Halderman ch103 lecture

© 2011 Pearson Education, Inc.All Rights Reserved

Automotive Technology, Fourth EditionJames Halderman

PARKING BRAKE OPERATION,

DIAGNOSIS, AND SERVICE

103

103 PARKING BRAKE OPERATION, DIAGNOSIS, AND SERVICE



ObjectivesObjectives• The student should be able to:

– Prepare for the Brakes (A5) ASE certification test content area “E” (Miscellaneous Systems Diagnosis and Repair).

– Describe what is required of a parking brake.

– Describe the parts and operation of the parking brake as used on a rear drum brake system.




ObjectivesObjectives• The student should be able to:

– Describe how a parking brake functions when the vehicle is equipped with rear disc brakes.

– Explain how to adjust a parking brake properly.




PARKING BRAKEPARKING BRAKESTANDARDSSTANDARDS




Parking Brake StandardsParking Brake Standards• Background

– Before 1967, most vehicles had only single master cylinder operating all four brakes

– If fluid leaked at just one wheel, operation of all brakes was lost





– Required alternative mechanical method to stop vehicle using two wheel brakes

– After 1967, federal regulations required use of dual master cylinders





– In case one-half of system fails, other half keeps operating

– Term parking brake has replaced emergency brake




Parking Brake StandardsParking Brake Standards• FMVSS 135

– Parking brake must hold fully loaded vehicle stationary on slope of 20% up or down grade

– Hand force required cannot exceed 80 lb (18 N) or foot force greater than 100 lb (22 N)




Figure 103-1 Typical parking brake cable system showing the foot-operated parking brake lever and cable routing.




PEDALS, LEVERS,PEDALS, LEVERS,AND HANDLESAND HANDLES




Pedals, Levers, and HandlesPedals, Levers, and Handles• Parking brakes are applied by pedal,

lever, or handle• Foot pedals and floor-mounted levers

most common• All parking brake controls incorporate

ratchet mechanism to lock brake in position




Figure 103-2 A typical parking brake pedal assembly.




Figure 103-3 Typical hand-operated parking brake. Note that the adjustment for the cable is underneath the vehicle at the equalizer.




Figure 103-4 A ratchet mechanism is used to lock parking brakes in the applied position.




Pedals, Levers, and HandlesPedals, Levers, and Handles• Parking Brake Pedals

– Applied by depressing with foot– Released by a pull or small T-handle or

lever under dash




Pedals, Levers, and HandlesPedals, Levers, and Handles• Parking Brake Pedals

– Some systems required driver to depress pedal to release parking brake once it was set

• Rubber pad on parking brake pedal usually states “push to release”




Figure 103-5 A remote-mounted parking brake release lever.




Pedals, Levers, and HandlesPedals, Levers, and Handles• Automatic Parking Brake Release

– Some vehicles with pedal-operated parking brakes have automatic release mechanism




Pedals, Levers, and HandlesPedals, Levers, and Handles• Automatic Parking Brake Release

– Disengages parking brake using vacuum servo controlled by electrical solenoid

– Metal rod connects vacuum servo to upper end of brake release lever




Pedal Levers and Handles

• Automatic Parking Brake Release– When engine running (to provide vacuum)

and shifter placed in gear, electrical contact closes to energize solenoid and route vacuum to servo

– Servo diaphragm retracts rod, releasing parking brake

Pedals, Levers, and HandlesPedals, Levers, and Handles




Figure 103-6 Automatic parking brake release mechanisms usually use a vacuum servo to operate the release lever.




Figure 103-7 The two plastic vacuum tubes on the steering column are used to release the parking brake when the gear selector is moved from park into a drive gear.




PARKING BRAKEPARKING BRAKEWARNING LAMPWARNING LAMP




Parking Brake Warning LampParking Brake Warning Lamp• Red brake warning lamp lights on dash• Same lamp that lights for hydraulic or

brake fluid level problem• Warns driver that parking brake is

applied or partially applied




Parking Brake Warning LampParking Brake Warning Lamp• If light on, check that parking brake

released• If light still on:

– Parking brake switch may be defective or out of adjustment

– May be hydraulic problem




PARKING BRAKE PARKING BRAKE LINKAGESLINKAGES




Parking Brake LinkagesParking Brake Linkages• Transmit force from pedal, lever, or

handle to brake friction assemblies• Linkage Rods

– Rods made from solid steel commonly used with floor-mounted actuating levers to span short distance to intermediate lever or equalizer




Parking Brake LinkagesParking Brake Linkages• Linkage Cables

– Woven-steel wire encased in reinforced rubber or plastic housing

– Housing fixed in position at both ends




Parking Brake LinkagesParking Brake Linkages• Linkage Cables

– Routed under vehicle through mounting brackets that allow small amount of movement

– Cable slides back and forth inside housing to transmit application force

– Subject to damage from water, dirt, other debris thrown up by tires




Figure 103-8 The cable from the activating lever to the equalizer is commonly called the control cable. From the equalizer, the individual brake cables are often called application cables. These individual cables can usually be purchased separately.




Parking Brake LinkagesParking Brake Linkages• Linkage Levers

– Driver cannot apply enough physical force to engage parking brake

– All parking brake linkages contain one or more levers that increase application force




Figure 103-10 Intermediate levers in the parking brake linkage increase the application force.




Parking Brake LinkagesParking Brake Linkages• Linkage Equalizers

– Transmits equal force from parking brake control to each friction assembly

– Simplest is cable guide attached to threaded rod

• Pivots or allows inner cable to slide back and forth to even out force




Parking Brake LinkagesParking Brake Linkages• Linkage Equalizers

– Simplest is cable guide attached to threaded rod

• Another type installs in long application cable from linkage at front of vehicle to one rear brake




Figure 103-11 A cable guide is a common type of parking brake linkage equalizer.




Figure 103-12 Some parking brake equalizers are installed in the brake cable.




Parking Brake LinkagesParking Brake Linkages• Linkage Design

– Most combine intermediate levers and equalizers in various ways

– Most use from one to four cables to actuate friction assemblies




Figure 103-13 Many parking brake linkages use both an intermediate lever and an equalizer.




FRONT AND REAR FRONT AND REAR ENTRY PARKING BRAKE ENTRY PARKING BRAKE

CABLESCABLES




Front and Rear Entry Parking Brake Front and Rear Entry Parking Brake CablesCables

• Many drum parking brake systems attach parking brake lever on secondary (rearward) shoe and push primary (forward facing) brake shoe against drum

• Parking brake cable enters backing plate from front of vehicle (front entry)





• Because primary shoe attached to secondary shoe on dual-servo brakes, forward motion of vehicle wedges primary shoe into brake drum and forces rear secondary lining against drum





• Applying only forward brake shoe tends to hold vehicle best when on a hill with front pointing downward

• To provide same holding power to keep vehicle from backing up, some vehicles reverse parking brake arrangement for right side





• Cable is rear entry: brake has parking brake lever installed on primary shoe

• Creates reverse servo action when vehicle parked with rear facing downward




DRUM PARKING DRUM PARKING BRAKESBRAKES




Drum Parking BrakesDrum Parking Brakes• Most common types on vehicles and

light trucks• Make excellent parking brakes because

of high static coefficient of friction combined with self-energizing action




Drum Parking BrakesDrum Parking Brakes• Integral Drum Parking Brakes

– Mechanically apply rear drum service brakes to serve as parking brakes

– Most common type– All such brakes operate in essentially same

manner




Figure 103-14 Notice the spring at the end of the parking brake strut. This antirattle spring keeps tension on the strut. The parking brake lever is usually attached with a pin and spring (wavy) washer and retained by a horseshoe clip.




Figure 103-15 The parking brake cable pulls on the parking brake lever, which in turn forces the brake shoe against the drum.




Drum Parking BrakesDrum Parking Brakes• Rear Disc Auxiliary Drum Parking

Brakes– Rear disc service brakes with fixed calipers

commonly have parking brake drum formed into hub of brake rotor




Drum Parking BrakesDrum Parking Brakes• Rear Disc Auxiliary Drum Parking

Brakes– Dual-servo parking brake friction

assemblies operate in essentially same manner as service brakes except that wheel cylinder eliminated and friction assembly actuated mechanically




Figure 103-16 The inside “hat” of the disc brake rotor is the friction surface for the parking brake shoes.




Figure 103-17 A typical rear disc brake auxiliary drum brake friction assembly.




CALIPER-ACTUATEDCALIPER-ACTUATEDDISC PARKING BRAKESDISC PARKING BRAKES




Caliper-Actuated Disc Parking BrakesCaliper-Actuated Disc Parking Brakes• Basic Operation

– Used on vehicles whose rear disc brakes equipped with floating or sliding brake calipers

– Single-piston construction makes them easier to mechanically actuate than multiple-piston fixed calipers

– Special mechanism in caliper applies caliper piston mechanically




Caliper-Actuated Disc Parking BrakesCaliper-Actuated Disc Parking Brakes• Ball and Ramp Actuation

– Found in Ford rear brake calipers– Has three steel balls located in ramp-

shaped detents between two plates




Caliper-Actuated Disc Parking BrakesCaliper-Actuated Disc Parking Brakes• Ball and Ramp Actuation

– As parking brake cable moves lever and rotates operating shaft, balls ride up ramps and force plates apart, applying brake

– Adjustment within the caliper automatic, and takes place during service brake application




Figure 103-18 A Ford rear brake caliper ball and ramp-type apply mechanism.




Figure 103-19 Operation of a ball and ramp-type rear disc brake caliper parking brake.




Figure 103-20 Automatic adjustment of a ball and ramp-type rear disc brake parking brake occurs when the service brakes are applied.




Caliper-Actuated Disc Parking BrakesCaliper-Actuated Disc Parking Brakes• Screw, Nut, and Cone Actuation

– General Motors’ rear disc parking brake design




Figure 103-21 A typical General Motors rear disc brake with an integral parking brake. This type uses a screw, nut, and cone mechanism to apply the caliper piston.




Figure 103-22 Parking brake application of a General Motors rear drive brake caliper.




Figure 103-23 Automatic adjustment of a General Motors rear disc brake caliper.




REAR DISC BRAKE REAR DISC BRAKE SERVICESERVICE




Rear Disc Brake ServiceRear Disc Brake Service• Most rear disc brake calipers replaced

as assembly• Calipers should also be replaced in

pairs to provide equal braking force • Follow instructions in service

information when rebuilding rear disc brake caliper assembly




Figure 103-24 Removing the piston from a typical General Motors rear disc brake caliper.




Figure 103-25 Installing the piston into a General Motors rear disc brake caliper.




Figure 103-26 A piston installation tool is often needed to complete the installation of the piston in a General Motors rear disc brake.




Figure 103-27 A spanner wrench (or needle-nose pliers) can be used to rotate the caliper piston prior to installing the disc brake pads. A notch on the piston must line up with a tab on the back of the brake pad to keep the piston from rotating when the parking brake is applied.




Figure 103-28 After removing the parking brake lever and thrust bearing, remove the antirotation pin.




Figure 103-29 Unscrew the thrust screw from the piston with an Allen (hex) wrench. After removing the thrust screw, push the piston out of the caliper bore.




Figure 103-30 To test the piston adjuster, thread the thrust screw into the piston. Hold the piston and pull the thrust screw outward 1/4 in. (6 mm). The adjuster nut should not turn when the thrust screw retracts. Replace the piston assembly if not functioning correctly.




Figure 103-31 To adjust the parking brake cable on a Ford vehicle equipped with rear disc brakes, start by loosening the cable adjustment until the cables to the calipers are slack. Tighten until the caliper lever moves. Position a 1/4-in. drill bit or dowel into the caliper alignment hole. Adjustment is correct if the parking brake lever does not hit the 1/4-in. dowel.




PARKING BRAKEPARKING BRAKECABLE ADJUSTMENTCABLE ADJUSTMENT




Parking Brake Cable AdjustmentParking Brake Cable Adjustment• Make certain that rear service brakes

adjusted correctly and lining serviceable

• With drums installed, apply parking brake 3 or 4 clicks– Should be slight drag on both rear wheels




Parking Brake Cable AdjustmentParking Brake Cable Adjustment• Adjust cable at equalizer until slight

drag on both rear brakes• Release parking brake; both rear brakes

should be free and not dragging– Repair or replace rusted cables or readjust

as necessary




Parking Brake Cable AdjustmentParking Brake Cable Adjustment• NOTE: Rear parking brake adjustment

should always be checked whenever replacing rear brake linings.– May be necessary to loosen parking brake

cable adjustment to allow clearance to get drum over new linings





should always be checked whenever replacing rear brake linings.– This could happen because someone may

have adjusted parking brake cable during life of rear linings





should always be checked whenever replacing rear brake linings.– With new thicker linings, parking brake

adjustment can keep brake shoes pushed outward toward drum




Figure 103-32 After checking that the rear brakes are okay and properly adjusted, the parking brake cable can be adjusted. Always follow the manufacturer’s recommended procedure.




Figure 103-33 Many hand-operated parking brakes are adjusted inside the vehicle.





should always be checked whenever replacing rear brake linings.– May be necessary to loosen parking brake

cable adjustment to allow clearance to get drum over new linings





should always be checked whenever replacing rear brake linings.– This could happen because someone may

have adjusted parking brake cable during life of rear linings





should always be checked whenever replacing rear brake linings.– With new thicker linings, parking brake

adjustment can keep brake shoes pushed outward toward drum




Figure 103-34 Always check that both brake shoes contact the anchor pin.




Parking Brake Cable AdjustmentParking Brake Cable Adjustment• To prevent possible parking brake cable

adjustment problems when installing new rear brakes:– Both brake shoes should make contact with

anchor pin at top• If not, check parking brake cable for

improper adjustment or improper installation of brake shoes





adjustment problems when installing new rear brakes:– Feel tension of parking brake cable

underneath vehicle• Should be slightly loose (with parking brake

“off”)





adjustment problems when installing new rear brakes:– Lubricate parking brake cable to ensure

that water or ice will not cause rust or freezing

• Stuck parking brake cable could cause linings to remain out against drums





adjustment problems when installing new rear brakes:– If parking brake needs to be adjusted,

check and adjust rear brake adjustment before adjusting parking brake cable





adjustment problems when installing new rear brakes:– NOTE: Some vehicles are equipped with an

automatic adjusting parking brake lever/cable. Simply cycling parking brake on/off/on three times is often all that is required to adjust parking brake cable.

– Replace any stuck, corroded, or broken parking brake cable




Figure 103-35 A 1/8-in. (3-mm) drill bit is placed through an access hole in the backing plate to adjust this General Motors leading-trailing rear parking brake. Adjust the parking brake cable until the drill can just fit between the shoe web and the parking brake lever.




ELECTRIC PARKING ELECTRIC PARKING BRAKEBRAKE




Electric Parking BrakeElectric Parking Brake• EPB systems available using two

different designs:– Cable-pulling type that uses electric motor

to pull parking brake cable– More advanced unit using computer-

controlled motor attached to brake caliper




Electric Parking BrakeElectric Parking Brake• Some vehicles already use EPB that can

be activated when vehicle stops and goes off as soon as gas pedal pressed




Figure 103-37 An electric parking brake button on the center console of a Jaguar.

Halderman ch103 lecture

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