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Brake Types

Service brakes – the primary brake system.
Use 4 wheel disc or disc and drum brakes
and use hydraulics to operate them.

Parking brakes – used to keep a parked
vehicle from moving. Usually located on the
rear wheels and are mechanically operated.
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Disc
Drum
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Power Brakes
Power brakes are standard hydraulic brakes
with a power assist unit located between
the brake pedal and the master cylinder.
 Since disc brakes are not self energizing, a
power assist unit is needed to help provide the
extra braking power.
Two Basic Types of Power-assist Units
 Vacuum assist – uses engine vacuum or
sometimes an external vacuum pump.
 Hydraulic assist – uses hydraulic pressure
from a power steering pump.
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Friction
 Kinetic


(moving) Service Brakes
Is caused by rotating brake parts.
Changes kinetic energy into thermal energy
(heat).
 Static

friction
friction
(stationary) Parking Brake
Holds the car in place when stopped.
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Four Friction Factors!!
Determine A Vehicles Braking Power
– the amount of friction generated
depends in part on the pressure exerted on the
surfaces. More pressure = more friction.
 Pressure
of Friction – the amount of friction
between two surfaces , determined by dividing
the force required to pull an object across a
surface by the weight of the object.
 Coefficient
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Four Friction Factors!!
Determine A Vehicles Braking Power

Frictional Contact Surface – the amount
of surface or area that is in contact. Larger
pads or shoes will stop a car faster.

Heat Dissipation – the ability to handle or
conduct the generated heat away from
the pad and rotor (or shoe and drum) and
absorbed by the air. Brake fade will
occur if there is excessive heat.
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Friction Material Classifications




Organic (non-metallic)
Semi-metallic
Fully metallic
Synthetic
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Hydraulic Brake Systems

Uses brake fluid to transfer hydraulic pressure
from the master cylinder to the wheel brake
mechanisms .

Fluids are not compressible.

In a closed system the pressure is equal to
every part in the system at the brake lines
regardless of the length line.
Output force can be increased by using a larger
piston.
 The condition of the piston seals in the master
cylinder will influence the amount of pressure
developed.

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Hydraulic Brake Systems
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Dual Braking Systems

1967 federal law requires all vehicles be
equipped with two separate brake systems.
If one system fails the other provides enough
braking power to stop the vehicle.

This is done by using a tandem master
cylinder in a dual braking system.
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Dual Braking Systems
Two Types of Systems Used
 Front/Rear Split System
Older dual brake systems
 Diagonally Split System
Newer dual brake systems
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Brake System Components
1.
2.
3.
4.
5.
6.
7.
Brake fluid
Master cylinder
Power booster
Control valves
Wheel brake assemblies
Parking brake
ABS system
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Brake Fluid
Three Basic Types
Dot 3 – most common
Dot 4 – has a higher boiling point
Both are polyglycol based
Both are hydroscopic – (absorb water)
Dot 5 – has a higher boiling point than dot 3 or 4
Dot 5 is silicone-based
Brake fade can occur when brake fluid boils
Most manufacturers recommend changing the
fluid periodically.
Do not use any other fluid in the brake system.
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Master Cylinder
Converts mechanical force
to hydraulic pressure
needed to apply the
brake mechanisms.
Generates the hydraulic
pressure needed to
apply the brake
mechanisms
A) Integral type
B) Composite Type
Always keep the caps tightly
sealed to keep moisture and dirt
from contaminating the fluid.
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Master Cylinder
Some master cylinders use residual check
valves. Used only with drum brakes.
 General Motors uses a quick-take-up
master cylinder on disc brakes with low
drag caliper pistons.
 Some master cylinders have a fluid level
warning switch. When the fluid level gets
low a warning light in the dash comes on.

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How the Master Cylinder Works
o
o
o
o
The master cylinder pushrod is connected
to a piston.
Hydraulic fluid is in front of the piston.
When the pedal is pressed, the piston is
pushed forward.
The fluid transmits force throughout the
system.
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Brake Lines and Hoses
Their purpose is to carry brake fluid from
the master cylinder to the calipers and
wheel cylinders.
 Brake lines are made of steel. The ends
are made with a special double flare to
prevent leaks.
 Two types of flare are used – inverted flare
and the ISO flare.
 Brake hoses offer flexible connections to
allow for wheel movement.

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Brake System Valves
 Metering
valve
Delays application of front disc brakes until
pressure builds to rear drum brakes.
 Proportioning
valve
Applies more hydraulic pressure to the disc
brakes to balance braking.
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Brake System Valves
 Pressure
Differential Switch
Used to operate a warning switch to alert
the driver if pressure is lost in the
system. If pressure is lost the switch
activates the warning light in the dash.
 Combination
valve
Combines several functions in one valve.
Metering, proportioning, and pressure
differential valve in one unit.
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Brake System Valves

Height-Sensing Proportional Valve
When the vehicle is not loaded hydraulic
pressure is reduced, and when the vehicle is
carrying a load the actuator changes the valve
setting to allow full hydraulic pressure.

Stop Light Switch
Activates the brake lights when the pedal
pressed. May also deactivate the cruise control.
 Residual Check Valve
Used only with drum brakes, keeps slight
pressure in the lines to keep air from getting past
the wheel cylinder seals.
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Hydraulic System Bleeding

The purpose of bleeding a hydraulic brake
system is to :
1) to force trapped air out of the brake fluid
2) replace the old brake fluid
3) remove dust particles and moisture
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Hydraulic System Bleeding
3 Types of Bleeding Procedures
 Manual Bleeding – requires 2 people, one to
pump the brake pedal, and the other to open
the bleeder screw.
 Pressure Bleeding – using pressure bleeding
equipment that forces fluid through the system
to remove the air.
 Vacuum Bleeding – Uses a vacuum pump to
draw fluid out of system
Some antilock brake systems require the use
of a scan tool to help bleed the brakes.
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