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101 DISC BRAKES

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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.

Automotive Technology, Fourth Edition James Halderman

© 2011 Pearson Education, Inc. All Rights Reserved

101 DISC BRAKES

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.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

DISC BRAKES

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-1

An exploded view of a typical disc brake assembly.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

Disc Brakes • Disc Brake Advantages – Fade resistance • Resistant to all kinds of fade – Mechanical fade – Lining fade

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101 DISC BRAKES

Disc Brakes • Disc Brake Advantages – Fade resistance • Resistant to all kinds of fade – Gas fade – Water fade

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-2

Braking force is applied equally to both sides of the brake rotor.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES 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.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-4

Slots and holes in the brake linings help prevent gas and water fade.

Automotive Technology, Fourth Edition James Halderman

© 2011 Pearson Education, Inc. All Rights Reserved

101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

© 2011 Pearson Education, Inc. All Rights Reserved

101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES 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.

Automotive Technology, Fourth Edition James Halderman

© 2011 Pearson Education, Inc. All Rights Reserved

101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

© 2011 Pearson Education, Inc. All Rights Reserved

101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

Disc Brakes • Disc Brake Disadvantages – Brake noise • Sometimes make various squeaks and squeals during application

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

Disc Brakes • Disc Brake Disadvantages – Brake noise • Antirattle clips help prevent vibration

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

Disc Brakes • Disc Brake Disadvantages – Brake noise • Shims between brake pad and caliper piston damp vibrations

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

Disc Brakes • Disc Brake Disadvantages – Brake dust – Poor parking brake performance

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-6

Antirattle clips reduce brake pad movement and vibration.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-7

Antivibration shims are used behind the pads on many disc brake caliper designs.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

DISC BRAKE CONSTRUCTION

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-8

This brake caliper attaches to the front spindle.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES 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.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

DISC BRAKE PADS

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

© 2011 Pearson Education, Inc. All Rights Reserved

101 DISC BRAKES Figure 101-10

A typical disc brake pad.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-11 caliper housing.

To prevent noise, bent tabs on the backing plate hold some brake pads to the

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-12

Holes in the backing plate are a common method of locating a pad in the caliper.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-14

The lining edges of some brake pads are tapered to help prevent vibration.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

© 2011 Pearson Education, Inc. All Rights Reserved

101 DISC BRAKES 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.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-16 replacement.

Electrical wear indicators ground a warning light circuit when the pads need

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-17

Mold-bonded linings are commonly used in many applications.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES CHART 101–1

Typical compositions for asbestos (organic) lining used on older vehicles.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

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101 DISC BRAKES

Disc Brake Pads • Brake Lining Composition – Semimetallic friction material • Require very smooth finish on rotor

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES CHART 101–2

Typical compositions for semimetallic disc brake pads

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES CHART 101–3 pad material.

The SAE brake pad edge codes are used to indicate the coefficient of friction of the

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101 DISC BRAKES

BRAKE ROTORS

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-18

Disc brake rotors can be either solid or vented.

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101 DISC BRAKES

CALIPER DESIGNS

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101 DISC BRAKES

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

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES 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.

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES Figure 101-20 suspension.

This floating caliper mounts on a separate anchor plate that bolts to the vehicle

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101 DISC BRAKES 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.

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-22

Caliper flex can cause tapered wear of the brake lining.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES 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.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-24

Floating calipers are supported by rubber O-rings or plastic bushings.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-25

Metal guide pins and sleeves are used to retain and locate floating calipers.

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101 DISC BRAKES

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

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101 DISC BRAKES

Caliper Designs • Sliding Calipers – Calipers move on ways cast and machined into caliper body and anchor plate

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101 DISC BRAKES

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

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-27

Exploded view of a typical sliding brake caliper.

Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES Figure 101-28

Sliding calipers move on machined ways.

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101 DISC BRAKES

REAR DISC BRAKES

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES

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

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101 DISC BRAKES 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.

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101 DISC BRAKES Figure 101-30 brake.

This single-piston brake caliper is mechanically actuated to serve as a parking

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101 DISC BRAKES Figure 101-31 disc brakes.

Drum parking brakes are fitted inside the rotors on this vehicle equipped with rear

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101 DISC BRAKES

TECH TIP BACK TO PRESENTATION

• Check the Tire Size for a Pulling Problem

• Tire can braking vary from one tireis being – If diameter an unequal problem manufacturer another even the size diagnosed,tocheck that the though front tires designation is the same. Even slight differences match and that the rear tires match. in the wear or inflation pressure of tires can Brakes slow and wheels. cause a different tire stop diameter and,Unequal therefore, a diameter tiresforce. create an unequal braking different braking

force. The result may be a pulling toward one side while braking. Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

TECH TIP BACK TO PRESENTATION

• Wax the Wheels – Brake dust from semimetallic brake pads often discolors the front wheels. Customers complain to service • A coat of wax onoften the wheels or wheel covers technicians about and this makes problem, but ittois helps prevent damage it easier normal the dust. front wheels to become wash off thefor brake dirty because the iron and other metallic and nonmetallic components wear off the front disc brake pads and adhere to the wheel covers. Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

TECH TIP BACK TO PRESENTATION

• Competitively Priced Brakes

• In fact, according to warehouse distributors and – The term competitively priced means importers, the box often costs more than the lower cost. Most brake manufacturers brake lining inside. offer “premium” as well as lower-price • Professional brake service technicians should linings, to remain competitive with other only install brake linings and pads that will give manufacturers orequal with to importers of original brake braking performance that of the factory brakes. For produced best results, always purchase lining material overseas by U.S. high-quality parts from a known brandor foreignbrake companies. name manufacturer. Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

FREQUENTLY ASKED QUESTION

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BACK TO PRESENTATION

• Aftermarket (replacement) brake pads and shoes 3 • are What Does “D not required to EA” meetMean? the FMVSS standard. – Original equipment brake pads and shoes However, several manufacturers of replacement brake and shoes are using standardized arepads required to comply witha the Federal testMotor that closely matches FMVSS (FMVSS) standard Vehicle Safety the Standard and135, is called thespecifies “Dual Dynamometer Differential which maximum stopping 3 Effectiveness Analysis” or D This test is for distances. There is alsoEA. a requirement currently voluntary and linings that pass the test fade resistance, but no standard for noise can have a “D3EA certified” seal placed on the or wear. product package. Automotive Technology, Fourth Edition James Halderman

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101 DISC BRAKES

FREQUENTLY ASKED QUESTION

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BACK TO PRESENTATION

• What Is a Low-Drag Caliper?

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.

• Because of this further movement, the brake – A low-drag caliper differs from a standard pads are pulled farther from the rotor and are indrag. the area of the square-cut Olesscaliper likely to The negative aspect of this ring.is Athat V-shaped the O-ring design greater cutout volume allows of brake fluid is to deflect morea and, a result, is needed to achieve brakeas application. Toable to pull the caliper back into brake the bore compensate for this piston need for greater fluid volume, quick-take-up cylinder was whenathe brakes aremaster released. designed and is used whenever low-drag calipers are used. Automotive Technology, Fourth Edition James Halderman

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