2. Disc Brake System Components and Operation
Chapter 12
Disc Brake System Components and Operation
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3. Objectives Identify the components of a disc brake.
Identify the two main types of rotors.
Identify the three types of front caliper piston arrangements.
Identify and explain the operation of fixed and floating calipers.
Identify floating caliper mounting methods.
Identify and explain the operation of rear calipers.
Identify brake pad materials and construction.
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4. Disc Brake Rotor
Rotor provides a smooth braking surface for disc brake pad contact.
Stationary pads contact spinning rotor:
Friction slows rotor.
Wheel rotation stops.
Rotor absorbs and dissipates frictional heat.
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5. Rotor Construction Majority made of cast iron.
Sizes vary between vehicles.
Sides machined to provide smooth braking surface.
Same thickness throughout:
Variations would cause pulsation when brakes applied.
Ventilated or solid.
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6. Rotor Construction Size of rotor depends on intended use:
Larger diameter rotors provide more braking area and expose more area to air for dissipation.
Rotors must have sufficient metal to absorb heat.
Extra metal thickness allows for machining or turning:
Minimum thickness usually stamped on hub or inner part of body.
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7. This rotor has its minimum allowable thickness stamped on the hub.
Rotor Construction
(General Motors)
This rotor has its minimum allowable thickness stamped on the hub.
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8. Rotor Construction Solid rotors: Ventilated rotors:
No openings between machined surfaces.
Cooled by air passing over outside surfaces.
Smaller than ventilated rotors.
Ventilated rotors:
Have internal fins between friction surfaces.
As rotor spins, fins draw air into center of rotor and discharge it from edges.
Variation of ventilated rotor, has internal fins and holes drilled into braking surfaces.
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9. Ventilated Rotor (Saab)
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10. Cross-Drilled Rotor (Porsche)
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11. Rotor Attachment Rotor must be accurately attached to hub:
Rotor must rotate without lateral runout.
Most rotors are separate from hub, held in place by lug nuts and/or wheel studs.
Some rotors are integral with hub:
Common on front brakes of rear-wheel drive vehicles.
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12. Secured to hub with wheel studs.
Rotor Attachment
(Chrysler)
Secured to hub with wheel studs.
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13. Rotor and hub integrated into single unit.
Rotor Attachment
(Chrysler)
Rotor and hub integrated into single unit.
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14. Splash Shield
Splash shield deflects water and debris from rotor and brake assemblies.
Covers part or all of rotor’s inner surface.
Usually fastened to spindle/steering knuckle.
Allows air circulation over rotor:
Some designed as air scoops to direct air over the rotor as vehicle moves.
Holds emergency brake shoes on some rear disc brake assemblies.
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15. Front Disc Brake Caliper
Caliper provides housing for:
Hydraulic components.
Brake pads.
Made of cast iron or aluminum.
Usually attached to the spindle assembly.
Dust boots cover pistons to:
Keep dust and water away from inner seals.
Reduce possibility of piston sticking.
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16. Front Disc Brake Caliper
(Chrysler)
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17. Caliper Operation Master cylinder develops hydraulic pressure.
Pressure travels to caliper:
Piston seal prevents leaks between piston and housing.
Piston moves outward.
Piston forces pads into contact with rotor.
Friction slows rotor and vehicle.
Piston seal retracts when pressure removed:
Linings just clear rotor.
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18. Caliper Operation (Delco)
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19. Higher Pedal Effort Disc brakes have no servo action:
Wheel rotation does not help brakes apply.
Disc brakes require more pedal force than drum brakes.
Power assist units commonly used with disc brakes.
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20. Pad-to-Rotor Clearance
Disc brakes have almost no clearance between lining and rotor when brakes released:
Even with low clearances, there is almost no brake drag or wear.
Low-drag calipers have more clearance:
Removal of all brake drag increases fuel economy.
Use quick take-up master cylinders.
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21. Caliper Types
Two methods of mounting disc brake calipers, depending on piston arrangement:
Most common type are floating calipers.
Fixed calipers used on high-performance vehicles.
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22. Floating Caliper Construction
Use one or two pistons located on same side of caliper.
Caliper can move back and forth in relation to rotor.
Caliper slides on mounting bolts called guide pins or slider pins.
Guide pins contact bushings to reduce wear of caliper metal:
Actual movement between bolts and caliper is through bushings.
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23. Floating Caliper Construction
On some vehicles, sliding takes place between machined ways:
Flat surface machined smooth.
Caliper and spindle ways move against each other with minimum friction.
Caliper movement over ways controlled by supports, called keys:
Held in place by single mounting screw.
Leaf spring, called clip, cuts down on caliper rattling.
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24. Floating Caliper Construction
(Ford)
Caliper slides on machined ways.
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25. Floating Caliper Construction
(Ford)
Caliper slides on locating pins and insulators.
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26. Floating Caliper Operation
Pressure builds in cylinder bore behind piston and seals.
Pressure forces piston outward:
Piston forces inner brake pad into contact with rotor.
Seal is deformed outward by piston movement.
Pad-rotor contact prevents more outward piston movement.
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27. Floating Caliper Operation
(Cadillac)
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28. Floating Caliper Operation
When inner pad contacts rotor, it takes less pressure to push caliper backward than to push piston out:
Caliper slides inward on bolts or ways.
Outer brake pad contacts rotor.
Pad pressure equalizes on both sides.
Rotor slows.
When brakes are released, outer seal draws piston in:
Pads move away from rotor.
Caliper floats back to resting position.
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29. Floating Caliper Operation
(Chrysler)
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30. Fixed Caliper Construction
Rigidly bolts to spindle:
Does not move during braking.
Modern fixed calipers have four pistons:
Two on each side.
Older fixed calipers used two pistons:
One on each side.
Transfer tubes or internal passages direct pressure between the sides.
Caliper body may be one piece or split.
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31. Fixed Caliper Construction
(Kelsey-Hayes)
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32. Fixed Caliper Operation
When brakes applied:
All four pistons are pressurized at once.
Pistons move outward, deforming piston seals outward.
Pistons force brake pads into contact with spinning rotor.
Rotor slows.
When brakes released:
Hydraulic pressure decreases.
Pistons are pulled clear of rotor by piston seals.
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33. Rear Disc Brake Calipers
Do same job and have same components as front brake calipers:
Usually smaller.
Most are single piston floating designs.
May include a parking brake mechanism to apply the pads:
Screw type.
Ball-and-ramp type.
Cam type.
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34. Disc Brake Pads Disc brake pads: Lining designed to: Shoe:
Create friction when pressed against rotor.
Composed of the lining and shoe.
Lining designed to:
Absorb heat and transfer it to shoe assembly.
Give best coefficient of friction with acceptable wear, smoothness, and quiet operation.
Shoe:
Provides support for lining material.
Provides rigid area for pistons to push against.
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35. Lining Construction
Constructed by mixing heat resistant materials with bonding agents:
Mixture is controlled to create proper coefficient of friction.
Mixture is molded, compressed, and heated.
Finished pad is machined to smooth surface.
Some pads are grooved to:
Provide self-cleaning.
Increase air transfer for cooling.
Reduce noise.
Indicate wear.
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36. Shoe Construction Shoe is made of flat, heavy gauge steel:
Punched or cast to match caliper mounting and lining.
May have alignment dowels stamped into metal.
Anti-noise springs or clips:
Reduce rattles and squeal.
May be riveted or welded to shoe.
May snap on shoe.
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37. Lining-to-Shoe Attachment
Lining may be attached to shoe by riveting:
Brass rivets attach lining to shoe.
Brass rivets cause less damage if lining wears and contacts rotor.
Lining may be attached to shoe by bonding:
Special high temperature cement or epoxy resin placed between lining and shoe.
Lining and shoe pressed together until cement dries or cures.
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38. Noise Reduction Devices
Brake noise may be reduced by:
Anti-rattle clips.
Springs.
Flexible heat-resistant material, called insulators.
Anti-squeal compounds applied to the back of pad before installation.
Mechanical noise reduction devices form tension fit with pad and other parts of brake assembly when pad installed.
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39. Noise Reduction Devices
(Chevrolet)
A—Shims and springs. B—Anti-rattle springs.
C—Anti-squeal springs.
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40. Lining Wear Warning Devices
Wear indicator:
Small piece of flat spring steel attached to one shoe.
When pads are excessively worn, high-pitched squeal produced when brakes not applied.
Electrical indicator:
Electrical lead attached to a sensor next to pad or molded into pad.
When brakes are worn, applying brakes completes circuit and illuminates dashboard warning light.
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41. A—New pads. B—Excessively worn pads.
Wear Indicator
(Chevrolet)
A—New pads. B—Excessively worn pads.
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42. Electric Wear Sensor (Bendix)
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43. Review Questions
The disc brake rotor provides a(n) ______ braking surface for the pads.
smooth
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44. Review Questions
A solid rotor provides less cooling than a(n) __________ rotor.
ventilated
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45. Review Questions
A disc brake caliper with four pistons is a(n) _____ type.
fixed
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46. Review Questions
True or False? Many floating calipers are mounted to the spindle with special mounting bolts that allow the caliper to slide on them.
True.
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47. Review Questions Screw and cam are types of disc _______ brakes.
parking
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48. Review Questions
The disc brake lining is attached to a(n) ____ made of heavy metal.
shoe
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49. Glossary Anti-rattle clip Anti-squeal compound Bonding Bushing
One or more metal components designed to keep brake pads from vibrating and rattling.
Anti-squeal compound
Chemical insulation that can be applied to the metal side of brake pads.
Bonding
Process that glues the lining to the pad or shoe.
Bushing
A tubular friction bearing, used to guide and reduce friction of moving parts.
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50. Glossary Caliper Disc brake pad Dust boot
Disc brake component that forms cylinder and houses piston and brake pads (linings). It creates clamping action on rotating disc to stop car.
Disc brake pad
Disc brake friction lining. Designed to stop the vehicle when forced into contact with the rotor.
Dust boot
Rubber seal that keeps dust and water out of calipers and wheel cylinders.
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51. Glossary Fixed caliper Floating caliper Guide pins
Brake caliper that is rigidly bolted to the spindle and does not move during braking.
Floating caliper
A caliper that can move or “float” back and forth in relation to the rotor.
Guide pins
Mounting bolts that allow the caliper to move over them. Also called slider pins.
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52. Glossary Lining Machining Riveting Rotor
The actual brake material on a brake pad.
Machining
The removal of a layer of metal from a rotor or drum to restore the surface finish. Also referred to as cutting or turning.
Riveting
Process using brass rivets to attach the lining to the pad or shoe.
Rotor
A flat metal disc that serves as the friction surface for the front brake assemblies.
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53. Glossary Shoe Slider pins Solid rotor Splash shield
The metal lining support on a brake pad.
Slider pins
Mounting bolts that allow the caliper to move over them. Also called guide pins.
Solid rotor
A brake rotor that has no openings between the friction surfaces.
Splash shield
Sheet metal stamping or molded plastic assembly installed over the inner surface of a rotor.
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54. Glossary Turning Ventilated rotor Way
Also referred to as cutting or machining. The removal of a layer of metal from a rotor or drum to restore the surface finish.
Ventilated rotor
A rotor that has internal fins and/or holes drilled between the two friction surfaces.
Way
A flat surface designed to allow smooth movement between itself and another component that slides over it.
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55. Glossary Wear indicator
A small piece of flat spring steel attached to one of the brake pads. As the pad linings wear down, the end of the spring contacts the spinning rotor, notifying the driver of the need for brake service.
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