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Brake System

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... rotor Rattles caused by missing anti-rattle clip or loose parts Most manufacturers recommend a periodic inspection of the brake system When inspecting ... – PowerPoint PPT presentation

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Title: 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
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