Disc Brake System

1
Chapter 32

• Disc Brake System

2
Introduction (1 of 2)

• Disc brakes use friction to create braking power.
• Disc brakes create braking power by forcing flat
  friction pads against sides of rotating disc

3
Introduction (2 of 2)

• Higher applied forces can be used in disc brakes
  than in drum brakes, because the design of the
  rotor is stronger than the design of the drum.

Disc versus drum brakes.
4
Disc Brake System (1 of 6)

• Modern vehicles always equipped with disc brakes
  on at least the front two wheels.
• Rotor
• Caliper
• Brake pads

5
Disc Brake System (2 of 6)

• Pushrods transfer force through brake booster.
• Master cylinder converts pedal force to hydraulic
  pressure.

6
Disc Brake System (3 of 6)

• Hydraulic pressure transmitted via brake lines
  and hoses to piston(s) at each brake caliper.
• Pistons operate on friction pads to provide
  clamping force
• Rotors are free to rotate due to wheel bearings
  and hubs that contain them
• Hub can be part of brake rotor or separate
  assembly that the rotor slips over and is bolted
  to by the lug nuts

The hub and hubless rotors.
7
Disc Brake System (4 of 6)

• The brake caliper assembly is normally bolted to
  the vehicle axle housing or suspension

Caliper mounting methods.
8
Disc Brake System (5 of 6)

• Advantages
• Greater amounts of heat to atmosphere
• Cooling more rapid
• Rotors scrape off water more efficiently
• Self-adjusting
• Dont need periodic maintenance
• Easier to service

9
Disc Brake System (6 of 6)

• Disadvantages
• Prone to noise (squeals and squeaks)
• Rotors warp easier
• Not self-energizing
• Hard to use as parking brakes

10
Disc Brake Calipers (1 of 11)

• Bolted to vehicle axle housing (steering knuckle)
• Two types of calipers fixed and sliding/floating

11
Disc Brake Calipers (2 of 11)
Fixed calipers with multiple pistons.
Fixed caliper being applied.
12
Disc Brake Calipers (3 of 11)

• When the brakes are applied, hydraulic pressure
  forces the piston toward the rotor.
• Takes up any clearance
• Pushes pad into rotor
• Once all clearance is taken up on outer brake
  pad, clamping force will increase equally on both
  brake pads, applying brakes.

Sliding/floating caliper application.
13
Disc Brake Calipers (4 of 11)
O-rings. A. Square cut O-ring and O-ring cut to
show square section. B.
Square cut O-ring groove in caliper.
14
Disc Brake Calipers (5 of 11)

• Square cut O-ring seals piston in disc brake
  calipers.
• Compressed between piston and caliper housing
• Keeps high-pressure brake fluid from leaking
• Prevents air from being drawn into system

15
Disc Brake Calipers (6 of 11)
Square cut O-ring. A. Square cut O-ring during
brake application. B.
Square cut O-ring during brake release.
16
Disc Brake Calipers (7 of 11)

• Low-drag calipers designed to maintain larger
  brake pad-to-rotor clearance.

17
Disc Brake Calipers (8 of 11)

• Although the phenolic pistons themselves do not
  corrode, the cast iron bore of the caliper does
  corrode and rust
• can cause a phenolic piston to seize in the bore

18
Disc Brake Calipers (9 of 11)

• Phenolic pistons transfer heat slower than steel
  pistons
• Helps prevent boiling of the brake fluid

Heat transfer. A. Phenolic piston (slow heat
transfer). B. Steel piston (fast heat transfer).
19
Disc Brake Calipers (10 of 11)

• Bushings must be lubricated with
  high-temperature, waterproof disc brake caliper
  grease.
• Floating calipers are mounted in place by guide
  pins and bushings

20
Disc Brake Calipers (11 of 11)

• Sliding calipers slide in the caliper mount and
  are held in place by a spring steel clip.

21
Disc Brake Pads and Friction Materials (1 of 11)

• Disc brake pads consist of friction material
  bonded or riveted onto steel backing plates.

22
Disc Brake Pads and Friction Materials (2 of 11)

• Backing plate has lugs that correctly position
  the pad in the caliper assembly and help the
  backing plate maintain the proper position to the
  rotor

Brake pad locating lugs.
23
Disc Brake Pads and Friction Materials (3 of 11)

• Amount of friction expressed as ratio
• Coefficient of friction
• Kinetic energy (motion) of sliding surfaces
  converts to thermal energy (heat).

24
Disc Brake Pads and Friction Materials (4 of 11)

• Composition of friction material affects brake
  operation
• Materials that provide good braking with low
  pedal pressures tend to lose efficiency when hot
• Wear out quicker
• Materials that maintain stable friction
  coefficient over a wide temperature range
• Generally require higher pedal pressures
• Tend to put added wear on disc brake rotor

25
Disc Brake Pads and Friction Materials (5 of 11)

• Disc brake pads and drum brake linings are made
  from materials that have a moderate coefficient
  of friction.

26
Disc Brake Pads and Friction Materials (6 of 11)

• Brake friction materials
• NAO materials
• Low-metallic non-asbestos organic (NAO)
• Semimetallic materials
• Ceramic materials

27
Disc Brake Pads and Friction Materials (7 of 11)

• Combination of weighted qualities
• Stopping power
• Heat absorption and dispersion
• Resistance to fade
• Recovery speed from fade
• Wear rate
• Performance when wet
• Operating noise
• Price

28
Disc Brake Pads and Friction Materials (8 of 11)

• Coefficients of friction
• C 0.15
• D 0.150.25
• E 0.250.35
• F 0.350.45
• G 0.450.55
• H gt0.55
• Z Unclassified

29
Disc Brake Pads and Friction Materials (9 of 11)

• Disc brakes more prone to squealing
• Due to vibrations between brake pad and rotor
• Shims and spring-loaded clips help reduce
  squealing.

30
Disc Brake Pads and Friction Materials (10 of 11)

• Anti-noise measures
• Softer linings
• Brake pad shims
• Springs to hold in place

Example of brake pad retainers.
31
Disc Brake Pads and Friction Materials (11 of 11)

• Anti-noise measures
• Contour and groove linings
• Bendable tangs
• Noise-reducing compounds

32
Wear Indicators

• Inspect brakes at regular intervals.
• Wear Indicators
• Spring steel scratchers
• Warning lamps
• Messages on dash

33
Disc Brake Rotors (1 of 7)

• Brake disc or rotor is main rotating component of
  disc brake unit.
• Withstand high temperatures
• Made of cast iron
• Two-part rotor
• Composite rotor

34
Disc Brake Rotors (2 of 7)

• Rotors can fail in two ways
• Parallelism
• Lateral runout
• Dust shields help to shield the rotor from dust,
  water, and debris.

35
Disc Brake Rotors (3 of 7)

• Types of rotors
• Solid
• Ventilated

36
Disc Brake Rotors (4 of 7)

• Some ventilated rotors are directional, meaning
  they are designed to force air through the rotor
  in one direction only.

37
Disc Brake Rotors (5 of 7)

• Some rotors are slotted and drilled
• Better dissipation of heat
• Better removal of water from the surface of the
  pads

38
Disc Brake Rotors (6 of 7)

• Most rotors have the minimum thickness stamped or
  cast on them.

39
Disc Brake Rotors (7 of 7)
Worn rotors cannot absorb as much heat and
therefore are subject to brake fade much sooner.
40
Parking Brakes (1 of 3)

• Parking brakes are designed to hold vehicles
  stationary when parked.
• Holds vehicle on specified grade in both
  directions
• Separately active from service brake
• Mechanically latches into applied position.
• Foot or hand operated

41
Parking Brakes (2 of 3)

• Two types of parking brakes used in standard disc
  brakes
• Integrated
• Top hat drum

42
Parking Brakes (3 of 3)

• Electric parking brakes
• Pull on a conventional parking brake cable
• Mounted on caliper and directly drive caliper
  piston
• Electric motor to apply disc brake assemblies
• Automatically released by electronic control
  module (ECM)

43
Diagnosis (1 of 12)

• Diagnosis starts with understanding customers
  concern.
• Communicate directly.
• Diagnosis should identify any and all issues.

44
Diagnosis (2 of 12)

• Tools used for diagnosis
• Brake lining thickness gauge
• Brake wash station
• Caliper piston pliers

45
Diagnosis (3 of 12)

• Tools used for diagnosis
• Disc brake rotor micrometer
• Dial indicator
• Parking brake cable pliers

46
Diagnosis (4 of 12)

• Tools used for diagnosis
• Caliper piston retracting tool
• C-clamp
• Off-car brake lathe

47
Diagnosis (5 of 12)

• Tools used for diagnosis
• On-car brake lathe
• Caliper dust boot seal driver set

48
Diagnosis (6 of 12)
Disc brake tools. A. Brake lining thickness
gauges. B. Brake wash station. C. Caliper piston
pliers. D. Disc brake rotor micrometer. E. Dial
indicator.
49
Diagnosis (7 of 12)
F. Parking brake cable tool. G. Caliper piston
retracting tool. H. Off-car brake lathe.
I. On-car brake lathe. J. Dust boot
seal/bushing driver set.
50
Diagnosis (8 of 12)
51
Diagnosis (9 of 12)

• To diagnose stopping, noise, vibration, pulling,
  grabbing, dragging, or pulsation
• Verify the customer concern by operating the
  vehicle if safe to do so.
• Remove and inspect calipers.
• Inspect caliper mountings, slides, and pins.
• Inspect brake pads and wear indicators.

52
Diagnosis (10 of 12)

• To diagnose stopping, noise, vibration, pulling,
  grabbing, dragging, or pulsation
• Check brake pads.
• Disassemble caliper.
• Reassemble calipers.

53
Diagnosis (11 of 12)

• To diagnose stopping, noise, vibration, pulling,
  grabbing, dragging, or pulsation
• Retract and readjust pistons.
• Inspect and measure disc brake rotors.
• Remove and reinstall rotors.

54
Diagnosis (12 of 12)

• To diagnose stopping, noise, vibration, pulling,
  grabbing, dragging, or pulsation
• Refinish rotors.
• Inspect and replace wheel studs.
• Install wheels and torque lug nuts, and make
  final checks.

55
Summary (1 of 7)

• Disc brakes create braking power by forcing flat
  friction pads against the outer faces of a rotor.
• The vehicles kinetic energy is transformed into
  heat energy by the disc brake components, which
  slow the vehicle when applied.
• Disc brake assemblies consist of a caliper, brake
  pads, and a rotor.

56
Summary (2 of 7)

• Caliper pistons use hydraulic pressure to create
  a clamping force of the brake pads to the faces
  of the rotor.
• Disc brake pads require much higher application
  pressures to operate than drum brake shoes
  because they are not self-energizing.

57
Summary (3 of 7)

• Advantages of disc brakes over drum brakes more
  effective at transferring heat to atmosphere,
  self-adjusting, resistant to water fade, and
  easier to service.
• Disadvantages of disc brakes compared to drum
  brakes more prone to noise, more prone to pedal
  pulsations due to warpage, and more difficult to
  use as an emergency brake.

58
Summary (4 of 7)

• Disc brake calipers come in two main styles
  fixed and floating/sliding.
• In disc brake calipers, the piston is sealed by a
  square cut O-ring.
• Floating/sliding calipers require clean and
  lubricated pins, bushings, or guides for proper
  operation.

59
Summary (5 of 7)

• Brake pad lining is either riveted or bonded to
  the pad backing plate.
• Brake pad lining is available in a variety of
  materials with varying amounts of coefficient of
  friction.
• Brake pads may use shims, spacers, guides, and
  bendable tangs to help minimize squealing.

60
Summary (6 of 7)

• Brake pad wear indicators, if used, can be of the
  mechanical or electronic type.
• Rotors rotate with the wheels and are usually
  made of durable cast iron with friction surfaces
  that run true and parallel.
• Brake rotors can be solid or ventilated.

61
Summary (7 of 7)

• Disc brake parking brakes can be of the
  integrated caliper style, top hat drum style,
  electric pull-cable style, and integrated
  electric motor caliper style.
• Diagnosing brake faults requires good information
  from the customer, an adequate test-drive when
  possible, and a good understanding of brake
  theory.