Larry’s New truck
1
Larry’s Truck Improvements
GIT-R-DONE
• Larry put a 6” lift kit on his
Ford F-150 and a set of
33’s Super Swamper
Thornbird Tires
• The Suspension System
has been modified but the
Brake System has not.
• Do You See Any
Problems?
2
What Parts Control the Stopping of
the Truck?
•
•
•
•
Master Cylinder
Brake Hoses/Lines
Wheel Cylinders
Brake Calipers
3
Larry has a Problem!
• What changes could you make to fix the
problem?
– Bigger parts
• Such as: Master Cylinder, Brake lines, Wheel
Cylinders, and/or Brake Calipers
4
Pascal’s Law
Unlock the mechanics of the
Hydraulic Braking System
5
Before we apply Pascal’s Law
We must first review and be familiar with…
 Diameter of a Piston
 Radius of the Piston
 Area of the top surface of the Piston
Mathematically speaking…
Diameter: The width of a circular or cylindrical object.
Radius: The radius of a circle is half the diameter
Area: Any particular extent of space or surface
6
Math – Hands on Practice
 Measure across the top
of the piston, through
the center and record
the diameter (inches)
 Calculate the radius of
the piston
 Calculate the area of
the top of the piston
A = π · r · r or
A = πr2
7
Area Example
 Diameter = 7 inches
 Radius = 3 1/2 inches
 Area = ?
A= π·r2
3.14 · (3 ½ in)2 = 38.465 in2
Area = 38.465 in2
8
Homework
 Practice skill work
 Read article: Effect of Oversize Tires on
Braking Characteristics
– www.aamva.org/Documents/
vehStudyEffectOfOversizedTiresOnAlteredHei
ghtVehicles.pdf -
9
Pascal’s Law
 In the 1600's, the French scientist Blaise
Pascal discovered a fact now known as
Pascal's Law. It states that pressure at any
point in a body of fluid is the same in every
direction, exerting equal force on equal
areas. This works for gases and liquids
(both are fluids).
10
Pascal’s Formula
 This brings us to a very important formula:
F
P
A
 P = Pressure, F = Force and A = Area
This expresses that Pressure is Force per Unit Area.
This is why pressure is usually expressed in
pounds per square inch (psi).
11
Variations of Pascal’s Law
 Pressure = Force
divided by area
F
P
A
 Force = Pressure times
area
F  P A
 Area = Force divided
by pressure
F
A
P
12
F =Force
F
P
P = Pressure
A
A = Area
13
Have you used formulas like
Pascal’s Law? Where are they used?
 Generic Inverse Variation
Problem
used in Algebra
 Time = Distance / Rate
15
y
x
 Ohm’s Law
used in science class
with electrical components
14
Using Pascal’s Law
Pascal's Law - gives us the
mechanics to do a great deal
of work with hydraulics. The
drawing on the left shows that
we can lift a large amount of
weight with a small amount of
effort. We can lift 100 pounds
by applying just 10 pounds of
force to the piston measuring
1 square inch
15
Basic automotive braking system
16
50 lbs force
.5 sq in area of top of piston
F
P
A
50lb
P
2
.5in
P  100lb / in
2
50 lbs divided by .5 = 100 psi
17
Where might Pascal’s Law be used?
 A twenty ton floor
jack has a hydraulic
piston with a 7 in
diameter.
 60 pounds of force is
being applied to the
piston.
 Calculate the line
pressure being exerted
on the piston.
18
Solving a Pascal’s Law problem
 Which version of Pascal’s Law will you use?
Pressure = Force divided by area
F
P
A
 Recall from earlier…..
A= π·r2
3.14 · (3 ½ in)2 = 38.465 in2
Area = 38.465 in2

P = (60pounds) / (38.465 in2)
P = 1.56 pounds/ in2
P = 1.56 psi
19
Using Pascal’s Law
 A caliper piston has a
diameter = 1.5 in
 The Master cylinder
has 50 pounds per
square inch (psi) line
pressure applied to it.
 Determine the force
exerted on the caliper
piston.
20
Solving a Pascal’s Law problem
 Which version of Pascal’s Law will you use?
Force = Pressure times area
F  P A
 Recall how to find area…..
A= π·r2

3.14 · (3/4 in)2 = 1.77 in2
Area = 1.77 in2
F = (50pounds/ in2) (1.77 in2)
F = 88.5 pounds
21
Did Larry have brake failure?
22
Remember Larry’s Truck ……..
 The truck has a major
GIT-R-DONE
braking problem.
 You suggested earlier
that we replace it with
bigger brake parts…
 What do we need to
know about the
original braking
system?
23
Facts about Larry’s Truck
¼ in brake lines
½ in bore master cylinder
7/8 in bore wheel cylinders
2 in caliper pistons
24
Can you fix Larry’s truck?
 Devise a plan to fix Larry’s truck based on
Pascal’s Law and your knowledge of
automotive systems that will remedy
Larry’s braking problems.
– Be sure to show all calculations and justify your
solution plan in a written paragraph.
Remember Larry doubled the size of the original
tire size…..
25
Be thorough..Larry is depending on
you…
 How would you
–“Git-R-Done”?
GIT-R-DONE
26