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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
al B
oost
er a
nd M
aste
r Cyl
inde
r Ass
embl
y In
stal
latio
n in
a H
ydra
ulic
Bra
king
Sys
tem
2
TO F
RO
NT
BR
AK
ES
TO F
RO
NT
BR
AK
ES
AB
S U
NIT
RES
ERVO
IR &
FIL
TER
STEE
RIN
G P
UM
P
STEE
RIN
G G
EAR
BR
AK
E SW
ITC
H
TO B
ATTE
RY
TO R
EAR
BR
AK
ES
TO R
EAR
BR
AK
ES
TO I
DP
TO IG
NIT
ION
( OPT
ION
AL)
MO
NIT
OR
MO
DU
LEGR
OU
ND
TO W
AR
NIN
G B
UZZ
ERTO
WA
RN
ING
LIG
HT
DIRE
CTIO
N O
F FL
OW
TO W
AR
NIN
G S
YSTE
M
TO W
AR
NIN
G S
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
ING
FLO
W S
WIT
CH
ASS
Y(O
PEN
)
INP
UT S
HAFT
SEA
LS &
BU
SHIN
G
FLO
W S
WIT
CH
ASS
Y
(
CLO
SED
)O
UTL
ET P
OR
TFI
LTER IN
LET
PORT
CHE
CK V
ALVE
SEA
T &
O-R
ING
CHE
C K B
ALL
POW
ER
PIST
ON
INPU
T SH
AFT
REA
CTI
ON
PIS
TON
THR
OTT
LE V
ALVE
POW
ER
PIST
ON
VALV
E RE
TURN
SPR
ING
POW
ER
PIST
ON
RET
URN
SPR
ING
CHE
CK B
ALL
BAC
KUP
PUM
P
END
CAP
POW
ER
PIST
ON
OUT
PUT
SHAF
T
FLO
W S
WIT
CH
FLO
W S
WIT
CH
ASS
Y
Figu
re 4
H
ydro
-Max
TM B
oost
er a
nd M
aste
r Cyl
inde
r
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