As the service technicion,
you need to find onswers to
these questions:
0
How is the broking
system octivoted
O Whot
is
?
o moster
cylinder?
@
Whoi is speciol obout
broke fluid? Why ore
there different types of
broke fluid?
Porking Brokes
flypes
\11 vehicles must have brakes.
' ::e
Although sometimes mistakenly called emergency brakes, parking brakes are brakes that are
of Brqkes
Without brakes,
no way to safely slow or stop a moving vehi. \Iost vehicles have two types of brakes-service
': r.iS and parking brakes.
iS
S,ervice Brqkes
Service brakes are the primary braking system.
,. applied to the service brake pedal is con" . i to hydraulic pressure by the master cylinder.
, :-ressure is transferred through the service
. :--. svstem until it reaches the wheel brakes.
':. orak€ force is applied to the vehicle's wheels,
: ,:-:lg the vehicle to slow or stop.
:igure
-
'
'
1-1 shows the major components (parts) of
::-cle's service brake system.
..- master cylinder serves as the brake fluid
,:r\-oir for the service brakes and converts
--=chanical force to hydraulic pressure for the
" .,king system.
- :,e brake hoses/lines can1, brake fluid under pres,-:e from the master cylinder to the wheel brakes.
- -. Cisc brakes include rotors
and disc pads, which
,- ,:=: brake force to the vehicle's wheels.
, ':um brakes include drums and brake shoes,
-* iransfer brake force to the vehicle's wheels.
' ,:
.i iLL'€T bra/u booster supplies the increased forces
.-:d
by the brakes. The booster does this with.
=quiring increased brake pedal pressure.
' : :iake pedal activates the master
cylinder.
used to keep a parked vehicle from moving. They
are usually on the rear wheels and are mechanically
operated.
Friction ond Broking
Friction and braking are closely related in vehicles.
Without friction, there would be no brakins.
Friction
Friction is the resistance to motion between two
objects or surfaces that touch. Friction varies by the
amount of force (often referred to as the load)
between the surfaces. Friction also varies by the
roughness of the surfaces and the materials from
which the objects are made. For instance, there is
more friction between a piece of sandpaper and a
block of wood than between an ice cube and
countertop.
A lubricant between the objects can reduce friction. Water between the melting ice cube and the
countertop allows the ice cube to move with less
friction. Similarly, wet brakes will not stop a vehicle as effectively as dry brakes,
Without friction, no moving object would slow
down or stop. A toy top, once set spinning, would
continue to spin. It is the friction between the top,
the surface it spins on, and the air around it that
slows
it down.
Power Broke Boosler
Reor Brokes
Porkinu Broke Lever
Broke Pedol
w Fig.
a
t-t The moiorcomponents in o iy'picol broking system. Whotarerhedifferences@l
e.b:*:.,',:j'":::!::!:':,::|-::..u:::!*:::i|r*!::o:'^:::-:':::::::.,....-...,...-_.,."-.si
Another example is the space shuttle as it
reenters the earth's atmosphere. Friction between
the shuttle's surface and the atmosphere reduces
the shuttle's speed. The reduction in speed creates
massive amounts of heat. Friction slows the space
shuttle from an orbital speed of about 18,000 mph
[28,800 kph] to a landing speed of about 500 mph
[800 kph].
There are two types of friction-static friction and
kinetic friction. Fig. 1-2.
Friction Stops!
A good driver's braking skills allow the brakes
to stop the vehicle. Unfortunately,lf a driver locks
his wheels and skids, the brakes cannot do their
job. Then the friction between the tires and the
road must stop the vehicle. The stopping distance
is much greater in a skid. The driver also has little
control of steering with locked wheels.
Let's examine an unfortunate situation. Two
older pickup trucks are traveling doum the freeway at 55 mph [BB kph]. The trucks are identical
except that one truck is fully loaded and the other
is empty. Suddenly several deer step onto the road-
way, right into the path of the trucks! The drivers
see the deer immediately and overreact. Each
slams on his brakes at exactly the same instant and
locks the wheels on his truck.
Under nor:rnal braking conditions more energy
will be required to stop the fully loaded truck than
the empty truck. The loaded truck would normally
require a greater stopping distance. The two trucks
with the locked brakes in this example have the
same tire surface area in contact with the road, but
they differ in weight. Under these conditions will
the lighter truck still be able to stop in a shorter distance? Does the weight of the truck make a difference if the truck is skidding?
Experimenting with Friction
Meels NATEF Scienre Slondords
for friction ond decelerolion.
Moteriols cnd Equipment
. Three lorge metol flol woshers
. Smoll piece of double-fored tope
.
O
Ruler or other stroightedge
Tape two of the washers together with the
double-faced tape. No tape should touch the
bottom surface of the stack. This stack represents the heavy, loaded truck. The single
washer represents the lighter, empty truck.
O Place the ruler on a smooth, level surface.
O Put the single washer and the double washer
side-by-side, touching the straight edge of
the ruler. Fig. A.
O Quickly shove and retract the mler to set the
washers in motion. \Arhich one stops first?
Results ond Anolysis As you should have
observed, the stopping distances of the objects
are not dependent on their weight. Why?
Explonotion The force of friction stops the
trucks and washers. The amount of friction is
proportional to the weight of the object. Each
truck's kinetic energ'y of motion is also proportional to its mass. You might expect that the
double washer would take longer to stop
because of its greater kinetic energ'y. However,
twice the mass results in twice the frictional
stopping force. Finally, doubling the amount of
friction causes the double washers to stop in
exactly the same distance as the single washer.
The single washer has half the kinetic energ'y
but also half the frictional stopping force.
Stotic Friction Static means ,,at rest.,,
Static fric_
:on is the resistance between objects that are in
rtact but at rest. Parking brakes ui" un example
of
':ic friction at work. Friction between the Lrake
:.rrg and the brake drum or rotor keeps the wheels
' :.ir moving. Friction between the
vehicle's
-: rhe pavement keeps the vehicle from sliding.tires
{inetic Friction Kinetic means ,,in motion.,, The
:-Sr?ltc€ between objects that are in contact
and
-:lative motion is called kinetic friction.
-
-ike the space shuttle, vehicles on earth use
-=tic friction to change their motion into heat
-:qv. Friction between the moving and nonmov_
- :arts of the service brakes creates heat.
rs the vehicle slows and stops, kinetic energ-y is
-,,rged to heat energy.
The brakes pass this heat
.re air and other wheel parts.
What are service brakes?
\\4rat is friction?
){ame the two types of friction.
(b)
*
*
f,t. t -2 There is more friction between obiects ot rest (o) €
ihon,between obiects in relotive motion (b). Mtre
force is !
needed to move on obfect ot rest thon n [eep
on oU;".t- i
moving. Obiects dt rest have what type oi frictionZ
;
w,:
Give an example of static friction.
Describe how kinetic friction is used to slow
or
stop a vehicle.
sltoes against
Service Broke Sysfem
-:e service brake system is one of the most
_
Fig. 1-3(a).
clamp
the inside of
a
rotating brake drum.
Disc brakes use hydraulic pressure to
brake pads against a
brake rotor. Fig. 1-B(b).
rotating disc called a
_'rtant systems on a vehicle. The engine
may get
ehicle moving, but it is the brakes-that slow
or
it.
- The service brakes are designed to be more
.rfui than the engine. \A4ren uppt"a. braKes can
,- stall the engine.
.
Broke Pods
Coliper
:3"oke Acfion
:=n1ce brakes, those operated by the vehicle's
,... pedal, have two basic parts. The first is the
,, :r cylinder. The
master qlinder
is the part that
.:es hydraulic (fluid) pressure throush ihe
brake
The second is the wheel brake mechaiisms.These
-,,cated at each of the vehicle's wheels. They are
ated by hydraulic pressure.
-
o types of service brakes are used on vehicles.
': brakes use hydraulic pressure to press brake
.'.
Piston
Broking
Pressure
Frictionol
Broke
Contoct
Rolor
Fig. l-3 There ore two types of service brokes: e,l
drum brokes (o) ond disc brokes
bt. why cl;
they have these names? (Robetloxh|;mbi) :
i
,r.i:r:rr.r:i.ii,,:i:!.:,,:ii _.r*...,,.-..,,,r",,.Y
]
Drum brakes have shoes that press against the
inside of the rotating brake drum. Fig. 1-4. Early
bicycle coaster brakes worked this way.
ru
Disc brakes have pads that clamp against a rotating rotor. Fig. 1-5. Hand-operated bicycle brakes
work in a similar way.
Weor Indicolor
Wheel(ylinder
(oliper
Anchor Pin
Secondory Shoe
Broke-Shoe
ond lining
Holddown
Inboord
Pod
Springs
Self.
Piston
Adiu$er
ioble
Porking
Broke
Lever
e rig. t-5
Adiu$er Spring
Adiusling Screw
*
Fig. t-4 Drum brokes hove shoes thot push ogoinst wl
the inside of o rototing drum. Whot fype of friction
t
:,
*w is ai wark here?
tfod l,laror (ompony)
Disc broke
pods clomp oround o
rototing rotor to slow the
vehicle. What is
crealed as a result of
the braking o,ction?
(Deko lltorotne
*:
*
Division
of Genuol
lllotorshrporofon)
Remember-Safety Firstl
Safety is important to both the customer and
the technician. If you, as the technician, are not
careful, you may harm yourself or your customer. And you may do serious damage to your
customer's vehicle.
An action as simple as using old brake fluid
that has been contaminated with water can cause
brakes to fail. Using the wrong fluid or not checking the fluid level properly can also lead to problems. To assure personal safety and proper
service of your customer's car-read!
Technicians must always look for visual clues.
Sometimes a manual will warn you about specific service products. Sometimes, the label on a
can or package will tell all. When you read the
Safety First sections in this chapter, you will be
given specific warnings about brake fluid. Stay
on the alert for safety information about all products and procedures that you use.
Meels NAIEF Communicotions Stondords for rollecting, evoluoting,
und using informolion.
Read the Safety First features later
in
this
chapter.
0
Where could you find this information
and other similar warnings?
O
Make a list of sources that warn or advise
about the products used in servicing a
vehicle.
0
Keep a list of specific warnings that you
find as you service cars. f-Ise this list as an
on-thejob resource.
Pushing the vehicle's service brake pedal forces
:'Luid through the braking system lines and hoses. The
'Jressure of this fluid activates the brakes. The brake
,hoes and brake pads are stationary. The drums and
.'otors are moving. Kinetic friction between the brake
.hoes and drums, or brake pads and rotors, slows and
.ren stops wheel rotation. Friction between the tires
,.rd the road stops the vehicle.
The first dual-braking systems separated the front
brakes from the rear brakes. Fig. 1-6(a). More recent
dual-braking systems are separated diagonally. Each
system on a diagonally split system controls one
front brake and one rear brake. Fig. 1-6 (b).
Primory Reservoir
(Front Broke Sy$em)
Secondory Reservoir
(Reor Broke Sy$em)
The service brakes can be applied hard enough
from rotating). When
::akes are locked, they no longer convert the vehie's motion into heat. Success in stopping a vehicle
'-en depends entirely on the kinetic friction
:tween the tires and the road. If the kinetic fric,rn is not great enough, the tires lose their grip on
. e road and the vehicle begins to skid.
,,, lock the wheels (stop them
The best braking performance occurs just before
tires begin to lose traction. This is the principle
. antilock
(o) Front-Reor Split
Fronl Disc
:
Reor Drum
Brokes
Brokes
brakes.
Wheel
Moster (ylinder
Duql-Brqking Sysfems
Cylinder
Before 1967 most vehicles had a single-piston
-,.ster cylinder. This meant that brakes on all four
,.eels were activated by a single hydraulic system.
' -.nr. part of the hydraulic system failed, the whole
.,king system failed. In 1967, the U.S. Department
Broke Pedol
Secondory Sedion
Transportation (DOT) passed legislation requir. r ehicles to have dual-braking systems.
\
a dual-piston master
-:-Lder, two fluid reservoirs, and two separate
dual-braking system has
Primory Sedion
\Vhat are the two
parts of the
service
brakes?
0
What are the two types of service brakes used
on vehicles?
o \Vhat is the effect of kinetic friction
between
(or
pads
and
brake
the brake shoes and drums
rotors)
?
Reor Drum
Brokes
::'aulic systems. One hydraulic system controls
- rrakes of two wheels. The other hydraulic sys--. controls the remaining two wheels. This
,:rgement provides additional safety. If one sys'-. iaiis, the other system continues to work.
io
{b) Diogonolly Split
Front Disc
Brokes
w Fig. t-6 Duol-broking
'*l
systems ore split eith 'il
front to reor (o) or diogonolly (bl. what is
the benefit of
*
(tord
Alotar
I
a dual-brdking system?
[ompony)
@j
O What kind of pressure do drum brakes use to
press the brake shoes against the inside of a
rotating brake drum?
o
What are the main components of a dualbraking system?
a
Brqke Fluid
a
fluid is used to transfer hydraulic pressure
from the service brake's master cylinder to the
Brake
Brake fluid must:
Be compatible with the metals in the brake system.
Lubricate the moving parts of the braking system.
Brake fluid must not:
too thin or too thick as the temperature
. Become
changes.
wheel brake mechanisms.
Brqke Fluid Properties
Brake fluid must remain stable through a wide
range of temperatures and operating conditions.
a
Evaporate easily.
a
Soften
or damage rubber parts of the braking
system.
. Boil at high temperatures.
Converting lbmperatures
Vapor lock, overheated brakes, boiling radiators, and overheated engines all involve heat and
temperature changes.
The rate of change in Fahrenheit to Celsius is:
Most service manuals show temperatures in
For each increase of 1.8' Fahrenheit (1.8"F),
there is an increase of 1o Celsius (1"C). Note that
both degrees Celsius and degrees Fahrenheit.
However, you will sometimes need to convert
temperature readings from one system to the
other. You could use thermometers that give temperatures both in degrees Celsius ("C) and
degrees Fahrenheit ('F). Fig. A. But it's often
easier to convert a temperature mathematically.
- 32 180
loo-o:loo:t'o
212
OoC equals 32oF.
To convert Celsius temperatures to Fahrenheit
temperatures, use this formula:
F:
+
32
The rate of change in Celsius to Fahrenheit is:
100-0
Refer to Fig. A. Look at the temperature difference between the boiling point and the freezing point of water. The change in Fahrenheit
temperature from 2I2'F to 32'F corresponds to
a change in Celsius from 100"C to 0"C.
1.8 C
100 5
^__^
212-n:lgo:O:u'Jro
For each increase of 5"C there is an increase of
9'F. Note that 32'F corresponds to 0oC.
To convert Fahrenheit temperatures to Celsius
temperatures, you can use this formula:
Boiling Poinl
C:;(F*
of Woler
32)
or C:0.556(F-
32)
i
a
a
Meels NATEF Molhemolics Stondords for using formulos lo converl
meosuremenls between English ond melric systems.
Freezing Point
of Woler
O What is 98.6'F in oC?
O DOT 3 brake fluid boils at 401"F. \Arhat is
the equivalent temperature on the Celsius
scale?
0
What is the Fahrenheit equivalent temperature for 40'C?
a
I
I
C
f
I
n
I
rl
J
...r-,..,c e,,....3.,..,,s_.,e.
e-....J... r..,
Moteriols DOT 3 ond DOT 4 broke fluids
\{4ren brake fluid boils, it becomes a vapor (gas),
much like boiling water turns to steam. A vapor can
compressed.
Pressing on the service brake pedal will compress the
apor in the hydraulic lines instead of transferring the
"
'rressure through the fluid. This can lead to partial or
Broke Fluid Types The Society of Automotive
:ngineers (SAE) and the DOT have standards for
:rake fluid. The DOT specification is typically the
ne referred to. The three currently approved types
.:e DOT 3, DOT 4, and DOT 5. The higher the
.--rmber, the more strict the specifications, especially
'r the boiling point.
Iecl
the
T
monufocturer's specificotions. A vehicle's worif incorrect or incompotible
broke fluids ore used.
ronty moy be voided
DOT 3 and DOT 4 brake fluid types are
1r glycol-based. These are the most commonly
,-d. They are inexpensive and compatible with
. ,st service brake systems.
'
DOT 5 brake fluid is a silicone-based product.
.rcone-based brake fluid is more exDensive than
.r glycol-based brake fluid. It does not readily
.rd with DOT 3 and DOT 4 types, so it must not
: rrixed with them.
I OT 5 brake fluid offers some advantages. It has
.her boiling point than DOT 3 or DOT 4 types.
*.
ore olso sirong point solvents thot con
domoge o vehic'ieis finish. Toke core to ovoid
be compressed; a liquid cannot be
lomplete braking system failure, sometimes called
:,rake pedalfade.Infact, vapor in the hydraulic brakrg system is the primary reason for brake pedal fade.
.
)',
,
Moishrre gets into brake fluid through damaged
seals and loose or faulty connections on the master
cylinder. Moishrre also enters throug'h damaged brake
hoses and seals on wheel cylinders and calipers.
After containers of brake fluid have
been
opened, they must be kept tightly capped when not
in use. Brake fluid should not be stored for a long
period of time. The longer it is stored, the more
moisture it can absorb.
Pour brake fluid directly into the master cylinder
reservoir from a sealed and clean container. This will
decrease the chance of brake fluid contamination. It
is important to keep dust and dirt out of the master
cylinder reservoir.
lnsfolling Broke Fluid
As the disc brakes wear, the fluid level in the
reservoir will drop. If the level gets too low, there is
a possibility that air can get into the hydraulic system. To prevent this, the fluid level must be kept
above the minimum level at all times. Fig. 1-7.
Additionall|, whenever the hydraulic system is
serviced, the brake fluid will have to be replenished.
Mo$er (ylinder
Fluid Reservoir
not damage paint and does not absorb mois'. However, because of its higher cost, it is usuused only in heavy-duty applications. There
,rnly a few applications where silicone-based
.,e fluid is in common use. They are:
i-litary vehicles.
stal vehicles.
.. -,es
Broke Fluid
-rae cars.
i rorcycles.
':ier in Broke Fluid
The major disadvantage
, h glycol-based brake fluid is that it absorbs
,:ure. Because water boils at 212"F [100"C] and
- 3 brake fluid boils at 401'F [205'C], any
,-:re in the brake fluid lowers its boiling point.
.rng the boiling point of brake fluid increases
:ance of having vapor in the braking system.
ir'\
F*
s rig. t-z
I
I
I
I
I
t
Alwoys mointoin the broke fluid level obove€
the MIN mork on the reservoir. Do not overfill. whor
miglli cause ftre ffuid level ta becorne critically
* low?
(Chtlton is
o
registered trodemork
of
W.
6, Nkhlls, ln(.)
r
l
Key Poinfs
Review Gluesfions
Meets the following NATEF Standards for Brakes:
describing brake functions and principles; selecting,
handling, storing, and installing brake fluids.
o The service braking system is activated
hydraulically. The parking brake is activated
mechanically.
o Friction provides braking action in a vehicle.
o Service brakes have two main components:
the master cylinder and the wheel brake
mechanisms.
o The two basic types of service brakes are drum
and disc.
o Dual-braking systems can be identified by the
number of separate fluid reservoirs in the master
cylinder.
o Brake fluids are chosen on the basis of intended
O What
use.
t A vehicle must be safely supported for brake
servicing.
are the two types of braking systems on
most motor vehicles?
O
Explain how friction provides braking action in
a motor vehicle.
O What is the advantage of a dual-braking
system?
O How many
separate fluid reservoirs does a
dual-braking system master cylinder have?
O
FIow is the service braking system activated?
0
Explain the process for selecting and installing
brake fluid.
O
Describe the safe way to support a motor vehicle for brake servicin.q.
o
Explain why you should
avoid "locking up" your service brakes.
o
Is it safe to use brake fluid
from a container that has been opened, capped,
and stored for six months? Whv or whv not?
Applying Essential Knowledge in Apprenticeship Training
Serving an apprenticeship is an ancient, timetested way of learning how to do a job. In an
apprenticeship program affiliated with a training
center, you can learn and earn. Part of the time you
attend class. Another part of the time, you are a
paid employee of a local business. There you
receive on-thejob training.
Apprenticeship training can be a valuable part of
your education. By your work, you earn educational
credit. The employer rotates apprentices through different knowledge areas, such as electrical/electronic
systems, suspension and steering systems, and brake
systems. Apprentices generally find their automotive
course work more meaningful after applying it in a
real job. After graduation, the successful apprentice
finds job-hunting easier because of the knowledge
and experience he or she has gained.
The course work you've already completed will
be very helpful if you start an apprenticeship. Here
are tips on applying the essential knowledge in
automotive services to the work-based learning
experience of apprenticeship training:
. Compare what you learn in class to what you are
taught on the job. Determine what knowledge
from your course work you can apply at work.
. Ask whether there are different ways to look at
the same problem. What more do you want to
learn in class to help you do your job?
Action Actiuity
Ask whether apprenticeship placements in your
community are arranged through the training center or directly with individual businesses. Prepare a
short oral report detailing what a first-year apprentice in automotive services can expect to learn.
Answering the following praclice queslions will help you prepdre for the ASE certification tesls.
l. Two service technicians are discussing a car's pri6. You would expect your car's tires to have betmary braking system. They are talking about its:
ter traction with the road when the road is:
@ Parking brake system.
@ Just wet.
@ Air brake system.
O Wet and icy.
G) Service brake system.
@ Ice covered.
@ Emergency brake system.
Dry.
o
of the following types of wheel brakes
are found in a car's service braking system?
@ Drum and coaster brakes.
2. \Aihich
O
Disc and coaster brakes.
l. Two technicians are working on a can's service
brakes. The technicians determine that the car
has a dual-braking system. This means that the
car has:
@ Coaster and hand brakes.
O Drum and disc brakes.
@ Two hydraulic braking
O
systems.
Two types of brakes.
@ Two sets of brakes.
3.
j
t
,iII
:re
in
mt
are
lgt
L
Technician A and Technician B are talking
about which components in a moving vehicle's
wheel brake system are in relative motion.
Technician A says they are the drums and
rotors. Technician B says they are the brake
shoes and drums. \Arho is correct?
@ Technician A.
0 Technician B.
@ Both Technician A and Technician B.
0 Neither Technician A nor Technician B.
O
A and Technician B are discussing
the dual-braking system of a brand new front
wheel drive car. Technician A says it is more
likely that the brakes will be separated from
front to rear. Technician B says it is more likely
that they will be separated diagonally. \Arho is
8. Technician
correct?
@ Technician A.
0
Technician B.
@ Both Technician A and Technician B.
0 Neither Technician A nor Technician B.
{. \\rhen a vehicle's wheel brakes are locked up
u'here would you expect to find kinetic friction
at work?
@ In the wheel brake system.
O In the parking brake system.
O Where the tires meet the road.
O In the entire service braking system.
9. The most commonly used brake fluids are:
O DOT 3 and DOT b.
O DOT 3 and DOT 4.
O DOT 4 and DOT 5.
O DOT 5 and DOT 6.
iA
rb
Two master cylinders.
Gchnician A and Technician B are discussing at
rrhat instant a vehicle's braking system is most
effective. Technician A says it is just before the
r'-heels lock up. Technician B says it is just after
-,]re brakes have been applied.
Who is correct?
O Technician A.
O
O
O
Technician B.
Both Technician A and Technician B.
Neither Technician A nor Technician B.
10.
DOT 3 and DOT 4 brake fluids are:
@ Water-based.
0
Silicone-based.
@ Polyglycol-based.
O
Water- and polyglycol-based.