Halderman ch101 lecture

© 2011 Pearson Education, Inc.All Rights Reserved

Automotive Technology, Fourth EditionJames Halderman

DISC BRAKES

101

101 DISC BRAKES



ObjectivesObjectives

• 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.

101 DISC BRAKES



ObjectivesObjectives

• 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.

101 DISC BRAKES



DISC BRAKESDISC BRAKES

101 DISC BRAKES



Disc BrakesDisc 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

101 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

101 DISC BRAKES




• Disc Brake Advantages– Friction assembly has several significant

strong points– Only a few relatively minor weak points

101 DISC BRAKES



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

101 DISC BRAKES




• Disc Brake Advantages– Fade resistance

• Cooling ability helps avoid heat-induced fade– All major parts exposed to air– Have greater swept area

101 DISC BRAKES





• Resistant to all kinds of fade– Mechanical fade– Lining fade

101 DISC BRAKES





• Resistant to all kinds of fade– Gas fade– Water fade

101 DISC BRAKES



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

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.

101 DISC BRAKES



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

101 DISC BRAKES




• Disc Brake Advantages– Self-adjusting ability

• Any wear of linings automatically compensated for by action of brake caliper

101 DISC BRAKES





• When brakes applied, caliper pistons move out as far as needed to force brake pads into contact with rotor

101 DISC BRAKES





• When brakes released, piston retracts only small distance dictated by rotor runout and piston seal flex

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.

101 DISC BRAKES




• Disc Brake Advantages– Freedom from pull

• Stops straighter under wider range of conditions than drum brake

101 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

101 DISC BRAKES




• Disc Brake Disadvantages– No self-energizing or servo action

• Contributes to poor parking brake performance

101 DISC BRAKES





• Requires driver to push harder on brake pedal for given stop

101 DISC BRAKES





• High pedal pressure eliminated through use of brake power boosters

101 DISC BRAKES




• Disc Brake Disadvantages– Brake noise

• Sometimes make various squeaks and squeals during application

101 DISC BRAKES





• Usually caused by high-frequency rattling or vibration of brake pads

101 DISC BRAKES





• Antirattle clips help prevent vibration

101 DISC BRAKES





• Shims between brake pad and caliper piston damp vibrations

101 DISC BRAKES




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

101 DISC BRAKES



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

101 DISC BRAKES



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

101 DISC BRAKES



DISC BRAKE DISC BRAKE CONSTRUCTIONCONSTRUCTION

101 DISC BRAKES



Disc Brake ConstructionDisc Brake Construction

• Caliper– Hydraulic pressure creates mechanical

force to move brake pads into contact with brake rotor

101 DISC BRAKES




• Caliper– Front axle: caliper mounts to spindle,

caliper support bracket or steering knuckle– Rear axle: mount to support bracket on

axle flange or suspension

101 DISC BRAKES



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

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.

101 DISC BRAKES




• 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

101 DISC BRAKES



DISC BRAKE PADSDISC BRAKE PADS

101 DISC BRAKES



Disc Brake PadsDisc 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

101 DISC BRAKES




• 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

101 DISC BRAKES



Figure 101-10 A typical disc brake pad.

101 DISC BRAKES



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

101 DISC BRAKES



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

101 DISC BRAKES




• Brake Pad Assembly– Lining material can be one of a number of

products– Can be fastened to backing plate in several

ways

101 DISC BRAKES




• 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

101 DISC BRAKES



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

101 DISC BRAKES




• Pad Wear Indicators– Used for safety reasons– Signal driver when pad replacement

necessary

101 DISC BRAKES




• 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

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.

101 DISC BRAKES



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

101 DISC BRAKES




• Pad Assembly Methods– Riveted linings

• Brake block attached to backing plate with metal rivets

101 DISC BRAKES




• Pad Assembly Methods– Bonded linings

• Glue brake block directly to shoe pad backing plate

101 DISC BRAKES




• Pad Assembly Methods– Mold-bonded linings

• Combines advantages of bonding with mechanical strength of riveting

101 DISC BRAKES



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

101 DISC BRAKES




• Brake Lining Composition– Ingredients mixed and molded into shape

of finished product– Fibers in material only thing holding

mixture together

101 DISC BRAKES




• Brake Lining Composition– Large press forces ingredients together to

form brake block, which becomes brake lining

101 DISC BRAKES



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

101 DISC BRAKES




• Brake Lining Composition– Semimetallic friction material

• Uses metal rather than asbestos in its formulation

101 DISC BRAKES




• Brake Lining Composition– Semimetallic friction material

• Require very smooth finish on rotor

101 DISC BRAKES



CHART 101–2 Typical compositions for semimetallic disc brake pads

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• Brake Lining Composition– Nonasbestos friction material

• Use synthetic material such as aramid fibers instead of steel

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• Brake Lining Composition– Carbon fiber friction material

• Newest and most expensive of the lining materials

101 DISC BRAKES




• Brake Lining Composition– Ceramic friction material

• Most pads today are ceramic and use little, if any steel

101 DISC BRAKES




• 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

?

101 DISC BRAKES



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

101 DISC BRAKES



BRAKE ROTORSBRAKE ROTORS

101 DISC BRAKES



Brake RotorsBrake Rotors

• Provides friction surfaces for brake pads to rub against

• Largest and heaviest part of disc brake

101 DISC BRAKES



Brake RotorsBrake 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

101 DISC BRAKES



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

101 DISC BRAKES



CALIPER DESIGNSCALIPER DESIGNS

101 DISC BRAKES



Caliper DesignsCaliper Designs

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

pads

101 DISC BRAKES




• 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

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.

101 DISC BRAKES




• Fixed Caliper Advantages– Large and heavy, and can absorb and

dissipate great amounts of heat– Allows brake rotor and pads to run cooler

101 DISC BRAKES




• Fixed Caliper Advantages– Able to withstand greater number of

repeated hard stops without heat-induced fade

– Does not flex as much as other designs

101 DISC BRAKES




• Fixed Caliper Disadvantages– Add significant weight to vehicle– Service more difficult and greater

opportunity for leaks– Greater possibility of cracking

101 DISC BRAKES




• 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

101 DISC BRAKES




• 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

101 DISC BRAKES



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

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.

101 DISC BRAKES




• Normal Caliper Operation– Piston moves just enough to distort caliper

seal– Returns to original position when brake

pedal released

101 DISC BRAKES




• Normal Caliper Operation– As wear occurs, additional brake fluid

needed behind piston– Comes from master cylinder; brake fluid

level drops as brake pads wear

101 DISC BRAKES




• Floating and Sliding Caliper Advantages– Lower cost, simple construction, and

compact size– Smaller size allows better packaging of

caliper on vehicle

101 DISC BRAKES




• 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

101 DISC BRAKES




• 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

101 DISC BRAKES



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

101 DISC BRAKES




• 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

101 DISC BRAKES




• 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

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.

101 DISC BRAKES



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

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

101 DISC BRAKES




• Sliding Calipers– Body of sliding caliper mounts in direct

metal-to-metal contact with anchor plate

101 DISC BRAKES




• Sliding Calipers– Calipers move on ways cast and machined

into caliper body and anchor plate

101 DISC BRAKES




• Sliding Calipers– Retaining clips and design of caliper

prevent body from coming out of ways– Depend on good lubrication of ways for

proper operation

?

101 DISC BRAKES



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

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Figure 101-28 Sliding calipers move on machined ways.

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REAR DISC BRAKESREAR DISC BRAKES

101 DISC BRAKES



Rear Disc BrakesRear Disc Brakes

• Four-wheel disc brake systems have become more common

101 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

101 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

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.

101 DISC BRAKES



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

101 DISC BRAKES



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

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Halderman ch101 lecture