Brake System

1
Chapter 71
Brake System Fundamentals
2
Automotive 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

3
NON-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

4
Drum and Disc Brakes
5
Typical 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

6
Hydraulic System Action

• Hydraulic jack operation

7
Hydraulic Brake Action
8
Dual Master Cylinder
9
Piston and Cup
10
Brake Systems

• Often used on rear-wheel-drive vehicles

Often used on front-wheel-drive vehicles, with
high front to rear brake ratio
11
Vacuum Booster Operation
12
Brake 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

14
Brake Hoses

• Hoses
• made of reinforced rubber
• used where flexing action is necessary

15
Brake Line

• Lines
• made of double wall steel tubing
• tubing ends use double flare or ISO flare
  (international standards organization)

16
Single Piston Caliper

• Caliper slides as the piston moves in to clamp
  the brake pads against the rotor

17
How disc brakes work
18
Caliper Operation

• Brakes applied Brakes released

19
Disc Brake Pads

• Brake pad riveted or bonded to backing plate
• Linings
• organic
• semi-metallic
• Ceramic

20
Drum Brake Assembly
21
Brake Shoe Adjusters

• Cable-type star wheel adjuster with an overtravel
  spring

22
Brake Shoe Adjusters

• Lever-latch adjuster

23
Stop 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

24
Parking Brake Components

• Foot-operated parking brake pedal

Lever pushes the shoes against the drum
25
Rear Disc Brake Caliper

• Note the parking brake mechanism

26
Chapter 72
Brake System Diagnosis and Repair
27
Brake 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

28
Brake Vibration

• Possible causes
• warped disc
• out-of-round brake drum
• hard spots on the disc or drum

29
Grabbing 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

30
Excessive 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

31
Pulling 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

32
Spongy 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

33
Dropping 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

34
Low 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

35
Dragging 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

36
Dragging 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

37
No 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

38
Brake 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

39
Braking Noise

• Grinding Noise
• Metal-on-metal sound when braking
• caused by worn brake linings

40
Braking Noise

• Scrapping Noise
• Light scrapping noise, goes away when brakes are
  applied
• Caused by wear indicator rubbing on rotor

41
Disc Brake Inspection

• Inspect brake pad linings (minimum thickness 1/8
  or 3 mm)

42
Disc Brake Inspection

• Inspect rotors for scoring or heat damage

43
Drum Brake Inspection

• Check the drum for cracks or heat damage

A badly scored drum must be machined
44
Braking 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

45
Brake 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

46
Checking Brake Fluid
47
Checking 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

48
Checking 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

49
Master 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

50
Measuring Disc Thickness

• Using an outside micrometer, measure at several
  points around the disc

51
Resurfacing a Disc

• Always read the operating manual before using a
  brake lathe

52
Brake Drum Resurfacing

• This brake lathe has a shoe grinder which will
  arc shoes to fit the drum

53
Chapter 73
Anti-Lock Brakes, Traction Control, and Stability
Control
54
bb
55
Basic ABS Components
56
Wheel Speed Sensor
57
ABS Control Module

• Uses wheel speed sensor inputs to control the
  electro-hydraulic modulator

58
ABS Hydraulics

• Brakes are applied, pressure is dumped from one
  wheel to prevent lockup

59
ABS Modes of Operation

• Three modes of ABS operation are used
• ABS pulses brakes 15-20 times/sec.
• isolation mode
• dump mode
• reapply mode

60
ABS 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

61
Traction and Stability Control Systems
62
Traction 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

63
Stability 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

64
Stability Control System Inputs
65
Scanning ABS

• Typical scan tool connections