This document provides an overview of disc brake systems, including: - The main components of disc brakes and how they function to stop rotation of the brake disc. - Different types of disc brake caliper designs, including fixed, floating, and sliding calipers. - Construction and operation of brake pads, rotors, and other disc brake parts. - Techniques for diagnosing and repairing disc brake systems.

1. DISC BRAKES 101

2. Objectives The student should be able to: Prepare for the Brakes (A5) ASE certification test content area “C” (Disc Brake Diagnosis and Repair). Describe how disc brakes function. Name the parts of a typical disc brake system. Describe the construction of disc brake pads.

3. Objectives The student should be able to: Describe the difference between fixed caliper and floating or sliding caliper. Explain the difference between a standard caliper and a low-drag caliper.

4. DISC BRAKES

5. Disc Brakes Parts and Operation Piston(s) squeeze friction material (pads) on both sides of rotating disc (rotor) Used on front wheels of late-model vehicles

6. Disc Brakes Parts and Operation Used on rear wheels of increasing number of automobiles Adopted because supply greater stopping power than drum brakes with less likelihood of fade

7. Disc Brakes Disc Brake Advantages Friction assembly has several significant strong points Only a few relatively minor weak points

8. Figure 101-1 An exploded view of a typical disc brake assembly.

9. Disc Brakes Disc Brake Advantages Fade resistance Cooling ability helps avoid heat-induced fade All major parts exposed to air Have greater swept area

10. Disc Brakes Disc Brake Advantages Fade resistance Resistant to all kinds of fade Mechanical fade Lining fade

11. Disc Brakes Disc Brake Advantages Fade resistance Resistant to all kinds of fade Gas fade Water fade

12. Figure 101-2 Braking force is applied equally to both sides of the brake rotor.

13. Figure 101-3 Disc brakes can absorb and dissipate a great deal of heat. During this demonstration, the brakes were gently applied as the engine drove the front wheels until the rotor became cherry red. During normal braking, the rotor temperature can exceed 350°F (180°C), and about 1,500°F (800°C) on a race vehicle.

14. Figure 101-4 Slots and holes in the brake linings help prevent gas and water fade.

15. Disc Brakes Disc Brake Advantages Self-adjusting ability Any wear of linings automatically compensated for by action of brake caliper

16. Disc Brakes Disc Brake Advantages Self-adjusting ability When brakes applied, caliper pistons move out as far as needed to force brake pads into contact with rotor

17. Disc Brakes Disc Brake Advantages Self-adjusting ability When brakes released, piston retracts only small distance dictated by rotor runout and piston seal flex

18. Figure 101-5 The square-cut O-ring not only seals hydraulic brake fluid, but also retracts the caliper piston when the brake pedal is released.

19. Disc Brakes Disc Brake Advantages Freedom from pull Stops straighter under wider range of conditions than drum brake

20. Disc Brakes Disc Brake Advantages Freedom from pull Are not self-energizing to increase braking power Effects of loss of friction on one side far less pronounced

21. Disc Brakes Disc Brake Disadvantages No self-energizing or servo action Contributes to poor parking brake performance

22. Disc Brakes Disc Brake Disadvantages No self-energizing or servo action Requires driver to push harder on brake pedal for given stop

23. Disc Brakes Disc Brake Disadvantages No self-energizing or servo action High pedal pressure eliminated through use of brake power boosters

24. Disc Brakes Disc Brake Disadvantages Brake noise Sometimes make various squeaks and squeals during application

25. Disc Brakes Disc Brake Disadvantages Brake noise Usually caused by high-frequency rattling or vibration of brake pads

26. Disc Brakes Disc Brake Disadvantages Brake noise Antirattle clips help prevent vibration

27. Disc Brakes Disc Brake Disadvantages Brake noise Shims between brake pad and caliper piston damp vibrations

28. Disc Brakes Disc Brake Disadvantages Brake dust Poor parking brake performance

29. Figure 101-6 Antirattle clips reduce brake pad movement and vibration.

30. Figure 101-7 Antivibration shims are used behind the pads on many disc brake caliper designs.

31. DISC BRAKE CONSTRUCTION

32. Disc Brake Construction Caliper Hydraulic pressure creates mechanical force to move brake pads into contact with brake rotor

33. Disc Brake Construction Caliper Front axle: caliper mounts to spindle, caliper support bracket or steering knuckle Rear axle: mount to support bracket on axle flange or suspension

34. Figure 101-8 This brake caliper attaches to the front spindle.

35. Figure 101-9 A rear disc brake caliper often attaches to a mounting bracket on the rear axle housing on this rear-wheel-drive vehicle.

36. Disc Brake Construction Splash Shield Front axle: bolts to front spindle or steering knuckle Rear axle: bolts to axle flange or suspension adapter plate Protect inner side of brake rotor from water and other contaminants

37. DISC BRAKE PADS

38. Disc Brake Pads Brake Pad Assembly Block of friction material attached to stamped steel backing plate Some pad backing plates have tabs that bend over caliper to hold pad in place

39. Disc Brake Pads Brake Pad Assembly Others have tabs with holes in them Pin slips through holes and fastens to caliper body to hold pads Still others have retainer spring that locks pad to caliper piston

40. Figure 101-10 A typical disc brake pad.

41. Figure 101-11 To prevent noise, bent tabs on the backing plate hold some brake pads to the caliper housing.

42. Figure 101-12 Holes in the backing plate are a common method of locating a pad in the caliper.

43. Disc Brake Pads Brake Pad Assembly Lining material can be one of a number of products Can be fastened to backing plate in several ways

44. Disc Brake Pads Brake Pad Assembly Edges of lining material usually perpendicular to rotor surface A few larger pads have tapered edges to help combat vibration and noise

45. Figure 101-14 The lining edges of some brake pads are tapered to help prevent vibration.

46. Disc Brake Pads Pad Wear Indicators Used for safety reasons Signal driver when pad replacement necessary

47. Disc Brake Pads Pad Wear Indicators Mechanical: squealing or chirping noise when brakes are not applied made by tab contacting rotor Electrical: coated electrode in lining generates signal to turn on warning light

48. Figure 101-15 Typical pad wear sensor operation. It is very important that the disc brake pads are installed on the correct side of the vehicle to be assured that the wear sensor will make a noise when the pads are worn. If the pads with a sensor are installed on the opposite side of the vehicle, the sensor tab is turned so that the rotor touches it going the opposite direction. Usually the correct direction is where the rotor contacts the sensor before contacting the pads when the wheels are being rotated in the forward direction.

49. Figure 101-16 Electrical wear indicators ground a warning light circuit when the pads need replacement.

50. Disc Brake Pads Pad Assembly Methods Riveted linings Brake block attached to backing plate with metal rivets

51. Disc Brake Pads Pad Assembly Methods Bonded linings Glue brake block directly to shoe pad backing plate

52. Disc Brake Pads Pad Assembly Methods Mold-bonded linings Combines advantages of bonding with mechanical strength of riveting

53. Figure 101-17 Mold-bonded linings are commonly used in many applications.

54. Disc Brake Pads Brake Lining Composition Ingredients mixed and molded into shape of finished product Fibers in material only thing holding mixture together

55. Disc Brake Pads Brake Lining Composition Large press forces ingredients together to form brake block, which becomes brake lining

56. CHART 101–1 Typical compositions for asbestos (organic) lining used on older vehicles.

57. Disc Brake Pads Brake Lining Composition Semimetallic friction material Uses metal rather than asbestos in its formulation

58. Disc Brake Pads Brake Lining Composition Semimetallic friction material Require very smooth finish on rotor

59. CHART 101–2 Typical compositions for semimetallic disc brake pads

60. Disc Brake Pads Brake Lining Composition Nonasbestos friction material Use synthetic material such as aramid fibers instead of steel

61. Disc Brake Pads Brake Lining Composition Carbon fiber friction material Newest and most expensive of the lining materials

62. Disc Brake Pads Brake Lining Composition Ceramic friction material Most pads today are ceramic and use little, if any steel

63. Disc Brake Pads Edge Codes Lining edge codes help identify coefficient of friction First letter indicates coefficient of friction when brakes are cold Second letter indicates coefficient of friction when brakes are hot ?

64. CHART 101–3 The SAE brake pad edge codes are used to indicate the coefficient of friction of the pad material.

65. BRAKE ROTORS

66. Brake Rotors Provides friction surfaces for brake pads to rub against Largest and heaviest part of disc brake

67. Brake Rotors Usually Made of Cast Iron Solid rotors most often used on rear-wheel disc brakes Vented rotors have radial cooling passages cast between friction surfaces

68. Figure 101-18 Disc brake rotors can be either solid or vented.

69. CALIPER DESIGNS

70. Caliper Designs Fixed Caliper Design Body manufactured in two halves Uses two, four, or six pistons to apply brake pads

71. Caliper Designs Fixed Caliper Design Caliper rigidly mounted to suspension When brakes applied, pistons extend from caliper bores and apply brake pads with equal force from both sides of rotor No part of caliper body moves when brakes applied

72. Figure 101-19 (a) Many fixed caliper disc brakes use a simple retaining pin to hold the disc brake pads. (b) Removing the retainer pin allows the brake pads to be removed. (c) Notice the cross-over hydraulic passage that connects both sides of the caliper.

73. Caliper Designs Fixed Caliper Advantages Large and heavy, and can absorb and dissipate great amounts of heat Allows brake rotor and pads to run cooler

74. Caliper Designs Fixed Caliper Advantages Able to withstand greater number of repeated hard stops without heat-induced fade Does not flex as much as other designs

75. Caliper Designs Fixed Caliper Disadvantages Add significant weight to vehicle Service more difficult and greater opportunity for leaks Greater possibility of cracking

76. Caliper Designs Floating and Sliding Caliper Design Used in front brakes of most vehicles Caliper free to move within limited range on anchor plate solidly mounted to vehicle suspension

77. Caliper Designs Floating and Sliding Caliper Design When brakes applied, caliper piston applies inner brake pad At same time, caliper body moves in opposite direction on anchor plate and applies outer brake pad Caliper body moves every time brakes applied

78. Figure 101-20 This floating caliper mounts on a separate anchor plate that bolts to the vehicle suspension.

79. Figure 101-21 Hydraulic force on the piston (left) is applied to the inboard pad and the caliper housing itself. The reaction of the piston pushing against the rotor causes the entire caliper to move toward the inside of the vehicle (large arrow). Since the outboard pad is retained by the caliper, the reaction of the moving caliper applies the force of the outboard pad against the outboard surface of the rotor.

80. Caliper Designs Normal Caliper Operation Piston moves just enough to distort caliper seal Returns to original position when brake pedal released

81. Caliper Designs Normal Caliper Operation As wear occurs, additional brake fluid needed behind piston Comes from master cylinder; brake fluid level drops as brake pads wear

82. Caliper Designs Floating and Sliding Caliper Advantages Lower cost, simple construction, and compact size Smaller size allows better packaging of caliper on vehicle

83. Caliper Designs Floating and Sliding Caliper Disadvantages Certain degree of flex, which can contribute to spongy brake pedal Flex also allows caliper body to twist slightly when brakes applied, causing tapered wear of lining material

84. Caliper Designs Floating and Sliding Caliper Disadvantages Do not have mass of fixed calipers Flexible mounting systems slow transfer of heat from caliper body to anchor plate that aids cooling

85. Figure 101-22 Caliper flex can cause tapered wear of the brake lining.

86. Caliper Designs Floating Caliper Operation Body of floating caliper does not make direct contact with anchor plate Body supported by bushings and/or O-rings Allow it to “float” or slide on metal guide pins attached to anchor plate

87. Caliper Designs Floating Caliper Operation Depend on proper lubrication of pins, sleeves, bushings, and O-rings for smooth operation Special high-temperature brake grease must be used

88. Figure 101-23 A typical single-piston floating caliper. In this type of design, the entire caliper moves when the single piston is pushed out of the caliper during a brake application. When the caliper moves, the outboard pad is applied against the rotor.

89. Figure 101-24 Floating calipers are supported by rubber O-rings or plastic bushings.

90. Figure 101-25 Metal guide pins and sleeves are used to retain and locate floating calipers.

91. Caliper Designs Sliding Calipers Body of sliding caliper mounts in direct metal-to-metal contact with anchor plate

92. Caliper Designs Sliding Calipers Calipers move on ways cast and machined into caliper body and anchor plate

93. Caliper Designs Sliding Calipers Retaining clips and design of caliper prevent body from coming out of ways Depend on good lubrication of ways for proper operation ?

94. Figure 101-27 Exploded view of a typical sliding brake caliper.

95. Figure 101-28 Sliding calipers move on machined ways.

96. REAR DISC BRAKES

97. Rear Disc Brakes Four-wheel disc brake systems have become more common

98. Rear Disc Brakes Rear Disc Parking Brakes Two methods of providing parking brakes when rear discs are installed Adapt disc brake to also function as parking brake

99. Rear Disc Brakes Rear Disc Parking Brakes Two methods of providing parking brakes when rear discs are installed Use mechanically actuated drum brakes inside rear rotors

100. Figure 101-29 Exploded view of a typical rear disc brake with an integral parking brake. The parking brake lever mechanically pushes the caliper piston against the rotor.

101. Figure 101-30 This single-piston brake caliper is mechanically actuated to serve as a parking brake.

102. Figure 101-31 Drum parking brakes are fitted inside the rotors on this vehicle equipped with rear disc brakes.

103. TECH TIP Check the Tire Size for a Pulling Problem If an unequal braking problem is being diagnosed, check that the front tires match and that the rear tires match. Brakes slow and stop wheels. Unequal diameter tires create an unequal braking force. The result may be a pulling toward one side while braking. Tire diameter can vary from one tire manufacturer to another even though the size designation is the same. Even slight differences in the wear or inflation pressure of tires can cause a different tire diameter and, therefore, a different braking force. BACK TO PRESENTATION

104. TECH TIP Wax the Wheels Brake dust from semimetallic brake pads often discolors the front wheels. Customers often complain to service technicians about this problem, but it is normal for the front wheels to become dirty because the iron and other metallic and nonmetallic components wear off the front disc brake pads and adhere to the wheel covers. BACK TO PRESENTATION A coat of wax on the wheels or wheel covers helps prevent damage and makes it easier to wash off the brake dust.

105. TECH TIP Competitively Priced Brakes The term competitively priced means lower cost. Most brake manufacturers offer “premium” as well as lower-price linings, to remain competitive with other manufacturers or with importers of brake lining material produced overseas by U.S. or foreign companies. In fact, according to warehouse distributors and importers, the box often costs more than the brake lining inside. Professional brake service technicians should only install brake linings and pads that will give braking performance equal to that of the original factory brakes. For best results, always purchase high-quality brake parts from a known brand-name manufacturer. BACK TO PRESENTATION

106. FREQUENTLY ASKED QUESTION What Does “D 3 EA” Mean? Original equipment brake pads and shoes are required to comply with the Federal Motor Vehicle Safety Standard (FMVSS) 135, which specifies maximum stopping distances. There is also a requirement for fade resistance, but no standard for noise or wear. ? BACK TO PRESENTATION Aftermarket (replacement) brake pads and shoes are not required to meet the FMVSS standard. However, several manufacturers of replacement brake pads and shoes are using a standardized test that closely matches the FMVSS standard and is called the “Dual Dynamometer Differential Effectiveness Analysis” or D 3 EA. This test is currently voluntary and linings that pass the test can have a “D 3 EA certified” seal placed on the product package.

107. FREQUENTLY ASKED QUESTION What Is a Low-Drag Caliper? A low-drag caliper differs from a standard caliper in the area of the square-cut O-ring. A V-shaped cutout allows the O-ring to deflect more and, as a result, is able to pull the caliper piston back into the bore when the brakes are released. ? BACK TO PRESENTATION Because of this further movement, the brake pads are pulled farther from the rotor and are less likely to drag. The negative aspect of this design is that greater volume of brake fluid is needed to achieve a brake application. To compensate for this need for greater brake fluid volume, a quick-take-up master cylinder was designed and is used whenever low-drag calipers are used. Figure 101-26 In a standard disc brake caliper, the square-cut O-ring deforms when the brakes are applied and returns the piston to its original (released) position due to the elastic properties of the rubber seal. In a low-drag caliper design, the groove for the square-cut O-ring is V-shaped, allowing for more retraction. When the brake pedal is released, the piston is moved away from the rotor farther, resulting in less friction between the disc brake pads and the rotor when the brakes are released.