July 201 9\JaguarWorld|9 5QUESTIONSANDANSWERS
Ourtechnicalexpertsarereadytogiveyouhelpandadviceonanyproblem.Ifyourquestionisaparticularlycomplexone,itmaytaketimetorespond,and
insomecircumstancesitmaybebeyondourresourcestodoso.Inthisunlikelyevent,wewillletyouknow.Pleaseallowuptothreemonthsforaresponsevia
themagazine.Personalresponsescanbegiven,butatourdiscretion.Fax:(FAOJaguarWorldQ&As):+44(0)1 959541400 Email:[email protected]
Post(enclosinganSAE):JaguarWorldQ&As,KelseyPublishingGroup,POBox13,Westerham,KentTN1 63 WT,England.JWwouldliketothankMartinPikeofClassicEngineering,( 0199278896 7) KeithParringtonof
XjRestorations(0 132388511 0)andTomLenthallofTomLenthallLtd(0 118973161 4)XJ-Soutboardbrakeconversion
Q
My 1989 JaguarXJ-S3.6isinneedofrefurbishment
worktotherearsuspensionandbrakesystem.Isit
possibletoreplacetheexistinginboard-discrear-axle
assemblyonmycarwithalateroutboard-discset-upason
latermodelsofXJ40/X300XJsaloons?
DougSimonA
Whiletheentirerearsuspensionassemblyfroman
XJ40/X300isphysicallyincompatible,theoutboard
brakehubanddriveshaftassembliescanbeusedon
yourXJS.Thebasicsuspensionset-up(lowerwishbones,
carriercradleanddifferentialassembly)isphysicallyidentical
betweeninboard-andoutboard-brakeXJSmodels.
Theouter-hubcarrierpivotdimensionsalsomatch,sothelate
outboardrear-hubassemblywillboltstraightontotheexisting
wishbone.Thelatedriveshaftinnerflangepatternmatchesthat
ofthedifferentialoutputshaft,butaspacerwillbeneeded
tosubstituteforthedeletedinboardbrakedisc.Camberfine
adjustmentisachievedbywayofthestandardshims.
The‘outboard’XJSusesthestandardhandbrakecable,viaa
compensatorandtwosecondarycables,tooperatetheoutboard
drumhandbrakes–soyouwillneedeithertolocatethis
compensatorassemblyfromalateXJSorfabricateasubstitute.Similarly,itispossibletohavelongflexiblebrakepipesmade
(werecommendthebraidedAeroquiptype)toadaptfromthe
existingT-piecetotheoutboardcalipers.
Strictlyspeaking,theoutboardXJShasbespokeATEcalipers
withadifferentpistonsizetotheXJ40/X300tocorrectly
balancewiththefour-potGirlingfrontcalipers.But,inpractice,
thedifferencedoesnotseemtohaveanynoticeableeffect.A
OurXKspecialist,TomLenthall,
saysthatheisnotawareof
amethodtore-programthe
suspensiontogiveasofterride,nor
anyonethatofferssuchaservice.One
solutionhesuggests,though,istoobtain
asetofpassivesofterdampersand
springsandthenputaresistorinthe
electricalconnectorthatwillreplicatethe
activedamperandextinguishthesystem
failurewarninglight.
Toallowthehighlevelsofhandling
andstabilitythatyourcarpossesses,low-
profile(30/35percent)tyresarespecified.
However,inhavingsuchashallowsidewall
thereislittlecompliance,whichisapparent
intherelativeharshnessandridequality.
Bycontrast,theaverageVWPassat
isfittedwith60percentprofiletyres,
althoughhighperformancevariantsdogo
aslowas 40 percent.Fitting20inwheels
andwidetyreswithtinysidewallswould
alsogivetheVWabadrideandassociated
roadnoise.
Asanaside,suspensionwearcancause
clonks,whichsubliminallycomputeaspoor
ride.Also,age-hardenedrubbersuspension
busheswilltransmitexcessiveroadnoise.
Youcouldconsiderretro-fittingearlier
specificationwheelsandtyres(thefirstversionsoftheXKemployed4 5
percentprofiletyreson 18 indiameter
rims).Thisapproach,combinedwiththe
dampersuggestion,wouldofnecessity
compromiseyourcar’shandling,butmay
welloffertheearly-Jaguarcompliance
you’relookingfor.
It’sworthknowing,too,thatworntyres
tendtogeneratemorenoisethannew
ones,soyourappraisaloftheprevious
Continentaltyresmaybeunfair.Happily,
in 2012 ,theEUcametotherescueby
introducingmandatorytyrelabelling(an
exampleisillustrated)thatsaysnoiselevel
mustnowbeincludedontyrelabelssoyou
canmakeaninformedchoiceaboutyour
purchase.Beforethen,itwasnotpossible
toknowthenoiselevelofatyreuntilyou
actuallyfitteditandwentoutforadrive.
Noiseismeasuredindecibels(dB),and
thehumanearcanregisterthedifference
betweenthreedecibelratings.Tyrelabels
havethreedifferentnoisebands–the
morewavesshownonthesymbol,the
noisierthetyreis.Onewaveindicatesthe
bestperformance,whichmeansthatthe
noiselevelofthetyreisatleastthreedB
belowthelegallimit.Threeblackwavesis
theweakestperformanceandrepresents
anoiselevelthatisjustbelowthecurrent
maximumlimit,introducedbetween 2012
and2 016.