2Introduction (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
3Disc versus drum brakes. 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.
4Disc Brake System (1 of 6)Modern vehicles always equipped with disc brakes on at least the front two wheels.RotorCaliperBrake pads
5Disc Brake System (2 of 6)Pushrods transfer force through brake booster.Master cylinder converts pedal force to hydraulic pressure.
6The hub and hubless rotors. 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 forceRotors are free to rotate due to wheel bearings and hubs that contain themHub can be part of brake rotor or separate assembly that the rotor slips over and is bolted to by the lug nutsThe hub and hubless rotors.
7Caliper mounting methods. Disc Brake System (4 of 6)The brake caliper assembly is normally bolted to the vehicle axle housing or suspensionCaliper mounting methods.
8Disc Brake System (5 of 6) Advantages Greater amounts of heat to atmosphereCooling more rapidRotors scrape off water more efficientlySelf-adjustingDon’t need periodic maintenanceEasier to service
9Disc Brake System (6 of 6) Disadvantages Prone to noise (squeals and squeaks)Rotors warp easierNot self-energizingHard to use as parking brakes
10Disc Brake Calipers (1 of 11) Bolted to vehicle axle housing (steering knuckle)Two types of calipers: fixed and sliding/floating
11Disc Brake Calipers (2 of 11) Fixed calipers with multiple pistons.Fixed caliper being applied.
12Disc Brake Calipers (3 of 11) When the brakes are applied, hydraulic pressure forces the piston toward the rotor.Takes up any clearancePushes pad into rotorOnce all clearance is taken up on outer brake pad, clamping force will increase equally on both brake pads, applying brakes.Sliding/floating caliper application.
13Disc 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.
14Disc Brake Calipers (5 of 11) Square cut O-ring seals piston in disc brake calipers.Compressed between piston and caliper housingKeeps high-pressure brake fluid from leakingPrevents air from being drawn into system
15Disc 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.
16Disc Brake Calipers (7 of 11) Low-drag calipers designed to maintain larger brake pad-to-rotor clearance.
17Disc Brake Calipers (8 of 11) Although the phenolic pistons themselves do not corrode, the cast iron bore of the caliper does corrode and rustcan cause a phenolic piston to seize in the bore
18Disc Brake Calipers (9 of 11) Phenolic pistons transfer heat slower than steel pistonsHelps prevent boiling of the brake fluidHeat transfer. A. Phenolic piston (slow heat transfer). B. Steel piston (fast heat transfer).
19Disc 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
20Disc Brake Calipers (11 of 11) Sliding calipers slide in the caliper mount and are held in place by a spring steel clip.
21Disc Brake Pads and Friction Materials (1 of 11) Disc brake pads consist of friction material bonded or riveted onto steel backing plates.
22Disc 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 rotorBrake pad locating lugs.
23Disc Brake Pads and Friction Materials (3 of 11) Amount of friction expressed as ratioCoefficient of frictionKinetic energy (motion) of sliding surfaces converts to thermal energy (heat).
24Disc Brake Pads and Friction Materials (4 of 11) Composition of friction material affects brake operationMaterials that provide good braking with low pedal pressures tend to lose efficiency when hotWear out quickerMaterials that maintain stable friction coefficient over a wide temperature rangeGenerally require higher pedal pressuresTend to put added wear on disc brake rotor
25Disc 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.
26Disc Brake Pads and Friction Materials (6 of 11) Brake friction materials:NAO materialsLow-metallic non-asbestos organic (NAO)Semimetallic materialsCeramic materials
27Disc Brake Pads and Friction Materials (7 of 11) Combination of weighted qualities:Stopping powerHeat absorption and dispersionResistance to fadeRecovery speed from fadeWear ratePerformance when wetOperating noisePrice
28Disc Brake Pads and Friction Materials (8 of 11) Coefficients of friction:C: ≤0.15D: 0.15–0.25E: 0.25–0.35F: 0.35–0.45G: 0.45–0.55H: >0.55Z: Unclassified
29Disc Brake Pads and Friction Materials (9 of 11) Disc brakes more prone to squealingDue to vibrations between brake pad and rotorShims and spring-loaded clips help reduce squealing.
30Disc Brake Pads and Friction Materials (10 of 11) Anti-noise measures:Softer liningsBrake pad shimsSprings to hold in placeExample of brake pad retainers.
31Disc Brake Pads and Friction Materials (11 of 11) Anti-noise measures:Contour and groove liningsBendable tangsNoise-reducing compounds
32Wear Indicators Inspect brakes at regular intervals. Wear Indicators Spring steel scratchersWarning lampsMessages on dash
33Disc Brake Rotors (1 of 7)Brake disc or rotor is main rotating component of disc brake unit.Withstand high temperaturesMade of cast ironTwo-part rotorComposite rotor
34Disc Brake Rotors (2 of 7) Rotors can fail in two ways: ParallelismLateral runoutDust shields help to shield the rotor from dust, water, and debris.
35Disc Brake Rotors (3 of 7)Types of rotorsSolidVentilated
36Disc Brake Rotors (4 of 7)Some ventilated rotors are directional, meaning they are designed to force air through the rotor in one direction only.
37Disc Brake Rotors (5 of 7) Some rotors are slotted and drilled Better dissipation of heatBetter removal of water from the surface of the pads
38Disc Brake Rotors (6 of 7)Most rotors have the minimum thickness stamped or cast on them.
39Disc Brake Rotors (7 of 7)Worn rotors cannot absorb as much heat and therefore are subject to brake fade much sooner.
40Parking Brakes (1 of 3)Parking brakes are designed to hold vehicles stationary when parked.Holds vehicle on specified grade in both directionsSeparately active from service brakeMechanically latches into applied position.Foot or hand operated
41Parking Brakes (2 of 3)Two types of parking brakes used in standard disc brakes:IntegratedTop hat drum
42Parking Brakes (3 of 3) Electric parking brakes: Pull on a conventional parking brake cableMounted on caliper and directly drive caliper pistonElectric motor to apply disc brake assembliesAutomatically released by electronic control module (ECM)
43Diagnosis (1 of 12)Diagnosis starts with understanding customer’s concern.Communicate directly.Diagnosis should identify any and all issues.
44Diagnosis (2 of 12) Tools used for diagnosis: Brake lining thickness gaugeBrake wash stationCaliper piston pliers
45Diagnosis (3 of 12) Tools used for diagnosis: Disc brake rotor micrometerDial indicatorParking brake cable pliers
46Diagnosis (4 of 12) Tools used for diagnosis: Caliper piston retracting toolC-clampOff-car brake lathe
47Diagnosis (5 of 12) Tools used for diagnosis: On-car brake lathe Caliper dust boot seal driver set
48Diagnosis (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.
49Diagnosis (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.
51Diagnosis (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.
52Diagnosis (10 of 12)To diagnose stopping, noise, vibration, pulling, grabbing, dragging, or pulsation:Check brake pads.Disassemble caliper.Reassemble calipers.
53Diagnosis (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.
54Diagnosis (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.
55Summary (1 of 7)Disc brakes create braking power by forcing flat friction pads against the outer faces of a rotor.The vehicle’s 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.
56Summary (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.
57Summary (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.
58Summary (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.
59Summary (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.
60Summary (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.
61Summary (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.