
amount
of
energy
and the brake is applied to
storedthe
in flywheel
it. The driving
motor is disto a predetermined
slow
connected
and
the
brake
applied of
to
rpm or to a dead stop. Theis amount
slow theenergy
flywheelinto the
a predetermined
stored
flywheel is
rpm
or to
a dead
stop. The
known.
It is
equivalent
to a amount
fraction of
of
stored
energy
in
the
flywheel
is
the kinetic energy stored in a moving
known.
It
is
equivalent
to
a
fraction
of
car, or about one-third of the total
the kinetic
energy one
stored
in brake
a moving
front
and
energy
for testing
car,
or
about
one-third
of
one-sixth for one rear brake. the total
energy for testing one front brake and
Dyno testing tests a brake's energyone-sixth for one rear brake.
absorbing capaci ty for one or a series
testing
a brake's
energyof Dyno
complete
or tests
partial
stops. The
flyabsorbing
capacity
for
one
or
a
series
wheel can be stopped slowly
or
of
complete
or partial
The flyrapidly,
depending
on stops.
how much
hywheel
be stopped
slowly
or
pressure
is applied
to the
draulic can
rapidly,
depending
on
how
much
hybrake. Sophisticated dynamometers
draulic
pressure
is applied
to the
are
computer
controlled
and can
be
brake. Sophisticated
dynamometers
programmed
to duplicate
brake
are computerspeeds
controlled
and can be
and decelerations
applications,
programmed
to
duplicate
brake
encountered in city traffic, a mountain
applications,
speeds
anda race
decelerations
descent, or laps
around
track .
encountered
in city
a mountain
Another type
of traffic,
dynamometer
apdescent,
or
laps
around
a
race
brake.
plies constant power to thetrack.
Another
type of input
dynamometer
This
steady-power
can be atap-a
plies
constant
power
to
brake.
heats
up,
particular rpm. As the brakethe
This
steady-power
can be
its torque
changes.input
Torque
can atbea
particular
the brake .heats
up,
measured rpm.
with As
instruments
Friction
its
torque
changes.
Torque
can
be
change with temperature at a constant
measured
instruments.with
Friction
rpm can with
be determined
this
change with temperature at a constant
setup.
rpm can be Measuring-The
determined withsecret
this
Temperature
setup.
of proper brake-dynamometer testing
Temperature
Measuring-The
is
the instrumentation.
A good secret
setup
of proper
testing
will
havebrake-dynamometer
numerous temperatureis
the instrumentation.
A good
setup
measuring
devices mounted
in critical
will
have
numerous
temperaturelocations on the brake. Generally,
measuring
devices
mounted
thermocouples
are used
for this.in critical
locations
on the brake.
Generally,
is a joint
of two
A thermocouple
thermocouples
are
used
for
this.
wires with dissimilar metal. When the
A thermocouple
is a joint
of two
joint,
or thermocouple
junction,
is
wires
with
dissimilar
metal.
When
the
heated , it generates a small electrical
joint,
junction,
is
voltage.or
Thisthermocouple
tiny voltage can
be measheated,
it
generates
a
small
electrical
ured and converted to indicate a
voltage. temperature
This tiny voltage
be measwithcan
a pyrometer.
specific
ured
and converted
to indicate
If
the thermocouple
junction
is in con-a
specific
a pyrometer.a
the item towith
be measured,
tact withtemperature
If the thermocouple junction is in contact with the item to be measured, a
HOW MUCH HORSEPOWER
GOES INTO THE BRAKES?
HOW MUCHisHORSEPOWER
Horsepower
the rate at which
GOES is
INTO
THE BRAKES?
energy
delivered.
The heat energy
Horsepower = 0 .00268W ed M S
We = weight of car in pounds
Horsepower
= 0.00268WCd,S
decleration in g's
d M = maximum
W
weight of
of car
pounds
S, = = speed
the in
car
in miles per
Horsepower
is brakes
the rate
at awhich
d
, = maximum decleration in g's
hour.
during
stop
received
by the
S = speed of the car in miles per
energy
delivered. The
heat energy
can be isexpressed
as horsepower.
hour.
received
by the
a stop
For
example,
if brakes
a brakeduring
is driven
by
Because the speed of a car
canengine
be expressed
horsepower.
an
on a brakeasdynamometer,
changes during a stop, power to the
For
example,
if a brake
brake is
driventhe
by
Because
speedDeceleration
of a car
power
into the
equals
brakes
also the
changes.
an
engine
on of
a brake
dynamometer,
changes
during
a stop,
to the
power
output
the engine.
In a car,
during
the power
stop due
to
may change
power
intoenergy
the brake
brakes
changes. and
Deceleration
kineic
of the equals
moving the
car
the
this also
changesalso
in downforce,
power output
the engine.
In a that
car,
may change
duringtothethe
stopbrakes.
due to
supplies
the of
power.
However,
changes
power
the
kineic
energy
of the moving
car
changes
downforce,
and this
also
kinetic
energy
originally
came from
Obviously,inthe
highest power
is for
a
supplies
changes
to lots
the ofbrakes.
the
engine.the power. However, that
car with
downfast, heavypower
Obviously,
theracing
highest
power is for a
kinetic
energy originally
One horsepower
equalscame
550 from
ft-lb
force and big
tires.
the energy
engine. delivered each second,
fast,
heavy
with lots
of downof
calculations
Below
arecarsample
ft-lb
force
andexplain
big racing
One
horsepower
brakes
The
total
power intoequals
all four550
that may
whytires.
bra'k es are deof
energy
delivered
Belowtheare
during
a stop
is given each
by thesecond.
followsigned
waysample
they arecalculations
for various
The
total power into all four brakes
that
explain why brakes are deing formula:
typesmay
of cars.
during a stop i s given by the followslgned the way they are for various
ing formula:
types of cars.
d M (g's) Power(HP)
Ty,p eof Car
We (lb) S (mph)
515
0.8
4000
60
Large sedan, street tires
Type of Car
W, (Ib) S (mph)
d, (g's) Power(HP1
257
0.8
2000
Small sedan, street tires
60
51 5
4000
60
0.8
Large
street
tires tires
2573
1.2
Racingsedan,
stock car,
racing
200
60
0.8
257
Small
sedan,
tiresdownforce
2000
2680
200
2.5
Fast race
car street
with high
2573
4000
200
Racingrace
stock
tires
120
386
1000
1.2
Small
carcar,
withracing
low downforce
2000
200
2.5
2680
Fast race car with high downforce
386
1000
120
1.2
Small race car with low downforce
remote temperature measurement is
possible.
remote
temperature
is
Thermocouples
canmeasurement
be used on any
possible.
stationary brake part. To measure
Thermocouples
useda on
any
moving
parts, suchcan
as abe
rotor,
sliding
stationary
brake
part.
To
measure
contact or more-sophisticated instrumovingare
parts,
such. as
a rotor,
a sliding
ments
needed
Often,
rotor
temcontact
or
more-sophisticated
perature is measured with ainstrutherments are brought
needed. Often,
rotor temmocouple
into contact
with
perature
is
measured
with
therthe rotor immediately after thea brake
mocouple brought into contact with
stops.
theA rotor
immediately
after connected
the brake
hand-held
pyrometer
stops.
to a thermocouple probe is a useful
A hand-held
pyrometer
brakeconnected
and tire
device
for measuring
to
a thermocouple
probetrack.
is a useful
temperatures
at a race
When
device
for the
measuring
brake and they
tire
racers use
term pyrometer,
temperatures
at
a
race
track.
When
usually mean hand-held pyrometer or
racers
use the term pyrometer, they
thermocouple.
usually
hand-held
pyrometer
or
There mean
are many
interesting
comthermocouple.
parisons
to make when dynamometer
ThereHere
are are
many
comtesting.
someinteresting
possible tests:
parisons
to
make
when
dynamometer
• Comparison of brake friction matetesting.
some possible
tests:
rials
forHere
fadeareresistance
, wear
and
Comparison
of
brake
friction
matetorque.
rials
for fade resistance,
wear part
and
the most critical
• Determining
torque.
of
braking system when excessive
Determining
most critical part
temperatures
arethe
reached.
of
braking
system
whentemperature
excessive
• Finding the maximum
temperatures
are
reached.
a brake can withstand without failure.
the maximum
temperature
Comparison
of brake-fluid
perform• Finding
a brake
can withstand
without failure.
at high
temperatures.
ance
Comparison of brake-fluid performance at high temperatures.
• Testing different types of calipers,
brake drums or other hardware.
different
of calipers,
• Testing
Comparison
of types
different
ro tor
brake
drums
or other hardware.
designs
.
Comparison
rotor
• Testing
effectof ofdifferent
caliper-piston
designs.
insulators.
effect oftorque
caliper-piston
Finding maximum
the brake
• Testing
insulators.
is capable of achieving without strucFinding
torque the brake
tural
failuremaximum
.
is capable of achieving without structural failure.
.TESTING
COMPONENT
Manufacturers do a lot of brakeCOMPONENT
TESTING
system-part
testing.
They test master
Manufacturers
do cylinders
a lot of on
brakecylinders and wheel
test
system-part
testing. They test
master
rigs that automatically
apply
the
cylinders
andand
wheel
test
brakes over
over.cylinders
This testsondurarigs
that
automatically apply the
bili ty of
the parts.
brakes
over
over. cylinder
This tests
duraBy cyclingand
a brake
rapidly,
bility
parts.
much less time than
testingof the
takes
By testing.
cycling aInbrake
cylinder
rapidly,
track
addition
, components
testing
takes
much
less
time
subjected to internal pressure than
are
track
In addition,
components
testedtesting.
for bursting
strength
at pressubjected
internalthanpressure
sures
muchto higher
normal. are
It
tested
for
bursting
strength
must be proven that each itemathaspresthe
sures
much
higher than
It
strength
to withstand
the normal.
maximum
must
be
proven
that
each
item
has
the
possible pressure and have a signifistrength
withstand the maximum
cant
factortoofsafety.
possible
a signifiIf youpressure
wish and
to have
pressure-test
cant
factor
of
safety.
components, it is not difficult to set
you You
wishmustto getpressure-test
upIfa test.
a hydraulic
i t is
not difficult
to seta
components,
pump or build
a lever
to operate
up a test. You must get a hydraulic
pump or build a lever to operate
a
105
Complete line of temperature-measuring instruments is offered
by Omega Engineering, Inc. Digital meters shown are designed to
be
used with
By combininginstruments
a meter with
a therComplete
linethermocouples.
of temperature-measuring
is offered
mocouple
in a Inc.
special
probe,
you shown
C:ln custom-build
your
by Omega mounted
Engineering,
Digital
meters
are designed
to
own
pyrometer.
Such instrumentation
is useful
for testing
on a
be used
with thermocouples.
By combining
a meter
with a therbrake dynomounted
or race car.
courtesy
mocouple
in aPhoto
special
probe, Omega
you canEngineering.
custom-build your
own pyrometer. Such instrumentation is useful for testing on a
brake dyno or race car. Photo courtesy Omega Engineering.
Handy pyrometer kit is manufactured by AP Racing and sold by
Tilton Engineering. It comes with two probes; one for soft materials
such
as tires, kit
andisone
for hard materials
as brake
rotors.
Handy
pyrometer
manufactured
by APsuch
Racing
and sold
by
Instrument
can be used
to measure
brake
temperatures
on mateopenTilton
Engineering.
It comes
with two
probes;
one for soft
wheel
cars.asPhoto
AP hard
Racing.
rials such
tires, courtesy
and one for
materials such as brake rotors.
Instrument can be used t o measure brake temperatures on openwheel cars. Photo courtesy AP Racing.
Indicator Mount
---Force
! tp,,,,
Caliper
Master Cylinder
or High-Pressure Pump
Master Cylinder
or Pressure
High-Pressure
Caliper pressure-test setup:
gage Pump
should have minimum 1S00-psi range; 2000
psi is preferable. If maximum pressure is exceeded, gage will be damaged. Spacer gives
something
for pads to push
against.
Notegage
how should
dial indicator
is mounted:
Bracket
is attached
Caliper pressure-test
setup:
Pressure
have minimum
1500-psi
range;
2000
to
side of caliper
and gagepressure
is set square
against oPPosite
so it will read
totalgives
calipsione
is preferable.
If maximum
is exceeded,
gage willside
be damaged.
Spacer
per deflection.
Test to
can
alsoagainst.
be performed
on the
if a pressure
gage Bracket
is installed
in brake
something
for pads
push
Note how
dial car
indicator
is mounted:
is attached
line.
Remove
before
avoid excessive
pedal travel.
to
one
side ofgage
caliper
and driving
gage iscar
settosquare
against opposite
side so it will read total caliper deflection. Test can also be performed on the car if a pressure gage is installed in brake
line. Remove gage before driving car t o avoid excessive pedal travel.
brake master cylinder. The lever can
be operated by hanging weights on a
brake
pulley master
system.cylinder.
You can The
then lever
applycan
an
be
operated
by
hanging
weights
on a
exact load to the master-cylinder
pulley
You can itthen
an
pushrodsystem.
and maintain
so apply
you can
exact
load
to
the
master-cylinder
make measurements .
pushrod Deflections-It
and maintain itis so
you can
System
interesting
make
measurements.
to test the deflection of hydraulicSystem components
Deflections-It
interesting
system
whileis the
system
to
test
the
deflection
of
is pressurized . Of particular hydraulicinterest is
system
components
while the deflects
system
how
much
a caliper
is
pressurized.
Of
particular
interest
is
outwardly. You can measure this dehow much
a indicator
caliper mounted
deflects
flection
with a dial
outwardly. You can measure this deflection with a dial indicator mounted
106
to the caliper. You must also measure
either hydraulic pressure in the
to the caliper.
must
also measure
system
or forceYou
on the
master-cylinder
either
hydraulic
pressure
in the
be
piston. System pressure can then
system
or force
on the master-cylinder
calculated.
A hydraulic-pressure
gage
piston.
System pressure
can do
then
with
a large-enough
scale will
it. be
calculated.
A
hydraulic-pressure
gage
An engine oil-pressure gage won
't
with
a
large-enough
scale
will
do
it.
have enough capacity. Relatively inexAn engine
gage psi
won't
pensive
gages oil-pressure
reading to 2000
are
have enough
Relativelystores.
inexavailable
at capacity.
industrial-supply
pensive
gages reading
to 2000' s psi
are
Marsh Instrument
Company
J4878
available
at
industrial-supply
stores.
pressure gage is a 2000-psi gage that
Marsh
Instrument
Company's J4878
uses minimum
displacement.
pressure gage is a 2000-psi gage that
uses minimum displacement.
Put a tee in the hydraulic line and
install the gage. Make sure air cannot
a tee inin the
the gage
hydraulic
line high
and
bePut
trapped
or other
installinthethe
gage.
Make sure
air cannot
spot
system.
Pressurize
the
be trapped
the gage
or other
high
system
and inrecord
caliper
deflection
spotincremental
in the system.
Pressurize
pressures.
Drawthea
at
system
recordversus
caliper
deflection
pressure
deflection
. It
graph ofand
at
incremental
pressures. a Draw
should
be approximately
straighta
graph
of pressure
deflection.
It
line. If
it's not, versus
something
in the
should
be
approximately
a
straight
system has slack, which is being taken
line.
it's not, issomething
in the
up, orIfsomething
failing. Check
to
system
has deflection
slack, whichreturns
is beingto taken
see
if the
zero
up, orpressure
something
is failing.If Check
to
when
is removed.
some desee
if
the
deflection
returns
to
zero
flection remains without pressure,
when pressure
is removed.
If some
desomething
has bent
or crushed
.
flection
remains
without
pressure,
You can
measure
brake-hose
and
something
has bent
or crushed.
These deflecline deflection
as well.
You
can
measure
tions are small, but brake-hose
you should and
be
line
well. with
These
defleca dial
inable deflection
to measureasthem
tions arewhile
small,us ing
but extremely
you shouldhigh
be
dicator
able
to
measure
them
with
a
dial
insystem pressure. Take a number of
dicator
while just
using
extremely
high
measurements
to be
sure.
system pressure. Take a number of
measurements
just to be sure.
THE TEST TRACK
The only way to get the most from a
THE
brake TEST
systemTRACK
is to test it on the car.
The
only
way to
to get
You don
' t have
testthe
on most
a racefrom
track.a
brake
to test itbrake
on the
car.
Unlikesystem
chassisis testing,
testing
You
have tointest
a race track.
can don't
be done
a on
straight
line.
Unlike chassis
Therefore,
youtesting,
may brake
have testing
more
can
be
done
in
a
straight
line.
options.
Therefore,
havehasmore
Each area you
of themay
country
difoptions.
ferent facilities and laws. List possible
Each locations
area of the
country
difdon'thas
forget
testing
so you
ferent
facilities
and
laws.
List
possible
any. Pick the one most suitable for
testingpurposes.
locationsDon't
so you
don'ttheforget
your
ignore
legal
any.
Pick the
oneas most
for
limitations,
such
noise suitable
ordinances.
your
purposes.
Don't
ignore
the
legal
People next to your " test track" may
limitations,
such
noiseofordinances.
not
appreciate
the as
sound
screeching
People next to your "test track" may
not appreciate the sound of screeching
~'mzo",
Caliper
Deflection
(in)
Caliper
Deflection
(in.)
When testing a race car's brakes, do it on
the same type of track it will run on. This
track is
best for
testing
oval-track
When
testing
a race
car'sanbrakes,
do itdirt
on
car. same
It's not
much
good for
testing
a roadthe
type
of track
it will
run on.
This
racing is
car.
track
best for testing an oval-track dirt
car. It's not much good for testing a roadracing car.
Hydraulic Pressure (psi)
Hydraulic Pressure (psi)
Use data obtained from caliper-deflection test to plot pressure-versus-deflection curve.
Curve should be a straight line. If deflection increases at a faster rate at high pressure,
something
in the system
failing. Don't risk test
trouble
brakes in the problem zone.
Use data obtained
from is
caliper-deflection
to by
plotusing
pressure-versus-deflection
curve.
Curve should be a straight line. If deflection increases at a faster rate at high pressure,
something in the system is failing. Don't risk trouble by using brakes in the problem zone.
Stock car has pressure gage mounted
on brake line next to each master
cylinder.
pressures,
an
Stock carBy
hasrecording
pressure gage
mounted
exact
numerical
record
brake
balon brake
line next
to of
each
master
ance
is available.
Don't ,l eave
pressure
cylinder.
By recording
pressures,
an
gages numerical
in hydraulic
system
because
exact
record
of brake
balthey
increase
pedal
travel.
ance is
available.
Don't
leave Pressure
pressure
gages
testing only.
gages are
in for
hydraulic
system because
they increase pedal travel. Pressure
gages are for testing only.
WARNING
High-pressure testing is used
WARNING
only to find the limits of a design and
High-pressure
testing
determine
its safety
factor.is If used
you
to finda the
limits ofpump
a design
and
onlyusing
are
hydraulic
capable
determine
If you
3000 psiitsorsafety
more, factor.
you may
be
of
are
a items
hydraulic
pumpbecause
capable
to failure
ableusing
to test
of
3000
psisystems
or more,operate
you may
be
most
brake
below
able
test
itemsistosome
failure
because
1500topsi.
There
danger
asmost brake
systems
operate so
below
sociated
with
such testing,
be
danger
as1500 psi.Air
There
is some
careful.
trapped
in the
system
sociated
with
such
testing,force.
so be
explosive
If
can
escape
with
careful.
Air trapped
theflying
system
parts break,
they canin go
at
can escape with explosive force. If
parts break, they can go flying at
tires, even if you think your testing is
strictly legal.
tires,
even
if you think
your for
testing
is
Some
possible
locations
brake
strictly
legal.
testing are:
possible
locations
fortesting.
brake
• Some
Road-racing
track
rented for
testing are:
Road-racing track rented for testing.
high velocity. Isolate people from
the items being tested, and make
high tovelocity.
from
thesy.stem.
sure
bleed allIsolate
air frompeople
the
items
being
tested,before
and make
Always
relieve
pressure
looksure
bleed
all air from the system.
ing attothe
parts.
Always
pressure
before
lookIf yourelieve
pressurize
a part
to three
ing at the
times
its parts.
maximum rated capacity
If you
pressurize
to three
and
it does
nbt fail aorpart
distort,
it is
times
its maximum
rated .all
capacity
well designed.
However,
parts
and
it does
fail or distort,
it is
tested
to not
excessive
pressures
well
designed.
However,
all parts
should
not be used.
They should
be
tested
pressures
marked permanently
destroyedto or excessive
should
be used. TheyThere
shouldmay
be
for easynotidentification.
destroyed
marked
permanently
be damageorhidden
from
view that
for
easy
There
makes
the identification.
part unsafe to use
. . may
beIf damage
viewrig that
you are hidden
makingfrom
a test
for
makes the part
unsafe
use.
3000to
psi,
go to an
pressures
up to
If you are making
a test
rig Airfor
aircraft-surplus
shop for
parts.
pressures
up tosystems
3000 psi,
go to an
craft
hydraulic
operate
at
aircraft-surplus
shop for their
parts.highAir3000
psi. Consequently,
craft
hydraulic systems
operatecan
at
pressurehbses
and fittings
3000
psi. pressure.
Consequently,
their
take this
Check
withhighthe
pressure
andgetfittings
can
shop
to be hoses
sure you
parts rated
take3000-psi
this pressure.
Check
the
for
pressure.
Handwith
pumps
shop
to bepressurize
sure you get
rated
that can
a parts
system
to
for 3000-psi
pumps
3000
psi arepressure.
available.Hand
You'll
also
that
pressurize
to
3000-psi
need can
pressure
gages aforsystem
3000
psi are available. You'll also
capacity.
need
pressure
for lines
3000-psi
surplus
and
Before
using gages
capacity.wash them throughly with
fittings,.
Beforeto using
lines and
alcohol
removesurplus
dirt, moisture
fittings,
them throughly
with
aircraft wash
hydraulic
fluid. Aircraft
alcohol
to remove
dirt,different
moisturefrom
and
brake fluid
is totally
aircraft
hydraulic
fluid.
Aircraft
start
automotive
brake fluid.
Always
brakeclean
fluidcomponents.
is totally different from
with
automotive brake fluid. Always start
with clean components.
,
• Drag strip rented for testing.
• Large parking lot.
Dragairport,
strip rented
for testing.
• An
particularly
one with
Large
parking
lot.
light air traffic or unused runways .
An airport,
one with,
• Straight
road particularly
away from residences
light air traffic or unused runways.
Straight road away from residences,
intersections and with little traffic.
Race Tracks-Obviously, the best
intersections
with
place to test and
a race
carlittle
is atraffic.
race track
Race
Tracks-Obviously,
the best
like the one you will compete
on.
place
to
test
a
race
car
is
a
race
Even for testing a road car, a track
race
like
one advantages
you will compete
on.
track the
has the
of safety and
Even
testing
road are
car,available
a race
privacy.forSome
race atracks
track hasthetheweek
advantages
of safety fee
and.
during
for a nominal
privacy.
Some
race
tracks
are
available
You should be prepared to bring whatduring
the week
for a nominal
fee.
ever safety
equipment
the track
You
should
be prepared
to bring whatrequires,
even
if you consider
brake
ever
equipment
the
track
testing safety
much safer
than going
flat-out.
requires,
even
if
you
consider
brake
Chances are that track management
testing
much safer
than going
flat-out.
and
insurance
companies
won't
make
are that
track management
anyChances
distinction
between
one type of
and
insurance
companies
won't they'll
make
driving
and another.
Usually,
any
distinction
between
one
type
of
require the driver to wear a helmet
driving
another.
Usually,
and
use and
other
standard
racing they'll
safety
require
the driver
to wear
a helmet
equipment.
You and
all those
inand
use
other
standard
racing
safety
volved may also have to sign a waiver
equipment.
and of
all allthose
that relieves You
the track
legal inrevolved may ifalso
have tois sign
a waiver
sponsibility
someone
injured.
that
relieves
the track
of all legal car,
reIf you
are testing
a road-racing
sponsibility
if
someone
is
injured.
you should test on a road course . The
If you
are testing
same
holds
true fora road-racing
other typescar,
of
you should
test on
course.
The
cars.
Oval-track
carsa road
should
be tested
same
holdstrack-dirt
true for cars
otheron types
of
on an oval
dirt and
cars.
Oval-track
cars
should
be
tested
pavement
cars
on
a
paved
on
an oval track-dirt
dirt and
and
track-dragsters
on a cars
drag on
strip,
pavement
on will aallow
paved
on down the cars
line. This
you
track-dragsters
on a or
drag
and
to
run the car around
up strip,
and down
on
down
the
line.
This
will
allow
you
the track many times in succession
to runtest
thethe
car brakes
around for
or up
and down
and
temperature
the track
in succession
and
wear many
undertimes
simulated
racing
and test the
brakes
for betemperature
conditions.
This
will not
possible at
and wear
under
simulated
other
types of
test tracks.
If youracing
can't
conditions.
This
will
not
be
possible
at
test on a race track, you'll have
to use
other types
tracks. If"you
can't.
actual
racingof
fortest
"real-world
testing
test
on a racea track,
to use
Although
drag you'll
strip ishave
ideal
for
actual
racing
for
"real-world"
testing.
testing a drag-car brake system, one is
Although
a drag
strip
is ideal
also
useful for
testing
other
types for
of
testing
a
drag-car
brake
system,
is
cars. You can do one stop one
from
also
useful for
types
of
moderately
hightesting
speed other
at a drag
strip.
cars.
can allows
do one
stop
Or, if You
the track
, you
canfrom
run
moderately
high
speed
at
a
drag
strip.
several stops in succession by running
Or,
the track
you
can run
backif and
forth. allows,
Usually
, there
is
several stops in succession by running
back and forth. Usually, there107
is
Drag strip can be used to test brakes at medium to high speeds.
Dragster reaches top speed in quarter mile, so its brakes get a
realistic
workout.
will only
reach about
two-thirds
Drag strip
can be Typical
used toroad
testcar
brakes
at medium
to high
speeds.
of
its maximum
Regardless,
dragmile,
strips
usually get
safe
Dragster
reachesspeed.
top speed
in quarter
so are
its brakes
a
and
handy
for brake
testing.
realistic
workout.
Typical
road car will only reach about two-thirds
Small airports are potential brake-test sites. However, you must
first get permission from the airport manager.
Small airports are potential brake-test sites. However, you must
first get permission from theairport manager.
of its maximum speed. Regardless, drag strips are usually safe
and handy for brake testing.
plenty of room to bring the car to a
safe stop.
plenty
room to of
bring
the strip
car toarea
The of
advantages
a drag
safe
stop.
that it will be clean , smooth and level.
The advantages
of aconsiderations.
drag strip are
These
are important
that
it
will
be
clean,
smooth
and level.
The problem with a drag strip
is its
These
are
important
considerations.
length. You usually can't get a car
Tnear
h e problem
with speed
a draginstrip
is its
its maximum
a quarter
length.
You you
usually
get a a drag
car
mile, unless
are can't
running
near
its
maximum
speed
in
a
quarter
racer. Most road cars reach about twomile,
you are
running
a drag
thirds unless
maximum
speed
in a quarter
racer.
Most
road
cars
reach
about
twomile. This represents about one-half
thirds
maximum kinetic
speed in
a quarter
of
the maximum
energy
a car
mile.deliver
This represents
about
one-half
can
to the brakes.
Thus,
testof
the
maximum
kinetic
energy
a car
ing at a drag strip leaves some doubt
can
deliver
the brakes.
Thus, of
test-a
about
the to
ultimate
capability
ing
at system.
a drag strip leaves some doubt
brake
about
thecan't
ultimate
of a
If you
rent capability
the drag strip,
brake
system.
enter the car in a drag race . You may
you can't
be Ifallowed
to runrent
time the
only, drag
wherestrip,
you
enter
car in
a drag competition.
race. You may
don't the
engage
in actual
If
be allowed
to run
time hard
only,at
where
you
apply the
brakes
the you
end
don't
in actual
competition.
If
of
the engage
strip, you
can get
some idea of
you
the brakes
hard
at the end
how apply
the brakes
work at
medium-high
of the strip, you can get some idea of
speeds.
how
the racing
brakes will
worklimit
at medium-high
Drag
testing bespeeds.
cause carrying an observer during
Drag
will be
limit
testingAlso,
beeach
runracing
may not
allowed.
causewon't
carrying
observer
during
you
be ableanto get
as many
runs
each
maytest
notsession.
be allowed. Also,
as
in arun
private
you
won't
be
able
to
getlots
as many
runs
Parking Lots-Parking
are someas
in
a
private
test
session.
times available on weekends. The
Parking is
Lots-Parking
lotsenough
are someproblem
finding a lot big
for
times
available
on
weekends.
The
testing brakes. Most are too small.
problem
is finding
a lot problems
big enoughwith
for
Also,
you'll
run into
testing
brakes.
too small.
dirt,
bumps
and Most
nearbyare
people.
And,
Also,
run into
with
it
may you'll
be difficult
to getproblems
permission
to
dirt,
bumps
and
nearby
people.
And,
use a really large lot because they are
it may beowned
difficult
get permission
to
usually
by to
large
corporations.
use alarger
reallythe
large
lot because
they difare
The
company,
the more
usually owned by large corporations.
The
108 larger the company, the more dif-
ficult it will be to talk to the individual
who makes the decisions.
ficult
it will
talk to lot
the to
individual
If you
findbeatoparking
run on,
who
makes
the
decisions.
be aware of the legal and safety
If you find aAlways
parking run
lot to
run on,
requirements.
a muffled
be
aware
of
the
legal
and
safety
exhaust, unless you are really out
in
requirements.
Always
run
a
muffled
the "sticks." Test during hours when
exhaust,
unless
are really If
outyou
in
people will
not you
be disturbed.
the permission
"sticks." Test
when
get
to during
use thehours
lot, try
to
people
not be
disturbed.
If you
get
it inwill
writing.
Invite
the person
in
get
permission
to
use
the
lot,
to
charge to attend your test session.tryNot
get
writing.
Invite
person
in
onlyitisinthis
good PR,
butthe
if the
police
charge he
to attend
your
testasession.
Not
come,
can give
them
good story.
only is athis
good PR, but
if the police
Often,
well-meaning
bystander
will
come,
he
can
give
them
a
story.
call the police, because he'sgood
not aware
Often, obtained
a well-meaning
bystander
will
you've
permission
.
call the police,large
because
he'ssurface
not aware
Airports-A
testing
can
you've
obtained
permission.
be
found
at an airport.
The runways
Airports-A
large
testing
surface
can
are always long and
usually
smooth,
be
found
at
an
airport.
The
runways
level and relatively clean. The best
are
smooth,
placealways
to try long
is a and
smallusually
airport,
which
level
and
relatively
clean.
The
best
may be used occasionally by private
place
to
try
is
a
small
airport,
which
planes. They may have a runway not
may
beorused
occasionally
private
in
use,
possibly
an accessbyroad
that
planes.
They may
have a runway
not.
can
be closed
temporarily
for testing
in
use,
or
possibly
an
access
road
that
It helps if the airport manager likes
can
closed
temporarily
forask
testing.
race be
cars.
Don't
be afraid to
. You
It
helps
the airport
manager likes
might
be if
pleasantly
surprised.
race
cars. Don't
afraid
to ask. You
Airports
havebethe
advantage
of
might
be
pleasantly
surprised.
minimal noise problems and a lot of
Airports
havehave
theto advantage
of
room
. You may
sign a waiver
minimal
and a lot of
to
releasenoise
the problems
airport management
room. responsibility.
You may have Also,
to signthey
a waiver
from
may
to
release
the
airport
management
want proof of insurance. If you are
from
responsibility.
Also,
they may
professional
in your
approach
to
want
insurance.
If you are
testing,proof
it willofhelp
a great deal.
professional
in you
yourhave
approach
to
Public Roads-If
a road cat,
testing,
it
will
help
a
great
deal.
you can try a pu blic road as the last
Public ItRoads-If
you to
have
car,a
resort.
may be legal
stopa aroad
car in
you
can line
try if
a public
as the
last
straight
you do road
it safely.
If you
resort. It may be legal to stop a car in a
straight line if you do it safely. If you
do not speed , make excessive noise or
appear to be driving recklessly, you
do
excessive
noise
or
maynot
bespeed,
able tomake
convince
a police
offiappear
to
be
driving
recklessly,
you
cer to allow you to test. It helps to be
mayfrom
be able
to convince
police. offifar
houses
and other apeople
cer
to allow
you to test. testing
It helps while
to be
Race
Testing-Brake
far
from
houses
and
other
people.
running a race can be done as a last
Race
testing
while
resort. Testing-Brake
If you do this, pick
an event
running
a race
can be done
as atime
last
that offers
maximum
practice
resort.
If
you
do
this,
pick
an
event
and mlntmum competition . For
that offersa local
maximum
practice
time
example,
drag event
is much
and
minimum
competition.
better than a championship event. For
For
example,
a local
event
is much
road racers,
try a drag
solo-I
or time
trial
better
event.
For
rather than
than a achampionship
race. In solo-I
events,
road
racers,
try
a
solo-I
or
time
trial
the cars run one at a time. The practice
rather than
a race.quite
In solo-I
events,
sessions
are often
long. Another
the carsisrun
at athe
time.
option
to one
enter
carThe
in practice.
a racesessionsschool.
are often
quite
driving
But
firstlong.
, get Another
permisoption
is the
to enter
the car
in a race-.
sion
from
sponsoring
organization
driving school. But first, get permission
from the sponsoring
organization.
PLANNING
BRAKE TESTS
Plan your tests before you get to the
PLANNING
TESTS If you
track. Testing BRAKE
time is valuable.
Plantoyour
testswork
before
the
have
do any
on you
the get
car to
other
track. Testing
time is planned,
valuable. Ifyou'll
you
than
what you've
have
to do
on the
car waste
other
probably
runany
outwork
of time.
Don't
than
what
you've
planned,
you'll
time trying to think up what to do
probably
out. Plan
of time.
Don't waste
next at therun
track
ahead.
time
to thinkdown
up what
do
Starttrying
by writing
yourto test
Plan
ahead.
next
at
the
track.
plan. List what you'll be testing for.
Start by
writing down
test
Include
a step-by-step
planyour
of how
plan. List
whattesting.
you'll be
testing
for.
you'll
do the
While
writing
Include
step-by-step
of how
the test aplan
, think of plan
all the
test
you'll
do the tools
testing.
writing
instruments,
and While
parts needed
the
test
plan,
think
of
all
the
to do the job . List these separately.test
A
instruments,
tools isand
parts onneeded
sample
test plan
shown
page
to
doItthe
List
separately.
A
109.
willjob.
give
youthese
an idea
of what's
sample
test
plan
is
shown
on
page
needed . Determine exactly what's
109. It will
giveplan.
you an idea of what's
needed
in your
needed.
Determine
exactly
what's
Data Sheets-In addition
to the
test
needed in your plan.
Data Sheets-In addition to the test
SAMPLE TEST PLAN
SAMPLE LIST OF
BRAKE- TESTING EQUIPMENT
1.
2.
1.
Inspect brakes and record starting data .
SAMPLE TEST PLAN
Overall brake-performance test.
lnspect
brakes
and record
data.
a. Record
comments
on starting
performance.
2. Overall
brake-performance
test.as required.
b. Inspect
and adjust brakes
a. Record
comments
on performance.
3 . Balance
adjustment
tests.
b. Record
lnspect deceleration
and adjust brakes
required.
beforeassetting
balance.
a.
3. Balance
adjustment
b. Test
brakes andtests.
adjust balance.
Record deceleration
before
setting balance.
. a.
c. Continue
until maximum
deceleration
is attained.
b. Test brakes
4. Cooling-duct
testsand
. adjust balance.
c.
Continue
maximum
deceleration
is attained.
a. Tuft
tests until
to confirm
airflow
in duct.
4. Cooling-duct
b. Measuretests.
brake temperature after one stop.
a.
tomeasured
confirm airflow
in duct.
car for
time and
measure cooling effect.
c. Tuft
Run tests
b. Measure
brake
temperature
one stop.
d.
Modify ducts
and
test coolingafter
again.
c. Runlining
car fortests,
measured time and measure cooling effect.
5. Alternate
d. Modify
fluidducts
tests.and test cooling again.
6, Alternate
5. Alternate
liningtesting,
tests.
7.
Long-distance
6. Alternate
fluid
tests.
a. Check
temperature.
7. Long-distance
testing.
b. Check wear
rate after test.
a.
Recordtemperature.
driver comments and results of brake inspection,
c, Check
b. Check
rate
8. Bed-in
sparewear
linings
forafter
nexttest.
race .
Record
driverwith
comments
and results
of brake inspection.
balance
wings adjusted
to maximum
downforce settings,
9 . Setc.brake
8. Wet
Bed-in
spare
linings
forrain
nexttires,
race.and balance brakes for wet.
10.
down
track,
install
SAMPLE
OF work on car.
• Tool box LIST
for general
BRAKE-TESTING
for driver, fire
• Safety equipment EQUIPMENT
Tool box for general work on car.
extinguishers.
Safety equipment
driver, and
fire
• Spare
parts for forengine
extinguishers.
chassis,
parts
for engine and
• Spare
Spare tires
and wheels.
chassis.
• Brake linings, brake fluid, special
Spare tires and wheels.
brake-maintenance
tools.
Brake linings,
brake fluid, special
temperature~indicating
• Pyrometer,
brake-maintenance
tools.
labels,
temperature-indicating
paint.
Pyrorneter, temperature-indicating
• Stopwatch.
labels,
temperature-indicating
paint.
• Toppling.block
setup.
• Stopwatch.
Yarn for tufts, tape, scissors.
setup.
• Toppling-block
Video camera, still
camera, portafor tufts,
bleYarn
TV and
VCR. tape, scissors.
camera,
stilltank.
camera, porta• Video
Fuel, oil,
water, air
TV and VCR.
ble
• Jack,jack
stands, creeper.
oil, water,
tank.
Materials
for air
modifying
brake
• Fuel,
Jack,racer's
jack stands,
ducts,
tape, creeper.
rivets and rivet
Materials for modifying brake
gun.
ducts,
racer's
tape,pen.
rivets and rivet
• Notebook,
paper,
gun.
Notebook, paper, pen.
plan, make several copies of the blank
data sheet on this page for recording
plan, make
copies o
f the blank
test
results.several
Pertinent
information
data
sheet
on
this
page
for
recording
about the exact brake-system
setup
test results.
Pertinent
should
be included:
type information
of linings,
about balance-bar
the exact brake-system
setup
fluid,
setting, and similar
should
be
included:
type
o
f
linings,
information. These will be valuable
fluid, tobalance-bar
and similar
facts
determine setting,
what setting
caused
information.
These will be valuable
what
to happen.
facts
to determine
what on
setting
caused
Recorded
comments
brake
perwhat
to
happen.
formance versus temperatures are
Recorded
comments
brake pervital.
If you are
recordingo ndeceleration
formance
versus
temperatures
are
rates, make
a form
for that, too.
you are recording
deceleration
vital. I f test-data
These
forms can
also be
rates,
make
a to
form
for car
that,
too.
useful at
a race
record
settings
These
test-data
forms
can
also
be
and compare them to actual performuseful
a race
ance
onatthe
track.to record car settings
and
compare
them
to actual
ListsYou can
never
bringperformenough
ance
on
the
track.
tools or parts to a test session. If you
Lists-You
cantool
never
bring you
enough
leave
a part or
at home,
can
you
tools
or it's
parts
a test
session.
be sure
thetoone
you'll
need. IfMura part
or tool
at home, you can
leave
phy's Law
always
applies.
beMake
sure it's
the
one
you'll
need. Mand
ura list of tools, supplies
phy's Law always
instruments.
Addapplies.
to these lists anyMake
a list for
o f car
tools,
supplies and
thing
needed
maintenance
or
instruments.
Add
to
these
liststhings
anyrepair. Bring spare parts for
thing to
needed
car have
maintenance
or
likely
break.for
If you
room, also
repair.
Bring spare
parts
things
bring everything
that's
notforlikely
to
likely
break.to break. I f you have room, also
bring
everything
not likelyinto
to
Organize
parts that's
and supplies
break.
sturdy boxes and label them. This will
Organize
and supplies
into
make
taking parts
everything
much easier.
sturdy
boxes and
label one
them. pit
Thiscrew
will
If possible,
assign
make
taking
everything
much
easier.
member to keep track of things, and
If possible,
one pit after
crew
put
everything assign
back immediately
member
to keep track team
o f things,
and
use . A well-organized
is a must
putsuccessful
everythingtesting
back immediately
for
and racing. after
well-organized
team is sheets,
a must
use.
PutAyour
test plan, test-data
for
successful
testing
and
racing.
and parts and supplies lists into a notePutconsisting
your test plan,
test-data sheets,
book
of a three-ring
binder
and parts and supplies lists into a notebook consisting o f a three-ring binder
9.
10.
Set brake balance with wings adjusted to maximum downforce settings.
Wet down track, install rain tires, and balance brakes for wet.
HPBooks® BRAKE TESTING DATA SHEET Car _ _ _ Date _ _
1, Brake System Specification,
Date A, Balance-bar setting _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ __ _ _
1 . Brake System Specification.
B, Proportioning-valve setting _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ __
A. Balance-bar setting
C. Lining material: Brand _ _ ___ (Front) _ _ __ ___ (Rear)
HPBooksmBRAKE TESTING DATA SHEET Car
I
B. Proportioning-valve setting
D. Brake fluid : _______ Brand _ ______ Type
C. Lining material: Brand
(Front)
I
(Rear)
E, Rotor diameter & thickness: _ _ _ _ _ _ _ (Front) _ _ _ _ _ _ (Rear)
D. Brake fluid:
Brand T
y
p
e
F, Caliper brand & type: _ _ _ _ _ _ (Front) _ _ _ _
(Rear)
(Front)
(Rear)
2, Brake performance ,
& type:
(Front)
-(Rear)
F. Deceleration
Caliper brandreadings,
A.
2. Brake
performance.
B, Comments
on each test.
A.
Deceleration
readings.
C. Tires
used, size
and brand _ _ _ _ _ _ _ (Front) _______ (Rear)
E. Rotor diameter & thickness:
B.
on each
test._ __ __ (Weather) _ _ _ _ __ _ _
D, Comments
Road condition
_ __
C. Tires used, size and brand
(Front)
(Rear)
E, Comments _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
D. Road condition
(Weather)
3. Temperature testing,
I
I
(Front)
E. Comments
Maximum caliper
3. A.
Temperature
testing.temperature
(Front)
(Rear)
.
(Rear)
B, Maximum rotor-edge temperature
A. Maximum caliper temperature
C. Maximum hub temperature
I
I
B. Maximum rotor-edge temperature
D. Maximum lining temperature
C. Maximum hub temperature
I
I
1
E,
temperature
D. Maximum lining temperature
F, Comments _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ __
temperature
E.
testing.
4. Wear
(Front)
(Rear)
F. Comments
A, Lining
thickness-beginning
4. Wear
testing.
B, Lining thickness-ending
C, Wear (beginning/ending)
B. Lining thickness-ending
D, Test duration _ _ miles, _
C. Wear (beginning/ending)
1
I
(Front)
(Rear)
A. Lining thickness-beginning
_
laps, _ _ stops @ _ _ mph
E, Test track
Conditions _ _ _
D. Test duration -miles, -laps, -stops @ -mph
F. Comments _ _ _ _ _ __ _ _ _ _ __ _ _ _ _ _ _ _ _ _ __
E. Test track
Conditions -
F. Comments
or similar record-keeping system,
Bring a clipboard to write on, Keep
or
similar record-keeping
the notebook
with you during system.
all tests
Bringraces;
a clipboard
write on.
Keep
and
put all to
technical
informathe notebook with you during all tests
and races; put all technical informa-
I
tion in it. The notebook will becomeI
your "bible " after a year or so . Betion in test
it. The
will become
cause
datanotebook
is valuable,
make
your
after a year
so. Becopies"bible"
of everything
whenor you
'!et
cause test data is valuable, make
copies o f everything when you n_et
109
Pyrometer is used to measure brake temperature on open-wheel race car. This is difficult
on full-fendered cars. When checking temperature, quickly hold pyrometer probe firmly
against
rotor
until meter
needle
stops
rising. Peakontemperature
braking
cannot
be
pyrometer
is used
to measure
brake
temperature
open-wheelduring
race car.
This is
difficult
on
full-fendered
cars. When
checkingbecause
temperature,
quickly will
holdoccur.
pyrometer
probe firmly
measured
with hand-held
pyrometer
some cooling
Peak temperature
can
only rotor
be measured
withneedle
an on board
or temperature-indicating
label or
paints.
against
until meter
stopspyrometer,
rising. Peak
temperature during braking
cannot
be
measured with hand-held pyrometer because some cooling will occur. Peak temperature
can only be measured with an onboard pyrometer, or temperature-indicating label or paints.
Omega Engineering Inc. specializes in
temperature-measuring devices. Some of
their
paint and
Omegatemperature-indicating
Engineering Inc. Specializes
in
labels are shown here.devices.
Photo courtesy
temperature-measuring
Some of
Omegatemperature-indicating
Engineering.
their
paint and
labels are shown here. Photo courtesy
Omega Engineering.
0-800C (32-1472F) range. It is
useful for checking both tire and
(32-1472F)
range. It is
0-800C
brake temperatures.
The liquid-crystal
useful allows
for checking
tire ease
and
used with
display
it to be both
brake
temperatures.
The
liquid-crystal
in the sunlight. There are two
display
allows
it to
be for
usedtires
withand
easea
probes-a
sharp
one
in the
There are
flat
one sunlight.
for hard surfaces
suchtwo
as
probes-a
sharp oneI for
tiresrecomand a
brake components.
highly
flat
surfaces
suchserias
mendone
suchfor
an hard
instrument
for the
brake
components.
I
highly
recomous racer. I t can also be used fo r.
mend such
an instrument
the seriengine
tuning,
such asfor checking
ous racer.
It can
be used
for.
which
exhaust
pipe also
is running
hotter
engine
tuning,
such
as
checking
or cooler than the others.
which
exhaustwhen
pipe using
is running
hotter
Remember
a hand-held
or
cooler thanthat
the others.
pyrometer
the object being
Remember
whenrapidly.
using aTherefore,
hand-held
checked
will cool
pyrometer
that
the
object
it must be measured quickly being
after
checked
cool rapidly.isTherefore,
maximumwilltemperature
reached.
it
must be measured
quickly after
Unfortunately,
it is impossible
to
maximum
temperature
is reached.
measure the peak temperature
of an
Unfortunately,
is impossible
to
iron
brake rotorit with
a hand-held
measure
peak
of an
pyrometer.theBut
youtemperature
can come close
if
iron work
brake
rotor with a hand-held
you
quickly.
pyrometer. ButIndicators-You
you can come close
Temperature
mayif
you
work
quickly.
find that it's easier to use temperature
Temperature
Indicators
may
indicators rather
than a -You
pyrometer.
find that
easiertypes
to useof temperature
There
areit's
several
indicators.
rather changing
than a color
pyrometer.
indicators
Some
are paint,
when
There
are
several
types
of
indicators.
they reach a certain temperature
. DifSome are
color atwhen
ferent
colorpaint,
paintschanging
change color
difthey reach
a certain temperature.
Different
temperatures,
so by using variferent
color the
paints
change
color at difous colors,
peak
temperature
can
ferent
temperatures,
so
by
using varibe found.
ous
colors,
peak temperature can
One
line the
of temperature-indicating
be found.
paint
is available from Weevil Ltd . in
One line
of Tempil
temperature-indicating
Europe.
Also,
has a complete
paint
is
available
from
Weevil includLtd. in
line of temperature
indicators,
ing Tempilaq temperature-indicating
paint. Another is sold by Tilton
ing TempilaqUsually,
temperature-indicating
Engineering.
these paints are
paint.
Another
is soldofby
the Tilton
brake
applied to the periphery
Engineering.
Usually,
these
paints
are
rotor. They can be used on the caliper
applied
to the periphery of the brake
body as well.
rotor.
They temperature
can be used on
the caliper
Another
indicator
is a
body
as
well.
stick-on label. These are sold by
Another
temperature
is a
Tempil
(Tempilabel)
andindicator
Omega Enstick-on
label.
These
are
sold
by
gineering Products (Omega Label),
Tempil
(Tempilabel) and Omega Enrespectively.
gineering
Products (Omega
Label),
These adhesive-backed
labels
have
respectively.
white spots that turn black at increThese temperatures
adhesive-backed
have
mental
, aslabels
indicated
white
that turn
black
at on
increnext tospots
each spot:
If some
spots
the
mental
as do
indicated
label turntemperatures,
black and others
not , a
next
each spot: If was
somereached
spots on the
bepeak totemperature
label
turn
black
and
others
not, a
tween the values of the dohighestpeak
temperature
wasandreached
betemperature
black spot
the followtween
thespot.
values
theturnhighestwhite
If all of
spots
black ,
ing
temperature
black spot andonthethefollowthe
highest temperature
label
ing
white
spot.
spotsa turn
case,black,
you
was exceeded. IfInallsuch
the
temperature
on the label
needhighest
the next
higher-temperature
was
case,black
you,
label exceeded.
available. IfInnosuch
spot aturns
need
the
next
higher-temperature
the temperature of the lowest spot
label
available.
If In
no this
spotcase,
turnsgoblack,
reached.
to a
was not
the temperature oflabel.
the lowest spot
lower-temperature
was
not areached.
In this
go to a
Have
wide range
of case,
temperature
lower-temperature
label.
indicators for your first test. You
Have a have
wide no
range
temperature
idea ofwhat
the temprobably
indicators
for your
test.
perature ranges
will be.first
Once
youYou
get
probably
have
no
idea
what
the
temsome experience, you'll know which
perature
ranges
will be.toOnce
temperature
indicators
use . you get
some
experience,
which
If you
want to be you'll
able to know
get accurate
temperature
indicators
to use.
peak and non-peak
temperature
readIf you
want stopping
to be able the
to get
accurate
ings
without
car,
you ' ll
peak
non-peakpyrometel;
temperature
readneed and
a remote
a multi-
home. Store the copies somewhere
other than in the notebook. Notehome. get
Storelost,
the particularly
copies somewhere
books
at the
other than in the notebook. Noteraces.
books
get bring
lost, particularly
at the
Finally,
as many qualified
races.
helpers as possi ble, and all the equipFinally,
bring you
as ' llmany
ment
you think
need . qualified
Include
helpers
as
possible,
and
all the equipthe required safety equipment.
Even
ment
Include
if you you
are think
testingyou'll
in a need.
straight
line,
the
helmetequipment.
and drivingEven
suit.
bringrequired
a crash safety
if you
testing
a straight line,
never
be tooincareful.
You
canare
bring a crash helmet and driving suit.
You
can never be too careful.
BRAKE-TESTING
INSTR UMENTS
BRAKE-TESTING
Certain instruments are needed to
INSTRUMENTS
get
maximum benefit from a test
Certain Of
instruments
are needed to
session.
primary importance
is
get
benefit
a test
temperature.
It can from
be measured
brakemaximum
session.
Of aprimary
importance
is
with either
hand-held
pyrometer,
brake
temperature.
It
can
be
measured
remote pyrometer or with temperature
with
either
a hand-held
pyrometer,
indicators
placed
on the brake
.
remote
pyrometer pyrometer
or with temperature
Pyrometer-The
is a speindicators
placed on Itthehas
brake.
thermometer.
a probe that
cial
Pyrometer-The
pyrometer
is aTemspecan
be placed against
an object.
cial
thermometer.
It
has
a
probe
perature is then read from a meter.that
A
can
be placed
against anused
object.
Tempyrometer
is commonly
to measperature
is then
from a meter.
A
ure
race-car
tire read
temperatures.
It can
pyrometer
is
commonly
used
to
measalso be used to measure brake temure
race-car
tirethetemperatures.
can
perature
up to
limit of the It
meter
also beThe
used
to measure brake
temscale.
pyrometer-probe
tip must
perature
to contact
the limitwith
of the
meter
be
held inupfirm
the object
scale.
The
pyrometer-probe
tip
into
being checked so heat can soakmust
be
in firm
contact
with stabilizes,
the object
theheld
probe.
When
the meter
being
checked
so heat
can soak into
the
reading
is taken
and recorded.
theAnprobe.
Whendual-purpose
the meter stabilizes,
excellent
pyromethe
taken and sold
recorded.
ter reading
is AP's is
CP-2650-8
by Tilton
An excellentThis
dual-purpose
pyromeEngineering.
instrument
has a
ter is AP's CP-2650-8 sold by Tilton
Engineering. This instrument has a
110
Europe. Also, Tempil has a complete
line of temperature indicators, includ-
ings without stopping the car, you'll
need a remote pyrometel; a mirlti-
ap:
RACinG
Excellent temperature indicators are
manufactured by Tempil. Tempil's Tempilaq
paint
meltstemperature
when heated
to rated
Excellent
indicators
are
temperature. Tempilabel
spots turn
black
manufactured
by Tempil. Tempil's
Tempilaq
when heated
rated temperature.
paint
melts towhen
heated to Photo
rated
by Tom Monroe.
temperature.
Ternpilabel spots turn black
when heated to rated temperature. Photo
by Tom Monroe.
position switch and thermocouples to
put in contact with the test objects. A
position
thermocouples
to
full lineswirch
of and
remote
temperatureput
in
contact
with
the
test
objects.
A
measuring equipment, including therfull
line ofandremote
mocouples
leads, temperatureis available
measuring
equipment,
including
from
Omega
Engineering
Productsther.
mocouples
and
leads,
is available
Their 12-volt model 650K
digitalfrom
Omega
Engineering
readout
pyrometers
areProducts.
relatively
Their 12-volt
digitalcompact
and aremodel
easy 650K
to read
. All
readout
pyrometers
are
relatively
digital-readout pyrometers require excompact
and are
easy toseries-7000
read. All
ternal power.
Omega's
digital-readout pyrometers
pyrometers require
exdial-readout
are selfternal
power.
Omega's
powered,
compact
and lessseries-7000
expensive
dial-readout
pyrometers
areto selfthan digitals, but
not as easy
read
powered,
compact
and
less
expensive
accura tely.
than
digitals, butElectronic
not as easySystems'
to read
Nationwide
accurately.II digital-readout pyrometer
Slimline
Nationwide
Electronic12-volt,
Systems'
IDT-7726
is compact,
d-c
I1
digital-readout
pyrometer
Slimline
powered, and is easy to read. It reIDT-7726
is compact, d-c
12-volt,
d-c
quires a 100-0193-01
isolator
powered,
andsure
is easy
to read.type-K
It remodule
. Be
to specify
quires
a 100-0193-01
d-c isolator
thermocouples
when ordering.
Also
module.
Be
sure
to
specify
type-K
specify whether you want a pyrometer
thermocouples
when ordering.
Also
that displays temperature
in Fahrenspecify
whether you want a pyrometer
heit or Centigrade.
that displays temperature
in FahrenThermocouple
Installation
- Therheit
or
Centigrade.
mocouple attachment is important.
Thermocouple
-Ther-be
The
thermocoupleInstallation
junction must
mocouple
important.
in contact attachment
with the istest
object.
The
thermocouple
must
be
Otherwise
, readings junction
will be low.
Highin
contact
with
the
test
object.
temperature epoxy works well for atOtherwise,
readings will betolow.
Hightaching thermocouples
calipers.
temperature
epoxy
works
well
for
atThermocouples can be pinched under
taching
thermocouples
to
calipers.
the head of a screw. Or, silver solderThermocouples
be pinched
under
ing works well oncan
some
metals. Whatthe head
solderever
you of
usea, screw.
be sureOr,
thesilver
attachme
nt
ing worksinsulate
well on some
Whatdoesn't
the metals.
thermocouple
ever you
use,object.
be sure the attachment
from
the test
doesn't
insulate
the isthermocouple
Rotor temperature
difficult to
from the test
measure
withobject.
a thermocouple. The
Rotor temperature is difficult to
measure with a thermocouple. The
As with other temperature-indicating paints, AP Racing's indicators can be used to check
rotor or brake-drum temperature. Temperature indicators will tell you the highest tempera··
ture
reached,
you use the right range paints,
of paints.
Racing. can be used to check
As with
other iftemperature-indicating
APCourtesy
Racing's AP
indicators
rotor or brake-drum temperature. Temperature indicators will tell you the highest temperature reached, if you use the right range of paints. Courtesy AP Racing.
CB
DRILL RO 3 1
3 103 <i561
'.':..
iPIc lrC'CRC
0 13 181 0C LOWER
TUBE OPEN I D
GR IND
TO
18 f:!. IS ]
.41>.0
=-.::..:.:....----'''---'
MA X EI[rOR[
P L ACING 11\
L' ~ I N C.
~-008 .... ?(l·:' luiC :'~·5
J ~. LE R
r,O:;,-, ',(," I;:F C.C[
Drawings show how to install thermocouple plugs in disc and drum-brake linings so brake
temperatures can be monitored while running. For this purpose, you can make your own
type-K thermocouples
twisting
chromel and
alumel
and linings
silver soldering
Drawings
show how to by
install
thermocouple
plugs
in discwire
andtogether
drum-brake
so brake
the twisted end
a copper
tube.
You running.
can get For
this this
wirepurpose,
from companies
Omega
temperatures
canin be
monitored
while
you can such
makeas
your
own
Engineering.
Reprinted with
permission
© 1984
Automotive
type-K thermocouples
by twisting
chrome1
andSociety
alumel of
wire
together Engineers,
and silver Inc.
soldering
the twisted end in a copper tube. You can get this wire from companies such as Omega
thermocouples
must
be
silverin the lining
material
close to Inc.
the fricEngineering.
Reprinted
with permission
0 1984 Society
of Automotive
Engineers,
soldered or crimped into a small Oat
thermocouples
be springsilverprobe, insulated must
and lightly
soldered
or
crimped
into
a
small
flat
loaded against the rotor friction
probe,
insulated
and
lightly
springsurface. Brake manufacturers who
loaded against
the rotor with
friction
measure
rotor temperature
rubsurface.
Brake manufacturers
who
bing thermocouples
make their own;
measure
rotor
with rubthey are not
for temperature
sale.
bing
thermocouples
make
their
A practical alternative used by own;
most
they
are not brake
for sale.
American
and lining manuA practical
used by most
facturers
is to alternative
install the thermocouple
American brake and lining manufacturers is to install the thermocouple
tion surface. Temperatures measured
in
closelower
to the than
fricin the
thislining
way material
are slightly
tion
actualsurface.
rotor Temperatures
temperature . measured
However,
in
way are
slightly lower
the this
difference
is consistent
and thethan
inactual
rotor
temperature.
However,
stallation is much easier and
more
the difference
and the indurable
thanis consistent
the
rotor-rubbing
stallation
is much easier and more
thermocouples.
durable
than the end
rotor-rubbing
The thermocouple
is stripped
thermocouples.
back approximately 0.500 in ., twisted ,
The thermocouple
is stripped
inserted
into
a end
3/16-in.-long,
back approximately 0.500 in., twisted,
inserted
into
a
3116-in.-long,
111
HOLE MUST BE
OPE: ~
A r..O FRE E
>R O'..', SOLD ER SO .0.5 NC T TO
/
.I
,T STRlcr FLUI O FLOW WHEN
BLEE D' NG
*OLE MUST BE WEll ClliD FREE
FROM SOLDER SO 1 5 N O T TO
RESTRICT FLUtD FLOW W H E N
i
I
L
L5·cvE~
SO LDER
SECURELY
SECTI ON A- A
GRIN D O ~ F EXCE SS SOLDER
F LUS H WIT H SU RFACE SHOWN
SECURELY
SECTION A-A
RIND OFF EXCESS SOLDER
SURFACE SHOWN thermocouple for measuring brakeFLUSW WITH
Drawing shows
bleed-screw
fluid temperature. The screw is first drilled through, then twisted
thermocouple
is bleed-screw
silver-soldered
in place. Reprinted
with permisDrawing shows
thermocouple
for measuring
brakesion ©
1984 Society
of screw
Automotive
Engineers,
Inc.
fluid
temperature.
The
is first
drilled through,
then twisted
thermocouple is silver-soldered in place. Reprinted with permission 0 1984 Society of Automotive Engineers, Inc.
1/8-in.-OD X 0.086-in.-IO copper
tube and silver-soldered in place to
118-in.-OD
copper
form
a plug. XThe0.086-in.-ID
plug is installed
in
tube
and
silver-soldered
in
place
to
the friction material. Typical disc- and
form
a plug. installations
The plug isare
installed
drum-lining
shown in
in
the
friction material.
the drawing,
page Ill.Typical disc- and
drum-lining
are shown
in
If the pluginstallations
hole is drilled
through
the drawing,
11with
1 . a number-31
the
lining andpage
shoe
If the plug
hole
drilled
(O.IOO-inJ
drill,
theisplug
can through
be reset
the lining
andtheshoe
withwears
a number-31
easily
when
lining
down to
(0.100-in.)
drill, the
plugthermocouple
can be reset
the
plug surface.
If the
easily
when
the
lining
wears
to
plug is not reset, readings willdown
fluctuthe
plug
surface.
If
the
thermocouple
ate
between
rotor and
lining
plug
is not reset, readings will fluctutemperature.
ateThebetween
lining
drawing atrotor
top of and
page shows
temperature.
how to install a thermocouple on a
Thescrew
drawing
at top of page
shows
bleed
for measuring
brake-fluid
how
to installin a athermocouple
on a
temperature
caliper or wheel
bleed screw for measuring brake-fluid
cylinder.
temperature
in a caliper
or wheel
With a mUlti-positio
n switch,
many
cylinder.
thermocouples can be connected to
a multi-position
theWith
pyrometer
so they switch,
can be many
read
thermocouples When
can berunning
connected
to
individually.
therthe
pyrometer
so
they
can
be
read
mocouple leads from the brakes to the
individually.
Whento the
running
chassis,
band them
flexibletherhymocouple
leads
from
the brakes
to the
draulic line
with
plenty
of slack
so
chassis,
them
to the
hythey donband
' t break
when
the flexible
suspension
draulic line with plenty of slack so
moves.
they
don't Gage-Brake-tluid
break when the suspension
Pressure
pressure
moves.
can be measured with a simple presPressure
sure
gage .Gage-Brake-fluid
Marsh Instrument pressure
Compacan
be
measured
with
simple presny's 14878 gage has
lowa displacement
sure isgage.
Compaand
usedMarsh
widely.Instrument
Another pressure
ny's J4878
gageavailable
has low displacement
gage
is also
from Hurst
and is used widely.
Another pressure
Performance
.
gage
is
also
available
Hurst
used in
the
A pressure gage can befrom
Performance.
shop or at the track . If used at the
A pressure
canthe
bedriver
used or
in obthe
track,
mount itgage
where
shop orcan
at see
the ittrack.
usedtheatgage
the
server
easily.If Fill
track, mount it where the driver or observer
can see it easily. Fill the gage
112
U-tube decelerometer is made by AM MCO Tools Inc . It's calibratin feet per second per second (ft/sec/sec) rather than g's (1 gI
=
32.2 ftlsec/sec)
. Instrument
reads
down Tools
scale Inc.
for deceleration
U-tube
decelerometer
is made by
AMMCO
It's calibratandinup
scale
acceleration.
Deceleration
scale
is used
brake
(1 g
ed
feet
perfor
second
per second
(ft/sec/sec)
rather
thanfor
g's
testing;
accelerationlnstrument
scale can be
useddown
for engine
and shift= 32.2 ft/sec/sec).
reads
scale tuning
for deceleration
pointupdetermination.
Instrument
can be mounted
to windshield
and
scale for acceleration.
Deceleration
scale is used
for brake
with suction
cups or scale
bolted
to be
instrument
panel. tuning
Photo and
courtesy
testing;
acceleration
can
used for engine
shiftAMMCO
Tools Inc.
point
determination.
lnstrument can be mounted to windshield
Ied
with suction cups or bolted to instrument panel. Photo courtesy
AMMCO Tools Inc.
with fluid before mounting it. And
always put a valve at the gage so it can
with
fluid
beforenot
mounting
be shut
off when
in use andit.soAnd
the
it can
always won't
put a valve
the gage
gage
lose at its
bleedso when
be shut offThe
when
nottointhe
usegage
and can
so the
removed.
line
be
gage
won't
lose
its
bleed
bled by loosening the valve jamwhen
nut
removed.
The line
to the
gage can
be
while
applying
slight
pressure
to the
bled bypedal.
loosening
valvebegins
jam nut
brake
Whenthefluid
to
while
applying slight
pressure
to the
leak, retighten
the nut
to complete
brake
pedal.. When fluid begins to
the
bleeding
leak,
retighten
the nut relates
to complete
pedal
Hydraulic pressure
the bleeding.
effort
to actua l force on the brakes.
Hydraulic
pressure
relates pedal
When
used with
a decelerometer,
the
effort
to
actual
force
on
pressure gage can be usedtheto brakes.
deterWhen
used with a decelerometer,
mine brake-system
effective ness , the
or
pressure
gage can
be versus
used to vehicle
deterto plot pedal
effort
mine brake-system effectiveness, or
deceleration.
to plot pedal effort
vehicle
Camera-Photos
are a versus
good source
of
deceleration.
test data. Use a camera that provides
Camera-Photos
are a good
of
instant prints. Photograp
h thesource
car just
testthe
data.
Useslams
a camera
thatbrakes
provides
as
driver
on the
at a
instant prints.
Photograph
the car
prescribed
braking
point. You
mayjust
be
as
the
driver
slams
on
the
brakes
able to detect whether the front or at
thea
prescribed
be
rear wheelsbraking
lock uppoint.
first.You
It's may
someable
detecttowhether
thelocks
frontuporfirst
the
timestotough
tell which
rear
wheels lockTouphelp,
first.paint
It's asomeby observation.
large
times
tough
to
tell
which
locks
first
X on the wheels and tires with up
waterby observation.
To help, paint a large
soluble
white paint.
X Even
on the better
wheels and
with awaterthantires
using
still
soluble
white
paint.
camera to detect brake lockup is a
Evencamera.
better It than
still
video
can beusing
playeda back
camera
to detect
immediately
after brake
makinglockup
a shot.is Aa
video
be be
played
video camera.
camera It
cancanalso
usedback
to
immediately
after
making
a
shot. Aa
record instruments in the car during
video Tocamera
be must
used be
to
stop.
do this,can
thealso
camera
record
instruments
during
mounted
securely in
in the
a car
bracke
t. Aa
stop. To do this, the camera must be
mounted securely in a bracket. A
camera is an accura te data recorder-much more so than a person
camera
is an accurate data reusing his eyes.
corder-much
more decelerometer
so than a person
Decelerometer-A
is
using his for
eyes.
valuable
testing the stopping capaDecelerorneter-A
decelerometer
is
bility of a car. One can
be as simple as
valuable
for
testing
the
stopping
capatoppling blocks or as complex as a
bility
of a car.
One can
as simple as
recording
g-meter.
See be
accompanying
toppling blocks
as complex
and or
photos.
Buy the as
besta
illustration
recording
g-meler.
See
accompanying
decelerometer you can afford. Use the
illustration
and inphotos.
the besta
Tapley
meter
a car Buy
in which
decelerometer
you along
can afford.
Use the
passenger can ride
and observe.
Tapley
in a can
car in
whichthea
Perhaps meter
a camera
replace
passenger
ridecare
alongto and
passenger can
if you·
rig observe.
one up .
Perhaps
a
camera
can
replace
the
The Tapley meter indicates actual
passenger if you
rig one
deceleration
ratescareasto the
car up.
is
The
Tapley meter indicates actual
stopping.
deceleration
the car7350
is
AMMCO rates
Tools' as model
stopping.
U-tube decelerometer is easy to install
AMMCO
Tools' well.model
7350
and
adj ust. It works
This instruU-tube
decelerometer
is
easy
to
install
ment is used widely by the American
and
adjust.
well.
This instruautomob
ile Itanworks
d brake
industries,
and
ment
is
used
widely
by
the
American
many state vehicle-inspection
stations
automobile
in the U.S. and brake industries, and
many
vehicle-inspection
The state
simplest
decelerometerstations
is the
in
the
U.S.
toppling blocks. Set up a tray with recThe simplest
decelerometer
is the
tangular
blocks as
shown. The blocks
toppling
Seta up
a tray
recare
lined blocks.
up along
ledge
on with
the tray.
tangulartheblocks
as shown.
The blocks
When
car stops,
the taller
blocks
are
lined
up atalong
ledge on the rates
tray.
topple
over
lowera deceleration
When
the
car
stops,
the
taller
blocks
than the shorter ones. Deceleration
toppleis over
at lower
rate
between
the deceleration
tallest block rates
that
than
the
shorter
ones.
Deceleration
toppled and the shortes
t one that
rate is between the tallest block that
didn't.
toppled
andblocks
the shortest
that
Toppling
can be one
knocked
didn't.by bumps or vi brations, so make
over
Toppling blocks can be knocked
over by bumps or vibrations, so make
Forward
Motion
of
Car
Forward
X1 =~ = 067
H1
1.5
. 9
X2=~=090
H2
1.0
.
9
Motion
of Car
0.9
x3 - 0.8 0.679
1.339
x2 =-=
0.90g
HI
1.5
H1 1.0
H3 0.6
Dimensions of toppling blocks determine maximum deceleration they can take before
toppling. Blocks dimensions don't have to be precise as long as they are square. Measure
height
and width,
of each
block determine
and calculate
its toppling
deceleration
as shown.
Each
Dimensions
of toppling
blocks
maximum
deceleration
they can
take before
block is positioned
against adon't
thin have
ledgetoonbea precise
flat trayastolong
allow
to topple
whenMeasure
the car
toppling.
Blocks dimensions
as it
they
are square.
decelerates.
Tray can
be angled
toand
compensate
angle.
height and width,
of each
block
calculatefor
itsvehicle-dive
toppling deceleration
as shown. Each
block is positioned against a thin ledge on a flat tray to allow it to topple when the car
decelerates. Tray can be angled to compensate for vehicle-dive angle.
XI
=-
=
at least three runs to verify the
results. If you don ' t get consistent reat least
runs definitely
to verify work
the
sults
and three
the brakes
results.
If you
rethe same
eachdon't
time,get
tryconsistent
another test
sults
and
the
brakes
definitely
work
method. However, be aware that varithe same
time,
ations
in each
results
cantrybeanother
caused test
by
method.
However, be
aware that
varibrake-temperature
changes
or other
ations in results can be caused by
changes.
brake-temperature
changes or other
Tire-Test
Instruments-Don't
forchanges.
get that tire grip affects braking. Thus,
Tire-Test
Instruments-Don't
forto test brakes,
also test the tires. You
get
tiretogrip
affectstires
braking.
Thus,
maythat
wish
try other
during
the
to
testbalance
the tires.
testtest
andbrakes,
changealso
brake
to You
suit
may
wish to trytires.
otherBring
tires during
the
the different
along the
test and
change
brake balance
to suit
extra
tires
and instruments
needed
to
the
tires.
Bring and
along
the
test t1:different
em. A tire
pyrometer
an airextra
tiresgage
andare
instruments
needed to
pressure
the usual minimum
test
tkem.
A
tire
pyrometer
and
an airinstruments for tire testing .
pressure
gage Gages-One
are the usuallast
minimum
Air-Pressure
instruinstruments
for tire
ment to consider
is testing.
a gage for measurAir-Pressure
Gages-One
last instruing low air pressures in brake-cooling
ment
to
consider
is
a
gage
for
air ducts and at the exterior measursurfaces
ing the
low car.
air pressures
in brake-cooling
of
These pressures
are not
air
ducts and
exterior
surfaces
measured
in at
psi,thebut
in inches
of
of
the (in.Hp).
car. These
are not
water
Forpressures
comparison,
the
measured
butwater
in inches
pressure 27inin. psi,
below
surface of
is
water
(in.H,0).
For comparison, the
27 in.Hp,
or 1 psi.
pressure
below water
is
Gages 27
for in.
measuring
low surface
pressures
27
in.H20,
or
1
psi.
are very useful for developing brake
Gages
for measuring low
pressures
ducts
, engine-induction
ducts,
waterare very
usefulairfor
developing
brake
and
oil-cooler
ducts,
driver-cooling
ducts,
engine-induction
ducts,
waterducts and even car body-surface
and oil-cooler air
ducts,manometers
driver-cooling
aerodynamics.
U-tube
are
ducts
and
even
car
body-surface
used often for measuring
low air
aerodynamics.
manometers
pressures, but U-tube
a dial gage
is easierare
to
used
often
for
measuring
low air
read and install in a car.
pressures,
but a dial gage
is easier
to
2010
MagneDwyer Instruments'
read
helic and
gageinstall
readsinupa car.
to 10 in. Hp . This
Dwyer
2010
small
5-in.Instruments'
round gage can
be Magnemount10
in.
H,O. This
helic
gage
reads
up
to
ed temporarily on an instrument
small
gage of
canthe
be steering
mountpanel 5-in.
or in round
the center
ed temporarily on an instrument
panel or in the center of the steering
wheel of a cramped formula car.
Dwyer also carries all types of
wheel
of a cramped formula car.
manometers.
Dwyer also carries all types of
manometers.
BRAKE-PERFORMANCE TESTS
There are a few basic-performance
BRAKE-PERFORMANCE
TESTS
tests
that can be made without
much
Thereorare
a few basic-performance
trouble
expensive
instruments. All
tests
can beshould
made without
brakethat
systems
deliver much
minitrouble
or
expensive
instruments.
All
mum performance regardless of the
brake
car
type.systems should deliver minimum
performance
regardless of the
To run
a basic brake-performance
car
type.
test, pick a distance between stops,
To as
run0.4a mile,
basic or
brake-performance
such
a time between
test, pick
between
stops,
stops,
suchaasdistance
one minute.
Accelerate
such asrest
0.4atmile,
or a time
between
from
wide-open
throttle
to
stops,best
suchspeed-to
as one minute.
your
55 mphAccelerate
for a road
from
wide-open
throttlerace
to
car orrest
80 atmph
for a small
your
best maintain
speed-to that
55 mph
foruntil
a roadit
car-and
speed
car
or for
80 the
mph
a Distance
small race
is time
nextfor
stop.
or
car-and
maintain
that
speed
until toit
time between stops can be adjusted
is
time fororthedecrease
next stop.
Distance
or
increase
test
severi ty.
time
stops firmly
can be so
adjusted
to
the brakes
the car
Applybetween
increaserapidly
or decrease
severity.
stops
without test
locking
the
Apply the
brakes
so the
car
wheels.
After
the firmly
car stops,
record
stops
rapidly
without
locking
the
some comments on your data sheet:
wheels.
carwheels
stops,lock?
record
front the
or rear
• Did theAfter
some
on yourordata
• Didcomments
the car swerve
pullsheet:
to the
Did the front or rear wheels lock?
side?
Did there
the car
swerve inor deceleration
pull to the
a change
• Was
side?
as
the car slowed?
change
in deceleration
Was there
• Were
there anoises
from
the brakes?
as
the
car
slowed?
• Was the pedal firm?
there
noises
fromor
thewas
brakes?
• Were
Was the
stop
smooth
there
the pedal firm?
anyWas
vibration?
Was
the stop repeat
smooth the
or was
Immediately
test there
and
any
vibration?
record your comments. Do this until
Immediately
repeat
the performtest and
you
notice a change
in brake
recordoryour
this have
until
ance
untilcomments.
about tenD ostops
you
notice
a
change
in
brake
performbeen completed . It's important to be
ance or until
ten so
stops
consistent
with about
each stop
yourhave
test
been completed. It's important to be
consistent with each stop so your test
Dwyer's 2010 magnehelic gage is easier
to install and use than manometer for
measuring
air pressure.
Dwyer's 2010
magnehelic gage is easier
to install and use than manometer for
measuring air pressure.
is repeatable for later comparisons.
After you finish testing, carefully
is
repeatable
for where
later comparisons.
touch
the wheel
it bolts on.
After you
finish testing,
carefully
Record
the following
comments:
touch
the wheel
where
it about
bolts on.
• Are front
and rear
wheels
the
Record
the following comments:
same
temperature?
rearthe
wheels
aboutBoth
the
• Are
Can front
you and
smell
brakes?
same temperature?
sets?
youblack
smell
Both
dustthe
on brakes?
the outside
of
• Can
Is there
sets?
the wheels?
black
dust on
the outside
of
• Is
Is there
grease
leaking
from
the front
the
wheels?
hubs?
Is grease
leaking
from
the front
The
comments
you've
recorded
are
hubs?
for comparison with other cars or with
Thetests.
comments
recorded beare
other
There you've
are no numbers,
for
comparison
withusing
otherinstruments.
cars or with
cause
you are not
other
tests.you
There
no numbers,
beHowever,
canare
record
your comcause
you
are
not
using
instruments.
ments about specific parts of the
However,
youperformance.
can record your
combrake-system
The effect
ments
about specific
parts
of the
of
brake-system.
changes
should
be
brake-system
performance.
Thehow
effect
of learning
to
recorded as part
of
brake-system.
should be
maintain
and adjustchanges
a brake system.
recorded
as part ofperformance
learning howtest
to
The overall
maintainbeand
adjust abybrake
system.
should
followed
some
work on
overall
performance
test
theThe
brakes.
Usually,
there'll be one
should
be
followed
by
some
work
on
aspect of performance that you wish
the
brakes.
Usually,
there'll
be
one
to improve. See the trouble-shooting
aspect of
performance
that12you
section
following
Chapter
for wish
sugto improve.
gestions
on See
howthe
to trouble-shooting
correct specific
section
following Chapter 12 for sugproblems.
gestions on how to correct specific
problems.TESTING
TRACK
A race car or high-performance
TRACK
road
carTESTING
should be track tested .
A
race
car time
or high-performance
However, the
and effort that
road
car testing
shouldat abe
goes into
tracktrack
is nottested.
worth
However,
the timetransportation
and effort that
it for the ordinary
car.
goes
into testing
a track
is not worth
Performance
testsatjust
described
done
it for
the ordinary
on
a country
road transportation
should suffice.car.
In
Performance
just described
done
this section, tests
I discuss
track testing
on a country
roadtheshould
suffice.
In
highest
possible
aimed
at getting
this
section,
I
discuss
track
testing
performance from a brake system.
aimed at getting the highest possible
performance from a brake system. 113
Pushrod
Pushrod
Pushrod
Balance-Bar
Adjuster
Balance-Bar
Measure lining thickness with dial caliper
or micrometer before and after each test
session
determine
wear
Brake
Measure to
lining
thickness
with rate.
dial caliper
wear
can be related
toand
number
stops
or
or
micrometer
before
afterofeach
test
laps; particularly
important
session
to determine
wear for
rate.planning
Brake
strategy
racing.
Be sure
wear
canfor
be long-distance
related t o number
of stops
or
to
measure
pads in same
place for
eachplanning
time.
laps;
particularly
important
strategy for long-distance racing. Be sure
to measure pads in same place each time.
-
Torque
Force
Wrench
Position A
Torque
Wrench
Position A
Torque Wrench
Position B
.- ~.
o r---
o
.
o~
I
(!)
Force
Center of Wheel
Force
Wheel
Lug
Nut
Center of Wheel
w heel Lug Nut
To measure torque about wheel center, put
torque wrench in position B. Wrench in position
A willtorque
read about
low because
distance
To
measure
wheel center,
put
from wrench
to wheel
center
is
torque
wrench handle
in position
B. Wrench
in pogreater
length
wrench.
Don't
sition A than
will read
low ofbecause
distance
exceed
torque capacity
lug nutscenter
or bolts.
from wrench
handle toof wheel
is
greater than length of wrench. Don't
exceed torque capacity of lug nuts or bolts.
Locked wheels is indicated by the smoke.
Excessive wheel locking can flat-spot
tires,
testing
Locked making
wheels is brake-balance
indicated by the smoke.
expensive.
takes locking
a sensitive
and
Excessive Itwheel
can driver
flat-spot
careful
observation
to keep from testing
ruining
tires,
making brake-balance
tires.
expensive. I t takes a sensitive driver and
careful observation to keep from ruining
tires.
114
\.'-..--Jr--1
I
I
o
o
I ~ Reference
r-
Distance
When making brake-balance changes with a balance bar, make a reference measurement
so you know where you started. With this measurement, you can quickly return to your
starting
balance,
if required. changes with a balance bar, make a reference measurement
When
making
brake-balance
so you know where you started. With this measurement, you can quickly return t o your
starting
balance, if required.
Recommended
track tests are as
If you are unfamiliar with the race
follows:
Recommendedadjustment.
track tests are as
• Brake-balance
follows:
• Deceleration.
Brake-balance adjustment.
• Effectiveness.
Deceleration.measurements.
• Temperature
Effectiveness.comparisons.
• Brake-lining
Temperature
measurements.
Lining Thickness-Before
you start
Brake-lining
testing,
check comparisons.
brake lining thickness.
Lining Thickness-Before
you their
start
Remove
the linings and measure
testing,
check
brake
lining
thickness.
thicknesses with a micrometer. It's
Remove
the alinings
andcaliper.
measure
their
OK
to use
vernier
Record
thicknesses
a micrometer.
It's
on your data
each
lining with
thickness
OK
to
use
a
vernier
caliper.
Record
sheets. Also indicate where on the
each lining
thickness onwasyour
data
lining
each measurement
taken.
sheets.
Also
indicate
where
on
so
Disc-brake pads wear on a taper,the
lining eachthem
measurement
was taken.
measure
in the middle
and at
Disc-brake
pads wear
on a taper,linso
each
corner. Measure
drum-brake
measure
them
in
the
middle
and
at
ings at each corner and at the inside
each
corner.
Measure
drum-brake
linand outside edges of the center. Measings the
at each
corner and
at the of
inside
ure
combined
thickness
the
and
outside
edges
of
the
center.
Measlining and shoe plate. Subtract shoeure the
combined
of the
plate
thickness
to get thickness
lining thickness.
lining
and
shoe
plate.
Subtract
shoeThe purpose of these measuremen
ts
plate
thickness
get lining
is
to check
for to
lining
wear. thickness.
By recordof these measurements
ingThe
thepurpose
total number
of hard stops
is
to
check
for
wear.
By recordduring testing, lining
you can
calculate
the
ing the total
number
of hard
amount
of wear
per stop.
Youstops
can
during
testing, about
you can
calculate
the
then calculate
how
long your
amount
of
wear
per
stop.
You
can
brake linings will last.
then
aboutthehow
longareyour
Brakecalculate
Balance-If
linings
not
brake
linings
will
last.
bedded in, do it before testing. This
Brakealso
Balance-If
are and
not
will
warm upthe
thelinings
engine
bedded
in,
do
it
before
testing.
This
chassis. Check page 40 for details
will also
upbrakes.
the engine and
about
how warm
to bed in
chassis.
Check
page
for car,
details
If you are testing 40
a race
it
about how
bedadjustable
in brakes.balance bar.
should
havetoan
a race
car, init
you are
A Ifbalance
bar testing
is usually
mounted
should
have
an
adjustable
balance
bar.
the pedal and is adjusted from one
A balance
bar is ausually
mounted
in
end
by loosening
jam nut
and turnthe the
pedal
and aisscrewdriver.
adjusted from one
ing
bar with
end by loosening a jam nut and turning the bar with a screwdriver.
car, you may not know where to set
you are bar.
unfamiliar
with the
theIf balance
Start setting
it at race
the
car,
you
may
not
know
where
to seta
center of its adjustment and perform
the balance
bar. Starttest.
setting
at the
simple
brake-torque
Jackit up
the
center
of
its
adjustment
and
perform
car and put it on jack stands so thea
simple
brake-torque
Jack upHave
the
tires are
off the test.
ground.
car
and
put
it
on
jack
stands
so
the
someone sit in the car and lightly
tires are
off the With
ground.
Have
the brakes.
the helper
apply
someone
sit
in
the
car
and
lightly
holding the brake pedal, turn a front,
apply
helper
then athe
rearbrakes.
wheel With
usingthe
a torque
holding
the
brake
pedal,
turn
a
front,
wrench on a lug nut as shown in
the
then a rear wheel
usingRecord
a torque
accompanying
drawing.
the
wrench
a lugcan't
nut asmeasure
shown in
the
results. on
If you
brake
accompanying
drawing.
Record
the
torque with a torque
wrench,
use your
If
you
can't
measure
brake
results.
hands and estimate it.
torque
wrench,torque
use your
Start with
witha torque
front-brake
at
hands
and
estimate
it.
about 50% greater than rear-brake
Start ifwith
front-brake
torque
at
torque,
the car
has 50-60%
of its
about
50%
greater
than
rear-brake
weight on the rear wheels. If the car is
torque, if the
car has 50-60%
of its
extremely
nose-heavy,
set front-brake
weight
the rear
wheels.
the car
is
torque on
at about
100%
moreIfthan
rearextremely
nose-heavy,
set
front-brake
brake torque. But if it is extremely tailtorque
at about
than rearheavy, start
with100%
front-more
and rear-brake
brake
torque.
But if it is extremely
tailtorques
approximately
equal. This
heavy,
start
with
frontand
rear-brake
also confirms that both front- and
torques approximately
rear-brake
systems work. equal. This
also
confirms that
both isfrontand
If front-brake
torque
less than
rear-brake
work.
rear, adjustsystems
the balance
bar.
is less than
If front-brake
The
tricky part torque
of balance testing is
rear,
adjust
the
balance
bar.
figuring out which end locks up first.
The tricky
part ofhelpers
balancetotesting
is
You'll
need some
do this.
figuring
out
which
end
locks
up
first.
As suggested, this is the time to use a
You'll
need or
some
helpers
to With
do this.
still
camera
video
camera.
an
As
suggested,
this
is
the
time
to use
instant-replay video camera, you
cana
still
camera
or video
With an
observe
at leisure
whatcamera.
happened.
instant-replay
can
A driver willvideo
have camera,
difficultyyou
telling
observeend
at leisure
what
happened.
which
of a car
locks
up without
A driver will
telling
flat-spotting
the have
tires. difficulty
Instead, he
has
which
end
of
a
car
locks
up
without
to ease off the pedal the moment a
flat-spotting
thelock
tires.
he has
wheel starts to
up.Instead,
If he doesn't,
to ease off the pedal the moment a
wheel starts to lock up. If h e doesn't,
White spot on tire is cord showing through
where rubber was worn off. Locking
brakesspot
risks
tires and
also
White
on flat-spotting
tire is cord showing
through
going through
cord.worn
Tire is
and
where
rubber towas
off.ruined
Locking
must be risks
replaced.
brakes
flat-spotting tires and also
going through to cord. Tire is ruined and
must be replaced.
he can grind right through the tires.
Flat spots can ruin a tire. Be careful!
heDo
canthe
grind
through thetest
tires.
firstright
brake-balance
at
Flat
spots
can
ruin
a
tire.
Be
careful!
moderate speed-about 40 mph . If
DO
test to
at
you
gothe
too first
fast, brake-balance
the car will be hard
moderate
speed-about
observe safely.
If yo u're 40
not mph.
using Ifa
you
too fast,position
the car people
will be on
hard
to
both
videogocamera,
observe
safely.
If
you're
not
using
sides of the track . Use two observersa
video
camera,
on both
on
each
side ifposition
possible.people
Tell them
to
sides
of the
twoorobservers
try and
see track.
if the Use
front
the rear
on
eachlock
sideupif first.
possible.
them
to
Don Tell
't lock
up all
wheels
try
and
see
if
the
front
or
the
rear
four wheels. The test will then mean
wheels
up first.
Don't
lock up all
nothing,lock
so don't
brake
too hard.
four
wheels.
test lock
will first,
then adjust
mean
If the
frontThe
wheels
nothing,
so
don't
brake
too
hard.
the balance for more braking. Make
If the
lock first,
sure
youfront
turn wheels
the adjuster
in theadjust
corthe
forRecord
more braking.
Make
rect balance
direction!
the number
of
sure
adjuster
the data
corturnsyou
on turn
the the
adjuster
in in
your
rect direction!
Record
the number
of
sheet
and retest.
Continue
testing
turns
on
the
adjuster
in
your
data
until you are satisfied with brake
sheet
balance.and retest. Continue testing
until
are wheels
satisfied should
with brake
The you
front
lock
balance.
before the rears. Rear-wheel locking
The instability.
front wheels
should
lock
causes
If the car
is turning
before
Rear-wheel
or
has the
any rears.
side forces
on it, locking
it will
causesFront-wheel
instability. If locking
the car iscauses
turninga
spin.
or
has
any
side
forces
on
it,
it will
car
loss of steering control, but the
spin.
Front-wheel
locking
causes
usually goes in a straight line. Thea
loss of
steering
control,onbut
final
setting
will depend
the the
typecar
of
usually
goes
in 's
a preference.
line, l-he
car
and the
driver
final
setting
the type of
If your
carwill
has depend
wings oronaerodynamcar
and
the
driver's
preference.
ic downforce from ground effects,
If your
car has
or aerodynambrake
balance
maywings
be different
at high
ic downforce
effects,
rear
speeds.
A rearfrom
wing ground
loads the
brake balance
mayincreases.
be different
Onatahigh
car
wheels
as speed
A rear
wing
loads
thebrakes
rear
speeds.
that has only
a rear
wing,
if the
wheels
as speed
increases.
On a the
car
are
evenly
balanced
at 40 mph,
that has
only will
a rear
wing,
front
wheels
lock
first ifatthe
100brakes
mph.
areis evenly
balanced
at 40 the
mph,
the
impossible
to balance
brakes
It
100
mph.
front
wheels
will
lock
first
at
for all speeds on such a car.
It is impossible
Compromise
. to balance the brakes
forRace-car
all speeds
such more
a car.
brakes on
are used
at
Compromise.
high speed than at low speed. The
Race-carbraking
brakes speed
are used
more
at
minimum
on the
track
high
speed
at lowturn.
speed.
is
going
into than
the slowest
PickThe
an
minimum braking speed on the track
is going into the slowest turn. Pick an
rear of sports racer improves rear-tire traction for improved handling and braking
IatWinghighat speed.
-*.
As speed drops, so does wing downforce, increasing the chance of rear.-
I
wheelat
lockup
when
braking
tight corners.
-.id braking
Wing
rear of
sports
racerfor
improves
rear-tire traction f-. ....,.
at high speed. As speed drops, so does wing downforce, increasing the chance of rearwheel lockup when braking for tight corners.
Ground effects and rear wing provide maximum aerodynamic downforce. Wing also increases drag dramatically. NACA ducts optimize airflow to brakes with minimum drag.
Ground effects and rear wing provide maximum aerodynamic downforce. Wing also increases drag dramatically. NACA ducts optimize airflow to brakes with minimum drag.
average braking speed for the particUlar track and set the balance for that
average
speedstrongly
for the particuspeed
. Ifbraking
the driver
prefers
lar track
set theover
balance
for that
one
type and
of balance
another,
the
speed.
thebedriver
strongly
prefers
brakes If
may
balanced
perfectly
at
one
type of
over another,
the
top speed
andbalance
increasingly
unbalanced
brakes
perfectly at
speedmay
dropsbe. Abalanced
lot of experimenting
as
top
speed
and
increasingly
is needed to arrive at unbalanced
the best
as speed drops.
compromise
. A lot of experimenting
is Remember
needed tothatarrive
the isbest
bra ke at
balance
afcompromise.
fected by the foJ]owing:
Remember
that brake balance
is afchanges-could
be caused
• Tire-grip
fected
by
the
following:
by either track-surface changes or tireTire-grip changes-could
be caused
temperature
changes.
by
either
track-surface
changes
tire• Aerodynamic-force changes,or such
temperature changes.
Aerodynamic-force changes, such
as a wing-angle change.
temperature-fade
may
• Brake
as
a wing-angle
change.
at one end
of the car before the
occur
Brake
may
other
end . temperature-fade
occur
at
one
end
of
the
car
before
the
• Change to different-size or -comother
end.
pound tire.
Change to
to different-hardness
different-size or -cornbrake
• Change
pound
tire.
lining.
Change toto different-hardness
brake
the car weight distri• Change
lining.
bution.
Change intomaster-cylinder
the car weight
size.distri• Change
bution.
Because it is difficult for a driver to
Change
in master-cylinder
detect
small
brake-balance size.
changes,
Because
it
is
difficult for
a driver
to
don ' t be concerned
about
small
detect small However,
brake-balance
adjustments.
if youchanges,
make a
don't be concerned about small
adjustments. However, if you make
a
115
Severe changes in track conditions is why brake balance needs to be adjusted by the
driver. If Geoff Lee's Formula Ford was set up for the dry, front wheels would lock in the
wet. To changes
correct, in
balance
is is
changed
to give
more needs
rear-wheel
and
Severe
track adjuster
conditions
why brake
balance
to bebraking
adjusted
by less
the
front. During
testing,
can deliberately
wet
to find
correct
rain
settings.
driver.
If Geoff
Lee's you
Formula
Ford was set
upthe
fortrack
the dry,
front
wheels
would
lock Photo
in the
by Steven
Schnabel.
wet.
To correct,
balance adjuster is changed to give more rear-wheel braking and less
front. During testing, you can deliberately wet the track to find correct rain settings. Photo
by Steven Schnabel.
~A
A
1.0
1.0--
---
0.81--====::::::-=---
0.8
Average
Deceleration
-
-
(g)
Average
Deceleration
A.
(g)
o
40
80
~c
120
I
I
Speed When Brakes
Are Applied
(mph)
40
I
80
B
yc
I
I
0
---- B
120
balance-bar,
master-cylinder
valve
problems later.TESTS
DECELERATION
160
I
problems-it has lift at high speed. Most road cars have less deceleration at higher speeds,
but not as severe as curve B shows.
only a few laps, make only one
and then discuss with the ob-
change,
116
and
A verage Deceleration - This test is
I
I
160
Average deceleration tests will tell
you When
something
about
car's aerodynamic
downforce. If
Speed
Brakes
Are aApplied
(rnph)
deceleration
increases with higher-speed stops, stopping is improved with downforce, asI
I
shown bydeceleration
curve A. Curve
B will
reflects
a car
with littleabout
or noadownforce.
Curve Cdownforce.
is a car with
Average
tests
tell YOU
something
car's aerodynamic
If
problems-it has
lift at high
Most road
cars have lessisdeceleration
at higher
speeds,
deceleration
increases
withspeed.
higher-speed
stops,-stopping
improved with
downforce,
as
but not by
as curve
severeA.asCurve
curve BB reflects
shows. a car with little or no downforce. Curve C is a car with
shown
big adjustment, brake balance should
be checked by testing. The most imbig
adjustment,
balance
should
portant
factor is brake
tire grip,
caused
by
be
checked
by
testing.
The
most
either changing track conditions orimby
portant
tire grip,
by
the tires.factor
Tiresis often
lose caused
grip with
either
changing
track conditions
by
age , wear
or temperature
change.orTest
the
tires.
Tires
often
lose
grip
with
the car with the setup you will be runage,
temperature change. Test
ning wear
in theorrace.
theIfcar
with
you will be runyour
carthe
hassetup
a cockpit-adjustable
ning
in the
balance
bar,race.
check it during a test sesIf your
has aThe
cockpit-adjustable
sion
at thecartrack.
driver should
balance
bar,
check
it
during
seschange balance to see
howa test
it feels.
sion
the track.should
The driver
Also, atobservers
recordshould
what
change
see braking.
how it feels.
happens balance
during tohard
Run
Also,
observers
should
only a few laps, makerecord
only what
one
happens and
during
change,
then hard
discussbraking.
with theRun
ob-
deceleration. Remember, as deceleration increases, so must front-wheel
deceleration.
Remember, as decelerabraking.
tion
increases,
must front-wheel
If your car has so
well-balanced
brakes
braking.
and you want to change a master cylinyour
cara has
well-balanced
brakes
derIf or
go to
different
type of proporand
you valve,
want tothis
change
tioning
can abemaster
done cylinwithder or
go to a different
of proporout
changing
balance. type
However,
you
tioning
valve, this
be pressure
done withmust measure
and can
record
in
out
you
bothchanging
hydraulicbalance.
circuits However,
before changmust
measure
and be
record
in
ing parts.
This can
donepressure
by installboth
hydraulic
circuits
before
changing pressure gages downstream from
ing
This can
be doneand
by proporinstallthe parts.
front master
cylinder
ing
pressure
from
or downstream
the rear master
tioning
valvegages
the front Amaster
cylinderplace
and isproporcylinder.
convenient
at the
tioningandvalve
or thebleed
rearscrews.
master
frontrear-caliper
cylinder.
A
convenient
place
is
at the
by
Modify two spare bleed screws
frontand
rear-caliper
bleed
screws.
brazing the cross-hole shut, drilling
Modifythe
twocenter
spare hole
bleedand
screws
by
through
brazing
brazing
the
cross-hole
shut,
drilling
an adapter fitting to the end of the
through
the center
hole and
brazing
screw
. Install
one modified
screw
in a
an
adapter
to inthea rear
end caliper.
of the
front
caliperfitting
and one
screw.
Install
one modified
in a
Connect
a gage
to each screw
modified
front
caliper
and
one
in
a
rear
caliper.
screw with flexible brake hose or steel
Connect
a gage
modified
tubing and
bleed to
theeach
gages.
While
screw
withapplies
flexible the
brakepedal
hose to
or steel
someone
give
tubing and
the gages.
800-psi
frontbleed
pressure,
read theWhile
rear
someone
pedalmake
to give
pressure . applies
You canthenow
the
800-psi front
pressure,
rear
system
changes.
Withread
thethegages
pressure.
You can
make
the now
balance
bar the
or
installed, adjust
system
changes.
theandgages
proportioning
valve With
so front
rear
installed, read
adjustthethe
balance
bar the
or
pressures
same
as before
proportioning
valve
so
front
and
rear
change. Be sure to keep this gagepressures read the same
before itthe
and-bleeder-screw
setup as
because
is
change.
Be sure
keepsorting
this gagean excellent
toolto for
out
and-bleeder-screw
setup because itand
is
balance-bar,
master-cylinder
an
excellent
tool
for
sorting
out
valve problems later.
servers what they saw. If you make
more than one change before testing,
servers
whatbe they
If you make
won't
able saw.
to pinpoint
what
you
more
than
one
change
before
change to the brake system testing,
caused
you
be able change
to pinpoint
what
whichwon't
observable
in brake
change
to the brake system caused
performance.
which
brakea
If theobservable
track surfacechange
is dirty in
or wet,
performance.
balance test will be useless unless you
If the
dirty orsurface.
wet, a
plan
to track
race surface
on a is
similar
balance test
willa be
useless
unless
Instead,
make
crude
attempt
at you
setplan
to raceif on
similar
surface.
ting balance
the abrakes
were
never
Instead,
make
a crude deceleration
attempt at setset. Record
maximum
so
ting
if the
never
you balance
can judge
howbrakes
muchwere
to change
set.
deceleration
so
the Record
balance maximum
when traction
improves.
you
can
judge
how
much
to
change
After a few brake-balance tests, you'll
the
balance
when balance
traction settings
improves.
be able
to relate
to
After a few brake-balance tests, you'll
be able to relate balance settings to
DECELERATION
used to determine TESTS
how rapidly a car
Average
is
stops.
TheDeceleration-This
test can be done withtest
miniused
to
determine
how
rapidly
a
car
mum effort using a stopwatch. If you
stops.
test can
be done
withtominiknow The
the time
it takes
a car
stop
mum effort
using a speed,
stopwatch.
If you
calculate
from
a known
know the time it takes a car to stop
deceleration:
from a known speed, calculate
Average deceleration = :2t in g's
deceleration:
Average
deceleration
= stop
in g's
S = Car speed
before the
in miles
&
per hour
S
Car speed
theinstop
in miles
t ==Time
it takesbefore
to stop
seconds
per hour
do itthis
testtoyou
know the
t =ToTime
takes
stopmust
in seconds
speed of the car. If the car has a
To do this test
youthemust
know the
speedometer,
have
speedometer
speed
of
the
car.
If
the
car
has a
calibrated at a speedometer-repair
speedometer,
the speedometer
shop. If there ishave
no speedometer,
have
calibrated
at ashop
speedometer-repair
a speedometer
put the car on
shop.
there is no speedometer,
have
machine,
their Ifspeedometer-testing
aandspeedometer
shop
put
the
car
on
record the miles per hour that cortheir speedometer-testing
machine,
respond
to
various tachometer
and
recordMake
the miles
hour
that correadings.
sureper
you
record
the
respond
to
various
tachometer
gear ratio , driving-wheel tire size and
readings.
record
the
what
gear Make
the carsure
is inyou
when
making
gear ratio, driving-wheel tire size and
what gear the car is in when making
this test. Speedometer and tachometer
calibrations are necessary because
this
Speedometer
tachometer
they test.
usually
read in and
error,
causing
calibrations
are
necessary
because
errors in calculations.
they
usually
read in
error,
When
stopping
from
verycausing
high
errors indeceleration
calculations. changes during
speed,
stopping from
high
theWhen
stop. Therefore,
averagevery
deceleraspeed,
deceleration
changes
during
tion must be compared to other stopthe
decelerapingstop.
tests Therefore,
done at the average
same speed.
tion
must
be
compared
to
other
stopit
Bring the car up to speed and hold
ping
tests
done
at
the
same
speed.
steady. Start the stopwatch the instant
theare
carapplied;
up to speed
it
theBring
brakes
stopand
the hold
watch
steady.
Startthe
thecar
stopwatch
the instant
stops. Timing
can
the instant
the
brakes
applied; in
stop
be done
by are
a passenger
thethe
carwatch
or by
the
instant
the
car
stops.
Timing
an observer. Several tests should can
be
be done
by a passenger
in the
by
run
to minimize
errors,
butcar
letorthe
an
observer.
Several tests.
tests should
be
brakes
cool between
If you are
run to minimize
but leteach
the
about the errors,
same results
getting
brakes
cool testing
between
tests. Ifareyou
are.
time, your
methods
good
getting
about
the
same
results
each
However, it's difficult to do this test
time, your testing
methods
are good.
be surprised
if
accurately,
so don't
However,
it'sconsistent
difficult to
do this test
you
can't get
results.
accurately,
don't begin
be surprised
if
your stops
To reducesoerror,
you
can't
get
consistent
results.
from a higher speed. Start the stop
To reduce
error, begin reaches
your stops
watch
as the speedometer
the
from a speed.
higher Ifspeed.
Start observer
the stop
a trackside
desired
watch
as the
speedometer
the
is
timing,
you'll
need to reaches
signal him
desired
speed.
If
a
trackside
observer
when to start timing.
is It's
timing,
you'll toneed
to signal
him
interesting
measure
the averwhendeceleration
to start timing.
when braking from
age
It's interesting
measure
avervarious
speeds. Iftoyour
test the
methods
age
deceleration
when
braking
from
are consistent, you can plot a graph
of
various speeds.
If your
methods
deceleration
versus
car test
speed.
This
are
you can
plot aof
graph
of
will consistent,
indicate the
amount
aerodeceleration
versus
car
speed.
This
dynamic downforce . If average decelwill indicate
the amount
of aeroeration
increases
with stops
from
dynamic
downforce.
If average
decelhigher speeds,
the car
has increasing
eration
increases
stops
downforce
at higher with
speeds.
Mostfrom
cars
higher
speeds,
the
car
has
increasing
have less deceleration at high speed
downforce
higher The
speeds.
Mostrotatcars
for
several at
reasons.
wheels
have
deceleration
high speed
ing atless
high
speed takeat away
some
for several reasons.
Thethe
wheels
rotatdeceleration
the instant
driver
hits
ing
at
high
speed
take
away
the brake pedal. Also, many cars some
have
deceleration the
the driver
aerodynamic
liftinstant
at high
speed, hits
so
the
Also, . many cars have
theybrake
have pedal.
less traction
aerodynamic
lift at highdeceleration
speed, so
While
performing
they
have
less
traction.
tests, also measure stopping distance
performing
forWhile
each speed
. Providingdeceleration
you know
tests,
alsoand
measure
stopping
distance
car
speed
stopping
distance,
decelfor
each
speed.
Providing
you
know
eration can be calculated from the
folcar
speed
and
stopping
distance,
decellowing formula:
eration can be calculated from the folS2.,
·
lowing formula:
A
d
I
t
verage ece era Ion
=
29.9d
In
9s
a
S2
Average
deceleration =
in g's
S
= Car speed before the stop in miles
per hour
S
= Distance
Car speedit before
theto
stop
ininmiles
takes car
stop
feet
d=
per hour
Distance
takes harder
car to stop
feet
d=
This
test is itmuch
thaninusing
a stopwatch because it's difficult to hit
testatis amuch
harder
using
theThis
brakes
certain
spot. than
Observers
a stopwatch
becausethat
it's braking
difficult really
to hit
can
help confirm
the brakes
a certain
Observers
starts
whereatthe
driver spot.
intends.
can help confirm that braking really
starts where the driver intends.
Toppling Block
\J
Z
+
;
---y
Toppling Block
Wedge~
wedge
M
/rTra
Floor
Forward
Direction
Forward
Direction
To compensate for nosedive during a toppling-block test, first photograph car from the side
hard braking. From photo, measure dive angle A of car as shown. Make a wedge atI
this
angle and place
it under during
toppling
block tray. Usetest,
a protractor/level
to car
check
tray
To compensate
for nosedive
a toppling-block
first photograph
from
theangle
side
in car. hard braking. From photo, measure dive angle A of car as shown. Make a wedge at
during
Iduring
this angle and place it under toppling block tray. Use a protractor/level to check tray angle
in car.
Again, accelerate the car to a constant speed and make several practice
Again,
accelerate
the car
a contests.
If you
do both time
andtodistance
stant
speed andon
make
practice
measurements
eachseveral
test, compare
tests.
If you If
doyou
bothmeasured
time and the
distance
the results.
time
measurements
on
each
test,
compare
and the distance accurately, you
the results.
you same
measured
the time
should
get If the
deceleration
and
distance methods.
accurately,
using the
the different
On you
the
should
get errors
the same
deceleration
other hand,
in measuring
will
using inconsistent
the different methods.
On the
give
results. Because
other
hand,
errors
in
measuring
will
speed is squared in the stoppinggive
inconsistent
Because
distance
formula, theresults.
speed measurespeed
squared in the stoppingment is is
critical.
distance
formula,
the speed
If you are having
troublemeasuregetting
is
critical.
ment
accurate deceleration measurements,
youMark
are ahaving
tryIfthis:
line ontrouble
the roadgetting
or set
accurate
deceleration
measurements,
up markers
where braking
should
try
this:Start
Markthe
a line
on the road
or car
set
begin.
stopwatch
as the
up
markers
where
braking
should
crosses the line. To apply the brakes
begin. Start
theline,
stopwatch
as the
car
approach
it with
exactly
at the
crosses
theoff
line.
apply the
your
foot
theTothrottle
andbrakes
posiexactly
at the
approachpad.
it This
with
tioned over
theline,
brake-pedal
your
foot
off
the
throttle
and
posireduces driver-reaction time. It takes
tioned 1/2
oversecond
the brake-pedal
pad. This
about
to move your
foot
reduces
time.pedal.
It takes
from
the driver-reaction
throttle to the brake
about
second to read
movethe
your
foot
Have112
a passenger
speedfrom
the
throttle
to
the
brake
pedal.
ometer or tach. It may be necessary to
Have a passenger
read the
the instrument
for speedeasier
reposition
ometer
It may
to
reading. orOr,tach.
if you
havebea necessary
camera that
reposition
the
instrument
for
easier
can be tripped electrically - necessary
reading.
Or, if you have a camera
with
a single-seater-you
could that
use
can
tripped electrically
the be
brakelight
switch to-necessary
trip the
with
a and
single-seater-you
could
use
camera
take a photo of the
speedthe
brakelight
switch
to
trip
ometer the moment the brake pedalthe
is
camera
and take a photo of the speedhit.
ometer
thethe
moment
brake
pedalthe
is
To get
speed the
right
when
hit.
brakes
are applied, run some tests
To get the speed right when the
brakes are applied, run some tests
without hitting the brakes. Back off
the throttle at a mark on the road
without
hitting the
the line
brakes.
off
and Back
observe
before crossing
the
throttle
at
a
mark
on
the
road
the speed as you cross the line. Adjust
before
crossing
the line
so you
crossand
theobserve
line at
initial speed
the
speed
as
you
cross
the
line.
Adjust
the desired speed.
initial
speed
so youto cross
line of
at
If you
are going
run a the
number
the
desired
speed.
deceleration tests, you should invest
you are going to run a number of
in If
a decelerometer.
deceleration
tests, you should
invest
Maximum Deceleration
Tests-You
in
a
decelerometer.
can measure maximum deceleration
Maximum
Deceleration
You can alsoTests-You
test decelduring
a stop.
can measure
maximum
deceleration
eration
at particular
speeds
without
during a stop.
test decelstopping.
To doYou
this,can
usealso
a deceleromeration
at particular
eter
or toppling
b10cks.speeds without
stopping.
To
do
use athe
deceleromDecelerometer-this,
Follow
instruceter
toppling
tionsorthat
comeblocks.
with the instrument.
Decelerometer-Follow
the a instrucMost
decelerometers require
passentions
that
come
with
the
ger to take readings . On ainstrument.
single-seat
Most
require
a passenracer, decelerometers
this is not practical.
Instead,
use
ger
to take
readings.
On ainsingle-seat
a video
camera
mounted
the car to
racer,
is not practical.
Instead, use
recordthis
decelerometer
readings.
aToppling
video camera
mounted
in
the car to
Blocks-The toppling-block
record
decelerometer
readings.
method doesn't require a passenger.
Toppling Blocks-The
blocks-see toppling-block
drawing-can
Toppling
method
doesn't
require
a passenger.
be built in a home
workshop.
Make a
Toppling
blocks-see
drawing
-canA
flat surface for the blocks to rest on.
be built
in a can
home
Makeina
be workshop.
mounted firmly
flat
tray that
flat
the blocks
restthe
on.car
A
yoursurface
car is for
ideal.
Don't to
use
flat
tray
that
can
be
mounted
firmly
in
floor. Chances are it's not flat enough
youraccurate
car is measurements.
ideal. Don't use the car
for
floor.
are it's gradually
not flat enough
Set Chances
up the blocks,
bring
for
the accurate
car up tomeasurements.
speed and hit the brakes.
Set upwillthe blocks,
bring
You
topple gradually
the
blocks
the
car
up
to
speed
and
hit
the
brakes.
immediately, so you don't have to
You
will speed.
toppleWiththe
blocks
lose much
the blocks,
immediately,
so you ordon't
to
you'll
find maximum
peak have
deceler-
lose much speed. With the blocks,
you'll find maximum or peak deceler117
Temperature-indicating paint is best way
to measure rotor temperatures. Paint can
be applied to outer edgepaint
of rotor
and way
obTemperature-indicating
is best
served
after rotor
test run.
ExperimentPaint
with difto
measure
temperatures.
can
ferent
temperature
to rotor
get good
be applied
to outerranges
edge of
and test
obdata.
an test
open-wheel
car, a pyrometer
servedOn
after
run. Experiment
with difcan be temperature
used, but youranges
must act
fastgood
to avoid
ferent
to get
test
having
rotor
off before
data. On
an cool
open-wheel
car,measurement
a pyrometer
is taken.
can
be used, but you must act fast to avoid
having rotor cool off before measurement
is taken.
ation during that range of speed when
the brakes were applied . By running a
ation
during
that, you
rangecan
of plot
speed
when
number
of tests
a graph
the
brakes
were
applied.
By
running
of deceleration versus car speed.a
number
of tests,
can plot
graph
Again, this
is an you
indication
of avehicle
of deceleration
versus car
speed.
If deceleration
is higher
at
downforce.
Again,
is an aerodynamic
indication of vehicle
higher this
speeds,
downdownforce.
If deceleration
is higher at
force
is present
and vice versa.
higher
speeds,
aerodynamic
downEach block falls over at a certain
force is present
vice versa.
deceleration
. Mand
aximum
deceleration
Each a block
fallsbeover
at a certain
during
stop will
indicated
by the
deceleration.
Maximum
deceleration
shortest block that fell over. The
during acan
stop tell
will be
indicated bywhat
the
driver
immediately
shortest
block
that
fell by
over.
The
deceleration
he is
getting
looking
driver
can tell immediately what
the blocks.
at
deceleration
he iserror
getting
lookingThere is some
in thebytoppling
at
the
blocks.
block test. If the car nosedives while
There isthe
some
errorwill
in the
topplingblocks
tend
to fall
stopping,
block
the car
nosedives
while
more test.
easilyIf than
if the
car stopped
stopping,
the
blocks
will
tend
to
fall
level. Most race cars don't nosedive
more
easily
than
if
the
car
stopped
enough to matter, but the error may
level.
Most race
don't nosedive
on cars
a high-CG,
softly
be significant
enough
to matter,
but the error may
sprung road
car.
beTosignificant
on for
a nosedive,
high-CG, take
softlya
compensate
sprung
road
car.
photo of the car from the side while it
compensate
for nosedive,
take a
is To
stopping
at maximum
deceleration.
photo
car from
the side
while of
it
thethe
photo,
measure
the angle
Using of
is
stopping
at
maximum
deceleration.
tilt of the body. Compare it to a photo
Using
the photo,
measure
of
taken from
the same
anglethe
ofangle
the car
tilt of the
body.
Compare
it to angle
a photo
Once
the dive
is
sitting
level.
taken from , the
samethe
angle
the the
car
determined
adjust
trayof for
sitting
Once
dive up
angle
is
topplinglevel.
blocks.
Tip the
the tray
at the
determined,
adjust
the
tray
for
the
front , at the same angle the car
toppling
blocks.
tray up at the
nosedives.
This Tip
willthe
compensate
for
front,
at caused
the same
angle theOncara
the error
by nosediving.
nosedives.
Thisnosedive,
will compensate
for
car
with little
position the
the
error
caused
by
nosediving.
On
toppling-block tray level on the cara
car with little nosedive, position the
floor.
toppling-block tray level on the car
floor.
118
Check
Changes-When
making
deceleration tests , now's the time to
Check
making
deceleration is affected
by
check howChanges-When
deceleration
tests,
now's
the
time
to
changes other than to the brakes. For
check
how
deceleration
is
affected
by
example, you can combine the decelchanges
other
than
to the brakes.
eration test
with
aerodynamic
testsFor
to
example,
can combine
decel-.
see
how you
downforce
affectsthe
braking
eration test this
with aerodynamic
tests to
Combine
with brake-balance
see
how
downforce
affects
braking.
changes
to
achieve
maximum
Combine
with brake-balance
deceleration.thisRemember,
maximum
changes
achieve
maximum
decelerationto occurs
when brake
baldeceleration.
maximum
ance
is set soRemember,
all four wheels
lock
deceleration
occurs when brake balsimultaneously.
ance
is
set
so
wheels
Although tire all
gripfour
is the
most lock
imsimultaneously.
portant item affecting deceleration , it
tirebygrip
is theinmost
imis Although
also affected
a grade
the road
portant
item
affecting
deceleration,
it
or the wind. So test in both directions
is also
affectedthebyresults
a gradetoineliminate
the road
and
average
or
the effects.
wind. So
in bothday,
directions
these
Ontest
a windy
a large
and
average
the
results
to
eliminate
error is introduced . Wind forces
vary
these
a windy
day, a On
largea
the effects.
square On
of the
wind speed.
as
error isday,
introduced.
Wind will
forces
vary
change
windy
drag forces
as
the squaresignificantly.
of the wind speed. On a
deceleration
windy day, drag forces will change
deceleration
significantly.
EFFECTIVENESS
TESTS
Brake-system effectiveness is the
EFFECTIVENESS
TESTS
amount
of deceleration
obtained for a
Brake-system
effectiveness
the
particular pedal effort. A isbrake
amount
of
deceleration
obtained
for
system that is more effective stops aa
particular
effort. A brake
car
with less pedal
pedal effort.
system
that is more
stopsfora
Effectiveness
testseffective
are useful
car
with
less
pedal
effort.
comparing brake systems and also for
Effectiveness
tests
are tests
usefulmust
for
comparing
linings.
These
comparing
brakea systems
and also for
be run with
continuous-reading
comparing
linings.
tests must
decelerometer,
suchThese
as aU-tube
debe
run
with
a
continuous-reading
celerometer or reco rding g-meter and
such With
as a U-tube
deadecelerometer,
line-pressure gage.
a recording
celerometer
or tests
recording
g-meter, these
can beg-meter
run by and
the
adriver
line-pressure
With aa recording
alone. gage.
With
U-tube
g-meter,
these tests
be run by the
decelerometer,
ancan observer
is
driver
alone.
With
a U-tube
required.
decelerometer,
an
observer
is
To run an effectiveness
test, dri ve
required.
the
car at a predetermined speedTo as
run60an
effectiveness
drive
such
mphand applytest,
the brake
the
car
at
a
predetermined
speedpedal until a 100-psi pressure is
such
as 60
the brake
reached.
Atmph-and
that point ,apply
deceleration
is
pedal and
untilrecorded.
a 100-psi
is
read
Thenpressure
accelerate
reached.
At that
is
the car back
to 60point,
mph deceleration
and repea t the
read
and
recorded.
Then
accelerate
test in increasing 100- or 200-psi
the car backuntil
to 60lockup
mph and
repeat the
increments
is reached.
Be
test to
in allow
increasing
100-time
or between
200-psi
sure
sufficient
increments
lockupfor
is reached.
Be
each
pedal until
application
the brakes
sure
to
allow
sufficient
time
between
to cool.
each
pedal application
for the brakes
Following
each test , calculate
pedal
to cool.required for each pressure . Plot
effort
Following
each paper
test, calculate
pedal
with decelerathis
data on graph
effort
required
for
each
pressure.
tion in g's on the vertical axis Plot
and
this
on graph
paper
with deceleraon the
horizontal
axis.
pedaldata
effort
tion in
g's comparison,
on the vertical
axis and
For
easy
if you
test
pedal effort
thedifferent
horizontal
axis.
another
car oronwith
lining
on
For
easy car,
comparison,
if you
the same
plot the second
testtest
on
another
or with
lining on
the samecar
graph.
Fordifferent
a quick comparithe same
plot, the
on
son
and nocar,
graphs
run second
the teststest
at just
the same graph. For a quick comparison and no graphs, run the tests at just
Effect of scoop on brake temperature can
be tested by enlarging scoop. If you make
scoop
larger
andontemperature
drops, use
Effect of
scoop
brake temperature
can
this
information
to design
improved
be tested
by enlarging
scoop.anIf you
make
scoop. larger
Use theand
smallest
scoops drops,
to give use
acscoop
temperature
ceptable
brake temperatures
because
big
this
information
to design an
improved
scoops
increase
air drag.scoops to give acscoop. Use
the smallest
ceptable brake temperatures because big
scoops increase air drag.
one line pressure
decelerations.
and
compare
one line pressure and compare
decelerations.
BRAKE TEMPERATURE TESTS
Brake temperature is important to
BRAKE
the brakes get TESTS
too hot,
know . IfTEMPERATURE
Brake
temperature
is important
to
cha nges may be necessary.
By measurknow.
the brakes
get can
too check
hot,
ing the Iftemperature
, you
changes
mayofbeanecessary.
By ally,
measurthe success
ch ange. Usu
iming
the
temperature,
you
can
check
proved airflow to the brakes will
be
the most
success
of a change.
the
effective
change. Usually, improved
airflow
to temperature
the brakes will
Measure
brake
withbea
the
most
effective
change.
hand-held or remote pyrometer. You
brake
temperature with a
temperature-indicating
canMeasure
also use
hand-held
or remote
paint or labels.
The pyrometer.
hand-held You
pycan
also gives
use the
temperature-indicating
rometer
temperature at the
paint
The hand-held The
pytime or
of labels.
the . measurement.
rometer
gives
the
temperature
at
the
remote pyrometer with thermocoutime gives
of the
'measurement.
ples
continuous
temperatuThe
res.
remote pyrometer
with give
thermocouTemperature
indicators
maxiples
gives
continuous
temperatures.
mum temperature experienced at a
Temperature
indicators give maxispecific location.
m uThe
m disadvantage
temperature of
experienced
a hand- heldatpy-a
specific
rometerlocation.
is it takes time to stop the
of aand
hand-held
pycar,The
getdisadvantage
to the brake,
make the
rometer
is
it
takes
time
to
stop
the
measurement. By that time, temperacar,
to the
brake,
and make the
turesgethave
dropped
. Therefore,
the
By that time,
temperameasurement.
hand-held pyrometer
will be
useful
tures ifhave
dropped.
Therefore,
only
you can
get fast
access to the
the
hand-held
pyrometer
will
useful
spot to be measured . For be
example,
only
if you
get fast race
access
to but
the
it'll work
on can
open-wheel
cars,
spot
to beimpossible
measured.on For
example,
is almost
full-fendered
it'll work
on open-wheel
cars, but
cars
that don't
have largerace
openings
in
is
almost
impossible
on
full-fendered
the wheels.
cars
that are
don'tmany
haveways
largetoopenings
in
There
determine
the
wheels. Whatever you do, plan
temperature.
are and
many
waysthetowritten
determine
theThere
test first
follow
plan.
temperature.
Whatever
you
You must have good recordsdo,to plan
get
the
firstinformation.
and follow theIt written
plan.
doesn't
do
any test
useful
You must have good records to get
any useful information. It doesn't do
any good to say, "My brakes get to
lOOOF." You must know how many
any good
say, "My
get to
stops
weretomade,
from brakes
what speed,
1000F."
how
many
and
how You
muchmust
time know
elapsed
between
stopsstop.
wereAlso,
made,
from
speed,
each
a car
thatwhat
sits still
beand
how
much
elapsed than
between
tween
stops
is a time
lot different
if it
each
stop. Also,
a car
thatfor
sitsthe
still
bewas moving
at 100
mph
same
tween
stops is a lot different than if it
time period.
was
at 100
same
If moving
you don
' t mph
have fora theremote
time
period.
pyrometer,
use the next
best
If you don't
have aindicators
remote
thing-apply
temperature
pyrometer,
the and
nextlabelbest
to your brakes.use
The paint
inthing-apply
dicators
go on temperature
the edges of indicators
the brake
to yourand
brakes.
Thebody,
paint respectively.
and label inrotor
caliper
dicators
on temperature
the edges of gets
the brake
Usually, go
rotor
twice
rotor
and
caliper
body,
respectively.
that of the caliper.
Usually,
rotor temperature
gets twice
Accelerate
to a predetermined
that ofand
the caliper.
speed
make one full stop. Check
a predetermined
theAccelerate
temperaturetoindicators
and record
speed
and
make
one
full temperature.
stop. Check
the maximum-indicated
theyou
temperature
indicatorsasand
record
If
have a pyrometer
well,
use
theTemperature
maximum-indicated
temperature.
it.
rise in one
stop can
If
have a topyrometer
as well,
use
be you
compared
a calculated
number
it.
Temperature
rise
in
one
stop
can
using the formula on page 11. The difbe compared
to a calculated
number
ference
between
calculated-tempusing therise
formula
on measured
page 11. The
erature
and the
risedifis
ference
between
calculated-tempthe energy-heat-Iost elsewhere,
erature
and caliper,
the measured
is
such
as rise
to the
wheel, rise
brake
the
energyheat-lost
elsewhere,
hats and
air drag.
such
as to
thea caliper,
wheel,
If you
have
road-racing
car, brake
make
hats
and
air
drag.
a number of fast laps around the track
you have
a road-racing
at Ifracing
speed.
After aboutcar,
10 make
laps,
abring
number
the brake
track
the of
carfast
in laps
and around
measure
at
racing speed.
Afterthis
about
10 laps,
laps,
temperature.
After
many
bring
the
car
in
and
measure
brake
brake temperature should stabilize.
temperature.
many
laps,
To
check this, After
make this
several
multilap
brake
temperature
should after
stabilize.
tests, checking
temperature
each
To
this,Eventually,
make several
multilap
set check
of laps.
you'll
find
tests,
checking
temperature
after
each
how many laps it takes for the brakes
set
laps. maximum
Eventually,temperature.
you'll find
to of
reach
how many
laps get
it takes
the brakes
They
will not
any for
hotter
unless
to
reach
maximum
temperature.
there's a major track , car or driver
They
nota get
any pyrometer
hotter unless
change.will
With
remote
and
there's a major linings,
track, car
driver
thermocoupled
thisorcan
be
change.
With
a remote
and
done
easily
in one
seriespyrometer
of laps.
thermocoupled
be
Pay particular linings,
attentionthisto can
caliper
done
easily innear
one series
of laps.
temperature
the piston
(s). If the
Pay particular
to caliper
temperature
gets attention
close to the
braketemperature
near the
piston(s).
fluid
dry boiling
point,
watchIf the
for
temperature
gets close
to theatbraketrouble.
A caliper
running
over
fluid
dry boiling
point, watch
for.
SOOF (260C)
will experience
trouble
trouble.
caliper running
at ifover
The
sealsAeventually
leak even
the
500F doesn't
(260C) boil.
will experience
trouble.
fluid
So try to limit
caliThe
seals
eventually
leak
even
if the
per temperature to 3S0F (177C)
or
fluid
doesn't
boil. So
less, to
give longer
sealtry
life.to limit caliperTotemperature
to 350F (177C)
or
evaluate differences
between
less,
to
give
longer
seal
life.
different components or setups, such
evaluate
as Tocool
ing-duct differences
systems orbetween
rotor
different
setups,
such
types, it iscomponents
best to test or
one
configuraas
or right.
rotor
tion cooling-duct
on the left andsystems
one on the
types,, switch
it is best
to and
test rerun
one configuraThen
sides
the test.
tion
on
the
left
and
one
the right.
Caution: When runningontests
with
Then, switch
sidesonandeach
rerun
theoftest.
different
setups
side
the
Caution: When running tests with
different setups on each side of t h e
Temperature-indicating labels are for use
on disc-brake calipers. Note the word
CAUTION starting at 320F
(160C).
Temperature-indicating
labels
are forTemuse
perature
indicates
fluid may
on
disc-brake
calipers.
Note be
the boiling
word
inside caliper.
Photoatcourtesy
AP Racing.
CAUTION
starting
320F (160C).
Tern-
perature indicates fluid may be boiling
inside caliper. Photo courtesy AP Racing.
.'"
,
Temperature-indicating paint at different
locations on caliper : Paint on outboardpiston
housing is most important
because
Temperature-indicating
paint at different
it
indicateson
fluid
temperature
cooling
locations
caliper:
Paint where
on outboardair is minimal.
not because
exceed
piston
housing Caliper
is most should
important
350F
(177C)
at temperature
this point.
it
indicates
fluid
where cooling
air is minimal. Caliper should not exceed
350F (1 7 7 C ) at this point.
.
~
... ' ~ .
, ."'.
.
.
\.'
, ...\
'I.. "
,,~
I
. , >
'
.
......
'~
"
.., ..
-
"
+ L27
L
FL1
Wear
= =
La - LF
Wear
Wear
=top
Lo -= LFNo. of Stops
Wear/S
Wear
1000 x Wear
Stops
of Stops
Wear /1000 =
Wear/Stop
No. =of No.
Stops
1000 x Wear
Wear/1000 Stops = No, of Stops
LO
Wear per stop can be calculated using simple formulas shown. If pads weQr in a taper, use
I
average
final thickness T f to compute wear. Usually, wear per 1000 stops is more usefulI
than
per can
stop.beLining-wear
calculations
very important
for long-distance
racing.
Wear wear
per stop
calculated using
simple are
formulas
shown. If pads
wear in a taper,
use
Wear perfinal
lap or
wear per T,
hour
be most
important
pad per
changes
be planned
fuel
average
thickness
to may
compute
wear.
Usually,so
wear
1 0 0 0can
stops
is more at
useful
stops.wear
Have
make quick calculations
lining checks
during
tire changes
to double-check
than
per crew
stop. Lining-wear
are very
important
for long-distance
racing.
calculations.
Wear
per lap or wear per hour may be most important so pad changes can be planned at fuel
stops. Have crew make quick lining checks during tire changes to double-check
calculations.
car, watch out for uneven braking.
The driver can lose control!
car,
for careful
uneven you
braking.
Nowatch
matterouthow
are,
T
h e driver
lose control!
there
are can
always
test-to-test difNo matter
howeliminated
careful you
are,
ferences
that are
by runthere
are
always
test-to-test
difning both configurations at once.
ferences
that
are
eliminated
by
runRerunning a test with the configuraning
both configurations
once.
tions switched
and averagingat results
Rerunning side-to-side
a test with differences
the configuraeliminates
.
tions
switched
and parts
averaging
results
When
evaluating
designed
to
eliminates
run in oneside-to-side
direction differences.
only, such as
When evaluating
to
curved-fin
rotors, beparts
suredesigned
to switch
run in
oneyou
direction
only, such as
parts
when
switch sides.
curved-fin rotors,
be sure
to can
switch
Brake-Wear
Test-Brake
wear
be
parts
when
you
switch
sides.
tested only after many stops. Earlier
Brake-Wear Test-Brake wear can be
tested only after many stops. Earlier
in this chapter 1 suggested measuring
lining thickness befo re testing. If you
in this
suggestedlining
measuring
do
this,chapter
you canI measure
thicklining afterward
thickness before
testing.
you
ness
to judge
wear.If The
do this, you
can measure
lining But
thickamount
of wear
is interesting.
to
ness
afterward
judgeto wear.
The
be useful,
you toneed
determine
amount
wear is interesting. But to
wear per of
SlOp.
beTouseful,
you wear
need per
to determine
calculate
stop, you
wear
stop. the number of stops or
must per
know
Tooncalculate
stop,
you
laps
the pads.wear
You per
should
be able
must
know
the
number
of
stops
or
to find this in your records if you
laps on the
pads. Youin should
be able
recorded
everything
your notebook
to suggested.
find this in your records if you
as
recorded
everything
your notebook
After you
finish in
testing,
measure
as
suggested.
brake-lin ing thickness. Measure the
After you finish testing, measure
brake-lining thickness. Measure the
119
,r
/
pad
Backing
Plate
/
Plate
Riveted
Lining
Bonded
Lining
Lining
When measuring lining thickness to compute wear rate, take several measurements
and
them.
Because
brake
Whenaverage
measuring
lining
thickness
to shoes
comand
weartake
unevenly,
rates are
pute pads
wear rate,
severalwear
measurements
based
on average
over the
lining.
To
and
average
them.wear
Because
brake
shoes
compute
lining thickness,
look are
for
and
padsminimum
wear unevenly,
wear rates
thinnest
based
onspot.
average wear over the lining. To
compute minimum lining thickness, look for
thinnest spot.
linings in the same places as before
and compare thicknesses to the origilinings
in the sameWear
places
is as
the before
original measurements.
and
compare
thicknesses
to
the original thickness minus the thickness
nal measurements.
is theatorigiafter
testing. Look Wear
carefully
the
nal
the onthickness
liningthickness
to see if minus
it is worn
a taper.
after testing.
Look carefully
Make
a diagram
to recordat the
the
lining
to
see
if
it
is
worn
a taper..
information, as shown in theondrawing
Make a diagram to record the
Lining-wear per
stop = in
~ the drawing.
information,
as shown
Lining-wear
stop
in inches perper
stop
=r
W
W = Total amount of lining wear in
in inches per stop
inches
W
Total
amount
of lining wear in
N = =Total
number
of stops
inches
The
answer
from
this formula will
N=
Total
number
of stops
be very small. So, multiply it by 1000
answer
this formula
will
This figure
to The
get wear
per from
1000 stops.
it by 1000
be very
small.toSo,
will
be easier
use multiply
.
to Once
get wear
1000
stops.
This figure
you per
have
wear
per stop,
calcuwill
be
easier
to
use.
late the number of stops it takes to
Once
have
wear completely.
per stop, calcuoutyouthe
linings
To
wear
late this,
the number
stops it takes
to
lining
do
find theof minimum
wear
out
the
linings
completely.
To
thickness allowed. Your car manudo this, find
lining
facturer
or the
brakeminimum
manufacturer
thickness
allowed.
Your
car
manushould be able to supply this
facturer
or Obviously,
brake manufacturer
information.
you shouldshould
able to
to wear
supply
this
n't allow be
the lining
so much
information.
Obviously,
you
shouldthat the metal backing plate contacts
n't
to wear
much
the allow
rotor.the
Or,lining
if you
havesoriveted
that the it's
metal
contacts
the backing
distance plate
the rivets
are
linings,
the
rotor. into
Or, the
if you
havethat
riveted
recessed
lining
you
linings,be
it'sconcerned
the distance
should
with.the rivets are
recessed
the lining give
that miniyou
Most carinto
manufacturers
should be concerned with.
Most car manufacturers give mini-
120
--1 __
pad
Backing
Plate
k:king
Plate
Rivet Head
Minimum Lining
Thickness
+Minimum Lining
--11---c
1I
-t
Minimum Lining
Thickness
Minimum Lining
Thickness
To compute number
of stops available from a new lining, you must know its minimumThickness
I allowable lining thickness. This is different for riveted and bonded linings. Use depth-gageI
endcompute
of dial caliper
to measure
lining.you
More
wear
will result
in rotor
To
number
of stops available
availablewear
fromofa riveted
new lining,
must
know
its minimumor drum scoring.
allowable
lining thickness. This is different for riveted and bonded linings. Use depth-gage
end of dial caliper to measure available wear of riveted lining. More wear will result in rotor
or drum scoring.
mum lining thickness in their shop
manual. If you can't find this figure,
mum
thickness
in their
shop
assumelining
you can
wear the
linings
to
manual.
If
you
can't
find
this
figure,
within 1/16 in. of the plate or rivets.
assume
youminimum
can wearlining
the linings
to
Subtract
thickness
withinthe
1/16
in, of theofplate
or rivets.
from
thickness
a new
lining to
minimum
liningwear.
thickness
getSubtract
maximum
allowable
You
from
the
thickness
of
a
new
lining to
can then calculate the maximum
get
maximum
number
of stops: allowable wear. You
can then calculate the maximum
W
number of stops:
Number of stops allowed
=_M_
Ws
WM
Number of stops allowed = W M = Maximum lining wear w
allowed
in
s
inches
W,
Maximum
wearinallowed
Ws == Lining
wearlining
per stop
inches in
inches
per
stop
W, = Lining wear per stop in inches
perRemember
stop
that brake wear in-
creases with temperature. And, if you
Remember
that horsepower,
brake wear the
inincrease
engine
creases
with
temperature.
And,
if
you
brakes will get hotter because you'll
increase
horsepower,
the
be
stoppingengine
from higher
speeds. Wear
brakes
willwill
get also
hotterincrease.
because Aeroyou'll
per
stop
be stopping
from higher
Wear
dynamic
changes
also speeds.
affect lining
per
stop
will
also
increase.
Aerotemperature and wear. Therefore,
dynamic
changes
alsothickness
affect lining
keep records
of lining
each
temperature
and the
wear.brakes.
Therefore,
time
you inspect
Also
keep records
of lining
each
record
the number
of thickness
stops between
time
you
inspect
the
brakes.
Also
inspections so you can keep track of
record
thewear
number
stops track
between
changing
ratesof from
to
inspections
so you
can keep track of
to setup.
track and setup
changing
wear
from
track to
Wear rates
willrates
change
dramatically
track
and
setup
to
setup.
from track to track. One with long
Wear rates
dramatically
straights
and will
tightchange
flat turns
is much
from track to track. One with long
straights and tight flat turns is much
harder on brakes than one with short
straights and high-banked turns.
harder
on brakes
than one are
withimporshort
Lining-wear
calculations
straights
and
high-banked
turns.
tant in long-distance road racing. If
Lining-wear
calculations
are aimporyou
wear out linings
and ruin
rotor,
road inracing.
If
of long-distance
time will be lost
the pits
atant
lot in
you
wear
out
linings
and
ruin
a
rotor,
changing it. By determining lining
awear
lot during
of timepractice
will besessions
lost in and
the calpits
changing
it. number
By determining
of stops orlining
laps
culating the
wear during
sessions
calallowed,
youpractice
can predict
howandmany
culating
the
number
of
stops
or
laps
laps you can run before changing
allowed,
you can
predict
how sets
many
to have
enough
of
pads. Be sure
laps
can run
pads you
bedded-in
to before
go the changing
distance
pads.
have enough sets of
thesure
race to
starts.
beforeBe
pads
bedded-in
to go the isdistance
This sort of calculation
useful
before
the
race
starts.
only for race cars. Usually, you can
This sort both
of calculation
useful
determine
wear rate isand
the
only for
race of
cars.
Usually,
can
exact
number
possible
stopsyou
before
determine
wear rateTheand
the
is necessary.
brakes
a pad changeboth
exact
number
of
possible
stops
before
are always used as hard as possible, so
athepadwear
change
TheOn
brakes
rateisisnecessary.
predictable.
the
are always
as hard
as possible,
so
street,
the used
number
of stops
depends
the
wear
rate
is
predictable.
On
the
on the type of driving . City driving
street,
stops depends
takes the
morenumber
stops of than
freeway
on
the type
of driving.
driving
driving.
Fast driving
in theCity
mountains
takes
more
stops
than
freeway
is a lot different than taking the family
driving.
Fast driving
in the calculating
mountains
Therefore,
to the drive-in.
is
a
lot
different
than
taking
family
wear per stop is impossiblethe
. So,
for
to the drive-in.
street
use, keepTherefore,
a record calculating
of the car
wear
per each
stop is
impossible.
So, are
for
mileage
time
the brakes
street
use,
keep
a
record
of
the
car
inspected. This, along with a record of
mileage
each time
the you
brakes
are
lining thickness,
will give
an idea
inspected.
This,miles
alongyour
with brakes
a recordwill
of
of
how many
lining
thickness,
will
give
you
an
idea
last.
of how many miles your brakes will
last.
Maintenance
Proper maintenance is essential for
brake-system safety and performance.
maintenance
essential for
If Proper
you have
a good is maintenance
brake-system
safety
and
performance.
program, you can usually find a probIf
have
a good serious.
maintenance
it becomes
Don't
lemyou
before
program,
can usually
find a occur
probwait
untilyoubrake
problems
lem before
becomes serious.may
Don't
enbefore
doingitsomething-you
wait until
brake problems
occur
counter
a life-threatening
situation.
before
doing system
something-you
maymost
enThe brake
is one of the
counter
a life-threatening
situation.
critical parts
of a car. Luckily,
brakes
brakereliable,
system iseven
one of
the most
areThe
very
with
poor
critical
parts
of
a
car.
Luckily,
maintenance . Brake trouble can brakes
usualarebe very
even
poor
ly
sensedreliable,
at the pedal
, sowith
the driver
maintenance.
Brake trouble
usual-,
knows it immediately.
For can
example
ly
sensed
at the
pedal,
the driver
and so
lower
if the
thebepedal
gets
lower
knows
it
immediately.
For
brakes need adjusting. Andexample,
it goes
the pedal
getsinto
lower
lower
if the
theand
system
through
soft
if air gets
brakesseals.
need Worn-out
adjusting. linings
And it make
goes
bad
soft
if
air
gets
into
the
system
through
horrible noises as metal contacts
bad seals.
liningsevident
make
Most Worn-out
problems become
metal.
horrible
noises
as
metal
contacts
before a total brake failure occurs.
metal.
problems
become evident
One Most
of the
most dangerous
probbeforeisa total
brake
occurs. This
a line
or failure
hose failure.
lems
One of problem
the mostcan
dangerous
probpotential
go unnoticed
lems
is
a
line
or
hose
failure.
This,
until the brakes are used hard . Then
problem
can can
go occur
unnoticed
apotential
line or hose
rupture
with
until
the brakes
are used
hard. to
Then,
the pedal
suddenly
dropping
the
afloor.
line If
or the
hosecar
rupture
occur dualwith
has a can
modern
the
pedal
suddenly
dropping
to the
braking
system
, the driver
can usually
floor.
If the
modern
car. car
But,hasif athe
systemdualhas
stop the
braking
driver can
andusually
is in
only
twosystem,
wheelsthebraking
stop
car. But, if the
system
has
of maintenance,
it may
be imneed the
only
twoto wheels
brakingOnly
anda is
in
possible
stop quickly.
good
need
of maintenance, it may
impreventive-maintenance
effortbe will
possible
to stop
quickly. Only a good
prevent such
problems.
preventive-maintenance
effort plan
will
Schedule-A good maintenance
prevent
problems.
If the car is raced,
requires such
a schedule.
Schedule-A
goodbrake
maintenance
plan
maintenance
always
do some
requires
a
schedule.
If
the
car
is
raced,
before each race. Inspect the system
always
some
brakeAlso
maintenance
for
weardoand
damage.
bleed the
beforebefore
each each
race. event.
InspectIf the
fluid
yousystem
fail to
for this,
wearbrake
and performance
damage. Alsowill
bleed
the
suffer.
do
fluid
before
each
event.
If
you
fail
to
On a race car, major brake-system
do
this,
brake
performance
will
suffer.
maintenance is done each season - or
On often
a race ifcar,
major brake-system
more
problems
occur. Major
maintenance
doneinclude
each season-or
maintenance ismay
replacing
more
oftenand
if problems
Major
the seals
surfacing occur.
or replacing
maintenance
may
include
replacing
the rotors. Wheel-bearing lubrication
theusually
seals done
and at
surfacing
is
this time.or replacing
theOnrotors.
Wheel-bearing
lubrication
a road
car, your shop
manual
is
usually
done
at
this
time.
will give a recommended brakeOn a road schedule.
car, yourUsually,
shop manual
maintenance
it sugwill give
a recommended
brakethe fluid level
and
gests
inspecting
maintenance
schedule.
it sugchecking
the linings
for Usually,
wear after
cergests
inspecting
fluid level You
and
tain mileage
has the
accumulated.
checking
the
linings
for
wear
after
cercan modify this schedule if you find
tain mileagebuthasthe
accumulated.
You
manufacturer's
problems,
can modify this schedule if you find
problems, but the manufacturer's
II
Brake maintenance on race car should be done after each time car is raced. Mechanic prepares to disassemble and inspect brakes on this Indy Car after a practice session. He is
using
cleaningonfluid
remove
Cleanliness
when
workingpreon
Brakebrake
maintenance
racetocar
shouldcontamination.
be done after each
time carisisvital
raced.
Mechanic
brakes.to disassemble and inspect brakes on this lndy Car after a practice session. He is
pares
using brake cleaning fluid to remove contamination. Cleanliness is vital when working on
recommendation
is a good place to
BRAKE ADJUSTMENT
brakes.
start. Here is my brake-maintenance
recommendation
a good place to
schedule for a roadiscar:
start.
Here
is
my
brake-maintenance
Every 5000 miles: Inspect hoses
schedule
a road
car:level.
and lines;for
check
fluid
Every 10,000
5000 miles:
Inspect linings
hoses
Every
miles: Inspect
andwear.
lines; check fluid level.
for
Every
year:
Every 10,000
25,000 miles:
miles Inspect
or everylinings
for
wear.
Replace brake fluid .
Every 25,000
or every
year:
Every
50 ,000miles
miles:
Overhaul
Replace
brake
fluid.
calipers; wheel cylinders, master
Every 50,000 miles: Overhaul
cylinder.
calipers;
wheel cylinders,
This maintenance
schedulemaster
does
cylinder.
not
cover everything. It just outlines
schedule
does
theThis
mostmaintenance
common items
and approxinot
cover
everything.
It
just
outlines
mates
brake-maintenance
needs.
the most
items and
approxiYour
car'scommon
needs depend
on its
design
mates
and how brake-maintenance
it's used . If the car needs.
is not
Your
needs
its design
drivencar's
often,
youdepend
shouldoninspect
the
and how
used. If the
the car
is not
fluid
andit'soverhaul
hydraulic
driven often,
inspectthan
the
system
at you
lowershould
mileage
fluid
and overhaul
thelining
hydraulic
recommended
. Although
wear
system not
at belower
mileage
than
should
a problem,
corrosion
recommended.
Although
lining
wear
and seal leakage may be, because time
should
be ofa aproblem,
corrosion
becomesnot
more
factor.
and seal leakage may be, because time
becomes more of a factor.
Brake adjusting is not needed with
BRAKE
ADJUSTMENT
many
cars.
Disc .brakes are self adjustBrake
adjusting
is notbrakes
needed
with
usually
ing and modern drum
many
cars.
Disc,brakes
are
self
adjusthave automatic adjusters. If your car
ing such
and modern
has
features,drum
forgetbrakes
brake usually
adjusthave automatic
adjusters.
If yournew
car
ment
except when
installing
has
such
features,
forget
brake
adjustdrum-brake linings. Often, a drum
ment
exceptbe when
installing
brake must
adjusted
manuallynew
to
drum-brake
linings. adjuster
Often, ato drum
the automatic
work
allow
brakefirst
musttime.
be adjusted
manually
to
the
Automatic
adjusters
allow
the
automatic
adjuster
to
work
only maintain clearance-they don't
the first
Automatic
adjusters
make
largetime.
adjustment
changes.
only
clearance-they
don't
On maintain
drum brakes
without automatic
make large adjustment
changes.
adjusters,
periodic adjustment
is
On drum
brakes wear,
without
automatic
needed.
As linings
clearance
beadjusters,
periodic
adjustment
is
and drum
increases.
tween the shoes
needed.
As linings
wear, pedal
clearance
beThis
results
in more
travel.
tween
theparking
shoes and
drum
increases.
brake
requires
more
Also, the
This
results
in
more
pedal
travel.
travel. You can usually tell when
the
Also,
parking
brakebyrequires
more
brakesthe
need
adjusting
the increase
travel.
can However,
usually tellifwhen
the
in pedalYou
travel.
you wait
brakes
need
adjusting
by
the
increase
too long, the pedal may go to the floor
in
pedal fade
travel.
However,
if youadjust
wait
if brake
occurs.
Therefore,
too
long,
the
pedal
may
go
to
the
floor
the brakes often; don't take risks.
if brake fade occurs. Therefore, adjust
the brakes often; don't take risks.
121
>i~
Torn I nner Lining Restricts Flow,
Acts as Valve.
Torn Inner Lining Restricts Flow,
Fitting Leakage Seeps Out
or Forms Bubble.
Fitting Leakage Seeps Out
or Forms Bubble.
Although duo-servo brake uses automatic
adjuster, brakes must be manually adjusted
after brake-lining
replacement.
Although
duo-servo
brake usesBlade-type
automatic
tool
is used
to turn
adjuster
through
slot in
adjuster,
brakes
must
be manually
adjusted
backing
plate (arrow).
after
brake-lining
replacement. Blade-type
tool is used to turn adjuster through slot in
backing plate (arrow).
Inspecting and changing brake fluid is an
important part of brake maintenance. Race
car
is getting
filling of brake
AP Racing
fluid.
Inspecting
andachanging
fluid is
an
Note
reservoir
cap
withmaintenance.
rubber bellows.
It
important
part of
brake
Race
isolates
fluid from
the of
airAP
when
cap fluid.
is in
car
is getting
a filling
Racing
place,
but allowscap
fluid
to rise
and bellows.
fall.
Note reservoir
with
rubber
It
isolates fluid from the air when cap is in
place, but allows fluid to rise and fall.
Most modern road-car brakes are
discs on the front and drums in the
Most
modern
road-car brakes
are
rear.
With
this dual-braking
system,
discs
on
the
front
and
drums
in
the
only the drum-brake system can go
rear.
this dual-braking
system,
out ofWith
adjustment.
Typically there
is a
only
the drum-brake switch
system in
can the
go
brake-warning-light
out
of
adjustment.
Typically
there
is
system that senses excess movementa
brake-warning-light
switchWhen
in the
of
the rear-brake fluid.
the
system
that senses
excess
movement
brakes need
adjusting
, more
displaceof
the is rear-brake
fluid. the
When
the
ment
required than
master
brakes
need
adjusting,
more
displacecylinder can supply; the brake
ment is required
the on
master
turns
the
warning-light
switchthan
cylinder
can This
supply;
thewillbrake
warning light.
switch
also
warning-light
switch
detect fluid loss
causedturns
by a on
leakthe
in
warning
light.
This
switch
will
also
either system.
detect
fluid loss
caused
by agenerally
leak in
the rear
brakes
Adjusting
either
system.
requires
jacking up the car, supporting
theunderneath
rear brakes
generally
it, Adjusting
and getting
. There
are
requires jacking up the car, supporting
it, and getting underneath. There are
122
Bottom : Blistered brake hose is ready to
fail. Replace such a hose immediately!
Top:
Hidden
brake-hose
failure
restricts
Bottom:
Blistered
brake hose
is ready
to
flow to
or fromsuch
brake.
Thin layer
of inner
fail.
Replace
a hose
immediately!
lining Hidden
can lift off
surface and
restrict
flow
Top:
brake-hose
failure
restricts
of
fluid
This may
to
flow
to to
or brake.
from brake.
Thincause
layer brake
of inner
apply
laterliftonoffone
side, and
causing
carflow
to
lining can
surface
restrict
swerve.
brake
hoses
shouldbrake
be reof
fluid toOld
brake.
This
may cause
to
placed later
as aonsafety
precaution.
apply
one side,
causingDrawing
car to
courtesy
Bendix
Corporation.
swerve. Old
brake
hoses should be re-
placed as a safety precaution. Drawing
courtesy Bendix Corporation.
many types of brake adjusters. One is
a square bolt head projecting from the
many
types
of brake
adjusters. Onead-is
backing
plate.
Most domestic-car
a squarerequire
bolt head
projecting
from
justers
inserting
a tool
intothea
backing
plate.
Most
domestic-car
adslot in the backing plate and turning
justers
require
inserting
a
tool
into
the star wheel. There may be one ora
slot
the backing
plate
and dependturning
moreinadjusters
on each
brake,
the on
starthewheel.
ing
design.There may be one or
more
adjusters
each brake, dependthe on
shop-manual
instrucFollow
ing
on
the
design.
tions for brake adjustment. Be sure
the shop-manual
notFollow
to overtighten
the brakes. instrucA dragtions brake
for brake
adjustment.
Because
sure
will overheat
and can
ging
not
to
overtighten
the
brakes.
A
dragdamage, excess wear, lower mileage
ging
brake
will overheat and can cause.
or fade
.
damage,
excess
lower
mileage
Make sure
the wear,
parking
brake
is not
or
on fade.
when adjusting rear brakes.
Make sureyou
thewon
parking
braketo.isThe
not
Otherwise,
' t be able
on
when
adjusting
rear
brakes.
parking brake is applied to the rear
Otherwise,
youare
won't
be able
to. The
brakes, which
usually
drums.
You
parking
brake
is
applied
to
the
rearif
will think the brake is fully adjusted
brakes,
which
are
usually
drums.
You
you try it with the parking brake on.
will
think
the fool
brake
is fully adjusted if
Don't
let this
you.
you
try it with
thedrum-brake
parking brake
on.
Normally,
rear
adjustDon't
let this
fool
you.of parking-brake
ment will
take
care
Normally, rear
drum-brake
adjustment.
Except
on some adjustfourment
will
take
care
of
wheel, disc-brake cars,parking-brake
you should
adjustment.
on the
someparking
fournever need Except
to adjust
wheel,
disc-brake
cars,
you
should
brake unless it won't work ajteradjustnever
to adjust
the parking
ing the need
rear brakes.
Parking-brake
adbrake
unless
it
won't
work
afteradjustjustment is discussed on page
135.
ing the rear brakes. Parking-brake adjustment
is discussed on page 135.
HYDRAULIC-SYSTEM
INSPECTION
HY
DRAULIC-SYSTEM
Besides
brake adjustment, the most
INSPECTION
common
maintenance item is checkbrake adjustment,
ingBesides
the hydraulic
system . To the
be most
safe,
common
maintenance
item
is
check the fluid level about everycheck5000
ing
the Fluid
hydraulic
system.
be safe,
miles.
leakage
can To
cause
total
check
the fluid
about
every
5000
brake failure
onlevel
a single
brake
system.
miles.
Fluidcause
leakage
can cause
It
can also
problems
on a total
dual
brake failure on a single brake system.
It can also cause problems on a dual
system . If you discover that fluid level
has dropped each time you look at it,
system.
If you
discover
level
problem
andthat
fixfluid
it. Fluid
locate the
has
dropped
each
time
you
look
at it,
shouldn't leak from a brake system.
locate the aproblem
it. Fluid
Typically,
leak canand
be fix
traced
to a
shouldn't
leak from a brake
defective wheel-cylinder
seal, system.
caliper
Typically,
a leak canOr,be atraced
or master-cylinder.
leak to
maya
defective
wheel-cylinder
seal,
caliper
occur at a fitting or hole in a line or
or
master-cylinder.
a leak
brake
hose. Look forOr,drips
and may
wet
occur near
at a the
fitting
or holesystem.
in a line
or
areas
hydraulic
Fluid
brake
hose.
Look
for
drips
and
wet
be fixed
immeleaks should
areas
near the hydraulic system.
diately-procrastination
can Fluid
be
leaks should be fixed immedangerous!
diately-procrastination
can , you
be
In addition to fluid level
dangerous!
should check all brake hoses and
In This
addition
to done
fluid while
level,youyou
lines.
can be
' re
should
check
all
brake
hosesunder
and
performing other maintenance
lines.car,
This
canasbeadjusting
done while
the
such
the you're
brakes
performing
other
maintenance
or doing a lube job. Inspect the under
brake
the
car,
as adjusting
theLook
brakes
both ends
of the car.
for
hoses
at such
or doingchafe
a lube
job. Inspect
brake.
cracks,
marks,
or otherthe
damage
hoses
at both
the car. Look
for
on aends
hoseofindicates
failure.
A lump
cracks,
chafe
marks,
or other
damage.
Fluid can
seep
through
the first
few
A lump
a hose indicates
layers
of on
reinforcing
cord and failure.
form a
Fluid
can
seep
through
the If
first
few
lump or blister on the hose.
a hose
layers
reinforcing
cord and form
Don'ta
blisters,ofreplace
it immediately.
lump orsudden
blister brake
on the
hose. If a hose
chance
failure.
blisters,
replace
it
immediately.
Occasionally, a pinhole in a Don't
brake
chance
sudden
brake
failure.
hose can
allow air
to get
into the brake
Occasionally,
pinhole
a brake
fluid
. The hole acan
be theintype
that
hose can
allowwhen
air to get
the brake
leaks
only
the into
brakes
are
fluid.
The drawing
hole can in
be the
that
released,
air, type
creating
leaks
when
the brakes
are
bubblesonly
. When
pressurized
, this leak
released,
drawing
not let in
fluidair,
out. creating
If your
can
seal and
bubbles.
When
this leak
brake hoses
arepressurized,
old and weathered,
can
seal
and
not
let
fluid
out.
If your
replacing them may cure a recurring
brake
hoses
are
old
and
weathered,
spongy pedal.
replacing
them may
a recurring
can cure
fail because
of
Brake hoses
spongy
pedal.
improper installation. If a hose is
Brake or
hoses
can fail
of
twisted
installed
in because
the wrong
improper
installation.
If
a
hose
is
position, it can break. Or, if a car is
twisted onor rough
installed
in large
the wrong
driven
terrain,
wheel
position,
it can
if a car
is
movements
can .break.
strain Or,
a brake
hose.
driven
on
rough
terrain,
large
wheel
Also , hoses can be damaged by rocks
movements
can strain
or
road debris
throwna brake
up byhose.
the
Also,
damaged by
rocks
I've can
seenbebrake-hose
damage
wheels.hoses
or roadbydebris
thrown over
up bydebris
the
caused
a car running
wheels.
I've
seen
brake-hose
damage
that gets tangled in a wheel and
caused
a car running
over debris
wrappedby around
the brake
hose.
that
getscause
tangled
in damage
a wheelis and
Another
of hose
letwrapped
aroundcaliper
the hang
brakefrom
hose.
ting a disc-brake
its
Another
cause
of hose damage
lethose during
maintenance:
Use ofis corting
disc-brake caliper
hang fromwill
its
procedures
rect a maintenance
hose during
of coravoid
such maintenance:
potentially Use
dangerous
rect maintenance procedures will
situations.
avoid
potentially
Check such
Clearances
- If yourdangerous
car has
situations.
wide wheels, fat tires , or other suspenCheckmodifications,
Clearances-If look
yourforcarchafe
has
sion
wide
fat tires,
other. suspenmarkswheels,
on the
brakeorhoses
A tire
sion
modifications,
look for
touching
a hose eventually
can chafe
wear
marks
on
the
brake
hoses.
tire
through it. Even something Aminor
touching
a large-diameter
hose eventuallyheavy-duty
can wear
like
a set of
throughcanit.cause
Evensimilar
something
minor
shocks
problems.
like a set of large-diameter heavy-duty
shocks can cause similar problems.
To check clearances, turn the front
wheels to full right and left lock and
To check
the sides.
front
check
them.clearances,
Check atturn
both
wheels
to
full
right
and
left
lock
the
Clearances may not be exactly and
check Jack
them.upCheck
at and
bothlook
sides.
same.
the car
at
Clearances with
may the
not wheels
be exactly
the
clearance
at full
same.
at
Next, up
jacktheup car
oneand
rearlook
wheel.
droop. Jack
clearance
with
the
wheels
at
full
This will compress the diagonally
droop.
jack suspension.
up one rear wheel.
Check
oppositeNext,
front
This
will compress
thethediagonally
clearances,
then jack up
opposite
oppositeandfront
suspension.
Check
corner
recheck.
Conditions
and
clearances,
then
jack
up
the
opposite
clearances change a great deal as the
corner
and recheck.
Conditions
wheels travel
up and down
as they and
are
clearances
great deal
as the
steered. Trychange
every apossible
combinawheels
up Although
and down front
as they
are
tion to travel
be sure.
hoses
steered.
Try
every
possible
combinahave the most clearance problems,
tion
to be sure.
hoses
particularly
whenAlthough
turning, front
check
the
havehoses
the as
most
rear
well.clearance problems,
particularly
turning,
the
If your carwhen
has been
usedcheck
off road,
rear
hoses
as
well.
check the condition of the steel brake
If your
car the
has car.
beenIt's
used
off road,
lines
under
possible
to
check
the
condition
of
the
steel
brake
pinch a line when going over a rough
lines under
It's possible
to
If youthe
findcar.
a damaged
line, resurface.
pinch
a
line
when
going
over
a
rough
place it. Look closely. A crack or a
surface.
a damaged
thin spotIfisyou
veryfind
hard
to see. line, replace
it.
Look
closely.
A crack
or a
If your car is older, check
the steel
thin
hard to Rust
see. can eat
linesspot
foris very
corrosion.
If yoursteel
car is
older,
check
the steel
even
though
they
through
lines,
lines
for
corrosion.
Rust
eat
are about as corrosion-proof ascan
science
through
steel
lines,
even
though
they
can make them. The likelihood of
are
about
as corrosion-proof
science
having
rusty
brake lines is as
greater
if
can
make
them.
T
h
e
likelihood
of
you drive where salt is used on the
havinginrusty
greater
if
roads
the brake
winter.lines
You iscan
expect
you
drive
where
salt
is
used
on
the
trouble from salt-water spray. Older
roadsfrom
in the
Youand
canMidwest
expect
cars
the winter.
Northeast
trouble
from
salt-water
spray.
Older
are likely to require brake-line
cars
from
the
Northeast
and
Midwest
replacement. Rusty brake lines is a
are
to require
brake-line
usual likely
problem
on vintage
cars.
replacement. Rusty
brake lines
is a
most restorers
replace
Consequently,
usual
problem
on
vintage
cars.
them without bothering to check .
Consequently,the
most
restorers
Remember,
inside
rustsreplace
from
them
without
bothering
water in the brake to
fluidcheck.
as
Remember, the inside
rusts check
from
well-something
you can't
water
visually. in the brake fluid as
well-something
you
visually.
BRAKE BLEEDING
can't
check
Bleeding is important to proper
BRAKE
BLEEDING
brake-system
maintenance. It is usualBleeding
is important
to trapped
proper
ly done to remove
air bubbles
brake-system
maintenance.
in the system.
Bleeding isIt isa usualmust
ly donetime
to remove
air bubbles
trapped
every
the hydraulic
system
is
in the system.
Bleeding
opened
up for any
reason is
. Ita ismust
imevery
hydraulic
is
possibletime
to the
prevent
some system
air from
opened uptheforsystem
any reason.
It is imentering
if a fitting
is
possible
prevent
some
from
loosened. toMost
systems
haveairnumerentering
system
a fitting
is
ous
high the
spots
whereif air
will be
loosened.
Most
systems
have
numertrapped .
ous
highbleeding
spots can
where
air will be
Brake
be frustrating
or
trapped.depending on the system
easy,
Brake Some
bleedingbleeders
can be frustrating
or
are reached
design.
easy,
depending
on
the
system
easily on the inboard side of the
design.
Someunderneath.
bleeders are
brakes, from
On reached
others,
easily
on bethe
inboard
of the
they may
tucked
insideside
the suspenbrakes, from underneath. On others,
they may be tucked inside the suspen-
Someone previously installed wide wheels
on myoid Ford truck, but didn't check
brake-hose
clearanceinstalled
with front
wheels
at
Someone
previously
wide
wheels
full my
lock.old
After
some
use,but
wheel-rim
edge
on
Ford
truck,
didn't check
rubbed
through
line,with
causing
a leak.
brake-hose
clearance
front wheels
at
Fortunately,
was
discovered
full
lock. Afterdamage
some use,
wheel-rim
edge
during
maintenance,
rather athan
by
rubbed brake
through
line, causing
leak.
"accident."
Fortunately, damage was discovered
during brake maintenance, rather than by
"accident!'
sion where they are real "knuckle
busters" to get at. Some systems also
sion
theyother
are real
have where
bleeders
than"knuckle
at the
busters"
to
get
at.
Some
also
the master
wheels, such as on systems
have
bleeders
at the
cylinder.
Consultother
your than
shop manual
wheels,
such bleeders.
as on the
for any hidden
If youmaster
miss
cylinder.
Consult
your
shop
manual
one, you will wonder why your
pedal
for
any hidden
bleeders.
If you miss
is spongy
even after
bleeding.
one,
you will
wondercan
whyusually
your pedal
Bleeder
screws
be
is
spongy
even
after bleeding.
turned
with
a small
Six-pOint box-end
BleederA void
screwsusing
can anusually
be
wrench.
open-end
sk-point
box-end
turned
with
a
small
wrench to prevent rounded-off bleedwrench.
using knuckles.
an open-end
er
screwsAvoid
and bloody
For
wrench
to prevent rounded-off
bleeddifficult-to-get-to
bleeders, special
er
screws
and bloody
knuckles.
For
bleeder
wrenches
are available
at autodifficult-to-get-to
bleeders,
special
parts stores. These look like a box-end
bleeder
wrenches
available at autowrench with
a hugeare
offset.
parts
look like
box-enda
that there
is ausually
Be stores.
aware These
wrench
with
a
huge
offset.
bleeder at each brake, but some sysBe use
aware
that there
usually
tems
a single
bleederis to
servicea
bleeder
each brake, but some sysboth rearatbrakes.
tems
use anormally
single bleeder
to at:
service
Bleeders
are found
both
rear
brakes.
• Each drum-brake wheel cylinder.
normally are
found two
at: or
caliper• Bleeders
Each disc-brake
Each
drum-brake
wheel
more
bleeders
may be
used.cylinder.
or
Outlet disc-brake
port at caliper-two
some master
• Each
more
bleeders
may
be
used.
cylinders, particularly those mounted
O an
u t angle.
l e t port at some master
at
cylinders,
those
mounted
combination
valves
used
• On someparticularly
at
an
angle.
with disc brakes.
On some
combination
used
• On
accessories,
such valves
as trailer
with
disc
brakes.
brakes.
On accessories,
as trailer
Don't
forget to looksuch
for bleeders
on
brakes.sides of a disc-brake caliper.
both
Don't
forget
to look
for bleeders
bleeders on
Some
fixed
calipers
have
on
both
sides where
of a you
disc-brake
caliper.
the inside
would expect,
Some
fixed calipers
have bleeders
plus another
on the outside
hidden on
by
the
inside
where
you
would
expect,
the wheel. If you don't remove
the
plus another
on the
by
wheel,
you'll
missoutside
the hidden
outboard
the
wheel.
If
you
don't
remove
the
bleeder.
wheel,
you'llto miss
replacethetheoutboard
rubber
Be sure
bleeder.
Be sure to replace the rubber
When brake line rusts, fittings can seize on
steel tube. This can happen when seized
fitting brake
is turned
with a
wrench.
When
line rusts,
fittings
canAlthough
seize on
such tube.
a lineThis
maycan
nothappen
leak, it
should
be
steel
when
seized
replaced.
fitting
is turned with a wrench. Although
such a line may not leak, it should be
replaced.
Brake bleeding can be awkward and
messy. Consequently, it's easy to do the
job
wrong
or miss
a bleeder.
Take your
Brake
bleeding
can
be awkward
and
time,
the job right,
messy.plan
Consequently,
it'sand
easyuse
to correct
do the
tools.
Startorbymiss
jacking
up theTake
car your
and
job
wrong
a bleeder.
removing
wheels
to improve
access.
time,
planthe
the
job right,
and use
correct
tools. Start by jacking up the car and
removing the wheels to improve access.
bleeder-screw caps if your brakes
have them . They protect the bleederbleeder-screw
caps if from
yourmoisture
brakes
screw
seat and threads
have
them.
They
protect
the
bleederand prevent corrosion seizure. These
screw
seat andcan
threads
from moisture
caps, which
be purchased
from
and
prevent dealers,
corrosionareseizure.
Volkswagen
a goodThese
addicaps,
cancar.be purchased from
tion towhich
any road
Volkswagen
dealers,
are involves
a good addiAnother frustration
the
tion
to
any
road
car.
metering valve used on some road
Another
frustration
involves
the
to hold this
cars.
A special
clip is used
metering
on can
some
road
valve openvalve
so theused
brakes
be bled.
cars. A special clip is used to hold this
valve open so the brakes can be bled.
123
Note that caliper has a bleeder on each side. Forget to remove the
wheel and you'll miss bleeding outboard side. This can result in a
spongy
pedal.
Photo
Note that
caliper
hascourtesy
a bleederAP
onRacing.
each side. Forget to remove the
wheel and you'll miss bleeding outboard side. This can result in a
spongy pedal. Photo courtesy AP Racing.
Pressure bleeder is used in most repair shops because of its
speed. Huge can of fluid is used to fill pressure bleeder. Because
most racers
fear possible
of oldrepair
or contaminated
fluid, of
presPressure
bleeder
is used use
in most
shops because
its
sure
bleeders
areofnot
popular.
road
cars, they
offerBecause
speedy
speed.
Huge can
fluid
is usedFor
to fill
pressure
bleeder.
low-cost
brake
bleeding
in ause
shop.
most racers
fear
possible
of old or contaminated fluid, pres-
sure bleeders are not popular. For road cars, they offer speedy
low-cost brake bleeding in a shop.
If it's not held open , the brakes can't
be fully bled.
If Consult
it's not held
brakes
the open,
shop the
manual
forcan't
the
be
fully
bled.
correct information on your car. If
Consult
the shop
thea
you
don ' t have
a shopmanual
manual,for
visit
correct
information
on your It's
car.too
If
car
dealer
and ask a mechanic.
you
don't have
a shop manual,
dangerous
for guesswork
in thisvisit
area.a
car
a mechanic.
too
Youdealer
may and
also ask
have
to buy a It's
special
dangerous
for
guesswork
in
this
area.
tool from the dealer. This tool is often
may also
have to
to buy
special
aYouspring
designed
flex awithout
tool from the
often
damaging
thedealer.
valveThis
as tool
fluidis flows
athrough
springit. designed to flex without
damaging the
as fluid
flows
Sequence
of valve
Bleeding
- Bleeding
throughbe
it. done in a specific sequence
should
Sequence
to avoid the of
need Bleeding
to double-Bleeding
back and
should
be
done
in
specific
sequence
rebleed . Follow athis
sequence
if
to avoidbleeding
the need
double
you're
onetowheel
at aback
time:and
rebleed.
this itsequence
if
• Master Follow
cylinder-if
is bleeder
you're
bleeding
one
wheel
at
a
time:
equipped.
l Master cylinder-if
• Combination valve. it is bleeder
equipped.
• Bleeders on intermediate hardware
l Combination
valve.
in
system.
l Bleeders on intermediate hardware
• Wheel
farthest
from
master
in system.usually the right rear wheel.
cylinder,
W h e eIfl wheel
farthest
from have
master
Note:
cylinders
two
cylinder,
the one
rightfirst;
rear if
wheel.
bleeders, usually
do upper
a caliNote:
wheel
cylinders
have one
two
per hasIftwo
bleeders,
do inboard
bleeders,
do
upper
one
first;
if
a
califirst. If it has more, follow the manuper has two recommended
bleeders, do inboard
one
facturer's
bleeding
first. If it has more, follow the manusequence.
facturer's
recommended
bleeding
• Bleed
other
brake
at
that
sequence.
end - usually left rear.
e e d next
otherwheel
brake
at from
that
•B lBleed
farthest
end-usually
left rear. right front.
master cylinder-usually
Bleed next
farthest from
•l Bleed
wheel wheel
remaining-usually
master
cylinder-usually
right front,
left front.
l Bleed
wheelbleeding
remaining-usually
After the
process is
left front. check the system by presscomplete,
After the bleeding process is
complete, check the system by press-
124
ing hard on the pedal to be sure it
stays firm. If the pedal is spongy, reing
on or
thecheck
pedalfortoa leak.
be sure it
bleedhard
system
stays
firm.
If
the
pedal
is
spongy,
reTo check for air in the brake
bleed
system
or
check
for
a
leak.
system, have someone pump the
To several
check times,
for airthenin hold
the it brake
pedal
down
system,
have
the
firmly while
yousomeone
remove thepump
reservoir
pedal
several
times,
then
hold
it
down
cap. Watch the fluid surface while
firmly helper
while you
remove
the reservoir
your
slides
his foot
off the
cap.
the pedal
fluid snaps
surface
pedal Watch
pad so the
backwhile
and
your
slidesdrops
his immediately.
foot off the
systemhelper
pressure
pedal apad
so the pedal
snaps
back
With
well-bled
system,
there
willand
be'
system
pressure
drops
immediately.
a little turbulence at the surface of the
With
system,
there
will1/4
be'
fluid. aIfwell-bled
fluid boils
up more
than
ain.little
turbulence
at
the
surface
of
the
above the surface, there's probably
fluid.
If fluid
boils up more than 1/4
air in the
system.
in.
above
the
surface,
there'scommonly
probably
Bleeding Methods - Three
air
in the
system. for brake bleeding
used
techniques
Bleeding Methods-Three commonly
are:
used
techniques
for brake bleeding
bleeding.
• Pressure
are:
• Manual bleeding.
l
Pressuremethods,
bleeding. such as gravity
• Special
l
Manual
bleeding.
bleeding or vacuum bleeding.
l Special
suchargue
as gravity
These allmethods,
work. People
which
bleeding
or
vacuum
bleeding.
method works better. All good arguTheseare
all so
work.
People that
arguenothing
which
ments
complex
method
better.
good arguwill everworks
be settled
. So,All
I suggest
that
ments
are so
complex
that method,
nothing
if you have
trouble
with one
will
ever beuntil
settled.
try another
youSo,
findI suggest
the one that
that
if you best
havefor
trouble
with one method,
works
your car.
tryI'll
another
until
you of
findthe
theproblems
one that
explain
some
works
best
for
your
car.
with each method. Then I'll explain
I'lleach
explain
how
job issome
done. of the problems
with
each method.
Then requires
I'll explaina
Pressure
bleeding
how
each
job
is
done.
pressure-bleeder tool. The pressure
Pressure
bleeding
requires
bleeder
pressurizes
the fluid
in thea
pressure-bleeder
tool. The you
pressure
reservoir.
Once pressurized,
open
bleeder
pressurizes
fluid innoted
the
each
bleeder
in the the
sequence
reservoir. Once pressurized, you open
each bleeder in the sequence noted
until no air is left in the system.
The advantage of pressure bleeding
until
is leftand
in the
is
thatnoit air
is fast
onesystem.
person can do
The
advantage
of
pressure
the job. But, there
are bleeding
several
is
that
it
is
fast
and
one
person
can do
disadvantages: The tool is expensive
the ajob.
But,
are several
and
lot of
fluidthere
is wasted.
If you
disadvantages:
The toolbleeder
is expensive
don't use the pressure
often,
and
a lotin of
fluidcontaminated,
is wasted. If even
you
the fluid
it gets
don't
use
the
pressure
bleeder
often,
though it' s in a sealed container.
theFluid
fluid flow
in it gets
contaminated,
in the
lines is higheven
if a
though
a sealed container.
bleeder it'sis inopened
too far during
Fluid flow
the cause
lines isbubbles
high if toa
bleeding.
Thisin can
bleeder
is
opened
too
far
turbuform within the system from during
bleeding.
Thisas can
causeflows
bubbles
to
lence created
the fluid
around
form within
system
fromtheturbusharp
corners.theThis
defeats
purlence created
as the Conversely,
fluid flows around
pose
of bleeding.
rapid
sharp
corners.
This
defeats
the purfluid flow flushes out
air trapped
in
pose
bleeding.
rapid
high of
spots
in the Conversely,
system . Bubbles
fluid
flow
trapped
in
the wallsout
of air
rough
compoclinging
to flushes
high
spots
in
the
system.
Bubbles
nents will be washed away by the flow.
clinging
to the
the pros
wallsand
of rough
With all
cons, itcompois not
nents if
willpressure
be washed
away byis the
flow.
clear
bleeding
good
or
With
all
the
pros
and
cons,
it
is
bad . Most auto-repai r garages usenot
it
clear
if pressure
or
because
pressure bleeding
bleedingis isgood
fastbad.
use it
most Most
racers,auto-repair
don't duegarages
to potential
because pressure bleeding
fluid-contamination
problems.is fastmost
racers,bleeding
don't due
to advantage
potential
Pressure
has an
fluid-contamination
problems.
on an older car which has had little
Pressure
bleeding The
has an
advantage
brake
maintenance.
master
cylinon
older
which
hasstroked
had little
der an
does
notcar
have
to be
to
brake
maintenance.
Thesystem
master
cylinpush fluid
through the
. This
is
der
does
have to be stroked
to
unlike
thenot
manual-bleeding
method
push
fluid through
the system.
is
that requires
full strokes
of theThis
brake
unlike
theanmanual-bleeding
older car, there method
may be
pedal. On
that requires
themaster
brake
corrosion
andfull
dirtstrokes
insideofthe
pedal.
On
an
older
car,
there
may
be
cylinder. Stroking the pedal to the
corrosion
andthedirt
inside
theinto
master
floor
moves
piston
deep
the
cylinder.
Stroking
the itpedal
the
master cylinder,
where
would to
other-
floor moves the piston deep into the
master cylinder, where it would other-
Most racers prefer manual-bleeding method : One person opens and closes bleeders while
helper operates brake pedal. Although optional, it's helpful for third person to watch reservoir
add fluid
when
needed. Method
is reliable,
but success
on communication
Mostand
racers
prefer
manual-bleeding
method:
One person
opensdepends
and closes
bleeders while
between
those doing
job.
helper
operates
brake
pedal. Although optional, it's helpful for third person t o watch reser-
voir and add fluid when needed. Method is reliable, but success depends on communication
between those doing job.
wise never travel. Corrosion and dirt
would likely damage the seals, causing
wise
travel. Pressure
Corrosion bleeding
and dirt
them never
to leak.
would
likely
damage
the
seals,
causing
avoids this.
them
to
leak.
Pressure
bleeding
Manual bleeding is cheaper, but reavoids this.
quires
at least two people; while one
Manualthe
bleeding
cheaper,
reoperates
pedal, isthe
other but
opens
quires
at
least
two
people;
while
one
and closes the bleeders. The fluid
operates
the other
opens
reservoir the
has pedal,
to be topped
up during
and
closes the
bleeders.
the bleeding
process.
FluidThe
flowfluid
can
reservoir
has todepending
be toppedonuphow
during
be fast or slow,
fast
the
process. and
Fluidhow
flow
can
the bleeding
pedal is pushed
much
be
fast
or
slow,
depending
on
how
fast
each bleeder is opened. Manual bleedthe
pedal
is pushed better
and how
ing can
be controlled
thanmuch
preseach bleeding
bleeder is, so
opened.
Manual
bleedsure
most racers
prefer
it.
ing
be job
controlled
Andcan
, the
wastes better
little than
fluidpresand
sure
bleeding,
most racers
prefer it.
doesn't
requireso
expensive
tools.
And,
the
job
wastes
little
fluid
and
Gravity bleeding can be done only
doesn't
require
expensive
tools.
with certain brake systems. As you
Gravity
beforms
done bubonly
know,
air inbleeding
the brakecan
fluid
with
certain
brake
systems.
As
bles that float to high points in you
the
know,
thehigh
brake
fluid
bubsystem.airIfin
the
point
is forms
the master
bles that float
high points
the
cylinder,
air to will
come in out
system. If the high point is the master
automatically.
cylinder,
air
will
out
Gravity bleeding
is notcome
used often
automatically.
because it takes too long. Also , in
Gravity
bleeding
not used
thereoften
are
almost
every
brake is
system,
because
takesmake
too itlong.
Also, . in
high spotsit that
impossible
If
almostareevery
brake system,
are
you
designing
a brakethere
system
high spots
that you
makemay
it impossible.
If
from
scratch,
be able to
you
system
make areit designing
possible toa brake
self-bleed
by
from scratch,
yousystems
may be
to
gravity,
but most
are able
not demake
it
possible
to
self-bleed
by
signed that way.
gravity,
but most systems
aredone
not deVacuum-bleeding
can be
by
signed
that way.
one person.
A small hand-operated
Vacuum-bleeding can be done by
one person. A small hand-operated
eTA Manufacturing's bleeder hose, available at many auto-parts stores, makes it
possible
for one person
to manually
bleed
CTA
Manufacturing's
bleeder
hose, availabrakes.
Hoseauto-parts
is slipped
over makes
bleeder,
ble
at many
stores,
it
bleeder is
and free
end is put
in
possible
foropened
one person
to manually
bleed
catch canHose
or bottle.
Fluid orover
air can
only
brakes.
is slipped
bleeder,
flow
out isofopened
hose. When
pedal
bleeder
and free
endcomes
is putup,
in
one-way
closes.
This
air
catch
canvalve
or bottle.
Fluid
or prevents
air can only
from out
entering
hose.
Using
hose
requires
flow
of hose.
When
pedal
comes
up,
getting in valve
and out
of carThis
to check
for air
one-way
closes.
prevents
bubbles
in hose
andUsing
fluid hose
in reservoir.
from
entering
hose.
requires
Photo byinRon
getting
andSessions.
out of car t o check for air
bubbles in hose and fluid in reservoir.
Photo by Ron Sessions.
Master
Cylinder
-
1
t'.
To 0
Reservoir
To o
Master
Cylinder
-
Reservoir
-
Gravity
Bleeding
or Caliper
Master
Cylinder
I
-
.
Trapped
Bubbles
Master
Cylinder
-
No Gravity Bleeding
Possible
or Caliper
Gravity
Bleeding
Bleeding
If brake system
is free
of high spots that trap No
air,Gravity
bleeding
can be Possible
done automatically by
gravity. Air bubbles rise to reservoir. If system has high spots in lines, as shown at right,
system
not gravity
If brakewill
system
is freebleed.
of high spots that trap air, bleeding can be done automatically by
gravity. Air bubbles rise t o reservoir. If system has high spots in lines, as shown at right,
system will not gravity bleed.
vacuum pump is attached to a jar-or
plastic bottle-with a closed top. The
vacuum
is attached
to ableeder.
jar-or
jar
has a pump
hose that
goes to the
plastic
bottle-withfrom
a closed
the jartop.
and The
the
Air
is evacuated
jar
has a ishose
that goes
the bleeder.
bleeder
opened.
The to
vacuum
pulls
Air
evacuated
from
the the
jar hydrauand the
air bubbles
from
fluidisand
bleeder
is
opened.
The
vacuum
pulls
lic system and into the jar.
fluid
and airbleeding
bubbles sounds
from theneat,
hydrauVacuum
but
lic system and into the jar.
Vacuum bleeding sounds neat, but
it has a potential problem. Brakecylinder cup-type seals are meant to
it haswith
a potential
problem.
Brakework
fluid pressure
greater
than
cylinder
cup-type
seals are With
meant the
to
the outside
air pressure.
work
with
fluid fluid
pressure
greater
than
vacuum
pump,
pressure
is below
the
outside air.
air This
pressure.
Within the
the outside
may draw
air
vacuum
is below
past the pump,
seals, fluid
unlesspressure
your hydraulic
the
outside
may drawI in
system
has air.
cupThis
expanders.
donair
't
past the seals, unless your hydraulic
system has cup expanders. I don't
125
Vacuum bleeder sucks fluid or air into container through tube connected to opened bleeder.
Although tool is easy to use and requires only one person, I don't recommend it. Seals in
brakes
allowsucks
air to be
drawn
if vacuum
is applied
totube
brake
fluid.
Vacuumcan
bleeder
fluid
or airininto
container
through
connected
to opened bleeder.
Although tool is easy to use and requires only one person, I don't recommend it. Seals in
brakes can allow air to be drawn in if vacuum is applied to brake fluid.
Master Cylinder
Bleeder Hose
-Glassor
Clear-Plastic
Jar
Pressure Bleeder
Clear-Plastic
Jar
Pressure bleeder setup: Pressure-bleeder tank is charged with compressed air, which
pushes fluid into brake system. Adapter clamps to reservoir, sealing fluid entering system.
Drawing courtesy
Pressure
bleeder Bendix
setup: Corp.
Pressure-bleeder tank is charged with compressed air, which
pushes fluid into brake system. Adapter clamps to reservoir, sealing fluid entering system.
Drawing courtesy Bendix Corp.
Master
Cylinder
1 3
Press slowly on
brake ~ e d a l .
Bleeder Hose
,--1''-<-- G lass or
Clear Plastic Jar
Glass or
Clear Plastic Jar
Setup for manual bleeding: It takes two people, one at the brake pedal and another at the
bleeder. Person operating bleeder should give instructions to person operating the pedal.
Bleeder
openedbleeding:
only whenItpedal
being
pushed
is closed
pedal
is
Setup
foris manual
takesistwo
people,
onedown;
at thebleeder
brake pedal
andbefore
another
at the
returned.
Drawing
courtesybleeder
Bendix should
Corp. give instructions to person operating the pedal.
bleeder. Person
operating
Bleeder is opened only when pedal is being pushed down; bleeder is closed before pedal is
returned. Drawing courtesy Bendix Corp.
126
recommend the vacuum-bleeding
method, although some people use it.
recommend
theroadvacuum-bleeding
Many modern
cars are vacuum
method,
some
people
use it.is
filled
at although
the factory
. The
system
Many modern
roada cars
are vacuum
pumped
down to
nearly
perfect
filled at through
the factory.
The system
is
vacuum
the master
cylinder
pumped
down
to
a
nearly
perfect
by a very large vacuum pump. Then,
vacuum
through
master
fluid
is forced
in atthe
about
100 cylinder
psi. Beby a very
large all
vacuum
Then,
cause
virtually
the airpump.
is removed
fluid
is
forced
in
at
about
100
psi.
Bebefore the fluid is put in, no bleeding
cause
virtually
all
the
air
is
removed
is required. Systems filled like this
before
the fluid
put in, no bleeding
must have
cup is expanders,
but no
is
required. Systems
filled like this
residual-pressure
valves.
must
have and
cup manual
expanders,
but are
no
Pressure
bleeding
residual-pressure
valves.
detailed in the following pages. Before
Pressure
and manual
bleeding
starting,
consult
your shop
manualare
to
detailed
in theprocedures
following pages.
Before
see
if special
must be
folstarting,
yourI'llshop
manual
to
your car.
describe
what
lowed forconsult
see
if
special
procedures
must
be
folis done for a typical car, but be aware
lowed
for your
car.
I'll describe
that it may
not be
correct
for yourwhat
paris
done
for
a
typical
car,
but
be aware
ticular model.
that it may
not be correct
for- your
parHow
to Pressure
Bleed
Pressure
ticular
model.
bleeders are used to save time by
How
to Pressuremechanics.
Bleed-Pressure
most professional
It is a
bleeders
are
used
to
savefastest
timeway
by
one-man job. It is also the
most
professional
mechanics.
It
is
to bleed brakes . You must have a pres-a
one-man
job. Itto isdo
alsothe
thejob,
fastest
waya
sure bleeder
plus
to bleed of
brakes.
You mustair.
have
a pressource
compressed
Pressure
sure
bleeder
to do the
job, amount
plus a
bleeding
also requires
a large
source
of
compressed
air.
Pressure
of brake fluid to fill the pressure
bleeding
bleeder. also requires a large amount
of Abrake
fluidbleeder
to fillhasthe
pressure
pressure
a tank
conbleeder.
taining brake fluid, plus an air comA pressure
bleeder has
tank conpartment
to pressurize
thea fluid.
The
taining
plus anormally
n air comfluid
andbrake
air arefluid,
separated
by
to pressurize
fluid.moisThe
apartment
rubber diaphragm
to the
prevent
fluid
and
separated
normallythe
by
ture in
theairairare
from
contaminating
a rubber
to prevent
fluid.
Thediaphragm
fluid outlet
connectsmoisand
ture intothe
from contaminating
the
seals
theairmaster-cylinder
reservoir
fluid.
The
fluid
outlet
connects
and
with an adapter that fits in place of the
seals
to the
reservoir
onlymaster-cylinder
works on a master
cylincap. This
with
an adapterwith
that fits
in placeintegral
of the
der designed
a sturdy
cap.
This only
works
on acylinders
master cylinSome
master
with
reservoir.
der
designed
with
a
sturdy
integral
remote reservoirs cannot be pressure
reservoir.
Some
master
cylinders
with
bled. Again,
check
the shop
manual.
remote
reservoirs
cannot
be connectpressure
With the
pressure
bleeder
bled.
checkcylinder,
thz shoppressure
manual. is
ed
to Again,
the master
With
the
pressure
bleeder
connectapplied to the hydraulic fluid from
the
ed to
the master
pressure
is
pressure
in thecylinder,
tank. About
30 psi
air
applied
the hydraulic
from dethe
is used. to
Follow
bleedingfluid
sequence
air pressure
in the
About
30 psi
bleeding,
scribed
earlier.
To tank.
do the
is
used.
Follow
bleeding
sequence
each bleeder is opened about de1/4
scribed
do the bleeding,
turn - noearlier.
more.ToOtherwise,
excess
each flow
bleeder
is opened
about
114
fluid
results,
allowing
air and
turn-no
more.
Otherwise,
excess
fluid to escape. When only fluid
fluid
results,
allowing
comesflow
out, the
bleeder
is shut. air and
fluid
to
escape.
When
only fluid
Each pressure bleeder comes
with
comes out, theAlso
bleeder
is shut.
instructions.
supplied
are adapEach
bleeder
comes with
ters
thatpressure
fit popular
master-cylinder
instructions.
Also
supplied
are adap-a
reservoirs . Bled fluid flows through
ters that
fithose
popular
master-cylinder
pushed
on the bleedclear
plastic
reservoirs.
fluid flows
er
and intoBled
a container.
Oldthrough
fluid ora
clear
plastic
hose
pushed
on
the
bleedany fluid bled through a hydraulic
er
and
into
a
container.
Old
fluid
or
system should never be reused.
any fluid bled through a hydraulic
system should never be reused.
A pressure bleeder is convenient
for changing all the fluid in a brake
A pressure
bleeder
is convenient
system.
It allows
the whole
system to
for
changing
all
the
fluid
in atobrake
stop
be refilled without the need
system.
the master
whole system
to
and topIt allows
up the
cylinder.
be
refilled without
stop
However,
if you the
haveneed
theto fluid
and
top byupsomeone
the master
cylinder.
else, you
may
changed
However,
if
you
have
the
fluid
not get to choose the fluid that goes
in
changed
bysystem.
someone
else, you
your brake
Whatever
is inmay
the
not
choose
that goes
in
tankget
is to
what
you the
get,fluid
no matter
what
your
brake system.
is inThe
the
is best Whatever
for your car.
you think
tank
what
get, or
no itmatter
fluid is
may
be you
the best
may bewhat
the
you
think
is
best
for
your
cheapest the shop could buy.car.
AndThe
, it
fluid
maynew
be or
theold.
bestThis
or itismay
the
whybemost
may be
cheapest
theuse
shop
could buy.
And, it
racers won't
a pressure
bleeder.
may
be
new
or
old.
This
is
why
most
How to Manual Bleed-Manual
racers
won't
use a pressure
bleeder.
bleeding
is simple,
but takes
at least
How
to Manual
Bleed-Manual
one helper,
as mentioned
earlier. The
bleeding
is
simple,
but
takes at some
least
equipment needed includes
one
helper,
as
mentioned
earlier.
The
clear plastic tubing to fit the bleeder,
equipment
includes
jar to some
catch
and a glass orneeded
clear-plastic
clear
plastic
tubing
to fit have
the bleeder,
the bled
fluid.
You must
a quart
and
a
glass
or
clear-plastic
jar to
youcatch
are
or two of fresh fluid, unless
the
bled fluid.
have
a quart
changing
the You
fluid.must
Then,
you
may
or
two
of fresh
fluid, unless you are
about
one gallon.
need
changing
fluid. Then,
you may
Bleedingthesequence
remains
the
need
about
one
gallon.
same. Pedal pressure forces fluid and
remains Push
the
bubbles sequence
out the bleeder.
airBleeding
same.
Pedal
forces
and
down on
thepressure
pedal and
hold fluid
it. Open
air
bubbles Fluid
out should
the bleeder.
the bleeder.
flow outPush
the
down
on
the
pedal
and
hold
it. Open
bleeder, through the tube, and
into
the
Fluid
should
the bleeder.
jar. If the
jar-end
of flow
the out
tubethe
is
bleeder,
through
tube,
covered with
fluid,theyou
' ll beand
ableinto
to
the air
jar.bubbles
If the come
jar-endout.of the tube is
see
covered
with
fluid,
be ablethe
to
is opened,
After the bleeder you'll
see airshould
bubblesbecome
out. slowly until
pedal
go down
After against
the bleeder
is oropened,
the
it stops
the floor
stop . Close
pedal
should
be
go
down
slowly
until
the bleeder before the pedal is
it
stops against
the the
floorpedal
or stop.
released.
Usually,
will Close
have
the
before times
the to
pedal
is
to be bleeder
pumped several
" bring
released.
Usually,
the the
pedal
will
have
opening
next
bleeder
it up" before
to
be pumped
in the
sequence.several times to "bring
it up"
before
theatnext
Watch
the opening
reservoir
all bleeder
times.
in thetosequence.
Plan
add fluid at least once while
Watch each
the reservoir
times.
bleeding
wheel. If at
the all
reservoir
Plan
to
add
fluid
at
least
once
while
runs out of fluid, air will be drawn
bleeding
wheel.
If theand
reservoir
into
the each
master
cylinder
you'll
runs to
outstart
of bleeding
fluid, airallwill
drawn
have
overbeagain.
It
into
the
master
cylinder
and
you'll
helps if a third person watches
the
have to
start bleeding
again.the
It
fluid
reservoir
while all
oneover
pumps
helps and
if athethird
the
pedal
otherperson
bleeds watches
.
fluid
the
the one
hosepumps
off the
As reservoir
you pullwhile
pedal
and
the
other
bleeds.
bleeder, fluid in the hose will run out.
As you
you bleed
pull the
the next
hosewheel,
off the
the
When
bleeder,
fluid in
hoseairwill
first
bleeding
willthepush
outrun
of out.
the
When
you bleed
wheel, the
hose. This
makesthe
lotsnext
of bubbles
in
first
bleeding
will
push
air
out of
the jar. So don't assume this
is the
air
hose. the
This
makes lots of bubbles in
bleeder.
from
theOnjar.a So
don't
this is the
air
don't pump
road
car, assume
from
bleeder.
brake the
pedal
with the bleeder open ,
On though
a road the
car,hose
don'tis filled
pump with
the
even
brake
pedal
with
the
bleeder
open,
fluid and submerged in fluid in the jar.
even though
hose iscontaminatfilled with
There's
a risk the
of drawing
fluid
and
submerged
in
fluid
in .the
jar.
ed fluid back into the system
Fluid
There's a risk of drawing contaminated fluid back into the system. Fluid
Not a good setup for bleeding brakes :
Hose should be clear and free end immersed
in fluid
in clear
or jar.
BubNot a good
setup
for bottle
bleeding
brakes:
bles can
then be
andand
mess
is avoided.
Hose
should
beseen
clear
free
end im-
mersed in fluid in clear bottle or jar. Bubbles can then be seen and mess is avoided.
must always be pushed out the
bleeder, never drawn in. On a race
must
be pushed
the
fluid is usually
clean, out
so drawcar, thealways
bleeder,
drawn
in. On
a race
less risky
because
it
ing in oldnever
fluid is
car,
thebe
fluid
is usually
clean, so drawshould
relatively
fresh.
ing
in old fluid is less risky because it
Simultaneous
should
be relatively
fresh. bleeding is
BleedingSimultaneous
Simultaneous
another
manual-bleeding method
Bleeding
bleeding
is
sometimes Simultaneous
used on race cars
with dual
another
manual-bleeding
method
master cylinders. With this method, a
sometimes
raceare
carsbled
withatdual
rear on
brake
the
front and a used
master time.
cylinders.
With this method,
same
Simultaneous
bleedinga
front
a rear
brakeofareeach
bled master
at the
allowsand
a full
stroke
same
time.
Simultaneous
bleeding
cylinder and a straight motion of the
allows
full To
stroke
balance a bar.
do of
this,each
youmaster
need
cylinder helper
and a and
straight
another
tube motion
andjar. of the
balance
bar. To
do this, you
need
simultaneous
bleeding,
To perform
another
helper
and
tube
and
jar.
partially fill the jars with fresh brake
To. perform
bleeding,
Connect simultaneous
one end of each
tube to
fluid
jars withthefresh
bleederfill
andthe
submerge
otherbrake
end
apartially
fluid.
Connect
oneBleed
end ofthe
each
tubeand
to
in a jar
of fluid.
front
arear
bleeder
and
submerge
the
other
end
wheels farthest from the master
in a jar of
fluid.
Bleed
the front
cylinder
first.
If the
calipers
have and
two
rear
wheels
farthest
from
the
first.
bleeders, bleed the inboard side master
cylinder
first. Ifpressure
the calipers
have
two
With gentle
on the
pedal,
bleeders,
bleed
the
inboard
side
first.
simultaneously open both front and
With
gentle pressure
the pedal,
rear
bleeders.
Air will on
bubble
from
simultaneously
open
both
front
and
the hoses and some fluid will
follow.
rear
bleeders.
Air
will
bubble
from
With the bleeders open, slowly pump
the pedal
hoses up
andand
some
fluiduntil
willbubbles
follow.
the
down
With Then,
the bleeders
open,
slowly Go
pump
stop.
close the
bleeders.
to
the
pedal
up
and
down
until
bubbles
the other side of the car-inboard
stop.
Then,
close
thethem
bleeders.
o to
bleeders
if you
have
- and Gbleed
the other
side of
the car-inboard
those
brakes.
Remember,
always
and bleed
bleeders
you have them -level
keep
theif reservoir-fluid
high
those
brakes.
Remember,
always
enough to prevent running out
of
keep during
the reservoir-fluid
high
fluid
the bleeding. Iflevel
you suck
enough
to master
preventcylinder,
runningyouout
of
air
into the
must
fluid over.
during the bleeding. If you suck
start
-
air into the master cylinder, you must
start over.
Plastic bottle and clear plastic hose is
handy for brake bleeding. Note that bottle
is supported
wireclear
looped
over hose
bleeder
Plastic
bottlebyand
plastic
is
screw. for
Bottle
each wheel
minimizes
handy
brakeatbleeding.
Note that
bottle
mess
and brake-bleeding
Clear
is
supported
by wire looped chore.
over bleeder
plastic bottle
shown.
screw.
Bottle isat better
each than
wheelone
minimizes
Photo by
Tombrake-bleeding
Monroe.
mess
and
chore. Clear
plastic bottle is better than one shown.
Photo by Tom Monroe.
Once both sides are bled, test the
action of the balance bar. With the
Once
sides
bled,
the
tubes
stillboth
in the
jars,are
open
one test
bleeder
action
of the
thepedal
balance
bar.to With
the
and push
slowly
the floor.
tubes simulates
still in the jars,
open
This
failure
of one
onebleeder
set of
and
push
the
pedal
slowly
to
the floor.
brakes. The balance bar shouldn't
This
failurebottom.
of one IfsetOK,
of
bind, simulates
nor the pedal
brakes.theThebleeder
balanceandbarrelease
shouldn't
the
close
bind,
bottom.
If OK,
pedal. nor
Test the
the pedal
other brake
system
by
close
the
bleeder
and
release
opening a bleeder at the other endthe
of
pedal.
thetests
other
system
the car.Test
This
thebrake
balance
bar by
at
opening
a bleeder
the master
other end
of
its maximum
angle.atOne
cylinthe is
car.
Thiswith
tests
theunder
balance
bar at
der
filled
fluid
pressure;
its
maximum
angle.
One
master
cylinthe opposite one has no pressure
at
der
is filled
with fluid
under pressure;
all. If
everything
is properly
des igned
the
has no
at
and opposite
built, theone
balance
barpressure
should be
all.
If
everything
is
properly
designed
free at either . extreme angle. If it
and
barremedy
should the
be
outbalance
why and
bindsbuilt,
, find the
free
at either, extreme angle. If it
problem.
binds,
find out why
and remedy
the
Simultaneous
bleeding
is not
problem.
recommended for road cars. Unlike a
Simultaneous
not
race
car, brake fluidbleeding
in a road is
car gets
recommended
for road
bled infrequently,
so it cars.
will Unlike
be dirtya
race contaminated.
car, brake fluidDon
in a'troad
gets
and
risk car
pulling
bled
infrequently,
so
it
will
be
dirty
old fluid back into the system by
and contaminated.
risk bleeder
pulling
pumping
the pedal Don't
with the
old
fluid
back
into
the
system
by
open.
pumping
the
pedal
with
the
bleeder
Eliminating Bubbles-Brakes are
open.
sometimes
spongy after manual
EliminatingSlowBubbles
are
movement
bleeding.
pedal-Brakes
sometimes
spongy
after
manual
avoids fluid turbulence that would
bleeding. form
Slow bubbles.
pedal movement
otherwise
But, slow
avoids
fluid
turbulence
fluid flow will not dislodgethat
smallwould
bubotherwise
form tobubbles.
But, slow
rough surfaces.
If
bles that cling
fluidtap
flow
not dislodge
smalla plasbubthewill
calipers
gently with
you
blesmallet
that cling
rough surfaces.
If
tic
whileto bleeding,
this will
you
tap
the
calipers
gently
with
a
plashelp dislodge those stubborn bubbles.
tic mallet
while bleeding, thisbleedwill
Bleeder
Problems-Sometimes
help
dislodge
those
stubborn
bubbles.
ers cause trouble. A common problem
Bleeder Problems-Sometimes bleeders cause trouble. A common problem
127
To Master Cylinder With Fluid Being Bled Out.
To Master ~ylinder'with
Fluid Being Bled Out.
Penetrating oil is sprayed around studs
before removing stuck brake drum. Before
using
penetrating
make sure
adjuster
is
penetrating
oil isoil,sprayed
around
studs
loose, parts
are stuck
clean,brake
and drum.
all attaching
before
removing
Before
clips
screws are
removed.
usingand
penetrating
oil, make
surePenetrating
adjuster is
oil
mustparts
be removed
after and
use. all attaching
loose,
are clean,
Pedal
Master cylinder being bled strokes its piston forward until pedal hits stop. Other cylinder
piston doesn't travel as far. As a result, balance bar assumes extreme angle when one
master
bled. bled
Balance
bar must
not bind
at thisuntil
angle,
or breakage
result.
Master cylinder
cylinderisbeing
strokes
its piston
forward
pedal
hits stop.may
Other
cylinder
piston doesn't travel as far. As a result, balance bar assumes extreme angle when one
master cylinder is bled. Balance bar must not bind at this angle, or breakage may result.
Caution: Be careful to
avoid spraying brake
fluid.
Do not
hold face
Caution:
Be careful
to
directly
above reservoirs.
avoid
spraying
brake
fluid. Do not hold face
directly above reservoirs.
Press in and
release several
times.
Press in and
release several
Bleeder Tubes
Bleeder Tubes
Dry master cylinder should be bled as shown. This can be done off the car. Bleeder tubes
can be made of copper or steel brake tubing. When reinstalling master cylinder, transfer
lines
quicklycylinder
to minimize
fluidbeleakage.
courtesy
Bendix
Dry master
should
bled asDrawing
shown. This
can be
doneCorp.
off the car. Bleeder tubes
can be made of copper or steel brake tubing. When reinstalling master cylinder, transfer
lines quickly to minimize fluid leakage. Drawing courtesy Bendix Corp.
is a rusted bleeder that seizes. It must
be loosened with care with the correct
is a rusted bleeder
that seizes.
It must
wrench-no
open ends.
A broken-off
be
loosened
with
care
with
the
bleeder screw means you'll havecorrect
to rewrench-no
open component-wheel
ends. A broken-off
place the entire
bleeder
means
you'll cylinder
have to recylinder,screw
caliper,
master
or
place the entire
whateverbecausecomponent-wheel
it is almost imcylinder,
caliper,
master
cylinderhalf
or
remove
the broken
possible to
whatever-because
is almost
without damaging theitdelicate
seat. impossible
the broken
Loosentoa remove
stuck bleeder
screw half
by
without
damaging
the
delicate
seat.
cleaning the area around it with
a wire
Loosen
stuck bleeder
by
brush.
Try a turning
it after screw
cleaning.
cleaning
area try
around
it with
a wire
resort
a good
grade
of
As
a lastthe
brush.
Try oil.
turning
it aafter
cleaning.
penetrating
This is
last resort
beAs a oil
lastcan
resort
a good
grade of
get try
inside
and contamicause
penetrating
oil.
This
is
a
last
resort
benate the brake fluid. After using
cause
oil canoil,
get inside
penetrating
removeandit contamiby disnate the brake
fluid. After
using
the component
and cleanassembling
penetrating oil, remove it by dis-
assembling the component and clean-
128
ing it completely with brake-cleaning
fluid or alcohol.
ingThe
it completely
with brake-cleaning
best penetrating
oil I have
fluid
or
alcohol.
found is called Kroil. Available from
The best
penetrating
I have
Kano
Laboratories
in oil
Nashville,
Kroil. in
Available
found is called
Tennessee,
it comes
a sprayfrom
can
Kanoa plastic
Laboratories
Nashville,
tube that in
attaches
to the
with
Tennessee,
comesyou
in toa spray
nozzle. Thisitallows
direct can
the
with
a
plastic
tube
that
attaches
to less
the
oil exactly where you want it with
nozzle.
allows you to
direct
the
of This
contaminating
other
brake
risk
oil
exactly
where
you
want
it
with
less
parts. Be careful! If penetrating oil
risk on
of brake
contaminating
othermust
brake
linings, they
be
gets
parts.
Be careful! If penetrating oil
replaced.
gets
linings,
they corrosion
must be
prevent
internal
To on
helpbrake
replaced.
and sticking, install rubber bleederTo help
screw
caps. prevent internal corrosion
and
sticking,
rubber bleederFilling
Dryinstall
Tandem
Master
screw
caps.
Cylinders-Fill
a dry tandem master
Filling
Dry
Tandem
Master
Cylinders-Fill a dry tandem master
clips and screws are removed. Penetrating
oil must be removed after use.
cylinder with care. It's not good practice to pour in fluid and pump the
cylinder
with air
care.trapped
It's not inside,
good pracpedal. With
the
tice
to
pour
in
fluid
and
pumpcause
the
piston will bottom and possibly
pedal.
air trapped inside, the
internalWith
damage.
piston
bottom
and possibly
If thewill
master
cylinder
is off thecause
car,
internal
damage.
fill it at the workbench. Remove interthe master
cylinder itisasoffshown
the car,
nalIfbubbles
by bleeding
in
fill
at the workbench.
Remove interthe itaccompanying
photographs.
The
nal
bubbles
by bleeding
shown of
in
tubes
illustrated
can itbeas made
the
accompanying
photographs.
The
copper or steel. They install in the
tubes
illustratedoutlet
canports.
be made of
master-cylinder
copper
steel. They
in the
After or
bleeding
all theinstall
bubbles,
inmaster-cylinder
outlet
ports.
stall the master cylinder on the car.
After connecting
bleeding all the
the brake
bubbles,
inWhen
lines,
stall
the them
master
cylinder
on the
car.
transfer
quickly
to avoid
losing
When
brake makes
lines,
fluid. Thistheprocess
all the connecting
transfer
them
quickly
to
avoid
losing
bleeding easier, because no small buball
process
makes
the master
bles the
get fluid.
trappedThis
inside
bleeding easier, because no small bubcylinder.
bles
trapped
inside
master
A get
master
cylinder
usedthewith
disc
cylinder.
brakes usually doesn't have a resid ualA master
cylinder
with disc
Thus, used
bench-bleeding
pressure
valve.
a residualbrakes
usually
haveand
will only
movedoesn't
fluid back
forth in
pressure
Thus, bench-bleeding
the tube. valve.
To prevent
this, hold a
will
only
move
fluidofback
in
the end
the and
tubeforth
during
finger
over
the
tube.
To
prevent
this,
hold
the return stroke of the piston. Thisa
finger
over
thefrom
end of
the tube
prevents
fluid
being
drawnduring
back
the return
stroke
piston.stroke.
This
into
the tube
on of
thethe
return
prevents
fluid
from
being
drawn
back
The drum-brake side of a tandem
into the may
tubehave
on the
returnpressure
stroke.
cylinder
a residual
The
of flow
a tandem
reverse
of the
valve drum-brake
that preventsside
cylinder
maythe
have
a residual pressure
fluid
below
residual-pressure
setvalve
reverse flow of the
the prevents
valve.
ting ofthat
fluid below the residual-pressure setting
of the valve.
DRAINING
BRAKE FLUID
When changing brake fluid, drain
DRAINING
FLUID This
the hydraulic BRAKE
system completely.
Whenbe changing
brakethe
fluid,
drain
cannot
done through
bleeders.
the hydraulic
completely.
This
is due to system
the basic
function ofThis
the
cannot beBleeders
done through
the bleeders.
bleeder.
are designed
to let
This
is due
the basicsystem,
functionsoofthey
the
air out
of a tohydraulic
bleeder.
Bleeders
arehigh
designed
let
spot into the
are
located
at each
air out of After
a hydraulic
system,
so they
system.
draining
from
the
are located at each high spot in the
system. After draining from the
bleeders, fluid remains in all low
spots. Some people think that pumpbleeders,
fluid
in the
all fluid
low
ing the pedal
willremains
push all of
spots.
Some
people
think
that
pumpout. Although this gets most out,
ing the
pedal
push all of the fluid
some
fluid
willwill
remain.
out.
Although
this gets
most out,
To get
all new fluid,
one method
resome
fluid
will
remain.
quires refilling and pumping out the
To getmany
all new
fluid,This
oneforces
method
system
times.
all reof
quires
and the
pumping
out the
the
oldrefilling
fluid from
low spots
by
system
manythe
times.
of
mixing with
cleanThis
fluid.forces
This all
procthe
old
fluid
from
the
low
spots
by
ess is better than nothing at all, but it
mixing
with the
proc-a
is
expensive
to clean
do it fluid.
right This
because
ess of
is better
than
nothing
at all,
but it
fluid is
wasted.
And,
it never
lot
is expensive
to do
it right because a
gives
100% clean
fluid.
lotThe
of fluid
is
wasted.
And,
never
correct way to drain
olditfluid
is
gives
100%
clean
fluid.
to open up the system at every low
TheThis
correct
way tomeans
drain old
fluid is
usually
disassemspot.
to
open
up the
system removing
at every low
or
bling
wheel
cylinders,
spot.
This usually
means
disassembling
calipers,
and disassemunscrewblingfittings.
wheel The
cylinders,
or
master removing
cylinder will
ing
disassembling
calipers,
and
unscrewalso have to be removed and drained.
ing fittings.
masteras cylinder
will
involves
much work
Because
thisThe
alsoa have
to be removed
and drained.
as
hydraulic-system
rebuilding
job,
Because
as all
much
it
makes this
senseinvolves
to replace
the work
seals
as
a
hydraulic-system
rebuilding
job,
at the same time.
it makestoSense
to replace all changing
the seals
Glycol
Silicone-When
at the asame
time.
from
glycol-based
fluid to silicone
~
l
to
silicone-when
~ draining
~
~is a must.
changing
l To
fluid, complete
from
a
glycol-based
fluid
to
silicone
take full advantage of the properties
fluid,
complete
is a must.
of silicone
fluid,draining
drain every
drop To
of
take
full
advantage
of
the
properties
the old fluid, flush the system with
of siliconeand
fluid,rebuild
drain every
dropthe
of
alcohol,
all of
the old fluid, flush the system with
cylinders.
alcohol, and rebuild all of the
cylinders.
HYDRA ULIC-CYLINDER
REBUILDING
HY
LINDER
InDRAULIC-CY
time, the seals
in a wheel
REBUILDING
master cylinder or caliper
cylinder,
time,
the seals in
a wheel
willIn leak.
Contamination
or corrosion
cylinder,
master
cylinder
or
caliper
makes this happen sooner. Caliper
will leak.
Contamination
or corrosion
subjectseals
that are
old or have been
makes
thistemperature
happen sooner.
Caliper
also lose
their
ed
to high
seals
that
are
old
or
have
been
subjectelasticity and limit piston retraction.
ed
to highalltemperature
also lose
their
Usually,
brake-system
cylinders
elasticity
and limit piston retraction.
need rebuilding.
Usually,
all abrake-system
cylinders
cylinRebuilding
wheel or master
need
rebuilding.
der should start with getting your
Rebuilding
a wheel
or master
cylincar's
factory shop
manual.
There
are
der should
startbrake
withdesigns.
getting Some
your
many
different
car's factory
manual.procedures.
There are
require
specialshop
rebuilding
many
different
brake
designs.
Some
Most wheel or master cylinders can
be
require
special
rebuilding
procedures.
rebuilt, but some are impossible beMost wheel
or masterare
cylinders
be
cause
bore surfaces
usually can
pitted
rebuilt,corrosion.
but some The
are impossible
becylinder then
from
cause bore
surfacesTherefore,
are usually before
pitted
cannot
be honed.
from
corrosion.
The
cylinder
then
buying rebuilding kits, disassemble
cannot
be honed.
Therefore,
the cylinders
and inspect
them.before
Even
buying your
rebuilding
kits,
though
cylinders
can disassemble
theoreticalthe
cylinders
and
inspect
them.
Even
ly be rebuilt, they may be too
damaged
though
to
allow your
it. cylinders can theoretically To
be rebuilt,
may an
be too
damaged
entire
cylinbe safe,they
replace
to
allow
it.
der if it leaks. For older cars for which
Tocylinders
be safe, are
replace
an entire acylinnew
not available,
mader if it leaks. For older cars for which
new cylinders are not available, a ma-
Cleaning brake parts should be done with special brake-cleaning fluid. CRC Brakleen is
used at start of brake-maintenance job. Petroleum products should never be used on brake
parts,
as brake
is easily
courtesy
CRC Chemicals.
Cleaning
brakefluid
parts
shouldcontaminated.
be done with Photo
special
brake-cleaning
fluid. CRC Brakleen is
used at start of brake-maintenance job. Petroleum products should never be used on brake
parts, as brake fluid is easily contaminated. Photo courtesy CRC Chemicals.
chine shop can bore out the old cylinder and press in a stainless-steel or
chine
shop can
bore Post
out the
old cylinWhite
Restorations
brass sleeve.
der
and
press
in
a
stainless-steel
of White Post, Virginia, specializes or
in
brass sleeve.
White Post
Restorations
sleeving
collector-car
brake
cylinders.
of Brake-cylinder
White Post, Virginia,
in
rebuildspecializes
kits usually
sleeving
collector-car
brake
cylinders.
include rubber seals, dust boots and,
Brake-cylinder
rebuild
kits or
usually
sometimes,
internal
springs
seal
include rubber
seals,
dust boots
expanders.
Often,
an older
designand,
will
sometimes,
internalseals
springs
or seal
have newer-style
in the
kit.
expanders.
Often, ancup-type
older design
will
Many
replacement
seal kits
have newer-style
seals add
in reliabilithe kit.
include
expanders. These
Many
replacement
cup-type
seala kits
ty to the
seal. Rebuild
kits are
lot
include expanders.
These
add reliabilicheaper
than a new
cylinder,
particty
to the
seal.
Rebuild
are a lot
if you
have
to buy akits
caliper.
ularly
cheaper
than
a
new
cylinder,
particDisc-brake calipers usually must
be
ularly if you
have
buyfor
a caliper.
removed
from
theto car
rebuilding.
Disc-brake
caliperswheel
usually cylinders
must be
Some
drum-brake
removed
from
the
car
for
rebuilding.
can be left in place on the backing
Some
drum-brake
cylinders
plates for
rebuilding,wheel
providing
you
can reach
be left
in with
placea hone.
on the backing
them
can
plates
rebuilding, providing
you
Wheel for Cylinders
&
Master
can
reach
them
with
a
hone.
Cylinders- The first task is disassemWheel
Cylinders
&
Master
completely.
If it is
bling the cylinder
Cylinders-Theclean
firstup
taskthe
is disassemrebuildable,
cylinder
bling
the cylinder
completely.
If You
it is
bore with
a brake-cylinder
hone.
rebuildable,
clean
up
the
cylinder
can buy a hone at an auto-parts store.
bore awith
brake-cylinder
You
Get
honea with
three smallhone.
replaceacan
buy a hone
an auto-parts
store.
Theyatlook
like a miniature
ble stones.
Get a hone with three
engine-cylinder
hone.small
Usereplaceabrake
ble
stones.
They
look
like
a miniature
fluid-the type you'll be using
in the
engine-cylinder
Use brake
brake system-ashone.
a lubricant
while
fluid-the
typeuse
you'll
be or
using
the
solvent
any in
petrohoning. Never
brake
system-as
a
lubricant
while
leum product on brake parts.
Never use
or anyapetrohoning.
If a cylinder
cansolvent
be rebuilt,
light
leumproduct on brakeparts.
If a cylinder can be rebuilt, a light
Wheel-cylinder rebuilding kit typically contains cup-type seals, boots and spring.
Make sure wheel
cylinder
rebuildable
Wheel-cylinder
rebuilding
kit is
typically
conbeforecup-type
buying kit.seals, boots and spring.
tains
Make sure wheel cylinder is rebuildable
before buying kit,
honing is required to remove surface
imperfections. After honing, check
honing
is required
remove
surface
bore diameter
with to
a feeler
gage.
If a
imperfections.
narrow
0.006-in.After
feeler honing,
gage can check
be inbore diameter
feeler and
gage.bore,
If a
serted
betweenwith
the apiston
narrow
0.006-in.
feeler
gage
can
be
inyou should replace the cylinder. You
serted
pistonmicrometer
and bore,
can
alsobetween
use an the
outside
you
replacegage
the cylinder.
You
and should
telescoping
to measure
can
also
use
an
outside
micrometer
piston and bore diameters. If the difand telescoping
gage two
to measuremeasure
ference
between the
piston
bore in.
diameters.
If the
difments and
is 0.005
or more,
replace
ference
between the two measurethe cylinder.
ments
is 0.005 seal
in. is
or used
more,
If a cup-type
in areplace
cylinthe
cylinder.
der that has excessive clearance beIf a cup-type
useda in
a cylintween
the pistonseal
andisbore,
condition
der
that
has
excessive
clearance
beknown as heel drag can occur. The seal
tween
the
piston
and
bore,
a
condition
gets pinched in the space between the
known as heel drag can occur. The seal
gets pinched in the space between the
129
@
Cylinder
Cylinder
-
Pushrod
Seal
Seal
Motion
Piston
Cup-Type Seal
Pinched Between
Cylinder
Piston andSeal
Cup-Type
Pinched Between
Piston and Cylinder
Two types of brake cylinder hones: Upper hone one is made for a specific cylinder
diameter; lower one is more expensive, but will adjust to different bore sizes. Buy the adjustable
hone,
it will cylinder
be cheaper
in theUpper
long run.
Two types
of asbrake
hones:
hone one is made for a specific cylinder
diameter; lower one is more expensive, but will adjust t o different bore sizes. Buy the adjustable hone, as it will be cheaper in the long run.
If bore-to-piston clearance is too great,
rubber seal may wear excessively and can
inhibit
piston movement.
The cause
heel
If bore-to-piston
clearance
is too isgreat,
drag-seal
gets
pinched
betweenand
piston
seal
may wear
excessively
can
and
Honing beyond
inhibitbore.
piston
Thefactory
cause islimits
heel
causes
this condition.
drag-seal
gets pinched between piston
and bore. Honing beyond factory limits
causes this condition.
Wheel-Cylinder Clamp
Wheel-Cylinder Clamp
Hone is driven by drill motor while brake fluid lubricates hone and keeps stones from loading
up with metal particles. Never use oil or solvent for honing brake parts, as it will damage
seals.
Hone is driven by drill motor while brake fluid lubricates hone and keeps stones from loading
up with metal particles. Never use oil or solvent for honing brake parts, as it will damage
seals.
piston and bore. This causes the
piston to retract very slowly or stick.
piston
andheel
bore.
A
voiding
dragThis
is acauses
must the
for
piston
to retract very slowly or stick.
proper braking.
Avoiding
heelreplace
drag the
is aseals,
mustwash
for
When you
proper
braking.
all of the parts with clean brake fluid,
When you
wash
blowout
with replace
clean drythe
air,seals,
and lubriall of with
the parts
cleanfluid.
brakeAgain,
fluid,
cate
cleanwith
brake
blow out with
dry same
air, andtype
lubriremember
to clean
use the
as
cate
brakeinfluid.
Again,
what with
you ' llclean
be using
the system.
remember
to use thecleaner
same type
as
Use only brake-part
for the
what
you'll
be
using
in
the
system.
first cleaning, but use only new brake
Use for
onlylubricating
brake-part
cleaner
for thea
fluid
. Don't
assemble
first cleaning,
but and
use only
new
brake
grease
must
be
cylinder
dry. Grit
fluid
for of
lubricating.
kept out
the brake Don't
systemassemble
as well. a
cylinder
and greasea must
be
If youdry.
areGrit
rebuilding
master
kept
out
of
the
brake
system
as
well.
cylinder, fill it with the exact type of
If you
are rebuilding
master
fluid
you plan
to use and a bleed
it
cylinder,
fill it with
the the
exactcar.type
of
before installing
it on
This
fluid you plan to use and bleed it
before installing it on the car. This
130
will make brake bleeding much easier
later. Bench-bleeding a master cylinwill
brakeon
bleeding
much easier
der ismake
discussed
page 128.
later.
Bench-bleeding
a master
cylinWheel
cylinders don't
have to
be
der
is
discussed
on
page
128.
filled with fluid, only lubricated with
cylinders
to be
it. Wheel
They will
fill easilydon't
duringhave
bleeding.
filled
fluid,
with
Youwith
may
findonly
a lubricated
wheel-cylinder
-it.
Theyhandy
will filltoeasily
bleeding.
clamp
holdduring
in the
pistons
You installing
may find
a wheel-cylinder
while
a wheel
cylinder. The
clamp
handy
to
hold
in hold
the pistons
dust boots don't always
in the
while
installing
a wheel cylinder.
Thea
The wheel-cylinder
clamp,
pistons.
dust boots
always
the
simple
tool don't
available
at hold
most ingood
pistons.
The
wheel-cylinder
clamp,
auto-parts stores, keeps the internala
simple
tool pushing
available out
at the
mostpistons
good
spring from
auto-parts
and seals. stores, keeps the internal
spring from Rebuildingpushing out Disc-brakethe pistons
Caliper
and
seals.
caliper rebuilding is more complicated
Caliper
Rebuilding-Disc-brakethan rebuilding
a master cylinder or
caliper
rebuildingYou
is more
complicated
wheel cylinder.
usually
have to
than rebuilding a master cylinder or
wheel cylinder. You usually have to
Wheel-cylinder clamp is used to keep pistons inside wheel cylinder while shoes are
removed. Once clamp
shoes isand
return
springs
Wheel-cylinder
used
to keep
pisare reinstalled,
clamp
is removed.
Drawing
tons
inside wheel
cylinder
while shoes
are
courtesy Bendix
removed.
Once Corp.
shoes and return springs
are reinstalled, clamp is removed. Drawing
courtesy Bendix C q p .
disassemble the caliper to remove the
pistons. Don' t get brake fluid on the
disassemble
to remove
pads if you the
plancaliper
to reuse
them . the
On
pistons.
Don't
get
brake
fluid
on the
some calipers it is hard to remove
the
pads
youSpecial
plan tocaliper-piston
reuse them. On
pistonif(s).
resome
calipers
is hard
to remove
the
moving
tools itare
available.
Another
piston(s).
caliper-piston
remethod is toSpecial
use compressed
air at the
moving
tools
are
available.
Another
hole where the hose installs. If you
method
is to use compressed
air at will
the
use compressed
air, the pistons
hole where
installs. If
you
come
flying the
out.hose
Be careful!
Flying
use
the or
pistons
will
partscompressed
can cause air,
injury
damage!
come
flying
out.
Be
careful!
Flying
Wrap rags around the caliper and trap
parts
can And
causedon't
injuryuseortoo
damage!
the parts.
much
Wrap
rags Be
around
the caliper
andwhen
trap
pressure.
especially
careful
the
parts.
And
don't
use
too
much
removing plastic pistons. They are
pressure.
Be especially
careful
when
easily chipped
and scratched
.
removing
plasticbores
pistons.
are
Some caliper
can beThey
cleaned
easily
chipped
andothers
scratched.
up with
a hone;
cannot. Check
Someshop
calipermanual
bores canforbe cleaned
your
specific
up
with
a
hone;
Check
thosecannot.
that can
be
instructions. Forothers
your
manual isforsimilar
specific
honed, shop
the operation
to
instructions. For those that can be
honed, the operation is similar to
Caliper
Caliper
v
Usually, disc-brake piston can be removed
with low air pressure applied through
brake-hose
hole. Make
sure
in front
Usually,
disc-brake
piston
canarea
be removed
of piston
we"pressure
padded to
preventthrough
piston
with
low isair
applied
from flying hole.
out and
your
brake-hose
Makebouncing
sure areainto
in front
face.
Don't
apply
air pressure
until
you
of
piston
is well
padded
to prevent
piston
cover flying
everything
with bouncing
a rag. When
from
out and
intopiston
your
comesDon't
out, brake-fluid
spray will
follow!
face.
apply air pressure
until
you
Job can
be dangerous,
be careful.
Drawcover
everything
with so
a rag.
When piston
ing courtesy
Bendix Corp.spray will follow!
comes
out, brake-fluid
Job can be dangerous, so be careful. Drawing courtesy Bendix Corp.
Wooden or
Plastic Stick
Removing piston seal from Chrysler floating caliper: Seal is installed in groove in
caliper
bore.
Use seal
a plastic
woodenfloattool
Removing
piston
from or
Chrysler
to
damaging
edges.
Such in
a
ingavoid
caliper:
Seal isgroove
installed
in groove
tool
should
also
to or
install
sealstool
on
caliper
bore.
Usebea used
plastic
wooden
pistons.
courtesy
to avoidDrawing
damaging
grooveBendix
edges.Corp.
Such a
tool should also be used to install seals on
pistons. Drawing courtesy Bendix Corp.
honing a wheel cylinder or master
cylinder. Usually, caliper bores are
honing ato wheel
cylinder
or master
limited
O.002-in.
oversize.
Any
cylinder.
boresOnarea
larger,
andUsually,
the seals caliper
won't work.
limited that
to cannot
0.002-in.
oversize.
Any
caliper
be honed,
the bore
larger,
and the seals
work.
can
be refinished
withwon't
crocus
cloth.On a
caliper
cannotis benot
honed,
the bore
If itsthat
bore(s)
scratched
or
can be refinished
withbecrocus
cloth.
pitted,
a ca liper can
rebuilt.
When
If its bore($
is notthescratched
or
corrosion
has pitted
bore, you
pitted,replace
a caliper
can be or
rebuilt.
must
the caliper
sleeveWhen
it.
corrosion
has pitted
bore, you
Caliper bores
on oldthe
Corvettes
are
must replace
caliper or damage.
sleeve it. In
suscepti
ble tothecorrosion
Caliper
bores
old aCorvettes
are
fact,
this has
beenonsuch
problem that
susceptible
to
corrosion
damage.
a company has come up with In
a
fact, this has
been such aCorvette
problem calithat
solution.
Stainless-steel
a company
has
comeStainless
up with
pers
are avai lab
le from
Steela
solution. Stainless-steel Corvette calipers are available from Stainless Steel
Retracting caliper piston on Honda with a screwdriver. Some manufacturers recommend
using their special tool or a C-clamp. See your shop manual for specifics.
Retracting caliper piston on Honda with a screwdriver. Some manufacturers recommend
using their special tool or a C-clamp. See your shop manual for specifics.
Brakes Corp., in Clarence, New York.
These stainless-steel calipers miniBrakescorrosion
Corp., in damage,
Clarence, particularly
New York.
mize
These
stainless-steel
calipers
on cars using
glycol brake
fluid. minimize
corrosion
Some
two-piecedamage,
calipers particularly
can be dison cars usingfor
glycolrebuilding.
brake fluid. Others
assembled
Some even
two-piece
cal~pers
be discannot,
though
it maycan
appear
to
assembled
rebuilding.
be possible.for Consult
your Others
shop
i t may appear
to
cannot,
manual even
beforethough
disassembling
the calibe body.
possible.
Consultcaliper
yourwith
shop
per
A two-piece
an
manual
disassembling
thewhere
caliinternal before
fluid passage
has seals
per
body.
A
two-piece
caliper
with
an
the caliper splits. Make sure these
internal
fluid
passage
has
seals
where
seals are replaced before reassembling
the caliper.
caliper The
splits.
sure
the
boltsMake
holding
thethese
caliseals
are replaced
reassembling
per body
togetherbefore
are high-strength
the caliper.
bolts holding
caliand
require The
a specified
torque. the
Be sure
per
body
together
are
high-strength
to tighten these bolts to the specified
and
require
a specified
sure
torque
to avo
id potentitorque.
al catasBe
trophic
to tightenlater.
these bolts to the specified
problems
torque
to avoid
potential catastrophic
Removing
or installing
the seals on
problems
later.
some calipers can be tricky. They fit
Removing
or which
installing
the be
seals
on
into
a groove,
must
clean
some
calipers
can
be
tricky.
They
and free of burrs. Be careful not to cufitt
into
a age
groove,
which
must when
be clean
or
dam
the seal
or groove
inand
free
of
burrs.
Be
careful
not
to cut
stalling seals. Use pl astic tools
to
or damage
the sealcritical
or groove
when
in-,
avoid
damaging
parts.
Also
stalling
seals.
plastic
don't
ignore
the Use
rubber
pistontools
boot. to
It
avoid
damaging
critical
parts.
keeps moisture and dirt out of theAlso,
calidon't
ignore
theboot
rubber
piston
boot.
It
per
bore.
If the
is torn,
water
and
keeps
moisture
dirt out
of the calidirt
will
ruin theand
caliper
quickly,
parper bore.onIf athe
boot
ticularly
road
car.is torn, water and
dirt
will
ruin
the
quickly,
Before installingcaliper
calipers
on a parcar,
ticularly
onthey
a road
make
sure
arecar.
perfectly clean and
Before
calipers
on isa parcar,
free
of dirtinstalling
and corrosion
. This
make
sure
they
are
perfectly
clean
and
ticularly important on sliding calipers.
free of are
dirtcontacting
and corrosion.
parThere
partsThis
that ismust
ticularly
important
on sliding
slide
while
under load.
Thesecalipers.
sliding
There are contacting parts that must
slide while under load. These sliding
surfaces should be cleaned and lubricated with high-temperature brake
surfaces
be friction
cleanedand
andresist
lugrease to should
minimize
bricated
with
high-temperature
brake
corrosion. Your shop manual will progrease
to minimize
friction
and resist
vide specific
instructions
.
corrosion.
Your
shop
manual
proCaliper-mounting bolts will
typical
ly
vide
instructions.
are specific
high-strength
and should be
Caliper-mounting
torqued
to specificationbolts
using atypically
torque
are
high-strength
and
shouldbolts
be
wrench . If the caliper-mounting
torqued
to
specification
using
a
torque
loosen, serious problems can result.
wrench.
there caliper-mounting
So,
makeIf su
the correct boltsbolts
are
loosen,
serious
can result.
used, they are inproblems
good condition,
and
So,
sure the
correct
are
they make
are torqued
to the
value bolts
specified
used,
they
are
in
good
condition,
and
in the shop manual.
they are torqued to the value specified
in
the shop
manual.
LINING
REPLACEMENT
The most frequent brake job is
LINING REPLACEMENT
replacing
friction material. Before
The most
frequent
brake
job for
is
starting
thi s job,
check the
brakes
replacing
friction
material.
Before
roughness by driving the car at highstarting
this ajob,
brakes th
fore
way
speed
nd check
lightly the
applying
roughness
by
driving
the
car
at
highbrakes. If the brakes shudder or the
way speed
and
lightly the
applying
the
pedal
pulsates
, repeat
test using
brakes.
If
the
brakes
shudder
or
the parking brak e -if the brakes the
are
pedal
repeat
thepresence
test using
on
thepulsates,
rear whee
ls . The
or
the parking
brake-ifwill the
are
absence
of shudder
tell brakes
you which
on the
wheels.
The . presence
or
pair
of rear
brakes
is rough
Be careful
absence
of
shudder
will
tell
you
which
while apply ing the rear brakes.
pair of rear
brakes
is rough.
Becar
careful
Locked
brakes
make the
very
while
applying
the
rear
brakes.
unstable . Always have the release
Lockedorrear
brakes
make the
button
handle
activated
so car
you very
can
unstable.
Always
have
the
release
release the parking brake quickly.
button
handle activated
so you
can
Whenorreplacing
linings, you
should
release
the
parking
brake
quickly.
also inspect the rotor or drum surfaces
linings,
should
andWhen
otherreplacing
brake parts,
andyou
check
for
also
inspect
the
rotor
or
drum
surfaces
sea l leakage.
and other
brake parts, and disc-brake
check for
Pad
Replacement-Most
seal leakage.
Pad Replacement -Most
disc- brake
131
Rotor is being surfaced with tool mounted on car. Rotor can be rotated by engine with this
front-wheel-drive car. Tool machines both sides of rotor simultaneously, ensuring that surfaces
be parallel.
Rotors
be on
surfaced
on car
andengine
done on
a speRotor will
is being
surfaced
with that
tool cannot
mounted
car. Rotor
canare
beremoved
rotated by
with
this
ciallathe.
front-wheel-drive
car. Tool machines both sides of rotor simultaneously, ensuring that sur-
faces will be parallel. Rotors that cannot be surfaced on car are removed and done on a special lathe.
pads are easy to change. They can be
removed on many cars simply by
pads
are easy
to change.
They
removing
a wheel,
pulling
a can
pin be
or
removeddevice
on many
cars simply
by
locking
, and sliding
the pads
removing
a wheel,
a pinonly
or
Sometimes
thispulling
job takes
out.
locking
device,
and
sliding
the
pads
about fiv e minutes per wheel. The
out. Sometimes
this job
takes only
only
effort required
is pushing
the
about
five into
minutes
per wheel.
The
piston back
the caliper
cylinder
so
only
effort
required
is pushing
the
the new
thicker
pad can
be inserted
piston
back
the caliper
cylinder
so
between
theinto
piston
and rotor.
Your
the new
thicker
inserted
shop
manual
will pad
tell can
you be
how
to do
between
the piston
rotor.
Your
not to and
damage
a piston
this. Be careful
shop
manual
will
tell
you
how
to
do
by prying on it.
this.
Be
careful
not
to
damage
a
piston
With the pads out, inspect the rotor
by prying
on it.for cracks or scoring.
Check
face.
With the
pads out, inspect
the rotor
but
Minor
imperfections
are OK,
face.
Check
for
cracks
or
scoring.
large imperfections must be machined
Minor
imperfections
arebe OK,
but
out.
Rotors
usually must
removed
large
must berotors
machined
to do imperfections
this. Take damaged
to a
out.
Rotorsbrake
usually
must
removed
reputable
shop
for be
resurfacing.
to
do
this.
Take
damaged
rotors
If you resurface one rotor, do tothea
reputabletobrake
for resurfacing.
same
theshopopposite
rotor.
If
you resurface
one may
rotor,pull
dountil
the
the brakes
Otherwise,
same
to surfaced
the opposite
rotor is rotor.
worn
the newly
Otherwise, the brakes may pull until
smooth.
theAnnewly
rotor that
is worn
easily surfaced
made mistake
can
smooth.
when replacing disc-brake pads
occur
can
is An
thateasily
manymade
pads mistake
can be that
installed
occur
when
replacing
disc-brake
pads
backward.
Although
it
seems
is
that many
canfriction
be installed
obvious,
make pads
sure the
matebackward.
it rotor.
seems
rial is installedAlthough
so it faces the
If
obvious,
the friction
mateyou
put amake
pad insure
backward,
the brakes
rial is installed
so it faces
If
won't
work correctly
andthe
therotor.
rotor
you
put
a
pad
in
backward,
the
brakes
will be destroyed.
won't
correctly
and pistons
the rotor
Whenwork
retracting
caliper
to
will be destroyed.
When retracting caliper pistons to
132
install the new pads, make sure the
fluid reservoir isn't full. Otherwise,
install
thespill
neworpads,
surevent.
the
fluid will
squirtmake
out the
fluid will
reservoir
isn'tYou
full.may
Otherwise,
This
be messy.
find out
fluid
will glycol-based
spill or squirt
outworks
the vent.
how well
fluid
as a
This
will
be
messy.
You
may
out
paint remover. A void this by find
opening
how
well
glycol-based
fluid
works
as
the bleeder on the caliper before re-a
paint
remover.
AvoidFluid
this by
opening
come
tracting
the piston.
will
the
bleeder
on
the
caliper
before
reout the bleeder rather than being'
tracting
the
piston.
Fluid
will
come
pushed back to the reservoir. Run a
out
than tobeing'
hose the
into ableeder
jar fromrather
the bleeder
prepushed
back onto
to the
Run a
vent spillage
the reservoir.
floor.
hose
a jar from
bleeder
to preAs into
a policy,
mostthe
brake
shops
survent
spillage
onto
the
floor.
face rotors whenever pads are
As a policy,
most brake
shops
surreplaced
. This results
in good
braking
face
rotors whenever
are
is done pads
properly.
if surfacing
replaced.
This
results
in
good
braking
However, many times the job may not
if
surfacingTo is
done this,
properly.
be required.
determine
careHowever,
manythetimes
the job
not
fully
inspect
rotors
for may
damage
be required.
and
runout. To determine this, carefully
the cars,
rotorstheforpads
damage
On inspect
most road
wear
and
runout.
out long before any rotor work is
On most
roadsurface
cars, the
pads wear
needed
, Small
scratches
and
out long
before
any are
rotor
workpreis
scores
of little
concern
always
needed.
Small
surface
scratches
and
sent on a used rotor. And shops with
scores
little concern
arecan
always
poorly of
maintained
lathes
ruin prepersent
a used
rotor.orAnd
shops
witha
drums
. As
fectlyongood
rotors
poorly, maintained
lathes can
ruin perresult
avoid machining
unless
the
fectly
good
rotors
or
drums.
parts are scored heavily or As
youra
result,
machining
unless the
brakes avoid
are rough.
Roughness
is
parts
scoredrunout
heavily
or your
caused are
by rotor
or thickness
brakes are
Roughness
is
variation,
and rough.
drum runout
or ovality.
caused
by
rotor
runout
or
thickness
Consult your factory manual for
variation,
and drum runout or ovality.
specific information.
Consult
your factory
manual discfor
Since 1971,
all U.S.-made
specific information.
Since 1971, all US.-made disc-
Checking rotor runout is done with dial indicator clamped to a jack stand. Runout of
0.005
in. isrotor
considered
upper
most
Checking
runout is
donelimit
withfor
dial
incars.
dicator
clamped to a jack stand. Runout of
0.005 in. is considered upper limit for most
cars.
brake rotors have a dimension cast
into them. This is the minimum-wear
brake
rotors
have acalled
dimension
cast
thickness,
sometimes
the discard
minimum-wear
into
them.
This
is
the
thickness. A rotor is considered unsafe
thickness,
sometimes
called
discard
if
it's machined
thinner.
So, the
never
use
is considered
athickness.
rotor thatAisrotor
machined
to or lessunsafe
than
if
machined
thinner.discard
So, never
theit'sdiscard
thicknessit! use
aRotor
rotor Runout-Rotor
that is machined runout-wobto or less than
discard
it!
the discard
bling
of thethicknessrotor friction
surface-is
Rotor
critical,Runout-Rotor
particularly on runout-woba race car. It
bling of be
the checked
rotor friction
should
everysurface-is
time the
critical,
particularly
on
a race
It
brakes are serviced. Runout
can car.
cause
should
every
timepedal,
the
roughness
in the
vibrationbeorchecked
brakes are
serviced.
Runout
can direct
cause
excess
pedal
travel, or
can even
vibration
or
roughness
in
the
pedal,
air into the caliper past the seals.
excess
travel,
or can even
direct
Rotorpedal
runout
is usually
caused
by
air
into the caliper
the seals.
overheating.
You past
can expect
it if you
is usually hard.
caused
by
It can
useRotor
your runout
brakes extremely
overheating.
You
can
expect
it
if
you
also be caused by overtorquing the
use your brakes extremely
hard. repair
It can
wheel-mounting
nuts. Many
also
by wrench
overtorquing
the
shopsbe
usecaused
an impact
to tighten
wheel-mounting
repair
wheels. Don't letnuts.
them Many
use one
on
shops use
impact
wrench to tighten
your
car. anUsed
incorrectly,
impact
wheels.
them usetorque
one on
wrenchesDon't
apply letexcessive
to
your
car. lugs,
Used possibly
incorrectly,
impact
the wheel
warping
the
wrenches
apply flange.
excessive torque to
rotor-mounting
theCheck
wheelrotor
lugs,runout
possiblywith
warping
the
the rotor
rotor-mounting
flange.
mounted on the car. Before checking,
Check
runoutbearings
with thearerotor
make
surerotor
the wheel
admounted
on the preload.
car. Before
justed
to proper
Setchecking,
up a dial
make
suresotheitswheel
square are
to adthe
indicator
tip isbearings
justed
to
proper
preload.
Set
up
a dial
rotor surface near the outer edge
of
indicator
its tip Make
is square
the frictionsosurface.
sure to
the the
tip
rotor
surface
near
the outer edge of
is on the
friction
surface.
theTurn
friction
surface.
Makeyou
sure
the the
tip
the rotor until
find
is
on
the
friction
surface.
minimum indicated reading on the
Turn the
rotor
untila grease
you find
the
indicator.
Mark
it with
pencil,
minimum indicated reading on the
indicator. Mark it with a grease pencil,
Special puller is designed to remove brake drums. Thin jaws grasp
back of drum. Handle is then turned carefully by hand-not with a
wrench
lever.
Excess force
will break
ordrums.
distortThin
drum
or puller.
Special or
puller
is designed
to remove
brake
jaws
grasp
Tapping
drum lightly
a plastic
mallet
is OKbytohand-not
assist removing
back of drum.
Handlewith
is then
turned
carefully
with a
a
stubborn
drum. Excess force will break or distort drum or puller.
wrench
or lever.
Tapping drum lightly with a plastic mallet is OK to assist removing
blueing, or masking tape.
each side. Never cut
amachinist
stubborn drum.
Zero the indicator dial. Now, turn the
machinist
blueing,
or masking
tape.
rotor
and find
the maximum
reading.
Zero
the
indicator
dial.
Now,
turn
the
This is called total indicated runout
rotor
and
find
the
maximum
reading.
(TIR), or simply runouf. Mark it, too.
This
called total
indicated runout
runout
Theistolerance
for maximum
runout.
it, too.
(TIR), or
should
be simply
specified
in theMark
factory
shop
The tolerance
for maximum
runout
manual.
If not, make
sure the runout
should
be specified
is less than
0.005 in. in the factory shop
manual.
not, make
the runout
can sure
be reduced
by
Rotor Ifrunout
is
less
than
0.005
in.
one of two methods-resurface the
Rotoror runout
by
rotor
shim itcanat beits reduced
mounting.
one of two should
methods-resurface
the
Resurfacing
be used if the
rotor or
shim isit scored
at its or
mounting.
rotor
surface
deeply
Resurfacing
should
be
used
if the
scratched. If the rotor surface
is
rotor
surface
is
scored
or
deeply
smooth, shimming can be used.
scratched.
If the rotor
surface
is
Before shimming
a rotor,
make
smooth,
shimming
cancaused
be used.by outsure
wobble
is not
Before shimming
a is
rotor,
make
of-parallel
surfaces. This
commonly
sure
wobble
is
not
caused
by
outcalled thickness variation. Measure
of-parallel
surfaces.
is commonly
rotor
thickness
withThis
a micrometer
at
variation.
Measure
called
the highthickness
and low spots
you found
with
rotor
thickness
withThe
a micrometer
at
the dial
indicator.
rotor should
the
high
and
low
spots
you
found
with
have a constant thickness at all points.
thethedialwobble
indicator.
The rotor
should
If
was caused
by varying
have
a
constant
thickness
at
all
points.
thickness, the rotor must be surfaced.
If On
the road
wobble
was
caused
by
varying
cars, thickness variation is
thickness,
the rotor
surfaced,
the
biggest
causemust
ofbe disc-brake
On road cars,
thickness
variation
is
roughness.
Maximum
thickness
variathe
biggest
cause
of
disc-brake
tion on new rotors is 0.0005 in. If a
roughness.
Maximum
variarotor has 0.0010
in. or thickness
more variation,
tion
new rotors
is roughness
0.0005 in. and
If a
it
willonprobably
cause
rotor has
0.0010 in.ororreplaced.
more variation,
must
be machined
Rotors
it will be
probably
roughness
must
turned cause
on a lathe
with and
two
must
be
machined
or
replaced.
Rotors
cutting tools simultaneously-one
on
must be turned on a lathe with two
cutting tools simultaneously-one on
Brake-spring-removal tool is a must when working on
brakes. Bloody fingers or damaged springs can result from
pry
bars or screwdrivers-springs
be dangerous.
Brake-spring-removal
tool is a can
must
when working on
brakes. Bloody fingers or damaged springs can result from
pry bars or screwdrivers-springs can be dangerous.
rotors one side at
a time. This will cause thickness
each side. Never
rotorsrotors
one side
at
variation.
Most cut
racing
with
aremovable
time. This
will
cause
thickness
hats can be ground using a
variation. grinder.
Most racing rotors with
Blanchard
removable
can will
be ground
Shimminghats
a rotor
work if:using a
Blanchard
• Rotor is grinder.
flat and mounted on a tilt.
Shimming
rotoronwill
if:
You
can see athis
thework
indicator.
A
Rotor
is flat
tilt.
tilted
rotor
has and
one mounted
high spot on
anda one
You
can see
this 180
on 0 the
indicator.
A
low spot
exactly
apart.
Multiple
tilted
rotor
has
one
high
spot
and
one
high and low spots on a rotor require
low spot exactly 180" apart. Multiple
machining.
high
and low
spots ontoa rotor
require
• Rotor
is bolted
a machined
machining.
surface.
Some rotors are riveted on or
is bolted
a machined
areRotor
integral
with theto wheel-bearing
surface.
Some
rotors
are
riveted
on or
housing or axle. Such rotors cannot
are
integral with the wheel-bearing
be shimmed.
housing
or aaxle.
Such
To shim
rotor,
yourotors
must cannot
deterbe
shimmed.
mine the location of the high and low
To shim
must already
deterspots.
Youa rotor,
shouldyouhave
mine thethe
location
of the
high and
low
marked
two spots.
Roughly
calcuspots.
already
late the You
shim should
thicknesshave
required
to
marked thethetwo
spots. Roughly calcurotor.
straighten
late
the should
shim thickness
required
to
Shims
be made from
steel or
straighten
rotor. available in hardbrass shimthestock,
Shims
should
made from
steel or
ware
stores
in be
various
thicknesses.
brass
shim
stock,
available
in
Make sure you buy O.OOl-in. or hardthinwarematerial.
stores Otherwise,
in various you
thicknesses.
ner
may not
Make
sure
buy the
0.001-in.
be able
to you
adjust
rotor or
in thinfine
ner material.
Otherwise, you may not
enough
increments.
beSpecial
able totapered
adjust the
in fine
rotorrotor
shims
are
enough
increments.
available for Corvette rotors from
Special Steel
taperedBrakes
rotor Corp.
shims This
are
Stainless
available
for
Corvette
rotors
from
shim was developed to allow adjustStainless
Steel which
Brakesare Corp.
This
ment of rotors,
made as
an
shim was developed to allow adjustment of rotors, which are made as an
drum
using
drum
using
assembly with the mating part.
Normally, Corvette rotors cannot be
assembly with the mating part.
shimmed.
Normally,
Corvette
be
If you put
shims rotors
only atcannot
the low
shimmed.
spot, shim thickness should be about
If you putofshims
at the
low
one-fourth
total only
runout.
Install
spot,
shimonthickness
should
be about
shim (s)
the proper
bolt.
Place
one-fourth
of total
runout.
Install
shims
one-eighth
of total
runout
on
shim(s)
on
the
proper
bolt.
the two adjacent bolts. Install Place
rotor
shimstorque
one-eighth
runout on
and
boltsof tototal
specification.
the
two
adjacent
bolts.
Install
rotor
Remeasure rotor runout and adjust
and
torque
bolts
to
specification.
shim thickness as needed. More than
Remeasure
rotor
runout and adjust
one try may be
required.
shim
thickness
as needed.
than
Don't
worry about
runoutMore
less than
one
try
may
be
required.
0.002 in. It's all but impossible to
Don't
worryzero.
aboutAnd,
runout
less than
make
runout
surprisingly,
in. It's of
all runout
but impossible
to
can actually
a0.002
tiny amount
make
runout zero.
And,thesurprisingly,
help braking!
It keeps
pads from
a tiny amountrubbing
of runout
canrotor
actually
continuously
on the
surhelp
braking!
It
keeps
the
pads
from
face by pushing them back a small
continuously
amount from rubbing
the rotor.on the rotor surface
by pushingReplacement-To
them back a small
Brake-Lining
reamount
from
the
rotor.
place drum-brake shoes, you must
Brake-Lining
refirst
remove theReplacement-To
drum. Some drums
place
drum-brake
you ismust
come off
easily aftershoes,
the wheel
refirst
remove the are
drum.
Somedifficult.
drums
moved-others
more
come
off
easily
after
the
wheel
is reYou may have to use a special puller
moved-others
are
more
difficult.
to remove a stubborn brake drum.
You maythe
have
to useshop
a special
puller
Consult
factory
manual
for
to remove
a stubborn
brake
specific
instructions
before
youdrum.
start
Consult the factory shop manual for
working.
specific
youeasily
start
If the instructions
drum shouldbefore
come off
working.
but doesn't, don't use a prybar beIf thethedrum
come off
easily
tween
drumshould
and backing
plate.
If
don't
use
a
prybar
bebut
doesn't,
you pry against the backing plate,
tween the drum and backing plate. If
you pry against the backing plate,
133
Parking brake is at output shaft of transmission on this front-engine, rear-drive
car.
Brake
adjustment
compensates
for
Parking
brake
is at output
shaft of translining
wear.
brakes rear-drive
are rarely
mission
on Such
this parking
front-engine,
foundBrake
on late-model
cars. compensates for
car.
adjustment
Installing brake springs requires same tool used to remove them. End of tool is simply
hooked over anchor pin and spring is popped on. Doing this any other way invites injury to
yourself
the springs.
Installingand
brake
springs requires same tool used to remove them. End of tool is simply
hooked over anchor pin and spring is popped on. Doing this any other way invites injury to
yourself and the springs.
Lubricate the shoes with a dab of
high-temperature brake grease where
Lubricate
a dab
they
rub on the
the shoes
backingwith
plate
and of
at
high-temperature
brake
grease
where
. pivots. Always use brake grease,
not
they ruboronwheel-bearing
the backing plate
and Be
at
chassis
grease.
. careful
pivots. Always
useabsolute
brake grease,
not
to use an
minimum
chassis or
wheel-bearing
grease.
Be
amount
of grease.
It's critical
that you
careful
to
use
an
absolute
minimum
keep grease off the linings.
amount
of grease. It's critical
that you
Assembly-Drum-brake
assembly
is
keep
grease off
linings. Installing
the opposite
of the
disassembly.
Assembly-Drum-brake
is
the automatic adjuster andassembly
putting the
the
opposite
of
disassembly.
Installing
brake springs on are the only tricky
the
automatic
adjuster
the
parts.
Here, you
must and
use putting
the special
brake
areinstallation
the only .tricky
brake springs
tool for on
safe
The
parts. Here,
you must
special
springs
sometimes
canuse
be the
mixed
up
brake
tool
for
safe
installation.
The
and installed in the wrong place.
springs
be mixed
up
Refer tosometimes
the shop can
manual
and your
and installed
in notes
the wrong
place.
sketch,
photos or
to be sure.
If
Refer
to the adjuster
shop manual
and operyour
an automatic
was used,
sketch,
photos ortonotes
to beitsure.
If
ate it manually
be sure
works
an
automatic
adjuster
wasthe
used,
operproperly
before
installing
drum.
ateToit install
manually
to be you
suremay
it works
the drum,
have
properly
before
installing
the
drum.
to run in the adjuster to allow the
To install
drum,
have
drum
to fitthe
over
the you
newmay
linings.
to
run run
in the
allow necthe
Don't
it adjuster
in moreto than
drum to fit enough
over the
newthelinings.
essary-just
to get
drum
Don't
run goit too
in far,
more
than
necon.
If you
you'll
have
to
essary-just
enough
to
get
the
drum
adjust the shoes back out from under
on.
If you go too far, you'll have to
the car.
adjust
shoes
backare
outon,from
Oncethe
both
drums
you under
must
the
car.
adjust their clearances before driving
on, automatic
you must
theOnce
car. both
Evendrums
brakesarewith
adjust theirmust
clearances
driving
adjusters
be set before
close or
they
the car.
Even
brakes
automatic
won't
work
. Your
shop with
manual
will inadjusters
must be
set close or they
dicate
the correct
procedure.
won't work. Your shop manual will indicate the correct procedure.
PARKING-BRAKE-LINKAGE
SERVICING
PARKING-BRAKE-LINKAGE
Usually, a parking brake requires
SERVICING
little
servicing. All that's needed is an
Usually, greasing
a parking
brake
requires
occasional
of the
linkage.
On
little
All that's
needed parkis an
some servicing.
cars, however,
a separate
occasional
of the linkage.
On
ing brake greasing
needs adjusting
or other
some
cars,
however,
a
separate
parkserVICIng. Others have a parking
ing brake
needs
adjusting
or other
brake
on the
drive
shaft. Typically,
servicing.
Others drum
have brake,
a parking
this is a simple
often
brake an
on external-band
the drive shaft.
Typically,
with
drum
brake
this is to
a wheel
simplebrakes
drumused
brake,
often
similar
on an
anwith
an
external-band
drum
brake
tique car. The shop manual should
similar
wheel brakes
used onforan seranprovidetospecific
instructions
tique
car.
The
shop
manual
should
vicing this type of brake .
provide
specific
serParkingbrake instructions
linkages are for
adjustvicing
this type ofgenerally
brake. this is not
able , although
Parking-brake
linkages
required
. However,
if are
the adjustcable
able,
although
generally
this
is not
stretches, you may have to adjust
it.
required.
the cable
Do
not use However,
the "MickeyifMouse©"
Ustretches,
you adjuster.
may haveIt to
bolt-type slack
canadjust
breakit.a
D o notInstead,
use the "Mickey
Mouse@"
buy a new
cable ifUit
cable.
bolt-type
slacktoo
adjuster.
It can
breakora
has stretched
far to be
adjusted
cable.
Instead,
a new And,
cable only
if it
if it has
brokenbuy
strands.
has stretched
toobrake
far to after
be adjusted
or
the wheel
adjust
a parking
if
it has
strands.
And, only
brakes
are broken
operating
perfectly.
the wheel
adjust
brake affer.
One aofparking
the biggest
problems
with
brakes
are
operating
perfectly.
parking brakes on cars driven in
One of
problems with
winter
salttheis biggest
cable corrosion
and
parking brakes
carscandriven
in
sticking.
A stuck on
cable
burn up
winter
salt
is
cable
corrosion
and
brakes because it won't release , or
sticking.
stuck cable
burn up
makes theA parking
brakecanimpossible
brakes
it won't
release,
or
to apply.because
If you have
a sticking
cable,
makes
parking
brake
impossible
replace the
it. Don't
bother
with
lubricatto
you havecables
a sticking
cable,
ingapply.
them. IfEnclosed
are difficult
replace it. Don't bother with lubricating them. Enclosed cables are difficult
lining wear. Such parking brakes are rarely
found on late-model cars.
to lubricate and will probably stick
again anyway.
to Some
lubricate
willfour-wheel
probably stick
cars and
with
disc
again
anyway.
brakes have a drum brake inside the
Some cars
four-wheel
disc
rear-wheel
discwith
brakes
as a parking
brakes
have is
a drum
brake
the
adjusted
andinside
serviced
brake. This
rear-wheel
disc
brakes
as
a
parking
the same as a normal drum brake.
brake. This is adjusted and serviced
the
same &asLINKAGE
a normal drum brake.
PEDAL
MAINTENANCE
PEDAL
Except& LINKAGE
for periodic inspection,
MAINTENANCE
lubrication is about all a brake pedal
Except
periodic
inspection,
and
linkage for
needs.
Make sure
there is
lubrication
is about
all system.
a brakeExampedal
no
slop or failure
of the
and
linkage
needs.
Make
sure
there
ine the pedal pads and replace them is
if
nthey
o slop
failure
of or
thecoming
system.apart.
Examareorworn
slick
A
ine
pedal pads
replace
if
off aand
pedal
canthem
be as
footthe
slipping
they
are worn
coming apart. A
dangerous
as a slick
brakeorfailure.
foot
o.ff acan
pedal
can be for
as
Theslipping
brake pedal
be adjusted
dangerous
as
a
brake
failure.
free play. A brake pedal has a lot less
Theplay
brake
pedal
can
adjusted
for
free
than
a c1u
tchbepedal.
There
brakea pedal
a lot less
free play.beA only
should
slighthas
amount
of
free
than a between
clutch pedal.
There
pedalplay
movement
its fully
reshould
be only and
a slight
amount of
tracted position
the beginning
of
pedal movement between movement.
its fully remaster-cylinder-piston
tracted position
and manual
the beginning
of
Consult
your shop
for exact
master-cylinder-piston
movement.
specifications. Usually) free play
Consult
your shop
manualunless
for exact
never needs
adjusting,
the
specifications.
Usually,
free . play
master cylinder has
been replaced
never needs adjusting, unless the
master
cylinder has been
replaced.
BRAKE-BOOSTER
CHECK
If
power
brakes
are
causing
BRAKE-BOOSTER
problems , first checkCHECK
the hydraulic
If power
system
. This brakes
includes are
the causing
master
problems,
first
check
the
hydraulic
cylinder and wheel cylinders.
If the
system.
This
includes
theproperly,
master
system
operates
basic brake
cylinder
wheel cylinders. If the
check theand
booster.
basic
system operates
properly,
Thebrake
following
trouble-shooting
check
the
booster.
procedure is for a vacuum booster:
The following trouble-shooting
procedure is for a vacuum booster: 135
disassembled correctly. Often, a pressure of 1500 psi is involved. There's
also a very strong spring behind itl If
you don't have the proper instructions, leave the unit alone. Take
the car to a mechanic knowledgeable
of your type of car.
NOISY BRAKES
C~C Disc Brake Quiet compound is applied to backside of brake pads to reduce brake
nOise. CRC r~commends uSing compound on outboard pads. They can be reassembled on
the
carDisc
following
1 O-minute
curing is
time.
Photo
CRC
Chemicals.
CRC
BrakeaQuiet
compound
applied
tocourtesy
backside
of brake
pads to reduce brake
noise. CRC recommends using compound on outboard pads. They can be reassembled on
the car following a 10-minute curing time. Photo courtesy CRC Chemicals.
• With the engine off, press the brake
pedal several times. This bleeds off all
the engine
pressand
thethe
brake
theWith
vacuum
in the off,
booster
repedal several
sulting
power times.
assist. This bleeds off all
the
vacuum
in on
the the
booster
theand
re• Press
lightly
brakeand
pedal
sulting
power
assist.
start the engine. The pedal should
Press
lightlyunder
on theyour
brakefoot
pedal
drop
slightly
if and
the
start
theis working
engine. properly.
The pedal
should
booster
If there
is
drop
slightly
under your
if the
no drop,
the booster
is notfoot
working.
booster isthe
working
properly.
If there
is
Without
booster,
pedal effort
will
no
drop,
the
booster
is
not
working.
be much higher than normal.
Without
booster,
effortmake
will
• Before the
replacing
thepedal
booster,
be much
sure
it's higher
getting than
the normal.
correct supply of
Before Check
replacing
booster,
make
vacuum.
all the
vacuum
lines
for
sure
it's
getting
the
correct
supply
of
leaks and kinks. A vacuum leak often
vacuum.like
Check
lines
for
sounds
a hissallasvacuum
the engine
idles.
leaks and
kinks. A vacuum
leak with
oftena
Check
intake-manifold
vacuum
sounds
like
a
hiss
as
the
engine
vacuum gage and compare it toidles.
the
Check
specs intake-manifold
in your shop vacuum
manual. with
Poora
vacuum vacuum
gage andmay
compare
to the
engine
mean it burned
specs
in
your
shop
manual.
Poor
valves, hose or intake-manifoldengine
vacuum
may
mean
burned
gasket leak or some other engine
valves,
problems.hose or intake-manifoldgasket
or supply
some isother
engine
• If the leak
vacuum
OK, correct
problems.
the
booster. Most boosters are reIf therather
vacuum
supply
is OK, correct
than
overhauled
due to
placed
the
Most
boosters
are retheir booster.
low cost and
critical
construction.
placed
overhauled
duethe
to
• Makerather
a finalthan
check,
if you found
their
low
cost
and
critical
construction.
vacuum booster to be at fault. A
Make a final
if you found the
common
causecheck,
of vacuum-booster
vacuum isbooster
to be at fault. A
failure
automatic-transmissioncommon
of vacuum-booster
modulator cause
failure.
This
allows
failure
is
automatic-transmissionautomatic-transmission fluid (ATF)
modulator
failure. This allows
automatic-transmission fluid (ATF)
136
to be drawn into the engine and,
subsequently, the vacuum booster.
to be ATF
drawn attacks
into the the
engine
and,
The
booster
subsequently,
the vacuum
booster.
diaphragm,
causing
it
to
fail
The
ATF Transmission-modulator
attacks the booster
eventually.
diaphragm,
it toin the
fail
failure
shows causing
up as fluid
eventually.
Transmission-modulator
vacuum hose from the manifold to
failure
shows white
up assmoke
fluid out
in the
the
the booster,
vacuum
the manifold
to
exhaust, hose
or a from
malfunctioning
transo
the
booster,
white
smoke
out
the
mission . Replace the modulator if it is
exhaust,
at
fault. or a malfunctioning trans:
is
mission.
Replace booster
the modulator
If a hydraulic
is used,if itthe
at
fault.
troubleshooting
process is similar :
If a hydraulic
booster
used, the
• With
the engine
off, ispump
the
troubleshooting
process
is
similar:
brake several times to bleed off all hyWith pressure
the engine
pump the
draulic
in the off,
accumulator.
brake
several
times
to
bleed
hy• Push on the brake pedal off
andallstart
draulic
pressure
in
the
accumulator.
the engine. The pedal should drop
Pushyour
on foot,
the brake
pedal
and start
under
usually
followed
by a
the engine.
should
slight
surge. The
This pedal
confirms
thatdrop
the
under your
foot, usually followed by a
booster
is working.
slight
This
confirms
that test,
the
• If thesurge.
booster
doesn't
pass this
boosterthe
is working.
check
power-steering pump. ConIf the
test,
sult
yourbooster
shop doesn't
manualpass
for this
specific
check
the
power-steering
pump.
Conchecks. A slipping belt or low powersult your
shop
for specific
steering
fluid
maymanual
be the cause.
checks.
A slipping
belt
or low
• If there's
pressure
from
the powerpowersteering fluid
may consult
be the cause.
steering
pump,
your shop
If there's
fromonthe
powermanual
for pressure
instructions
servicing
steering
pump,
consult
your
your booster. Be sure to read theshop
inmanual for carefully.
instructions
on servicing
structions
High
pressure
your booster.
Be sure to read
instored
in an accumulator
can the
be exstructions
carefully.
High
pressure
tremely dangerous if the unit is not
stored in an accumulator can be extremely dangerous if the unit is not
Disc-brake squeal can be very
annoying on a road car, particularly if
the rest of the car is quiet-running.
Usually, squeal is caused by vibration
of the front brake pads against the
rotor. Some manufacturers use anti01 tne rront
paas devices
against detne
squeal
shims DraKe
or other
rotor.
Some
manufacturers
use
antisigned to damp these vibrations.
squeal
deWhen ashims
car or
getsother
old, devices
anti-squeal
signed
to damp
vibrations.
devices can
becomethese
ineffective.
ReWhen
a car
placement
of gets
parts old,
may anti-squeal
eliminate
devices
can
become
ineffective.
Renoise. Consult your factory shop
placement
of maintenance.
parts may eliminate
manual for this
noise.
Consult linings
your factory
High-friction
tend toshop
be
manual
for
this
maintenance.
noisier than low-friction linings. And,
High-friction linings
linings generally
tend to are
be
asbestos-filled
noisier than
linings.
And,
quieter
than low-friction
those without
asbestos.
asbestos-filled
linings
are
This
is the main
reasongenerally
why manuquieter
than
those
without
asbestos.
facturers have taken so long to develThis
is the mainlinings.
reason why manuop asbestos-free
facturers
have
taken socompounds
long to develThere are
anti-noise
deop
asbestos-free
linings.
signed to be applied the pad backing
There
are anti-noise
plate
as shown
at left. compounds
One of thesedeis
signed
to be applied
pad Quiet.
backing
CRC Chemicals'
Discthe
Brake
It
plate
as shown
left. One
of these is
is a thick
paste, atsimilar
in appearance
CRC
Chemicals'
Disc
Brake
It
to RTV sealer or bathtub calkQuiet.
. When
is
a
thick
paste,
similar
in
appearance
correctly applied, it can quiet squealto RTV
sealer orBefore
bathtub
calk.
ing
disc brakes.
using
thisWhen
type
correctly
applied,
canthe
quiet
squealof material,
make itsure
brakes
are
ing disc
usingcondition.
this type
clean
andbrakes.
in goodBefore
operating
of material,
surebythe
brakesmalare
Noise
can bemake
caused
serious
clean and or
in wear
good in
operating
functions
a brake. condition.
Noise
can be
caused
serious
malSanding
lining
and byrotor
surfaces
functions
or
wear
in
a
brake.
will quiet noise temporarily. Usually ,
lining
rotor
surfaces
theSanding
ends of
the and
linings
vibrate,
so
will quietchamfers
noise temporarily.
Usually,
grinding
on the leading
and
the
endslining
of the
linings
so
trailing
edges
will vibrate,
sometimes
grinding
chamfers
on
the
leading
and
eliminate noise.
trailing
lining
edges
willassometimes
If drum
brakes
squeak
you apply
eliminate
noise.
and release
the pedal, it's probably
brakes
you apply
theIf drum
edge of
the squeak
shoes as
rubbing
the
and
release
the
pedal,
it's
backing-plate shoe ledges. probably
Apply a
the
of high-temperature
the shoes rubbingbrake
the
thin edge
film of
backing-plate
shoeledges
ledges.
Applythea
grease
to the shoe
to quiet
thin
of high-temperature
brake
noise film
. Be careful
not to get grease
on
grease
to
the
shoe
ledges
to
quiet
the
the lining.
noise.
Be iscareful
not to
get for
grease
on
There
no sure
cure
brake
the
lining.
noise.
If one existed, the manufactursure
ersThere
would is
be no
using
it. cure for brake
noise. If one existed, the manufacturers would be using it.
Modifications
12
Grand Prix cars have some of the best-designed brakes. Mechanics modify brakes to suit course and temperature conditions on race day.
Lightest brakes that work are used to avoid excess weight. Smallest-possible cooling scoops are used to reduce aerodynamic drag. As
with engines
in highly-competitive
racing, brakes must
be pushed
to their
performance
or youand
don't
win!
Grand
Prlx cars
have some of the best-designed
brakes.
Mechanics
modify
brakes to limits,
suit course
temperature
conditions on race day.
Lightest brakes that work are used to avoid excess weight. Smallest-possible cooling scoops are used to reduce aerodynamic drag. AS
with
in highly-competitive
racing, brakes must be pushed to their performance limits, or you don't win!
If engines
your brake
system is not working
as desired, consider modifying it for
If yourperformance
brake system or
is notreliability.
working
better
as
desired,
consider
modifying
it for
Modifications are often the result
of
better
performance
or
reliability.
testing, either on the road or the
Modifications
are don't
often the
resultany
of
track. However,
attempt
testing, either
onyou:
the road or the
modification
until
track.
However,
don'ttheattempt
brakes any
so
• Inspect
and repair
modification
until
you:
they operate properly.
Inspect
repair
brakes
so
• Test
the and
brakes
and the
record
the rethey operate
properly.
know what aspects of
sults
so you'll
Testperformance
the brakes need
and improving.
record the retheir
sults
so
you'll
know
what
aspectsthe
of
• Analyze your car to determine
their performance
need improving.
forces
and pressures
in the brake
Analyze
your
the
system.
Also,
testcar
thetocardetermine
to determine
forces
and
pressures
in
the
brake
brake temperatures. You may have
system.
test the car to determine
done
thisAlso,
already.
brake
You may before
have
The temperatures.
first step is necessary
done can
this already.
you
justify spending time and
The first
step is necessary
money
on modifications.
Mostbefore
new
you
can
justify
spending
and
cars have well-engineeredtime
brakes.
money will
on modifications.
new
They
work fine ifMost
properly
cars have well-engineered
maintained.
However, jf the brakes.
car is
They will work fine if properly
maintained. However, if the car is
./
Numerous components are available to help improve a brake system. Trick is learning how
to
I choose and apply them. Some products available from AP Racing include: steel-braided I
hoses,
various
size master
vacuum
boosters,
and fluid
reservoirs.
courtesy
Numerous
components
arecylinders,
available to
help improve
a brake
system.
Trick Photo
is learning
how
Racing.and apply them. Some products available from AP Racing include: steel-braided
tAP
o choose
hoses, various size master cylinders, vacuum boosters, and fluid reservoirs. Photo courtesy
AP Racing.
137
Before you begin modifying a car's existing brakes, first make sure they are in top condition
and test them. Modification may be unnecessary. Don't fix something that doesn't need
fixing.
race
track
is ideal for
testing.
BeforeAyou
begin
modifying
a car's
existing brakes, first make sure they are in top condition
and test them. Modification may be unnecessary. Don't fix something that doesn't need
fixing. A race track is ideal for testing.
driven beyond its design limits or if it
is highly modified to different
driven beyond its
if it
specifications,
thedesign
brakeslimits
may orneed
is
highly
modified
to
different
modifying.
specifications,
brakes may
To do an theintelligent
jobneed
of
modifying. first identify what needs
modification,
To do The
an next
intelligent
job out
of
modifying.
step is to find
modification,
first
identify
what
needs
exactly what's wrong with brake
modifying.
T h e next
step is list
to findthese
out
performance.
If you
exactly
with tobrake
problems,what's
you arewrong
less likely
lose
performance.
If you
list these
track
of them during
the modification
problems,
you
are
less
likely
to lose
process.
track
of
them
during
the
modification
Be specific when listing the
process.
problems.
Don't just say, "The
Be are
specific
listing say
the
brakes
lousy."when
For example,
problems.
Don't
just
say,
"The
"The brakes fade after two stops from
brakes
are lousy."
For example,
say
100 mph,"
or "Temperature
reaches
"The brakes
two stops
600F
after fade
threeafter
stops
from from
100
100 mph,"
or "Temperature
reaches
mph."
The more
specific you are,
the
600F
after
three
stops
from
100
easier, cheaper and more effective
mph."
T h e more
you are, the
modifications
will specific
be.
easier,
cheaper
and inmore
effective
Use the
formulas
Chapter
9 to
modifications
will
be.
calculate internal brake-system forces
the formulas
to
andUse
pressures.
These in
canChapter
be found9 by
calculate
internalif brake-system
measurement,
you prefer. forces
You
and
These
canhow
be found
by
mustpressures.
understand
clearly
and why
measurement,
if
you
prefer.
You
you're modifying the brakes before
mustcan
understand
clearly Temperatures
how and why
you
do it properly.
you're
the brakes
before
must modifying
be
measured
by
testing
you
can d o i t properly.
Temperatures
modifications,
including
cooling
must be measured by testing
changes.
modifications,
including
cooling
Following are some
brake modificachanges.
tions and objectives to consider:
are s obrakes
m e brake
• Following
Install bigger
to modificaincrease
tions
and
objectives
to
consider:
brake torque and reduce brake
Install bigger brakes to increase
temperatures.
brake
torque
and reduce brake
• Improve
cooling.
temperatures.
• Eliminate fade.
Improvepedal
cooling.
effort.
• Reduce
Eliminate
fade. life.
• Increase lining
pedal
effort.
Add brakebalance-adjustmen
t
• Reduce
Increase lining life.
features.
Add brake-balance-adjustment
deflections.
• Reduce
features.
Reduce
138
deflections.
• Improve stability.
ImproveBRAKES
stability.
BIGGER
Bigger brakes almost always imBIGGER
BRAKES
prove
brake
performance. The addiBigger
brakes
always
imtional
weight
of a almost
bigger disc
or rotor
prove brake
performance.
h e addireduces
temperatures.
If Tdrum
or
tional weight
of aisbigger
disc or pedal
rotor
rotor
diameter
increased,
reduceswilltemperatures.
If drum
effort
also be reduced.
And, or
if
rotor diameter
is increased,
pedal
swept
area is increased,
the linings
effort
willwillalso
reduced. And, if
probably
wearbelonger.
swept
area
is
increased,
the linings
The disadvantage of bigger
brakes
probably
will
wear
longer.
is the adverse effects added weight
T h e on
disadvantage
bigger
brakes
have
accelerationof and
handling.
is
t
h
e
adverse
effects
added
weight
More weight slows acceleration. Addihave on
acceleration
and handling.
tional
rotating
weight makes
it even
More
weight
slows
acceleration.
Addiworse. Also, added unsprung weight
tional
rotating
weightdown
makeswith
i t even
bouncing
up and
the
worse. reduces
Also, added
unsprung
weight
wheels
traction
in bumpy
corbouncing
up accelerating
and down orwith
the
ners
and when
braking
wheels
reduces
traction
in
bumpy
coron bumpy surfaces. So, don't install
ners
and when brakes
accelerating
the heaviest
you or
canbraking
find.
on bumpy
So, the
don't
install
Select
brakesurfaces.
size to suit
performthe heaviest
brakes
ance
needs of the
car. you can find.
Select
brake Prix
size to
suitthe
thebrakes
performOn Grand
cars,
are
ance needs
of the
sized
closely
to car.
the performance of
Grand
Prixare
cars,nothebigger
brakesthan
are
theOncar.
They
sized
closely
to
the
performance
of
what's needed to do their job. On
the car.
are on
n o brakes,
bigger either
than
tracks
thatThey
are hard
what's
needed
o their per
job.rotor
On
bigger rotors
or to
twodcalipers
tracks
that
are
hard
o
n
brakes,
either
are used. On tracks with less braking
bigger rotors orbrake
two weight
calipersisper
rotor
requirements,
reduced
are used.
Oncomponents.
tracks with This
less braking
with
lighter
may be
requirements,
brake
carrying
things
tooweight
far is
forreduced
most
with
lighter
components.
This
maywith
be
applications, but serious racers
carrying
things
too
far
for
most
unrestricted funds do it to win in
applications,
but serious racers with
tough
competition.
unrestricted
do it application,
to win in
Regardless funds
of the
tough
competition.
always use the largest-diameter brakes
Regardless
of the application,
possible.
A large-diameter
drum or
always
use the pedal
largest-dic1n7eler
rotor reduces
effort and brakes
makes
possible.
A large-diameter
d r uelimim or
braking easier.
You can perhaps
rotor
reduces
pedal
effort
and
makes
nate power assist by installing larger-
braking easier. You can perhaps eliminate power assist by installing larger-
Formula Ford brake is small, light and
simple. It works great on a light race car
with 110 HP. If allowed, bigger brakes may
stop car faster, but lap times might be
slower due to added weight. Always use a
brake that's big enough, but not too big.
Extra weight hurts in racing.
brake that's big enough; but not -too big.
Extra weight hurts in racing.
diameter brakes. Thicker rotors are
not necessarily required when rotor
diameter brakes.
ThickerRemember:
rotors are
diameter
is increased.
not
necessarily
required
when
rotor
Add brake weight only if required
to
diameter
is
increased.
Remember:
cure a severe cooling problem. If a
Add brake
only ifwell
required
to
light,
solid weight
rotor cools
enough,
cure a use
severe
cooling problem.
If a
don't
a heavier,
vented rotor.
light, solid
rotortocools
enough,
When
changing
largerwell
drums,
condon't
use
a
heavier,
vented
rotor.
sider reducing weight by switching
W h e n iron
changing
to larger drums,
confrom
to aluminum.
Aluminum
sider reducing
weight
by switching
drums
cool better
than iron
drums of
from
iron size.
to aluminum.
Aluminum
the same
And they are
lighter.
dThey
r u m sare
cool
better
than
iron
drums of
well worth the expense.
theSeparate
same size.
And they
are lighter.
cooling
problems
from
They
are
well
worth
the
expense.
pedal-effort problems. If the brakes
Separate
cooling
problems
from
have
both high
pedal effort
and excespedal-effort
problems. Ifthethe needed
brakes
sive
temperatures,
have bothare
highobvious.
pedal effort
exceschanges
Yourandcar
will
sive
temperatures,
the
needed
benefit from both larger-diameter and
changes
are obvious.
Yourproblems.
car will
heavier brakes
to cure both
benefit
from
both
larger-diameter
and
However, if pedal effort is the only
heavier brakes
t o cure
bothrotors,
problems.
problem,
stay with
lighter
caliHowever,
if pedal effort is the only
pers or drums.
problem,
stay
with lighter
rotors,larger
caliIt's easy to predict
the effect
pers orordrums.
rotor
drum diameters will have on
It's easy
predict the
effect
larger
pedal
effort.to Because
pedal
effort
is
rotor
or
d
r
u
m
diameters
will
have
on
related directly to brake torque, use
pedal
effort. given
Because
pedal effort
is
the formulas
in Chapter
9. Calrelated the
directly
to brake
torque,
use
culate
new brake
torque
and comtpare
h e formulas
in Chapter
9. Calit to thegiven
old brake
torque.
The
culate
t
h
e
new
brake
torque
and
comnew pedal effort will be the indirect
pare of
it to
brake torque.
The
ratio
thethe
twoold
numbers.
Pedal effort
new pedal
effort with
will increased
be t h e indirect
always
decreases
brake
ratio of t h e two numbers. Pedal effort
diameter.
always
decreasesrise
withper
increased
brake
Temperature
stop can
be
diameter.
calculated if you know the weight of
per Because
stop cantembe
theTemperature
old and new rise
rotors.
calculated
if per
you stop
know
the weight
of
perature rise
is related
directthe
old
and
new
rotors.
Because
tem1y to brake weight, doubling rotor or
perature
rise per
stop reduce
is related
directdrum
weight
should
temperaly to rise
brake
weight, doubling
rotor
or
ture
by one-half.
The weight
of an
diron
r u mdrum
weight
should
temperaaffects
the reduce
temperature
rise
ture
rise by
T h e You
weight
an
the same
as one-half.
rotor weight.
canofpre-
iron d r u m affects the temperature rise
t h e s a m e as rotor weight. You can pre-
Small caliper on solid disc works well on
front of sprint car run on dirt. Photo courtesy AP Racing.
Small
caliper on solid disc works well on
front of sprint car run on dirt. Photo courtesy AP Racing.
dict how many stops from a certain
speed it will take to reach a certain
dict
how many
stopsthefrom
a certain
temperature
from
formula
for
speed
it will rise,
take page
to reach
certain
temperature
11. Ita doesn't
temperature
from the
formula
for,
indicate
anything
about
cooling
temperature
rise,
page
11.
It
doesn't
however.
indicate
about cooling,
is thing
nearly unchanged
with
Cooling any
however.
brake-size changes. Improve cooling
Cooling
is nearly or
unchanged
with
aerodynamic
with
air ducting
brake-size
changes.
Improve
cooling
changes to the car.
with
air ducting
or aerodynamic
Installing
Bigger Brakes
- Finding
changes
to the for
car. a road car can be a
bigger brakes
Installing
Bigger
Brakes-Finding
problem
. You
may find
a bolt-on conbigger
brakes
for
a
road
car can
be ifa
size
version that increases brake
problem.
You
may
find
a
bolt-on
conyou have a popul ar performance car.
version
increases
Or, you that
may find
biggerbrake
brakessize
on ifa
you
have
a
popular
performance
car.
station wagon that will bol t on. Often
Or,
you
may
find
bigger
brakes
on
these brakes will have wider drums ora
station
bolt on.diameOften
heavier wagon
rotors, that
but will
sometimes
these
brakes
willlarger.
have Look
widerfor
drums
or
ter may
also be
largerheavier
rotors,
but
sometimes
diamedi ameter wheels to go with la rge rter may also
be larger. Look for largerdiameter
brakes.
diameter
wheels
to manuals
go with for
largerBy studying
shop
difdiameter
brakes.
ferent
model
years for your car, you
By discover
studyingthat
shopthemanuals
for difmay
brake-drum
or
ferent
model
yearsforfor
your car,
you
rotor size
is larger
a certain
year.
If
may discover
discover that
brake-drum
you
this the
situation,
go to ora
rotor size
is larger
certainwhether
year. If
yardfor
anda check
dealer
or junk
you
discover
this
situation,
go
the brake will bolt on. It may be to
thata
dealer
yardofand
the sizeororjunk
design
thecheck
brake whether
mountthe also
brakechanged,
will bolt eliminating
on. It may be
ing
thethat
inthe
size
or
design
of
the
brake
mountterchange possibility. Another possiing
changed,
inis that
someeliminating
cars could the
be orbilityalso
terchangewith
possibility.
possidered
optionalAnother
heavy-duty
bility is Sometimes
that some cars
be are
orbrakes.
thesecould
brakes
dered
with
optional
heavy-duty
larger. Study the parts books for
brakes. Sometimes
are
options.
Your dealerthese
can brakes
help with
larger.Look
Study
for
for the
Police,parts
Taxi,books
or Heavy
this.
options.
Yourin the
dealer
help
with
Duty
listings
partscan
book
.
this.
Police,
Taxi, to
or bigger
Heavy
On Look
a raceforcar,
changing
Dufy listings in the parts book.
On a race car, changing to bigger
Porsche Can-Am car under hard braking: Because nose is so low to track surface, underbody airflow is blocked. Ducts route cooling air to brakes, page 141 .
Porsche Can-Am car under hard braking: Because nose is so low to track surface, underbody airflow is blocked. Ducts route cooling air to brakes, page 141.
brakes usually is easier than on a road
car. First off, special brakes typically
brakes
is easier
thanthey
on genera road
usedusually
on a race
car, and
are
car.
Firstavailable
off, special
brakessizes.
typically
ally are
in various
The
are
used onpattern
a race for
car,aand
they
genermounting
rotor
is usually
ally are available
in variousit.sizes.
The
when ordering
A rotor
specified
mounting
pattern
for
a
rotor
is
usually
I-in. or so larger in diameter may
specified
it. A rotor
accept thewhen
same ordering
caliper. Check
with
I-in. manufacturer
or so larger or
in diameter
may
the
dealer before
accept
the
same
caliper.
Check
with
assuming they will work. If you
the manufacturer
or either
dealer the
before
change
rotor thickness,
caliassuming
they
work.or If
to bewill
changed
the you
linper will have
change
rotor thickness,
either
the calithinner.
Companies
ings machined
per will
have Tilton
to be changed
or the and
linlike
Hurst,
Engineering
ings
machined
thinner.
Companies
JFZ can help with either approach .
like Hurst, Tilton Engineering and
JFZ
can helpIMPROVEMENTS
with either approach.
COOLING
Modifications to improve cooling
COOLING
commonIMPROVEMENTS
on race cars . Some road
are
Modifications
to improve
cooling
cars
can also benefit
from cooling
are
common on but
race your
cars. Some
improvements,
choicesroad
of
cars
cando also
benefit from cooling
what to
are limited.
improvements,
but ways
your to
choices
of
There are several
improve
what
do are limited.
braketo
cooling:
several
ways toto brakes.
improve
Add or are
enlarge
air ducts
• There
brake
cooling:
• Change or modify wheels for inAdd orairflow
enlarge
ducts to brakes.
creased
to air
brakes.
or modify
inChange from
solid towheels
ventedfor
rotors
• Change
creased
airflow
to
brakes.
on disc brakes.
Change from
solid to orvented
rotors
• Change
to finned
aluminum
on disc brakes.
drums.
to mOdify
finned dust
or shields
aluminum
• Change
Remove or
on
drums.
disc brakes.
Removebacking
or modify
dust on
shields
on
• Vent
plates
drum
disc
brakes.
brakes.
Vent water-cooling
backing plates
on drum
• Install
system.
brakes.
• Change car-body aerodynamics for
Install water-cooling
system.
increased
airflow to brakes.
aerodynamics
AirChange
Ducts -car-body
The easiest
and most for
efincreased
airflow
to brakes.
fective
way
to improve
brake cooling
Air Ducts-The easiest and most effective way to improve brake cooling
Vented rotors in place of solid rotors will
improve brake performance if temperatures are
too inhigh.
Scoops
modified
Vented
rotors
place
of solidorrotors
will
ducting
tried first .
improveshould
brakebeperformance
if tempera-
tures are too high. Scoops or modified
ducting should be tried first.
is to add air ducts . These start with
scoops or holes in the body on most
is to add airrace
ducts.
start with
full-bodied
cars.These
On open-wheel
scoops
holescan
in be
thescoops
body attached
on most
cars, theorducts
full-bodied
race
cars.
On
open-wheel
to the brakes, uprights or axle.
cars,
the ducts
attached
A brake
duct can
mustbebescoops
designed
careto thetobrakes,
uprights
or axle.
fully
get the
most air
for the least
A brake
must
beThe
designed
amount
of duct
added
drag.
most carecritifully
to
get
the
most
air
for
the localeast
cal parts of a duct are its entrance
amount
of
added
drag.
The
most
critition and where air exits the duct at the
cal
parts
of aconstant-diameter
duct are its entrance
locabrakes
. A
tube
to
tion and
air exits
thebetween
duct at the
the
carry
thewhere
air is often
used
brakes.
A constant-diameter
tube to
duct
entrance
and exit.
carry
the
air
is
often
used
between
When installing a brake duct, the
be
duct
and faces
exit. forward and is
sure entrance
its entrance
installing area.
a brake
in When
a high-pressure
Theduct,
verticbe
al
sure its entrance faces forward and is
in a high-pressure area. The vertical
139
Dual master cylinders are used in place of
stock tandem master cylinder on this dualpurpose car.
Aftermarket spoiler has holes for brake-cooling ducts. High pressure exists in front of
spoiler, making ideal spot for brake ducts. Spoiler without ducts adversely affects brake
cooling. On a race car, tubes should be used to route air directly to brakes.
Dual master cylinders are used in place of
stock tandem master cylinder on this dualpurpose car.
Aftermarket spoiler has holes for brake-cooling ducts. High pressure exists in front of
spoiler, making ideal spot for brake ducts. Spoiler without ducts adversely affects brake
cooling. On a race car, tubes should be used to route air directly to brakes.
This may help front-brake cooling, but not
looks. Neat brake scoops under bumper or
behind grille would do same job and not require cutting torch.
front surface of a car-body nose is
always a high-pressure area. So is an
This
may help
not
air dam.
A topfront-brake
surface ofcooling,
a body but
is usulooks.
brake scoopsarea,
under bumper
or
ally aNeat
low-pressure
so avoid
behind grille would do same job and not rethese
areas
unless
you
have
quire cutting torch.
aerodynamic-test data that shows
otherwise. Almost any duct that profront
a the
car-body
nose beis
trudessurface
forward of
into
air stream
always
high-pressure area,
area. but
So itisalso
an
comes aa high-pressure
air
dam. Adrag.
top surface
of a body
is usuincreases
A protruding
duct
will
ally
area,way
so toavoid
work;a itlow-pressure
may be the only
cool
these
areasHowever,
unless try you
have
rear brakes.
other ideas
aerodynamic-test
that shows
before resorting to data
a protruding
scoop
otherwise.
any duct that profor the ductAlmost
entrance.
trudes
forward into the engine-coolant
air stream beA front-mounted
comes
but it also
radiatora high-pressure
is always in aarea,
high-pressure
duct duct
will
increases
drag.into
A protruding
area. Tapping
it with a brake
work;
it
may
be
the
only
way
to
cool
for the front brakes will not add drag,
rear brakes. However, try other ideas
before resorting to a protruding scoop
for the duct entrance.
A front-mounted engine-coolant
radiator is always in a high-pressure
area. Tapping into it with a brake duct
for the front brakes will not add drag,
140
Brake ducts on McLaren Can-Am car are simple holes in body with tubes attached. Forward
surfaces of sloping front fenders are in high-pressure areas.
but will reduce engine cooling
known as a NACA duct, is often used
slightly. Engine-induction plenums
for rear-brake-duct entrance. If you
on Can Am and sports-racing cars
have a wind tunnel or do serious aerowith large overhead air scoops are
dynamic track testing, you can find a
Brake
on McLaren
Can-Am
arebe
simple holes in body with tubes attached. Forward
alwaysducts
at high
pressure.
Theycarcan
suitable high-pressure area in which
surfaces of sloping front fenders are in high-pressure areas.
tapped for rear-brake cooling without
to locate such a duct. A NACA duct
increasing drag. Testing should be
may flow some air in a mediumbut
willcheck
reduce
engine cooling
cooling
known
a NACA
oftenmuch,
used
done to
that reduced
or
pressureasarea,
but itduct,
won'tis flow
slightly.
for
rear-brake-duct
entrance.
If
plenum Engine-induction
pressure does notplenums
cause
if any, in a low-pressure area. If you
you
on
Can overheating
Am and sports-racing
have
windattunnel
engine
or reduce cars
top
must aguess
a spotorfordoa serious
duct, ataeroleast
overhead air scoops are
with
dynamic
tracktest
testing,
speed,large
respectively.
try a wool-tuft
first. you can find a
always
at
high
pressure.
They
can
be
suitable
high-pressure
in which
Wool-Tuft Testing-A area
wool-tuft
test
NACA Duct-A flush duct entrance,
tapped for rear-brake cooling without
increasing drag. Testing should be
done to check that reduced cooling or
plenum pressure does not cause
engine overheating or reduce top
speed, respectively.
NACA Duct-A flush duct entrance,
to locate such a duct. A NACA duct
may flow some air in a mediumpressure area, but it won't flow much,
if any, in a low-pressure area. If you
must guess at a spot for a duct, at least
try a wool-tuft test first.
Wool-Tuft Testing-A wool-tuft test
<8>= Possible High-Pressure Area
9= Possible
Possible Medium-Pressure Area
@=
High-Pressure Area
(0=
Low-Pressure Area
@= Possible
Possible Medium-Pressure Area
(&
High-pressure areas on car body
exist atLow-Pressure
nose leadingArea
edge and base of windshield. Low
Possible
pressure always exists behind tail. Accurate wind-tunnel tests or pressure measurements
must
be used toareas
find other
areas
suitable
fornose
ductleading
entrances.
High-pressure
on car
body
exist at
edge and base of windshield. Low
pressure always exists behind tail. Accurate wind-tunnel tests or pressure measurements
must be used to find other areas suitable for duct entrances.
Cooling duct on March Indy Car maximizes
airflow and minimizes drag. Rather than
projecting
intake
airstream,
Cooling ductduct
on March
lndyinto
Car maximizes
which would
increase
drag,
advantage
airflow
and also
minimizes
drag.
Rather
than
is
taken of existing
high-pressure
area at
projecting
duct intake
into airstream,
front
tire. Duct
directs air
fromadvantage
intake at
whichofwould
also increase
drag,
front
of tire,
through high-pressure
duct, and into area
center
is
taken
of existing
at
of suspension
brake
rotor.
front
of tire. Ductupright
directsand
air from
intake
at
Photo
bytire,
Tomthrough
Monroe.duct, and into center
front of
of suspension upright and brake rotor.
Photo by Tom Monroe.
Wool tufts are installed on car body before aerodynamic testing. Bits of yarn are taped in
even rows. Assuming body is symmetrical, tufts on one side of car are sufficient.
Wool tufts are installed on car body before aerodynamic testing. Bits of yarn are taped in
even rows. Assuming body is symmetrical, tufts on one side of car are sufficient.
requires driving the car. Tape short
lengths of yarn-tufts-on the body a
requires
driving
car. transparent
Tape short
apartthewith
few inches
lengths
of
yarn-tufts-on
thecontrast
body a
tape. The yarn strips should
few
inches
apart
with
transparent
with the body color so you can see
tape. .The
stripsabout
should5-in.
contrast
them
Cut yarn
the yarn
long
with tape
the each
bodypiece
coloracross
so you
canwith
see
and
the car
them.
yarn about
5-in.
the
tapeCut
in the
the middle.
When
thelong
car
and
each piece
across
car awith
motion,
the yarn
willthe
form
Uis intape
the tapepointing
in the middle.
the car
shape
in the When
direction
of
Uis in motion,
yarn
will formtoa the
airflow.
If the the
flow
is attached
shape
the directionyarn
of
body-itpointing
is not in
turbulent-the
airflow.
If
the
flow
is
attached
to
the
will lie flat and straight with little
body-it is not turbulent-the yarn
wiggling.
will
lie the
flat duct
and straight
withonlittle
Place
in an area
the
wiggling.
most forward-facing surface where
Place the
ductisinindicated
an area. on
the
smooth
airflow
If the
most
forward-facing
surface
where
yarn points rearward and wiggles
smooth airflow is indicated. If the
yarn points rearward and wiggles
slightly, such an area is a second
choice. This is turbulent attached flow,
slightly,
such
an area
second
and usually
is found
near isthea rear
of a
choice.
is turbulent
body. IfThis
the yarn
wiggles attachedflow,
violently and
and
usually
found near
theis rear
of a
in all is
directions,
this
separatpoints
body.
If
the
yarn
wiggles
violently
ed air. It is low pressure and not and
the
points
this is separatplace in
foralladirections,
duct entrance.
You'll
ed air. find
It is separated
low pressure
andbehind
not thea
always
airflow
place
for a duct
You'll
blunt entrance.
protrusions,
and
body, behind
always
find
separated
airflow
behind
often, all over the tail end. Regardlessa
body,
blunt
anda
of
the behind
indicated
flowprotrusions,
, never install
often,
all over the
tail end.
Regardless
duct entrance
on any
rearward-facing
of
the indicated
surface,
even ifflow,
it is never
only install
slightlya
duct
entrance
on
any
rearward-facing
rearward-facing.
surface,
even if ittheis ducts,
only slightly
After installing
retest
rearward-facing.
with wool tufts. Put tufts in and
After the
installing
the entrance
ducts, retest
around
brake-duct
and
with
wool
tufts.
Put
tufts
in and
check that air actually flows into
the
around the brake-duct entrance and
check that air actually flows into the
Brake ducts on Porsche Can-Am car use
different designs at front and rear of body.
Front
direct airflow;
rear
Brakeducts
ductsface
on Porsche
Can-Am
carducts
use
use
flush designs
NACA-type
ducts.
different
at front
andEffectiveness
rear of body.
of
rear
ducts
be confirmed
by
Front
ducts
faceshould
direct airflow;
rear ducts
testing-pressure
on top
of body
can't be
use flush NACA-type
ducts.
Effectiveness
determined
by simple
observation.
of rear ducts
should
be confirmed by
testing-pressure on top of body can't be
determined by simple observation.
opening . Some duct entrances have
air coming out of them because presopening.
entrances
sure
at theSome
exit duct
is higher
than athave
the
air
comingSo
out
of them
because
presentrance!
, test
the duct
entrance
sure atand
thewith
exit the
is higher
the
alone
entire than
brakeatduct
entrance!
So,
test
the
duct
entrance
installed. There may be critical
alone
and with the entire brake duct
differences.
installed. There
differences.
may
be
critical
141
Tuft test was to confirm that air flows smoothly over body at radiator-duct exit. Highpressure areas are indicated by tufts laying flat on body surface. Flow is somewhat
disturbed,
but intoproper
direction.
Tuft test was
confirm
that air flows smoothly over body at radiator-duct exit. High-
pressure areas are indicated by tufts laying flat on body surface. Flow is somewhat
disturbed, but in proper direction.
Brake ducts on this stock car are mounted under front bumper. A flexible hose leads cool
air to front brakes. This type duct is easily modified to change brake cooling .
Brake ducts on this stock car are mounted under front bumper. A flexible hose leads cool
air to front brakes. This type duct is easily modified to change brake cooling.
A well designed duct is simple and neat. Ducts sealed to center of rotor such as this are
much more efficient than those that just point at center of rotor. Flex hose used for air
ducts
cars is duct
available
in auto
surplus
stores.
Noticeofboth
A well on
designed
is simple
andparts
neat. or
Ducts
sealed
to center
rotorends
suchofashose
this are
securely
attached
with
hose
clamps.
much more
efficient
than
those
that just point at center of rotor. Flex hose used for air
ducts on cars is available in auto parts or surplus stores. Notice both ends of hose are
securely attached with hose clamps.
142
Air-Pressure Gage-An air-pressure
gage that measures in inches of water
Air-Pressure
Cin .Hp), pageGage-An
113, can air-pressure
be used to
gage
that
measures
inches
find high-pressure in
areas
andoftowater
im(in.H20),
pageMount
113, can
be used
to
prove
ducting.
the gage
so the
find
areas
and ortovinyl
imdriverhigh-pressure
can see it. Run
rubber
prove
the want
gage to
so test
the
tubing ducting.
from theMount
area you
it.
Run
rubber
or
vinyl
driver
can
see
to the high-pressure port on the gage.
tubingthe
from
the area
wantPosition
to test
body.
Tape
tubing
to theyou
to
high-pressure
portofon
gage.
thethe
tube
on the surface
thethe
body
so
Tape
theacross
tubingthe
to ends,
the body.
Position
air flows
not into
it.
theIf tube
the the
surface
of the bodyport
so
you on
leave
low-pressure
air
flows
across
the
ends,
not
into
it.
disconnected, the gage will measure
you leavedifference
the low-pressure
theIf pressure
between port
the
disconnected,
gage will
test area andthewhere
the measure
gage is
the
pressure
difference
between
the
located.
However,
you can
run a tube
test
area
and
where
the
gage
is
from the low-pressure port to the area
located.
you can
a tube
of the However,
car you want
therunduct
to
from
the low-pressure
the gage
area
pressurizethe brake port
rotor.toThe
of
the
car
you
want
the
duct
to
will then measure the pressure difpressurizethe brake
The gage
ference
between
the rotor.
test area
and
will
then measure
the pressure
brake-rotor
area. Before
running difthe
ference
between
the
test
areaofand
test, blow velY lightly at the end
the
brake-rotor
area.area.
Before
the
tube in the test
If therunning
gage readtest,
very lightly
at the
end of the
ing blow
increases,
it is
hooked
up
tube in theRun
test area.
readcorrectly.
the If
cartheatgage
constant
ing increases,
is read
hooked
up
pressure.
speed,
say 80 mph,it and
correctly.
carzero,
at constant
If the gage Run
reads the
below
the duct
speed,
80 .mph,
and read
will notsay
work
Air flows
frompressure.
high to
If
gage reads
below
zero,the
thehighduct
lowthepressure
only.
Tape
will
not
work.
Air
flows
from
high
to
pressure tube to different locations
low pressure
only.until
Tape
around
the body
youthe
findhighthe
pressure
tube toarea
different
highest-pressure
that is locations
practical
around
the
body
until
you find the
to accept a duct inlet.
highest-pressure
areaexit
thatthat
is practical
If you have a duct
seals to
to
ductyou
inlet.
theaccept
rotor aand
want to improve it
a ductfewer
exit that
seals
If you
have
with
larger
tubing,
bends
or toa
the
rotor
and
you
want
to
improve
it
different inlet location, drill a hole in
with
larger
tubing,
fewer
bends
or
the rotor plenum close to the rotor.a
different
drill a holeport
in
Connect inlet
it to location,
the high-pressure
the
rotorgage.
plenum
close to the
on the
Disconnect
the rotor.
lowConnect
to the
port
Run a constantpressure it
gage
port.high-pressure
on
the
gage.
Disconnect
the
lowspeed test before and after modifying
pressure
port. Run
a constantthe duct. gage
If pressure
increases
after
speed
test before, and
the modification
the after
duct modifying
will flow
the
If pressure
increasescan
after
moreduct.
air. The
same procedure
be
the
modification,
the
duct
will
flow
used for optimizing engine-induction
more
air. The and
sameradiator-inlet
procedure can
be
ram-air-scoop
sizes.
used
for
optimizing
engine-induction
Just be sure the high-pressure gage
ram-air-scoop
and of
radiator-inlet
pickup is in front
and close tosizes.
the
Just
be sure
the high-pressure gage
item being
pressurized.
pickup
in front
and close
to the
Thereis are
some ofcomplex
methodS
item
being
pressurized.
to determine the exact dimensions of
some
complex
a There
NACAare
duct.
The
easiest methods
way to
to determine
dimensions
of
design
a ducttheis exact
to copy
one from
a NACAcar.duct.
easiest waytestto
another
A lotThe
of wind-tunnel
design
a
duct
is
to
copy
one
from
ing and track testing has been done on
another car. Arace
lot ofcars
wind-tunnel
no
factory-built
. There'stesting
and track
testingtheir
has been
done
on
reason
to repeat
work.
They
factory-built
no
can't
hide therace
duct cars.
shape,There's
so go into
reason
to
repeat
their
work.
They
the pits with a camera and photograph
can't
duct shape,
so go into
ducts hide
on the
winning
factory-designed
the pits
with a camera
and photograph
cars.
Enhance
the information
you'll
ducts on winning factory-designed
cars. Enhance the information you'll
.
get with
with the
the photo
photo by
by measuring
measuring the
the
get
the car
car owner
owner will
will allow it.
it.
duct, ififthe
duct,
repeat, the front of
of a car
car body
body or
To repeat,
spoiler-air dam-is
dam-is an ideal
nose spoiler-air
nose
place to
to install
install a duct entrance
entrance for the
the
place
front brakes.
brakes. Make
Make aa round,
round, smoothfront
of the
the duct.
hole the
the size of
edged hole
the entrance miniRounded edges at the
Rounded
mize turbulence
turbulence inside the
the duct.
duct. Use
mize
a round
round tube or duct to route air to
to the
brake. Use smooth tube for straight
ducts and corrugated heater-type ducting for curves. Mount the duct securewon't fall off. Check wheel and
ly so it won't
suspension clearances in all turn and
wheel-travel extremes: bump, droop
and steering lock.
Exit-The duct exit should be
Duct Exit-The
at a specific location. On a drum
brake, direct the exit at the drum so
air hits both the drum edge and backIf tlie
the backing plate is
ing plate. If
vented, make sure air blows into the
vents. All race cars that use drum
brakes should have vented backing
plates-assuming
rules
allow
plates-assuming
them - bu t road cars may not. If there
them-but
are no vents, point the duct more at
the drum and less at the backing plate.
The accompanying drawing shows
how to locate a cooling-duct exit for
drum brakes.
A disc brake with a solid rotor
should have the duct pointing at the
forward edge of the rotor so both
sides of the rotor are cooled.
cooled. This is
not a suitable duct-exit location for a
vented rotor.
rotor. I discuss ducting vented
rotors later.
later.
It's difficult to cool both sides of a
solid rotor equally.
equally. A duct pointed to
the inboard side
side of the rotor will take
care
care of that side
side very well. However,
However,
the outboard side
side of the rotor gets
little
little or no air if it is close
close to the
the
wheel. Consequently,
Consequently, the
the duct should
be designed to force
force air between the
the
wheel and the
the outboard
outboard side
side of the
the
rotor.
rotor. If the
the rotor has
has one
one hot side
side and
one
one cool
cool side,
side, it may
may warp.
warp. A warped
rotor
rotor will
will adversely
adversely affect braking.
braking.
The
The nearby drawing shows
shows a duct
duct dedesigned
signed to cool
cool both sides
sides of a discdiscbrake rotor.
rotor. This
This may
may be easy or
or
impossible,
impossible, depending
depending on
on the
the specific
specific
configuration.
configuration.
A duct
duct design
design must
must be
be proven by
by
testing.
testing. This
This isis because brake
brake cooling
cooling
isis complicated
complicated by
by other
other factors.
factors. For
For
example,
example, wheel
wheel design
design also
also affects
affects
cooling
cooling of
of the
the outboard
outboard side
side of
of the
the
rotor.
rotor. Measuring
Measuring temperature
temperature on
on both
both
sides
sides of
of the
the rotor
rotor and
and caliper
caliper will
will concon-
I
T
JI
Drum
Drum
Vented
Vented
8ackingBackingPlate
Plate
Scoop
Scoop
I
I
I
I I
Backing Plate
Vented Backing
Drum
I
Non-Vented
Non- Vented Backing
Backing Plate
-
Cooling
Cooling duct should be pointed
pointed as shown depending on backing-plate design.
design. If there are
cooling holes or scoops in backing
backing plate, duct should point toward backing
backing plate and drum.
drum.
holes in backing
backing plate, point
pOint duct entirely toward drum.
If there are no holes
Rotor~
~DiVider
Duct
I
Hot Side
HotSide~~1
I
I
I
I
,
Cool Side
LJ
~
Original Shape
Shape
Original
It is
is essential
essential to
to get cooling
cooling air to both
both
sides
sides of a solid
solid rotor.
rotor. Divider
Divider in
in duct will
will
split
split airflow
airflow so
so it
it can
can be
be directed to
to each
each
side
side of rotor.
rotor. Some
Some experimenting
experimenting with
with
dividers and
and duct
duct locations
locations may
may be
be necesnecesdividers
sary
sary to
to get it
it right.
right.
rotor is
is cooled
cooled more
more on
on one
one side
side than
than
If aa rotor
the other,
other, it
it can
can warp
warp as
as shown
shown here.
here. Hot
Hot
side expands
expands more
more than
than cold
cold side
side and
and rotor
rotor
side
takes the
the shape
shape of a saucer.
saucer. Braking
Braking is
is not
not
good
good on
on aa warped
warped rotor.
rotor. Equal
Equal cooling
cooling on
on
each side
side prevents
prevents this
this situation.
situation.
each
firm
firm how
how successful
successful aa duct
duct design
design is.
is.
A disc
disc brake with a vented rotor
should
should have
have the
the cooling air directed to
to
the
the center of the
the rotor.
rotor. As
As itit turns,
turns, the
the
rotor
rotor acts
acts as
as an
an air
air pump,
pump, although
although
not an
an efficient
efficient one.
one. Air isis drawn
drawn into
into
the
the center
center of
of the
the rotor and
and isis thrown
out
out the
the edge.
edge. Vented-rotor ducts
ducts can
can
be sealed
sealed to
to the
the center
center of
of the
the rotor.
rotor.
be
much more
more efficient
efficient than
than
This isis much
This
merely
merely pointing
pointing the
the duct
duct at
at the
the rotor
rotor
center
center because
because air
air isis forced
forced through
through
the
the rotor.
rotor. See
See the
the drawing
drawing for
for how
how aa
vented
vented rotor
rotor should
should be
be ducted.
ducted. If
If
more
more cooling
cooling isis required,
required, seal
seal the
the duct
duct
to
to the
the center
center of
of the
the rotor.
rotor.
Area-The
ideal air-duct crossDuct AreaThe ideal
sectional area
area should
should be at
at least
least as
as
sectional
large as
as the
the rotor cooling-passage-inlet
cooling-passage-inlet
large
area. To
To determine
determine this
this area,
area, measure
measure
area.
the distance
distance between the
the inboard
inboard and
and
the
outboard rotor
rotor side
side plates.
plates. Also
Also measoutboard
ure the
the inner
inner diameter
diameter of
of the
the inboard
inboard
ure
rotor side
side plate.
plate. Calculate
Calculate the
the area
area
rotor
this formula:
formula:
using this
Inlet area
area == (3.14)
(3.14)(inboard-plate
Inlet
(inboard-plate
ID)(distance
between plates)
plates)
10)
(distance between
For aa rotor
rotor with
with aa 6.25-in.
6.25-in. inboardinboardFor
plate 10
ID and
and 0.63
0.63 in.
in. between
between plates:
plates:
plate
Inlet area
area == (3.14)
(3.1 4 )(6.25
( 6 . 2 5in.l(O.63
in.I(O.63in.)
in.)
Inlet
1 2 . 3 6sq
sq in.
in.
== 12.36
143
o
o
o
~Rotor
D
Rotor
=
0
0
Fiberglass scoop on this Indy Car brake is
sealed to front upright. Air is ducted directly
to centerscoop
of vented
rotor.
This
was
Fiberglass
on this
lndy
Carduct
brake
is
obviously
designed
with
of the
car,
sealed to front
upright.
Air rest
is ducted
directand
merely
added
on This
afterduct
brakes
ly to not
center
of vented
rotor.
was
overheated.
Photo bywith
Tom Monroe.
obviously designed
rest of the car,
and not merely added on after brakes
overheated. Photo by Tom Monroe.
Common duct diamet