Hydro-Max™ Hydraulic Brake Booster and Master Cylinder HydroMax Booster... · Hydro-Max™ Hydraulic Brake Booster and Master Cylinder Technical Manual

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  • Hydro-Max Hydraulic Brake Boosterand Master Cylinder

    Technical Manual

  • Hydro-Max Technical Manual2

    Important Service NotesThe information in this publication was current at the time of printing. Theinformation presented in this publication is subject to change without notice orliability.

    The information contained in this publication is intended for use by properly trainedand equipped professional technicians. It is NOT for the "Do It Yourselfer".

    Failure to follow safety and repair procedures can result in personal injury, ordamage to vehicles, components and equipment.

    Correspondence concerning this manual should be addressed to:

    Robert Bosch CorporationATTN: Hydraulic Actuation & Truck Brake Engineering401 North Bendix DriveSouth Bend, Indiana 46628

    Fax: 574-237-2210

    August2003

  • Hydro-Max Technical Manual3

    PrintedintheUnitedStatesofAmerica2002RobertBoschCorp.Allrightsreserved.

    Table of Contents

    GeneralDescription.............................................................................................................................

    Hydro-MaxTMBooster................................................................................................

    MasterCylinder.........................................................................................................

    PrincipleofOperation........................................................................................................................

    Hydro-MaxTMBooster................................................................................................

    MasterCylinder.........................................................................................................

    ElectricalOperatingSystem......................................................................................

    BasicOperationofBoosterandMasterCylinder......................................................

    ElectronicMonitorModule........................................................................................

    ApplicationInformation......................................................................................................................

    HydraulicFluids........................................................................................................

    BrakeFluidTubing,HosesandFittings....................................................................

    BoosterFluidTubing,HosesandFittings.................................................................

    BoosterFluidSource..................................................................................................

    InstallationRecommendations...................................................................................

    PedalReturnSprings.................................................................................................

    PedalStopandProperSpringLoad..........................................................................

    TroubleShooting..................................................................................................................................

    1

    1

    3

    3

    5

    7

    8

    9

    13

    13

    13

    14

    15

    16

    17

    18

    19

    1

  • Hydro-Max Technical Manual4

    Figure 1 Hydro-MaxTM Booster and Master Cylinder Assembly

    TheHydro-MaxTMisahydraulicallypoweredbrakeboosterwhichprovidespowerassistforapplyinghydraulicbrakes.Aboostercombinedwithamastercylinder(refertoFigure1)formsthehydraulicbrakeactuationunit.AtypicalassemblyisshowninFigure1.Theboosterreducesthepedaleffortrequiredtoapplythebrakesascomparedtoanon-powersystem.

    General Description

    Hydro-MaxTM BoosterThehydraulicboosteriscomprisedofanopencentervalveandreactionfeedbackmechanism,apowerpiston,a12and24-voltbackuppumpandanintegralflowswitch.Itispoweredbyeitherthepowersteeringpumporotherhydraulicsource.Thebackuppumpprovidesasecondarypowersourceforthehydraulicboosterandiscontrolledbytheintegralflowswitch.

    Master CylinderThemastercylinderisasplitsystemtypewithseparatefluidchambers,pistonsandoutletportsforthefrontandrearbrakecircuits.Adifferentialpressureswitch,fluidlevelindicatorswitch,andremotereservoirarealsoavailable.

    AtypicalHydro-MaxTMboosterandmastercylinderassemblyinstallationinahydraulicbrakingsystemisshowninFigure2.

    1

    FLUID LEVEL INDICATOR SWITCHDIFFERENTIAL PRESSURE SWITCH

    SECONDARY OUTLET PORT

    RELAYBACKUP PUMP

    MOUNTING FLANGE

    OUTLET PORT

    INLET PORT

    FLOW SWITCHBRAKE FLUID RESERVOIR

    MASTER CYLINDER

    PEDAL ROD

    PRIMARY OUTLET PORT

    HYDRO-MAXTM BOOSTER

  • Hydro-Max Technical Manual5

    Figu

    re 2

    T

    ypic

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    r Cyl

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    YSTE

    M

  • Hydro-Max Technical Manual6

    Principle of Operation

    Hydro-MaxTM BoosterDuringnormalsystemoperation,(refertoFigure4)fluidflowfromahydraulicpowersource(usuallythepowersteeringpump)enterstheinletportoftheHydro-MaxTMbooster,flowsthroughthepowerpiston,aroundthethrottlevalveandthroughtheflowswitch,exitingthroughtheoutletport.

    Forceappliedtothebrakepedalbythevehicleoperatorismultipliedbytheleverratioofthepedalmechanismtomovethepedalrodofthebooster.Thismovementclosesthethrottlevalve,whichrestrictsflow.Thisrestrictionofflow,whichresultsinapressureincreaseactingonthepowerpiston,appliesanamplifiedforcetothemastercylinderprimarypiston.Areactionpiston,insidethepowerpistonsubassembly,providesthedriver"pedalfeel"duringanapplicationofthebrakepedal.

    Fluidflowthroughtheflowswitchopensthebackuppumpelectricalcircuitduringnormaloperation.Aseparatecheckvalveinthebackuppumppreventsback-flowthroughthepumpduringnormalpowerapplications.

    Intheeventnormalflowfromthepowersourceisinterrupted,thebackuppumpprovidesthepoweratareducedrateforstopping.SeeFigure3 forperformancecurve.Uponflowinterruption,theintegralflowswitchcloses,energizingarelay,providingelectricalpowertothebackuppump.

    Duringbackupoperation,thepumpre-circulatesfluidwithintheboosterassemblywithpressurebuiltondemandviathethrottlevalve.Fluidisretainedwithintheboosterbytheinletportcheckvalve.

    Figure3illustratesthetypicalrelationshipofmastercylinderpressureandinputforceofthebooster.

    Figure 3 Typical Performance Curve

    3

  • Hydro-Max Technical Manual7

    PRES

    SUR

    E RE

    GUL

    ATO

    R SP

    RIN

    GPE

    DAL

    RO

    D

    GR

    OM

    MET

    REA

    CTI

    ON

    PIN

    FLO

    W P

    ISTO

    NFL

    OW

    SPR

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    W S

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    ASS

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    TM B

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    4

  • Hydro-Max Technical Manual8

    Master Cylinder

    Inthereleasedposition,(refertoFigure5)actuatorsofboththeprimaryandsecondarypistonsareinwiththeirrespectivecompensatingvalvestems,whichprojectintothecylinderbore.Thiscontacttiltsthevalvestoanopenposition,whichallowshydraulicfluidinthereservoirsectionstocommunicatewiththeprimaryandsecondarypressurechambers.Eachpressurechamberhasapiston/actuatorsubassemblycontainingapreloaded(caged)springandreturnspring.

    Initialforwardtraveloftheprimarypistonmovestheprimaryactuatorawayfromitscompensatingvalve,permittingthevalvetoseat.Closureofthisvalveshutsoffthepassagebetweentheprimarypressurechamberandthereservoirsectionservingtheprimarychamber.

    Furthermovementoftheprimarypistoncreatespressureintheprimarypressurechamber,causingthesecondarypistonandactuatortomove.Asthesecondarypistonandactuatormove,thesecondarycompen-satingvalvecloses,shuttingoffthepassagebetweenthesecondarypressurechamberandthereservoirsectionservingthesecondarychamber.Additionalmovementoftheprimarypistoncausesbothchamberstobuildpressure.

    Whentheloadontheprimarypistonisremoved,fluidpressureineachchamber,combinedwithreturnspringforce,causestheprimaryandsecondarypistonstoreturntotheirinitialreleasedpositions.Eachactuatoropensitsrespectivecompensatingvalve,reopeningthepassagebetweentheindividualreservoirsectionsanditsassociatedpressurechamber.

    Shouldtherateofreleasebegreatenoughtocauseapartialvacuuminthechamber,thecompensatingvalvewillopentoallowreplenishmentoffluidintothecylinderbore.

    Anyexcessfluidremainingattheendofthestrokedueto"pumping"and/orvolumechangeduetotempera-turefluctuationisreleasedtothereservoirasthecompensatingvalvesopen.

    Theprimarycircuitisseparatedfromthesecondaryhydrauliccircuit.Hydraulicleakageinonecircuitdoesnotaffectthefunctionoftheothercircuit.

    Afluidlevelindicatorswitchisavailable.Itilluminatesalightonthedashpaneltowarnoflowbrakefluidlevelinthemastercylinderreservoir.Alowfluidlevelcanresultfrombrakeshoeliningwear,oritcanoccurifthereisanexternalleakinthevehiclebrakesystem.

    Adifferentialpressureswitchisavailable.Itilluminatesalightonthedashpaneltowarnwhenthereisapressuredifferentialbetweentheprimaryandsecondarybrakecircuitscausedbyaleakinonecircuit.Thismayoccurwhenonecircuitleaksorisimproperlybled.

    Aremotereservoirapplicationisavailablewhereunder-the-hoodspaceconstraintsprohibittheuseofaconventionalboosterandmastercylinderassembly.Inaremoteapplication,themastercylinderreservoirismountedseparatelyfromthemastercylinder.

    5

  • Hydro-Max Technical Manual9

    Figu

    re 5

    M

    aste

    r Cyl

    inde

    r

    6

  • Hydro-Max Technical Manual10

    Figure 6 Schematic of Electrical Operating System

    Electrical Operating Systems

    7

  • Hydro-Max Technical Manual11

    Basic Operation of Hydro-MaxTM Booster Assembly andMaster Cylinder

    ReferenceFigure6forthefollowingelectricalcomponentsoftheboosterandmastercylinder.

    BackupPump:TheHydro-MaxTMhydraulicboosterhasabackuppumpwhichwillprovidehydraulicboostatareducedrateifthenormalsourceoffluidisinterrupted(refertoFigure3).Thesignalforoperationofthebackuppumpcomesfromtheflowswitch.Ifnormalflowisinterrupted,theflowswitchwillcloseandactivatetherelay,whichwillturnonthebackuppump.Thebackuppumpisavailablefor12and24-voltsystems.

    The12-voltbackuppumpcandrawasteadystatemaximumof55ampsatapowersteeringfluidtemperatureof100F.The24-voltbackuppumpcanhaveasteadystatemaximumdrawof27.5ampsat100F.

    Relay:Anoptionalrelayisavailableforattachmenttothebooster.Therelayconnectstoasealedandmechanicallylatchedwiringconnector.Thefunctionoftherelayistoprovidecurrenttothebackuppumpwhentriggeredbytheflowswitch.

    FlowSwitch:Thefunctionoftheflowswitchistoactivatetherelaywhennormalhydraulicpowersourcefluidflowisinterrupted,turningonthebackuppump.Theflowswitchhastwoterminals(AandB).Aispositive.Bisconnectedtotheboosterhousingandcanbeusedasanoptionalharnessground.Theflowswitchitselfisgroundedthroughtheboosterhousing.Asealedandmechanicallylatchedconnectorconnectstheflowswitchtothebackuppumprelaycircuitry.

    DifferentialPressureSwitch:Thedifferentialpressureswitchreactstoalossofmastercylinderhydraulicpressureineithersideofthesplithydraulicsystemandcanilluminateawarninglightattheinstrumentpanel.Whenpressureislostineithertheprimaryorsecondarycircuitofthemastercylinder,theswitchcloses.Theelectricalswitchwillremaincloseduntilthemalfunctioniscorrected.Whenbothsystemsdevelopnormalpressure,theswitchwillreturntocenterandopentheelectricalswitchcircuit.Amechanicallylatchedconnectorisattachedtotheswitch.Theswitchhastwotabsonacommonterminal(positive)andisgroundedthroughthemastercylinder.

    FluidLevelSwitch:Whenthefluidreachesapredeterminedlevel(lowfluidlevel),theswitchclosesandcanilluminateawarninglightattheinstrumentpanel.Asealedandmechanicallylatchedconnectorisattached.Theswitchhastwoterminals,positiveandnegative,whichareinterchangeable.

    ChassisGround:Theboosterandmastercylinderassemblymustbeprovidedwithagroundpaththatwillcarrythemaximumcurrentofthebackuppump.

    8

    1.

    2.

    3.

    4.

    5.

    6.

  • Hydro-Max Technical Manual12

    Electronic Monitor Modules (12-volt only)Boschrecommendsthatamonitormodulebeincludedtomonitortheelectricalintegrityofthebackupsystem.Boschofferstwotypeswiththefollowingfeaturesandfunctions:

    Monitor Module Type I

    Features

    1. Performsstart-upselftestforproperelectricalsignaltoreservebackuppump.

    2. Continuouslytestforanopencircuitinbackuppump.

    3. Turnsonvehiclewarninglightandbuzzerifanyoftheabovetestsindicateabackupsystemelectricalmalfunction.Thewarningsarecontinuousuntilthemalfunctioniscorrectedorthepowerisshutoff.

    4. Conveyssignaltoprovideelectricalpowertothebackuppumpviatherelay.

    5. Providesacentralizedhousingfordiodes.

    6. Includesanintegraldifferentialpressureswitchlightcheckatstartup.

    Figure 7 Schematic of Electronic Monitor Module Type I

    9

  • Hydro-Max Technical Manual13

    Pin Functions

    Pin Function

    1 a)Providespathtoflowswitchtogroundforpin2toallowtestofredlightduringvehiclestartup.

    b)Suppressesnegativevoltagetransientsintopin5fromtherelaycoil.

    2 Providespathtopin1toflowswitchtovehiclegroundtoallowtestofredlightduringvehiclestartup.

    Note:Pin1and2areconnected,withadiodein-between.Withthekeyinthe"on"position,thereddashpanellightshouldilluminateanytimehydraulicflow(fromthefluidpowersource)dropstoarangeof0.5to1.1gpm.(Therangeatwhichflowswitchcontinuityoccurs).

    3 Opencircuitwhenallisokay,butswitchestoground(pin4)duringvehiclestartorduringadetectedfault.Connectiontogroundturnsonwarninglightandbuzzer.

    4 Connectsmonitormoduletovehicleground.

    5 Suppliespowerfrommoduletoamberlight,buzzerandrelaycoil.Currentflowthroughthisterminalmustbelimitedto300mA.

    6 a)Monitorsforvoltagetobackuppumpduringstartup.Ifnonedetected,pin3remainsgrounded(connectedtopin4).

    b)Monitorsforcontinuitythroughthebackuppumptovehiclegroundduringvehicleoperation(engineon).Pin3switchestoground(pin4)ifcontinuityislost.

    7 Bringspowerintomodulefromignitionswitch.

    8 Bringspowerintomodulefrombrakeswitch.Onlyneededwhenignitionswitchisoff.Enablesbackuppumptooperatewhenignitionisoff.

    10

  • Hydro-Max Technical Manual14

    Figure 8 Schematic of Electronic Monitor Module Type II

    Monitor Module Type II (12 volt only)

    Features

    1. Performsstart-upselftestforproperelectricalsignaltobackuppump.

    2. Continuouslytestsforanopencircuitinbackuppump.

    3. Testsforvoltageduringbrakeapplicationinbrakelightcircuitandbackuppumprelaycoilcircuitonvehiclesequippedwithdualbrakeswitches.

    4. Turnsonwarninglight(s)andbuzzerifanyoftheabovetestsindicateabackuppumpsystemelectricalmalfunction.Thewarningsarecontinuousuntilthemalfunctioniscorrectedorthe

    powerisshutoff.

    5. Absenceormalfunctionofthemodulewillnotaffectbackupsystemoperation.

    6. Turnsonlight(s)andbuzzerwhenintegraldifferentialpressureswitchisactivated.

    11

  • Hydro-Max Technical Manual15

    Pin Functions

    Pin Function

    A SuppressesnegativevoltagetransientsintopinEfromtherelaycoil.

    B Notused.

    C Opencircuitwhenallisokay,butswitchestoground(pinD)duringvehiclestartuporduringadetectedfault.Connectiontogroundswitchesonwarninglightandbuzzer.

    D Connectsmonitormoduletovehicleground.

    E PowerinputtomonitormodulefromignitionswitchorHydro-MaxTMbrakepedalswitch.

    F 1)Monitorsforvoltagetobackuppumpduringvehiclestartup.Ifnonedetected,pinCremainsgrounded(connectedtopinD).

    2)Monitorsforcontinuitythroughbackuppumptovehiclegroundduringvehicleoperation(engineon).PinCswitchestoground(pinD)ifcontinuityislost.

    G Monitorsoutputofthebackuppumpswitchthatturnsonthebackuppump,toallowcomparisonwithpinH.Ifdifferentfor>145seconds,thenpinCswitchestoground(pinD)andlatches.

    H MonitorsoutputofstoplightswitchtoallowcomparisonwithpinG.Ifdifferentfor>145seconds,thenpinCswitchestoground(pinD)andlatches.

    J Notused.

    K Notused.

    12

  • Hydro-Max Technical Manual16

    Application Information

    Hydraulic Fluids

    TheHydro-MaxTMboosterusespowersteeringfluidasthemediumoftransmittingpower.

    ThemastercylinderusesDOT3brakefluidperSAEJ1703,unlessotherwisespecifiedonthetopofthereservoir.ServicemaintenanceofmotorvehiclebrakefluidinmotorvehiclebrakeactuatingsystemsiscoveredinSAEJ1707informationreport.

    Brake Fluid Tubing, Hoses and FittingsBrakefluidlines(tubingandflexiblehose)transmitfluidunderpressurebetweenthemastercylinderandthebrakes.Thehosesaretheflexiblelinksbetweenwheelsoraxlesandtheframeorbody.Thehosesmustwithstandfluidpressurewithminimalexpansionandmustbefreetoflexwithoutdamageduringnormalsuspensiondeflectionandwheelturns.ThefollowingSAEspecifications,ortheirsuccessorsifappropriate,arerecommendedforconsiderationasaminimumrequirementwhenoutfittingavehiclewithbrakefluidtubing,hosesandfittings.ThehosesshouldconformtoSAEJ1401HydraulicBrakeHose-Automotive.ThetubingshouldconformtoSAEJ1047Tubing-MotorVehicleHydraulicBrakeSystem.ThefittingsshouldconformtoSAEJ516a-HydraulicHoseFittings,orSAEJ512-AutomotiveTubeFittings.Contactthevehiclemanufacturerforspecificrequirementsforindividualapplications.

    Before using any other type of fluid in the booster or in the master cylinder, contactthe Bosch Hydraulic Actaution and Truck Brake Engineering Department.(See inside of front cover).

    The booster and the master cylinder use two (2) distinctly different incompatiblehydraulic fluids. They must not be mixed. Using the incorrect fluid willpermanently damage the seals and can cause the brakes to malfunction.

    13

  • Hydro-Max Technical Manual17

    Figure 10 Tube Flare Configuration

    Booster Fluid Tubing, Hoses and Fittings

    Thepressurelinethatsuppliesfluidtotheboostermustbea1/2"diameterflexibleorrigidpressurelineconformingtoSAEJ188andtypicallydesignedtorunfromthesteeringgeartotheHydro-MaxTMinlet.TheHydro-MaxTMinletportutilizesatube"O"arrangementasshowninFigure9(notsuppliedbyBosch).Fortubeflareconfigurationsee Figure10.

    TUBE O.D.

    Thereturnlinemustbea1/2"diameterhydraulichoseattachedtotheHydro-MaxTMoutletport(SeeFigure11).Thereturnlineandclampmustbeselectedsothatitwillwithstandworstcasevehicleoperatingconditions,suchasbackpressuresresultingfromstartupatextremelycoldtemperaturesorfromdevicesinstalleddownstreamofthebooster.

    14

    TUBE AND NUT ASSEMBLY 2771464 (TIGHTEN TO 22 - 34 Nm)

    O-RING 2772007

    CHECK VALVE SEAT & O-RING

    CHECK BALL

    MINIMUMTHREAD

    NOT SUPPLIEDBY BOSCH

    Figure 9 Tube"O" Fitting and O-ring Seal

  • Hydro-Max Technical Manual18

    Figure 11 Outlet Port

    Theboosterisdesignedtoperforminaflowrangeof3.2to5.0gpm.Flowratethroughtheboostercanimpactvehiclestoppingdistance;therefore,thevehiclemanufacturermustdeterminetherequiredminimumflowrate.Flowratesbelow3.2gpmcancauseslowerresponsetimeswhentheboosterisapplied.Flowrateshigherthan5.0gpmmaycontributetotheboosterself-applying,whichwillcausebrakedragorfluidoverheating.

    Thefluidpowersourcemustbecapableofsupplying1,000psitotheboosterplusanyadditionalpressurerequiredbyotherdevicesinthesystemsuchasapowersteeringgear.

    Ifapowersteeringgearisused,thesteeringgearmustbe"balanced"sothatitcanhandlethepressuresgeneratedinthesteeringgearreturnline.Itmustalsohaveaninternalreliefvalvesettinglowerthanthepumprelieftoallowthesteeringgeartorelievebeforethehydraulicpumpdoes.Itmustalsohaveaninternalby-passtoallowmanualsteeringduringboosterbackupsystemoperation.ThemanufacturermustadheretotheflowpathillustratedinFigure2.

    Booster Fluid Source

    15

  • Hydro-Max Technical Manual19

    CLEVIS

    SINGLE EYE

    THREADED

    Figure 12 Basic Pedal Rod Designs

    16

    Installation Recommendations

    TheHydro-MaxTMboosterisgenerallymountedtoavehicle'sdashpanel.Ifnecessary,theHydro-MaxTMboosterandmastercylindermaybemountedremotelyfromthevehicledashpanelandactuatedbyappropriatelinkage.

    Fourmountingholesareprovidedintheboosterhousingthroughwhichuptofourstudscanbepressed.Useof(Grade5)3/8-16orM10locknuts,havingself-containedprevailingtorquefeaturesthatarefrictionallyresistanttorotation,arerecommended.

    SeeFigure12forthethreebasicpedalroddesignsoffered.Thethreadedpedalrodscrewsintothecustomersuppliedattachmenttothebrakepedal.Thepinthatattachesthepedalrodtothebrakepedalmustinsertfreely.Theattachmentmechanismofthepedalrodshouldbeofsufficientstrengthtopreventlinkagebinding.

  • Hydro-Max Technical Manual20

    Pedal Return Springs

    AnyvehicleapplicationutilizingaHydro-MaxTMboosterandabrakepedalreturnspringmusthave:

    1.Aproperlyadjustedpedalstop

    2.Alimitedspringloadatthepedalreleasedposition.

    ATTENTIONRegardlessofmountinglocation,thefollowingrequirementsmustbefollowed:

    a. Mounttheunitsuchthatthepedalrod,throughoutfullpedaltravel,doesnotarticulatemorethanplusorminus5aboveorbelowboostercenterline.Thebrakepedallevermustbealignedsidetosidewiththeboostercenterlinetopreventlinkagebinding.

    b. Thebrakepedalandmechanicallinkagemustprovideenoughtraveltofullystrokebothboosterandmastercylinder,i.e.,thebrakepedalmustnotbottomonthefloorofthevehicle.Apedalratioofbetween2.8:1and3.3:1isrecommendedtoprovidethedesired"pedalfeel".

    c. TheHydro-MaxTMboosterandmastercylinderassemblymustbemountedhorizontally.

    d. Thereservoirofthemastercylindermustbeupright.Thebackuppumpmustalwaysbeatthebottomofthebooster.

    e. Theunitmustbeprotectedfromenvironmentalandfluidtemperaturesover250F.

    171817

    General Safety NoteUniqueusageorapplicationsoftheHydro-MaxTMboosterandmastercylinderassemblyrequiresinputfromBoschandvalidationbythevehiclemanufacturer.

  • Hydro-Max Technical Manual21

    Thepedalstopmustbeadjustedsuchthatwhenthebrakepedalisfullyreleased,thereisnoloadonthegrommetthatretainsthepedalrodtotheHydro-MaxTMbooster.Whenthebrakepedalisfullyreleased,thespringloadmustnotbegreaterthanthatrequiredtosupportthepedalweight.

    ThereasonforaproperlyadjustedpedalstopandforthelimitationonspringloadistopreventthespringfrompullingonthegrommetwithintheHydro-MaxTMboosteranddamagingthegrommet.Thegrommetisnotdesignedtobeloadedinthismanner.

    Anyadjustmentofthebrakeswitchandbackuppumpmustnotcompromisetheadjustmentofthepedalstop.

    Pedal Stop and Proper Spring Load

    It is a commmon practice to stack vehicles on top of each other to deliver thevehicles. An air cylinder is typically used to apply the brake pedals in the towedvehicles. When installing such a cylinder, be sure that the backup pump turns offwhen the towing vehicle brake pedal is released.

    18

  • Hydro-Max Technical Manual22

    TROUBLE SHOOTING

    Contactdealerforservice

    Contactdealerforservice

    Repair/replacepowersteeringpump,checktensioninbelt

    Repair/replacepowersteeringpump,checktensioninbelt

    Replacepowersteeringpump

    Seevehicleservicemanualfortypeoffluidrequired.Drain,flushandrefillsystem,replaceboosterormastercylinderasappropriate,andpowersteeringreservoirfilterasnecessary

    Replacemastercylinder

    Replacebooster

    Replacepartscontainingblockedpassages

    HardPedal

    Excessivepedaltravel(pedalgoestothefloor)

    Improperpedaladjustment Seevehicleservicemanualforpedalrodadjustment(ifsystemisadjustable)

    Bindingpedallinkage

    Pedalmisaligment(sidetoside)

    Lowboostersupplyflow

    Powersteeringpumpflowcontrolvalve

    Powersteeringpumpreliefvalvesettingtoolow

    Fluidcontamination

    Mastercylinder

    Booster

    Tubeandhosepassagesareblockedshut

    19

    Condition Cause Remedy

  • Hydro-Max Technical Manual23

    TROUBLE SHOOTING

    20

    Condition Remedy

    Excessivepedaltravel(pedalgoestothefloor)

    (continued)

    Pulsatingbrakepedal

    Soft,spongybrakes

    Actuatedpedaldoesnotreturn

    Checkallfittingsandconnectionsforthemastercylinder,calipers,hoses,andtubes,replaceifnecessary

    Replacemastercylinder

    Bleedsystem

    Inspectandadjust,orreplacebrakeshoes,ifnecessary

    Replacemastercylinder

    Replacehoses

    Drainthesystem,flushandrefillwiththerecommendedfluid.

    Seevehicleservicemanual(ifbrakesareadjustable)Bleedbrakesystem

    Drainthesystem,flushandrefillwithrecommendedfluid

    Replacedefectivehoses

    Contactdealerforservice

    Cause

    Externalleakinbrakefluidsystem

    Internalmastercylinderleak

    Airinbrakefluidsystem

    Brakelinings

    Mastercylinder

    Weakbrakehosesthatexpandunderpressure

    Poorqualitybrakefluid(lowboilpoint)

    BrakeselfadjustingmechanismAirinhydraulicbrakesystem

    Poorqualitybrakefluid(lowboilpoint)

    Weakbrakehosesthatexpandunderpressure

    Bindingpedallinkage

  • Hydro-Max Technical Manual24

    Seevehicleservicemanualfortypeoffluidrequired.Drain,flushandrefillsystem,replaceboosterormastercylinderasappropriate,andpowersteeringreservoirfilterasnecessary

    Replacemastercylinder

    Replacebooster

    Repairorreplacepowersteeringpump.

    Seeappropriateservicemanual

    Seeappropriateservicemanual

    Seeappropriateservicemanual

    Seeappropriateservicemanual

    Repairorreplacepowersteeringpump

    Cleanventpassageinreservoircap

    Repairorreplacepowersteeringpump

    TROUBLE SHOOTING

    21

    Condition Cause Remedy

    Fluidcontamination

    Mastercylinder

    Bindingbooster

    Selfappliedbooster(fluidflowtoohigh)

    ABSoperation

    Wheelbearingslooseorworn

    Excessiverotorhicknessvariation

    Parkingbrakecontrolvalve(HR1)hasinternalleak

    Selfappliedbooster(fluidflowtoohigh)

    Constrictedmastercylinderreservoirvent

    Selfappliedbooster(fluidflowtoohigh)

    Actuatedpedaldoesnotreturn

    (continued)

    Pulsatingbrakepedal

    Brakeselfapply

    Draggingbrake

  • Hydro-Max Technical Manual25

    TROUBLE SHOOTING

    22

    RemedyCondition Cause

    Seeappropriateservicemanual

    Replacebooster

    Contactdealerforservice

    Replacemastercylinder

    Flushoutoldbrakefluidthenreplacemastercylinderandaddnewbrakefluid

    Replacethepartscontainingtherestriction

    None-Doesnotaffectoperation

    Seevehicleservicemanual

    Seevehicleservicemanual

    Seevehicleservicemanual

    Removeswitchcomponents,clean,inspectfordamageorcontaminationandreplaceifnecessary

    Contactdealerforservice

    Stuckorboundcaliperpinsorrails

    Bindingbooster

    Bindingpedallinkage

    Mastercylinder

    Softorswollenmastercylindersealsduetobrakefluidcontamination

    Tubeandhosepassagesrestricted

    Inherentinsomeboost-ers(whistle)

    Brakeswitch

    Monitormodule

    Relay

    Flowswitch

    Bindingpedallinkage

    Draggingbrake

    (continued)

    Noise/Whistle

    Backuppumpoperatescontinuously

  • Hydro-Max Technical Manual26

    TROUBLE SHOOTING

    23

    Remedy

    None-Doesnotaffectoperation

    Condition Cause

    Backuppumpdoesnotoperate

    Siliconefloatinginmastercylinder

    Fluidcontamination

    Repeatasabove

    Seeservicemanual

    Replacebackuppump

    Replacemastercylinder

    Replacebooster

    Replacediaphragmsandcaps

    Seevehicleservicemanualfortypeoffluidrequired.Drain,flushandrefillsystem,replaceboosterormastercylinderasappropriate,andpowersteeringreservoirfilterasnecessary

    Replaceseals

    Replaceo-ring

    Seevehicleservicemanual,tightenandreplaceifnecessary

    Leakage

    Sameasabove

    Electricalground

    Backuppump

    Mastercylinder

    Booster

    Mastercylinderreservoirventcaps

    Thismaterialisanassemblylubricant

    Backuppumpmountingseals

    Flowswitchseal

    Hydraulicfittingsandconnections

  • Hydro-Max Technical Manual27

    TROUBLE SHOOTING

    24

    Condition Cause Remedy

    Inspectbrakepads,replaceasnecessary,addfluidasrequired

    Replacemastercylinder

    Inspectbrakepads,replaceasnecessary,addfluidasrequired

    Seevehicleservicemanual

    Lowfluidlevel

    Fluidlevelindicatorswitch

    Brakepadswornout

    Vehiclespecific

    Fluidlevelindicatorlightcomeson

    Brakeindicatorlightandbuzzermalfunction

  • Correspondence concerning this manual should beaddressed to:

    Robert Bosch CorporationHydraulic Acutation & Truck Brake Engineering

    401 North Bendix Drive South Bend, Indiana 46628

    Fax: 574-237-2210

    PrintedintheUnitedStatesofAmericaCopyright2002RobertBoschCorporation