1. 2 Disc Brake System Components and Operation Chapter 12 Permission granted to reproduce for educational use only. © Goodheart-Willcox Co., Inc

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2

Disc Brake System Components and Operation

Chapter 12

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

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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.

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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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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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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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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Rotor Construction


This rotor has its minimum allowable thickness stamped on the hub.

(General Motors)

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Rotor Construction

Solid 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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Ventilated Rotor


(Saab)

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Cross-Drilled Rotor


(Porsche)

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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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Rotor Attachment


Secured to hub with wheel studs. (Chrysler)

13© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Rotor Attachment

Rotor and hub integrated into single unit. (Chrysler)

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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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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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Front Disc Brake Caliper


(Chrysler)

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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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Caliper Operation


(Delco)

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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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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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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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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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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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Caliper slides on machined ways. (Ford)

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Caliper slides on locating pins and insulators. (Ford)

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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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(Cadillac)

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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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(Chrysler)

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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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Fixed Caliper Construction


(Kelsey-Hayes)

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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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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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Disc Brake Pads

Disc brake pads: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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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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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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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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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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Noise Reduction Devices


A—Shims and springs. B—Anti-rattle springs.

C—Anti-squeal springs.

(Chevrolet)

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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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Wear Indicator


A—New pads. B—Excessively worn pads.

(Chevrolet)

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Electric Wear Sensor


(Bendix)

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Review Questions

The disc brake rotor provides a(n) ______ braking surface for the pads.


smooth

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Review Questions

A solid rotor provides less cooling than a(n) __________ rotor.


ventilated

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Review Questions

A disc brake caliper with four pistons is a(n) _____ type.


fixed

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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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Review Questions

Screw and cam are types of disc _______ brakes.


parking

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Review Questions

The disc brake lining is attached to a(n) ____ made of heavy metal.


shoe

Documents

1. 2 Disc Brake System Components and Operation Chapter 12 Permission granted to reproduce for educational use only. © Goodheart-Willcox Co., Inc