about parking brake cable

8/10/2019 About Parking Brake Cable

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h apt r 18

Parking Bra kes

After studyi ng th is chapter, you wi II be able to:o Explain the function of the parking brake.o Identify the components and e xplain the operation of driver applied parking brake levers.o Describe the construction and explain the operation of automatic parking brake release

mechanisms.o Identify the components and operation of parking brake warning lights.o Identify the components of parking brake linkage.o Explain the operation of parking br a ke levers and linkage.o Describe the construction and operation of drum brake parking brakes.o Describe the construction and operation of disc brake parking brakes .

Im por ta nt Term s

Pad


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3 4

his chapter is desi gned to explain the purpose ,design, and operation of parking brakes, sometimes calledemergency brak es. The parking brake is ohen ignoredsince most drivers u se th e parking pawl in the automatictransmission to hold the ve hicle. So me te c hnici lns alsooverlook the parking brake during routine brake service,since it is seldom the source of customer complaints. Thisc h a pter co ver s the d es ign and operation of both drum anddis c parking br akes. It also covers th e use o f manual


3/16

3 hapter 8 Parking Brakes

the parking brakes a re applied. Additional applic ations ofthe ped a l increase the tension on the parking brake cable.By allowing more than one pedal application, this parkingbrake design can compensate for play in the cables and connectin g linkage caused by lining we a r This is impo/tantwhen re ar disc brakes are used, since pad wear can greatlyinc rease th e amount of distance required to apply thebrakes. See Figure 18-2.

Foot Brake Vacuum ReleaseSome foot brakes are relea sed by an automatic vac uum

relea se. The vacuum release is a lway s used on vehicleswith au tomatic transmissions. This release consists of asmall diaphragm assembly attached to the brake releaselever . The chamber can be called a vacuum canister orvacuum motor. Inside, a flexible rubb er diaphragm dividesthe chamber into two sections. One side is attached to arod and return spring, and the other side is sea led, exceptfor a vacuum port. The vacuum port is connected toe ng ine vac uum by hoses and a co ntrol va lve. Some vehicles use a sepa rate pump to create the vacuum.

The vacuum control valve is attached to the shiftse lector. When the shift lever is in the park position , novacuum ca n reach the vacuum chamber. The return springkeeps the rod in the applied po sitio n. When the shift leveris moved to put the transmission into any other gear position , the control valve is moved by the shifter. The valveallows vacuum to reach the canister, which draws thediaphra gm in, moving the rod and compressing the returnspring. This releases the parking brake.

Most a utomatic vacuum re le ases have an emergency manual release lever. If vacuum fails to reach thechamber , the brake may still be relea sed by pulling the

manu a l release le ver

On some vehicles, a small handoperated vacuum pump is in sta lled next to the vacuumchamber. Operating this pump creates enough vacuumto release the brake when the shift lever is moved. Onetype of vacuum operated brake assembly is Illustrated inFigure 18 3.

Hand Operated Parking BrakeTh e two major types of ha nd-operated parking brake

lev ers differ only in where they are loc ated . The dashboardoperated pu sh-pull hand brake lever is used on older ca rsand so me current imported trucks. The floor-mountedhand lev e r is common on vehicles with bucket seats. Ea c htype is shown in Figure 18-4.

Push Pull Hand BrakeThe push pull hand brake is a metal rod which

travels in s ide a support tube. The push-pull brake leveris loc ated directly under the dashboard near the steeringwheel. One side of the rod is flat, and contains a seriesof teeth. The rod is attached to a T-handle. When theT-handl e is pulled outward , the end of the rod pulls onthe cable, engaging the p a rking brakes. A pawl assemblylo ca ted near the end of the suppo rt tube engages th e

\ \ Multi-strokeL_J

cableFoot

pedal

Figure 18-2. A multi-stroke foot operated parking brake unit.Pontiac)

Vacuum sourceFirewall connection

Vacuum chamber~ I ~ - r ~

rf I ~

/': Ratchet ~ I teethNut

Manual releaselever Brake

pedal

Figure 18-3. A vacuum released parking brake unit. Note themanual release lever which s used to release the brake n theevent of a vacuum or vacuum operated p rt failureDaimlerChrysler)

teeth on the rod, holding it in the applied position. Onm ost modern vehicles, a warn ing light will be illuminatedwhen the parking brake is applied and the ignitionswitch is in the on position .


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316 uto Brakes

Lever Padded handle Push button relea se Cables Fully covered

Rubber coated No joints

A

Parkingbrake

- Push-pull parkingbrake control handle

Proportioningvalve

Power brakeunit

Figure 18 4. A A floor mounted hand brake lever nd cable assembly . B A dashboard , hand operated , push-pull hand brakeassembly with related parts . DaimlerChrysler , Toyota)

To rele as e th e par kin g br a ke th e T-ha ndl e is turn e d to T-ha ndl e ba c k in re leas in g th e p a rkin g brak e. O n so m eth e left o r rig ht. Thi s twist s th e ro d t ee th awa y fro m th e pu sh pull le ve rs th e p a wl is dis e n gage d b y pu shi n g ap a wl di se n gag in g th e m. Th e driver ca n then pu sh th e butt on lo cat ed on th e T-h a ndl e. See Figure 18 5.


5/16

31hapter 18 Parking Brakes

Support tube

A

Button

2Turn

PressB cFigure 18 5. A T-handle push-pull hand brake . A T handlebeing pulled to set parking brakes. he pawl is engaging the rodteeth. o disengage the pawl from the rod teeth, pull out

ward slightly, turn the T-handle , and push in . C S o m e T-handies use a push button to disengage the pawl and teeth.Hyundai, Toyota)

Floor Mounted Lever

The operation of the floor-mounted lev er is simi lar tothe foot-operated parking brake. The hand l ever is a hol-low steel tube or flat steel covered b y a plastic sleeveand /or leather boot attached to the floorboard throu gh asupport plate. The support plate contai ns teeth wh ic hengage a pawl in the bottom of the l eve r asse mbly . A

sp rin g-loaded push rod inside the tube connects the pawlwith a pu sh button at the top of the lever. See Figure 18 6.

When the lev e r is pulled up, it pivots on the supportplate, tightening the brake cable and applying the parkingbrake. s th e lever mo v es up, the pawl will slide over theteeth on th e s upport bracket. The pawl holds the lever inplace when it is applied. The red Brake warning light iilluminated when the ignition switch is on and the parkingbr ake is applied.

To re lease the brake , the driver pulls up slightly on theleve r a nd depresses the push button. Depressing the pushbutton relea ses the pawl from the support bracket teethThe driver ca n then push the lever downward removingca ble tension and relea s ing the parking brake. A few floormounted brake levers have an automatic adjustmentdevice. Thi s devi ce will take up any slack in the parkingbrake ca bles when the lever is operated.

Parking rake Warning lightA parking br a ke warning lig ht is u se d on almost all

m ode rn vehicles to inform the driver when the parkingbrake i s applied. Some sys tem s also have a buzzer thatworks in conjunction with the warning light. The audibleton e alerts the driver in case he or she fails to notice thewarning lig ht or if the lightbulb burn s out.

The parking brake warning light is the red Brake warning light on th e instrum e nt panel, Figure 18-7. The switch iinsta lle d o n th e parkin g brake support bracket in a positionwhere it ca n co nta ct the movable parking brake linkage.Switch operation is the same for hand and foot parkingbrak es . Switch operation and other electrical fundamentalswill be discussed in mor e detail in Chapter 20.

Push Hand leverbutton Support plate

j Bolt Control Parking brakePawl 'od

Teelh~

1 >i ~~ ~ . : : : : : ;

Floor~ .

bracket /

Boot / ~ ~ ~ ~ l l > = ' = ~ ~ = : = S'

utlEqualizer Boot

r..1{

' ~ t /c a b l / ,

/

/ / . 1

/ /

Cable adjuster

Figure 18 6. A floor mounted , hand operated, lever assembly Toyota)


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__ __

318 Auto Brakes

Brake warning light

Figure 18-7. A brake warning light nd its location on theinstrument cluster. Toyota)

Most wa rnin g light switches have a single positiveterminal. Batt e ry vo ltage is av a ilabl e at th e terminal whenever the ignition switch is on. The ci rcuit supplying thisvoltage is wired through th e ignition swit c h, a fuse , a nd thewarning lightbulb , Figure 18-8.

0.50 BLK

3 ~ ~ ; ~ F ~ B ~ ~

When the p arking brake is actu a ted, some part of thelinkage will co ntact the switch , depressing th e plunger.Depressin g the plunger cau se s co nta cts on the swi tc h tocl ose . This co mpletes the ci r cu it by grounding th e positive terminal to th e switch body. The switch body isground ed to the batter y negative terminal throu gh thesupport br ac ket and frame. Current flows through theign ition switch , fu se, and red Brake warning lamp bulb ,causing it to illumin ate . A parking brak e as sem bly showing one type of sw itch a nd its lo ca tion is illu strated inFigure 18-9.

P a r king B rake pp y LinkageThe following sections cover th e c on st ruction and

operation of the linkage w hich co nn ec t the driver operatedparking brake lever w ith the w hee l brakes. Thi s linkage co ns ists of cables, rod s, and le ve rs. Th ese an d other relat ed part sa re cove red in this sec tio n .

nC2

~ I K - - : = : ~ N ~ - l~ ~ ~ O N- I . O.\I.IP DET ilS DISTRIBUT ION I

L_ ____ ___~ ~ ~ _ _ __ ~ ~ ~___j0.50 BLK

11 i l s - G2030.508LK

0.50 BRNi, WHT S206 BLKIWHT SEeFUSE BLOCKBLK DETAILSCEll 11, 0.50 BlK!

0.50 BLKlWHT7 i;,2 - : = _ 2 - : : : = _ 2 : : : : _ 2 - : ~4r - - 1 NSTRUMENTI SEE INSTRU olENT I PANELI PANEL :IVITH . ' BRAKE' I -

I g ~ ~ : SCLUSTER:l_______________INDICATOR Iww-:_____J

5 CANADA.4 USA

0.50 REDIBLKr -C ~ ~ I- - - - 0.50 RED/BLK- 5 ~ ~.50 RED/BLK , S232. =: - - 0.50 RED/BLK- - - - - ~USA

2BRAKEFLUID

CANADA

LEVELSWITCHCLOSEDWrrHLOWBRAKE v

0.50 RED/BLK11 FLUIDLEViL0.50 BLK n u BlK

O50PPUGRN ,SEE GROUND 0.50 BLKI 10 4 DISTRIBUTION BLK SEE GROUND

r---PowER-z------F----l DArnMEELL14 .


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3 9

Push

Front brake

Support

Equalizer

Rear brakecables

Chapter 8 Parking Brakes

Parking rake CablesParking brake cables are usually made from strand

ed steel wire. Cable thickness is usually around 3 / 164.76 mm) . Because cable is flexible , it can be bent

around corners and through openings under the vehiclebody. Figure 18-10 shows a typical parking brake cablesetup. Most vehicles have at least three cables, one from

Wire to dash Pawl Switchwarning light engagement electrical

teeth connector

Supportbracket

Release lever

Mountingbolt

Light switchassembly

lever sheath

Figure 18-9. A foot operated brake showing the brake warninglight switch nd its location. DaimlerChrysler)

Cable

cable assembly Clamp bolts

the apply lever to the equalizer, and two from the equalizer to the wheel brakes.

Some cables are coated in plastic to allow them to movemore easily If one of the cable wires breaks , the plastic coating keeps it in place , so it is not likely to jam the cable.

Cable FittingsFormed c ble fittings are pressed on or bolted to the

ends of the cables. A common fitting is a round ball, cylinder, or flat end, which installs into a slot in a bracket orlever, Figure 18-11. These fittings allow the cable to beattached to the parking brake apply lever and other leversand components.

J ) Cable

Parking brakecable retaining

bracket1 = = = = : 1 I V

Figure 18-11. A cylinder-type cable fitting that has beenswage d on pressed) under pressure. This part icular one iused to connect the cable to the equalizer. DaimlerChrysler)

Rotor

Figure 18-10. A floor-mounted h nd lever nd cable assembly used with rear disc brakes. Note that three separate cables are used.Mazda)


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32

able Sheaths

Parking brake cables are furnished as complete units .For much of its length, the cable s enclosed in a cablesheath. These sh e aths, sometimes called conduits aremade of steel wire wrapped tightly together. The she a thguides and protects th e cable . om e sheaths are co veredwith rubber to help prevent the entry of dirt and water. Thesheath is flexible , aI/owing the cable to move inside . A typical cable sheath is shown in Figure 18-12.

Parking brake

oa

Sheath Cable

Equalizer

Sheath

Left rearbrake

Figure 18-12. Brake cable sheaths as used on one parkingbrake assembly Bendix)

Note: The entire cable assembly is simplyreferred to as a cable.

uto Brakes

Cable PulleysSometimes cable pulleys Figure 18-13 ar e used to

carry the cable around sharp bends. The pulleys are oftenused at the apply lever to reduce wear on the cable. Pulleysar e sometimes used und e r th e vehicle. ca sionally a pieceof solid conduit is bent into position and used to carry thecable around a sharp point.

Linkage RodsOn a few vehicles, linkage rods are used as part of the

parking brake linkage. The entire linkage system or just aportion can make use of rods. One brake system utilizinga c ontrol rod is shown in Figure 18-14.

Brake MultiplierThe parking brake lever is designed so that driver

forc e is ali that i s needed to apply the wheel brakes. In

Controlrod

To rea'brakes

Equalizer-.,

To hand or foot

generated parkingbrake lever

Figure 18-14. A brake cable apply system that incorporates acontrol rod. FMC)

30 29 28 27 26 25 24 23

13 14

22 21 20

Figure 18-13. A hand operated parking brake which uses a cable pulley assembly (6) on the equalizer. The pulley provides smootheroperation, longer cable wear etc. 1-lnside support attachment. 2-Rubber cover. 3-Lever . 4-Shaft . 5-Pul l rod . 6-Pulley7-Cable . 8-Rubbercover. 9-Front attachment. 10-Cable sleeve. 11-Attachment. 12-Brake drum. 13-Secondary brake shoe.14-Return spring. 15-Star wheel. 16-Lever. 17-Movable rod. 18-Anchor bolt . 19-Return spring. 20-Rear attachment.21-Rubber cable guide. 22-Pawl. 23-Ratchet segment. 24-Rivet. 25-0utside support attachment . 26-Warning valve switch.27-Push rod 28-Parking brake. 29-Spring. 3D-Pushbutton. Chevrolet)


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brake assembly

Pivotpoint

Chapter 8 Parking Brakes 32

some applications, however more lev e rage is needed. Thebrake multiplier (also called an intermediate lev e r isincorporated into some parking brak e systems to increasecable pull leverage. The multiplier creates extra mechani-cal advantage by careful placement of the input, output,and pivot points. This creates more leverage , but at theexpense of distance traveled. If the brakes are properlyadjusted, this decrease in distance will not be a factor. Abrak e multipli e r is illustrated in Figure 18 15.

To foot or hand operated Intermediate Returncable spring

Figure 18 15. The brake multiplier as used on one parkingbrake control setup. The multiplier acts somewhat like pry barfulcrum). The longer the leverage, the more pulling force it will

generate. The equalizer takes up slack in the cables.General Motors)

Brake EqualizerA brake equ lizer is in stalled in the parking brake sys-

tem to provide a balanced, or equal pull on the btakelevers. The equalizer does this by allowing th e applicationcable to center itself. The equalizer is a steel bar withattachments for the brake cables or rods. The input is fromthe application cable or control rod. There are one or twooutput cables. Note that the cable adjuster is usuallyinstalled at the equa I zer , Figure 18 15.

In operation , the input cable pulls on the equalizer,which then pulls the wheel brake cables. If one cabletightens the wheel brake before the other, the equalizerwill pivot on that cable, Figure 18 16. This allows thecable on the other side to continue to move until the ten-sion on that wheel brake matche s the tension on the firstwheel.

Support Brackets Guides nd Heat ShieldsThe parking brake cables and other parts must b e

secured and protected . As mentioned earlier, many cablesare routed through rigid or flexible conduit and some arecovered with rubber. The cables, control rods, multiplier,and equalizer are attached to the vehicle body by variousbrack e ts and clips. To protect the parking brake compo-nents from road splash and exhaust heat, shields are ofteninstalled. Some typical brackets, gUide , supports, and heatshields are depicted in Figure 18 17.

Input cable

Thiscable

/

Equalizerloose pivots on

tightercable

A

Input cable

qual iZer\pivots on

tightercable

B

Figure 18 16. Brake cable equalizer operation . A-Lef t cable isloose, equali zer pivots travels) to the right to take up the slack.B-Right cable is loose, equalizer travels to the left to take upthe slack.

Linkage Adjusting DevicesAs the brake linings a nd linkage parts wear, it is some-times necessary to adjust the parking brake to ensure thait operates. Many times , the adjustment is made at thewheel brak es. This is common on drum brake systems.Som e disc brake designs are self adjusting. However, manyparking brake systems have linkage adjustment devicesMost of these are located on the equalizer and consist ofthreaded rod held in position by locknuts. Other vehiclesmay have tumbuckles or adjustable levers.

Two adjusters are shown in Figure 18 18. Most othem a re operated by loosening the holding fasteners andtightening the adjuster device to remove any slack in the

cable.

Par ki ng Brake Types

Previous section s discuss e d the I nkage that trans-ferred the driver s hand or foot application to the wheels.This section covers the parking brake components installedat the wheels. The wheel parking brakes operate by usingmechan cal I nkage to apply brak e fricti on I nings. Thebrake linings normally operated by the brake hydraulic

Thiscable


10/16

322 Auto Brakes

Mounting stud ever Heatlocknut assembly . shield

. / - \ Parking brakeW warning light switch

Mounting

, bolt

~ : ~ / Release cable andI handle assembly

." "

,

(;.

Bracket

spring

Front parkingbrake cable Equalizer

bracketEqualizer

Bracket

Left rearcable

Figure 18-17. A foot operated parking brake system illustrating the support brackets, guide clamps, nd a heat shield. OaimlerChrysler)

Clip Right rearcable

system are called the service brakes Most parking brakemechani sms apply th e service brakes me c hanically . Afew parking brakes operate separ a te friction linings thata re not connected to the hydrauli c system. Modern vehi-cles are equipped with three main types of parkingbrake s:

o Integral drum parking brake which applies the brakeshoes on a rear dl'um brake system.

o Self- co ntained drum parking brake us ed with somerear disc brakes.

o Integral disc parking brake which applies the brakepads on a rear disc brake system.Use of the se parking brakes dep e nds on the type of

servi ce brake used on the wh ee l. Most parking brak es areinstalled on the I'ear wheels. A few vehicles have the parking brake installed on the front wheels.

Note: A few very old cars and large trucksuse a parking brake mounted on the rearof the transmission. This type is known as

a driveshaft parking brake, and is generally used onheavy duty trucks.

Integral Drum Parking BrakeThe integral drum parking brake is part of the vehi

cle's drum brake assembly. It applies the same brake shoesused by the hydrauli c sys tem. The parking brake cabl esheath is so lidly attached to the backing plate. Most areattached by a retaining prong. The retaining prong is a setof metal fingers, Figure 18-19, which can be pressedthrough the backing plate. After the fingers enter the backing plate opening , they expand and cannot be removed .Other cables are held by clamps, clips, etc.

Inside the drum , the cable is attached to the lowere nd of the parking brake apply lever The leve r is attached

to the web o f the secondary shoe. The secondary and pri-mary shoes are linked through th e parking brake leverstrut The apply lever pivots on the lever strut.

Operation Servo Drum BrakesWhen the parkin g brake is applied on servo drum

brakes, the cab le pulls on the lo w e r end of th e parkin gbrake lever. The lever mov es forward a nd pushe s the leverstrut, which m oves the secondary shoe into contact w iththe drum. The secondary shoe contacts the drum , and alsodirects apply pressure through the star wh ee l assembly to


11/16

32hapter 18 Parking Brakes

A

B

Parking brake leverCheck for smooth

operation

Wiringswitch

connector

Bracketbolts

Bracket

Bracket

t ~

Front cableassembly

Cableclamp

Parking brake cableCheck for faulty

movement

Tensionspring -

Equalizer

Adjusterlocknut

Clamp ,/ \

L - - , Cablefitting

Clamp bolt

Rear cableassembly (R.H .)

Rear cableassembly (L.H.)

Adjuster

c a b l e

Cable

,Clamp o l t ~

- - - - B O l t

Boot

A d j n g \ Equalizer nut

igure 18-18. wo parking brake systems using different methods of linkage adjustment. A Adjuster and locknut used on one side.B When both cables are attached to the equalizer, correct adjustment can be obtained by turning the adjusting nut . Honda, Nissan)

the primary shoe . After the lever strut has applied the secondary shoe , it cannot move any more . The parking brake

lever then pivots on the lever strut and applies additionalpressure to the primary shoe. This action is shown inFigure 18-20.

When the parking brake is released by the driver, thelever returns to its released position and the brake shoereturn springs release the shoes.

Operation Non Servo rum rakes

Pal king brake operation on a non-servo brake drumis similar to that on a servo brake. However, the action of Figure 18-19. Parking brake cable assembly held in the backingthe lever strut is taken by the ad juster assembly. Si nce the plate with a retaining prong unit. Chevrolet)

Parkingbrake cable

Parking brakecable


12/16

3 4 uto Brakes

Brake shoereturn spring

Secondarybrake shoe

Lever strut

Parkingbrake cable

Star wheel

Brake shoeretu rn spring

Primarybrake shoe

Figure 18 20. Operation o one particular servo brake parking brake assembly. There are number o different servo brakestyles , OaimlerChrysler)

bottom a n c h o r is fixed no pressure is transferredbetween the primary and seconda ry shoes. The brakelever pivoting ac tion throu gh the adjuster assemblyappl ies both shoes. Figure 18 21 shows the parkin g brakeoperation on a typi ca l non-servo drum brake.

Self C ont aine d Drum Parking Brake

Self contained drum parking brakes are us ed onsome vehicles with rear disc brak es The parking brakeassembly consists of two shoes and a brake drum. Theshoes are smaller than co nventional brakes since they actonly as parking brakes. Th e d um is an integral part of therotor ass emb ly

A ba ckin g plate is fasten ed to the axle hou sing as aplace for brake sho e attachment a nd a splash shield. Afixed anchor or star whe e l is install ed at the bottom of thebacking plate. The shoes a re attached to the backing plateand anchor with conventiona I hold-down and retractor

Primary shoe

Parkingbrake

Secondaryshoe

~ ~ ~ ~~ ~ ~ ~ ~N I I - - \ - - TAdjusterrod end

Backingplate

Figure 18 21. Operation o one type o non-servo parkingbrake assembly. This assembly uses a fixed anchor at the bottom o the backing plate. This prevents transfer o pressurebetween the primary and secondary brake shoes. Delco)


13/16

325hapter 18 Parking rakes

sprin gs. Brak e s hoe operation i s s imil a r to the op e ration ofco nventi o na l drum brak es . Th e re is a lev e r and strut ,whi c h m ov es th e tops o f th e s ho es into co nt ac t with thedrum , Figure 18 22. Ho we ver , there i s no hydrauli c wh eelc y linder o r aut o mati c adju ste r

Pullin g on the br a ke c a ble c auses the lev e r to m ove ,fo rcin g th e s hoe s a part. This pres ses th e s hoes into thedrum . When the ca ble t e nsi o n is re le as e d th e returnsprin gs dr aw th e s hoes away from th e drum , re le asin g thebrak es . This ac tion i s shown in Figure 18 23.

Integral Disc Parking BrakeTh e use o f re ar di sc br a kes is incr eas ing . On ve hicl es

with no dr um br a kes there must b e a m e thod o f usin g thedi sc br a ke s a s parkin g br a ke s. Sev er a l meth o ds ar e used toappl y di sc br a ke s with me c ha n ic a l link age. Th e y includ escr e w, ball- a nd -ra mp, a nd ca m t ypes .

Note : A few older cars and large trucks use

a lever parking brake which clampsan

extra set of pads to the rotor. This type ofparking brake is independent of the hydraulic discbrake caliper.

crew Disc Parking rakeTh e screw disc parking brake is the m o st co mm o n

typ e o f ca liper p a rkin g bra ke actu a tor. ll part s exc ept f o rthe JPply l ev er a re loca ted insid e the ca lip e r hou s ing.

Backingplate

Wheelhub

Parkingbrake cable

Shoes trut

Parkingbrake le ver

i n ~Front s hoe

Star wheel adjUster. /

TenSion s Pring /

Actuating levereccentric cam

Shoe returnspring Backing

plate

Shoe returns pring

Figure 18 23. A self-contained drum parking brake assembly

he actuating lever turns the eccentric cam which moves theshoes into drum contact . Parker)

H yd ra ulic sys tem o per a tio n i s s imil a r to th at of a con ve ntional floa tin g c alip e r di sc brak e.

In th e simple st versi o n of thi s d e s ign , the pi stonJs sembl y co ntain s a nut and co ne a ssembly. Th e nut ith re ad e d int o a lev e r o pe ra ted ac tuator scr ew. Th e le ve r ibolted t o the a c tuator sc rew and h as a return spring. Th e

Rear

Jalipershoe

Shoe return bolt

,p og '

1/Rear disc br a ke

assembly

CfI , ~ P U

Shoe hold-down cup Rotor withShoe hold-down spring integral drum

Figure 18 22. An exploded view of a self-contained drum parking brake setup . he parking brake lever nd strut moves the shoeinto drum contact. Lexus)


14/16

3 6 Auto rakes

act uator screw a nd lever ca n rotate but cannot slide in orout. Th e nut is sp lined to the cone a llow i ng it to slideinside th e con e and piston This allows the cone and piston to move independently of the nut wh e n the piston isapplied with hydraulic pressure. This allow s the screw toremain stationary when the service brakes are app lied.

When the lever i s ro ta ted by the cable the screwturns. Since the screw is fixed in place and cannot travelin or out turnin g it move s the nut outw ard. Movement ofthe nut forces th e co ne and piston outward. The pistonpresses the brake pads against the rotor app lying theparki ng brake.

When the parkin g brake is released th e returnspring pulls the lever back to its relea sed position. Theactuator screw will then draw the nut back allowin g thepiston seal and boot to retract the piston slightly releasing the brakes. A cu taway of th e brakes being applied isshown in Figure 18 24. The screw type brake adjustsitself automatically each time it is app lied if any padwear has taken place.

Piston Cone Caliper Thrustseal seal Piston washer

Outboard ball

Lever seal

Levernut

Lever

Brakerotor Retainer

Check Boot Actuatingvalve screw

Figure 18-24. A cutaway view o a screw type disc parkingbrake assembly showing the brakes being applied. The actuating screw forces the piston pads in contact with the rotor Thecaliper is a sliding type, which applies the outboard brake padto the rotor EIS)

Ball and Ramp Disc Parking BrakeThe ball and ramp disc parking brake is located inside

the caliper housing. Ball-and-ramp brake units a re alwaysused with Single piston sliding brake calipers. The balland-ramp assembly consists of three steel balls between anoperating shaft and a thrust screw Figure 18-25. The operating shaft is attached to the apply lev er and has threeslots which hold the steel balls in position. The operating shaft and lever can turn but cannot move in or out.The thrust screw has ramps or tapered areas where itcontacts the balls.

Operatingshaft

Operatinglever

A

B

Steelball

Releasedposition

Thrustscrew

Appliedposition

Caliperpiston

Caliper

Figure 18-25. A A cross-sectional view showing an assembled bal/-and-ramp unit B-Bal/-and-ramp assembly in thereleased and the applied positions. Bendix)

When the parkin g brake is applied the cable rotatesthe lever and operating shaft. The three steel balls turn withthe operat ing shaft and ride up on th e thrust screw ramps.This increases th e space between them forcing th e thrustscrew away from the operatin g s haft. Since the operatingshaft cannot move in or out the effect of this increase inspace is to move the thrust screw outward. When the thrustscrew is attac hed to the piston outward movement of th ethrust screw moves the piston outward forcing the padsagainst the rotor.

When the parking brake is released the balls rollback to their lowest point allowing the seal to retract thepiston. If pad wear has caused excess ive play in the applyunit the threaded shaft on the thrust screw turns slightlyduring release to maintain minimum c learance .

Cam Disc Parking BrakeTh e cam disc parking brake is used on some Asian

built vehicles. It consists of a lever operated cam sometimescalled an eccentric, which pushes on a pin or actuatorrod. The actuator rod is attached to the caliper piston.Figure 18-26 shows a typical cam type parkin g brake.

When the parking brake is applied the lever rotatesturning the cam. s the cam rotates t o its high point itmoves the actuator rod outward . s the rod moves outward it pushes the piston outward causing the pads tocontact the rotor.


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Piston Adjustingseal spring Adjusting

boltPin

Camboot

Cam

Caliperbody

Piston Caliper Piston sleeveboot piston

Chapter 18 Parking Brakes

igure 18 26. A cutaway view of a cam disc parking brake. sthe cam rotates brakes being applied), the pin will push on thepiston sleeve, adjusting bolt , and caliper piston. This actionforces the caliper piston outward, thus applying the brakes bypinching the rotor between the pads not shown). Honda)

When the parking brake is rel e ased , the cam moves to

its lo w es t position, and the pi ston se al moves the pistonand actuator rod inward. To adjust for pad wear, the camis tapered so as it turns, the actuator rod moves outward. Ifclearance is at the minimum , the cam turns the rod in theopposite dir e ction when the brake is released. If there isexcessive play in the apply unit, the cam los es contact withthe apply rod and the thread e d shaft does not turn back.Thi s maintains minimum clearance.

u mary

The parking brak e is used to keep the vehicle frommoving while it is not bein g used. It can also be us ed as abackup br ake sy stem in an emergency. Th e brake linkag econsists of a series of cables, rods , and leve rs. A hand orfoot lever is used to move the linkag e and apply th e parking brake.

Foot brakes are held in the applied position by aratchet mechanism. Some foot brakes used with discbrakes require several applications to apply th e parkin gbrake. Most foot brakes are released by hand, but a few areautomatically rel eas ed by a vacuum operated diaphragmand control system. Hand br ak es can be the common floorlev er, used on bucket seat vehicles, or the push-pull typewith a T-handle mounted under the dashboard. A warninglight illuminates when the ignition is on, tellin g the driverthe pa rking brake is a pplied.

Bra ke cables are mad e of stranded steel with fittings oneach end for attachment to other parking brake components. Cables are partially or completely installed insid e ofa cab le she a th to protec t th e m from road splash and damage. A parking brake multiplier is us ed on some parkingbrake linkages to increas e brake pedal force. The equalizeris used to provide a balanced pull betwe e n the brake cablesat each wheel. These parts are held and protect e d by

support brackets and guides. Some parking brake linkageare protected from the exhaust system and road splash bheat and splash shields.

The integral drum parking brake is part of the servicdrum brake system. It applies the service brakes through aapply lever installed inside the drum. A lever strut helps ttransmit braking force between the primary and secondaryshoes. The brake linkage can be adjusted to compensate

for wear.One type of parking brake used with rear disc brakeis the self-contained drum brake, which is mechanicallyopel'ated and has no connection with the brake hydraulisystem. Most rear disc systems have an integral parkinbrake which mechanically applies the brake pads. Ththree main kinds of integral disc parking brakes are thscrew type , ball-and-ramp type, and cam type. All rely othe movement of a lever that is converted into pressure onthe disc brake pads.

Review Questions Chapter 18

Please do not write in this te xt. Write your answers ona separate sheet of paper.

1. What is the primary purpose of the parking brake?

2. What is another us e of the parking brake?

3. Th e des ign of the parking brake lever increa seme c hanical

4. A multi-stroke foot parking brake is usually usedwhen the rear brakes ar e brak es .

5. Automatic foot brake rel eases are operated by engine

6. The floor mounted hand lever i s used on vehicleswith

7. What are parking brake cables usually made from?

8. A parking brake multiplier increases parking brake_ _ _ at the exp e ns e of _ _ _ .

9. The equalizer ensures th at the same amount of forceis applied to each _ _ _ brake.

10. Match the brake with its description.

_ _ Integral drum (A) Applies th e serviceparking brake disc brakes.

Self-contained (8) Applies separatedrum brakes.drum parking brake

(C) Applies a dri ve sha nt eg ra l discbrake.parking brake

(0) Applies the servicedrum brakes .

11. On a drum type parking brake , the parking brakecable is attached to the _ brake shoe throu ghlev er.


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uto rakes

12. The most common type of disc brake parking brak e isthe ype.

13. Moving the cable causes the screw to turn, movingthe _ forward. This causes the brake pads topress against the rotor, setting the brake.

14. The cam type disc parking brake is found on _vehicles.

15. The ca m , sometimes called an eccentric, pu shes onan attached to the hydraulic piston .

1. Technician A says that the foot brake is held in theapplied position by a ratchet. Technician B says thatthe vacuum release brake will release the brake whenvacuum is removed. Who is right?

(A) A only.

(B) B o nly.(C) Both A & B.(0) Neither A nor B.

2. Th e multi-stroke parking brake is usually u sed withvehicles h av ing _

(A) rear di sc brakes

(B) re a r drum brak es

(C) front di sc brakes

(0) manual transmissions

3. Techni c ian A says that most hand operated parkingbrake levers are dash mounted. Technician B says thatth e br a ke warning lights are illuminated only whenth e ignition is on with the parking brake applied. Whois right ?

(A) A only.

(8) B only.(C) Both A & B.(0 ) Neither A nor B.

4. All of th e following statements about parking brakecables are true , EXCEPT:

(A) brake cables have fittings on their ends.

(B) brake cables are made to be very rigid.(C) brake cables a re often enclosed.

(0) many vehicles have three brake cables.

5. The multiplier is a kind of .

(A) adjuster(8) strain rel ief device

(C) lever

(0) pulley

6. Technician A says that the integral drum parkingbrake operates the service br a ke s. Te c hnici a n 8 says

that the integral drum parkin g brake operates a se parate set of brake shoes. Who is right?

(A) A only.

(B) B only.

(C) Both A & B.(0 ) Neither A nor B.

7. The parking brake s attached to the seco ndaryshoe.

(A) apply lever(B) equalizer

(C) cable

(0) sheath8. When a drum parking brake is applied, the brake

transfers parking brake forc e between theshoe s.

(A) multiplier

(B) apply le ve r(C) front cable

(0) lever strut

9. All of the following disc parking brake mechanismsa re located inside the caliper, EXCEPT:

(A) ball-and-ramp.

(B) screw.(C) lever.

(0) cam.

10. Technician A says that a screw type di sc p a rking br akeadjusts itself a utomatically each time it is applied.Technician B says that a ball-and-ramp disc parkingbr a ke ad ju sts itse lf automatically each time it i sap plied. Who is right ?

(A) A only .

(B) B only.

(C) Both A & B.

(0) Ne ither A nor B.

about parking brake cable

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