Title: Brake System
1Chapter 71
Brake System Fundamentals
2Automotive Brakes
- Provide a means of using friction to either slow,
stop, or hold the wheels of a vehicle - When a car is moving, it has energy stored in the
form of inertia (kinetic energy) - To stop the vehicle, the brakes convert kinetic
(moving) energy into heat
3NON-Friction Brakes
- Engine Braking (Jake Brakes)
- Opens exhaust valve during compression stroke
- Exhaust brake
- Butterfly valve restricts exhaust flow
- Magnetic
- Electric motor generates electricity
- Used on hybrid cars
4Drum and Disc Brakes
5Typical Braking Ratios
- Rear wheel drive vehicles
- front brakes may handle 60 to 70 of the
braking, rear brakes handle 30 to 40 - Front wheel drive vehicles
- more weight is concentrated on the front wheels
- braking ratio is even higher at the front wheels
6Hydraulic System Action
7Hydraulic Brake Action
8Dual Master Cylinder
9Piston and Cup
10Brake Systems
- Often used on rear-wheel-drive vehicles
Often used on front-wheel-drive vehicles, with
high front to rear brake ratio
11Vacuum Booster Operation
12Brake Fluid
- Brake fluid must have the following
characteristics - correct viscosity at all temperatures
- high boiling point
- noncorrosive
- water tolerant
- lubricates components
- low freezing point
13- DOT 3
- Lowest boiling point
- DOT 4
- Middle boiling point
- DOT 5
- Highest boiling point
- Can mix DOT 3 4
- Can not mix DOT 5
14Brake Hoses
- Hoses
- made of reinforced rubber
- used where flexing action is necessary
15Brake Line
- Lines
- made of double wall steel tubing
- tubing ends use double flare or ISO flare
(international standards organization)
16Single Piston Caliper
- Caliper slides as the piston moves in to clamp
the brake pads against the rotor
17How disc brakes work
18Caliper Operation
- Brakes applied Brakes released
19Disc Brake Pads
- Brake pad riveted or bonded to backing plate
- Linings
- organic
- semi-metallic
- Ceramic
20Drum Brake Assembly
21Brake Shoe Adjusters
- Cable-type star wheel adjuster with an overtravel
spring
22Brake Shoe Adjusters
23Stop Light Switch
- Operates the rear brake lights
- Normally open switch, usually mounted on the
brake pedal mechanism - When the brake pedal is pressed, it closes the
switch
24Parking Brake Components
- Foot-operated parking brake pedal
Lever pushes the shoes against the drum
25Rear Disc Brake Caliper
- Note the parking brake mechanism
26Chapter 72
Brake System Diagnosis and Repair
27Brake Vibration
- Shows up as a chatter, pulsation, or shake in the
brake pedal or steering wheel - Occurs only when the brakes are applied
- Front brake problems may be felt mostly in the
steering wheel - Pulsation in the brake pedal may be caused by
brake problems at any wheel
28Brake Vibration
- Possible causes
- warped disc
- out-of-round brake drum
- hard spots on the disc or drum
29Grabbing Brakes
- Brakes apply too quickly, even with light brake
pedal application - Possible causes
- malfunctioning brake booster
- brake fluid or grease on the linings
- worn brake linings
- faulty metering valve
- mechanical problem in the wheel brake assembly
30Excessive Pedal Effort
- Noticeable increase in the amount of foot
pressure needed to apply the brakes - Possible causes
- seized wheel cylinder or caliper piston
- collapsed brake hose or crimped line
- faulty master cylinder
- contaminated linings
- disconnected brake booster vacuum line or
defective booster
31Pulling Brakes
- Vehicle veers to the right or left when the
brakes are applied - Possible causes
- seized caliper or wheel cylinder piston
- grease or fluid-coated lining
- leaking cylinder
- faulty automatic adjuster
- brake lining dust in a drum brake assembly
32Spongy Brake Pedal
- Brakes will apply, but the pedal does not feel
solid - Possible causes
- air in the brake system
- faulty residual check valve in the master
cylinder - maladjusted brake shoes
33Dropping Brake Pedal
- Pedal slowly moves all the way to the floor when
steady pressure is applied to it - Pumping usually restores pedal height momentarily
- Possible causes
- internal leak in the master cylinder
- external fluid leak in any component
34Low Brake Pedal
- Pedal travels too far toward the floor before
braking - Possible causes
- inoperative brake adjusters
- maladjusted master cylinder push rod
- mechanical problem in the wheel brake assemblies
35Dragging Brakes
- Brakes remain partially applied when the brake
pedal is released - To detect dragging brakes, carefully feel each
brake assembly - dragging brakes will be abnormally hot
36Dragging Brakes
- Possible causes
- seized wheel cylinder pistons or parking brake
cables - overadjusted parking brake or master cylinder
push rod - weak return springs
- master cylinder problems
37No Brake Pedal
- Very dangerous condition in which the brake pedal
moves to the floor with no braking action - Possible causes
- hydraulic system leak which causes the loss of
the brake fluid - faulty master cylinder
- Complete loss of braking is unlikely on a system
with a dual master cylinder
38Brake WarningLight On
- Indicates either an internal leak (master
cylinder) or an external leak - Unequal pressure in the dual master cylinder
system has caused the warning light switch to
shift to one side
39Braking Noise
- Grinding Noise
- Metal-on-metal sound when braking
- caused by worn brake linings
40Braking Noise
- Scrapping Noise
- Light scrapping noise, goes away when brakes are
applied - Caused by wear indicator rubbing on rotor
41Disc Brake Inspection
- Inspect brake pad linings (minimum thickness 1/8
or 3 mm)
42Disc Brake Inspection
- Inspect rotors for scoring or heat damage
43Drum Brake Inspection
- Check the drum for cracks or heat damage
A badly scored drum must be machined
44Braking Noise
- Squeak when braking
- caused by glazed or hardened brake linings, dry
brake drum backing plate, or wear indicator
rubbing on the rotor - Rattles
- caused by missing anti-rattle clip or loose parts
45Brake System Inspection
- Most manufacturers recommend a periodic
inspection of the brake system - When inspecting the brake system, check the brake
pedal action, fluid level, and the condition of
the brake lines, hoses, and wheel brake assemblies
46Checking Brake Fluid
47Checking for Leaks
- Inspect for leaks whenever the fluid level in the
master cylinder is low - Check brake lines, hoses, calipers, and wheel
cylinders - Check below the master cylinder mounting point at
the cowl or booster - Leaks show up as darkened, damp areas
48Checking the Parking Brake
- Apply the parking brake
- Pedal or lever should not move more than 2/3 of
full travel - Parking brake should keep the vehicle from moving
with the engine idling and the transmission in
drive - Inspect cables for fraying and high friction
49Master Cylinder Service
- A faulty master cylinder may leak fluid past the
rear piston or leak internally - Inspect for external leakage where the master
cylinder mounts to the booster or cowl - Internal leakage will cause the pedal to slowly
sink to the floor when applied
50Measuring Disc Thickness
- Using an outside micrometer, measure at several
points around the disc
51Resurfacing a Disc
- Always read the operating manual before using a
brake lathe
52Brake Drum Resurfacing
- This brake lathe has a shoe grinder which will
arc shoes to fit the drum
53Chapter 73
Anti-Lock Brakes, Traction Control, and Stability
Control
54bb
55Basic ABS Components
56Wheel Speed Sensor
57ABS Control Module
- Uses wheel speed sensor inputs to control the
electro-hydraulic modulator
58ABS Hydraulics
- Brakes are applied, pressure is dumped from one
wheel to prevent lockup
59ABS Modes of Operation
- Three modes of ABS operation are used
- ABS pulses brakes 15-20 times/sec.
- isolation mode
- dump mode
- reapply mode
60ABS Warning Light
- Mounted in the dash
- Used to alert the driver to an ABS malfunction
- Turned on during engine cranking and ABS
self-check at startup to verify operation
61Traction and Stability Control Systems
62Traction Control Systems
- Designed to prevent the vehicles wheels from
spinning and losing traction under hard
acceleration - Most systems work with the anti-lock brake system
to cycle hydraulic pressure to the wheel spinning
the fastest
63Stability Control Systems
- Advanced system that reduces tire spin upon
acceleration and prevents tire skid when
cornering too quickly - Uses more input signals from various sensors to
provide greater control under severe cornering,
braking, and acceleration conditions
64Stability Control System Inputs
65Scanning ABS
- Typical scan tool connections