Hello everyone,
I have just purchased my second XJS. This one is a 1992 Facelift V12 converted to 5-speed manual with Bilstein shocks, uprated springs, AP racing clutch and brakes with huge discs and 18" BBS wheels. Better yet...... it has only done 31,000 miles!! A bit of an animal to say the least.
My initial question is: has anyone had experience of tramlining and/or brake shudder with low profile, wide tyres on the XJS while under braking? Mine suffers from this even though all parts are new. I can't believe I have warped discs already - but that is what it feels like.
Appreciate any feedback.
V12 Manual
Moderators:davidr, BigCatXJS, dhdove
V12 Manual
KevtheRev,
Welcome to the Bulletin Board and great choice of car - facelift V12 manual - love it!
I'm sure that Ralph and some of the other racing boys might be able to give you some better input but here's a couple of my thoughts:
As you probably know, XJSs seem really prone to building up a bit of play in the front wheel bearings. Mine always seem to need nipping up at each service. They are supposed to have some degree of end-float even well when adjusted. Some mechanics seem to tighten them as if they were a modern car and this seems to exacerbate the speed at which they then wear the bearings and loosen themselves up. Might be worth a look.
The second thing is that with such high-spec brakes, this might in itself be causing the problem at low speeds when cold. I use sintered Double-H brake pads on one of my bikes and whilst they are great when hot, they can feel very grabby and juddery when cold. Also, are the pads matched well to the discs and are the calipers allowing the pads to back off properly when the brakes are released? I know people who have fitted new discs and pads but certain makes don't seem to like each other and can end up warping the discs slightly very, very quickly. Also, if the calipers aren't releasing, you can get heat buildup back to the pads and little bits of deposits get left on the discs leading to juddery brakes. Again, the racing boys may better advise.
Whilst the discs are new, are you aboslutely sure that they were fitted properly? It only needs a tiny amount of corrosion on the mounting flange to cause excess run-out on the disc.
Last point is to check some of the suspension bushes, particularly top wishbone bushes. They are prone to causing handling probs when worn and with such big tyres can lead to tramlining.
Good luck with resolving it.
When you get a chance, can you please enter your vehicle in the register. PLEASE ensure you have all the necessary info including paint and trim codes before you make the entry. Any probs, please get in contact with me. Tks.
Paul Sinnott
XJS Registrar
Jaguar Enthusiasts Club
Welcome to the Bulletin Board and great choice of car - facelift V12 manual - love it!
I'm sure that Ralph and some of the other racing boys might be able to give you some better input but here's a couple of my thoughts:
As you probably know, XJSs seem really prone to building up a bit of play in the front wheel bearings. Mine always seem to need nipping up at each service. They are supposed to have some degree of end-float even well when adjusted. Some mechanics seem to tighten them as if they were a modern car and this seems to exacerbate the speed at which they then wear the bearings and loosen themselves up. Might be worth a look.
The second thing is that with such high-spec brakes, this might in itself be causing the problem at low speeds when cold. I use sintered Double-H brake pads on one of my bikes and whilst they are great when hot, they can feel very grabby and juddery when cold. Also, are the pads matched well to the discs and are the calipers allowing the pads to back off properly when the brakes are released? I know people who have fitted new discs and pads but certain makes don't seem to like each other and can end up warping the discs slightly very, very quickly. Also, if the calipers aren't releasing, you can get heat buildup back to the pads and little bits of deposits get left on the discs leading to juddery brakes. Again, the racing boys may better advise.
Whilst the discs are new, are you aboslutely sure that they were fitted properly? It only needs a tiny amount of corrosion on the mounting flange to cause excess run-out on the disc.
Last point is to check some of the suspension bushes, particularly top wishbone bushes. They are prone to causing handling probs when worn and with such big tyres can lead to tramlining.
Good luck with resolving it.
When you get a chance, can you please enter your vehicle in the register. PLEASE ensure you have all the necessary info including paint and trim codes before you make the entry. Any probs, please get in contact with me. Tks.
Paul Sinnott
XJS Registrar
Jaguar Enthusiasts Club
1995 XJS 4.0 Convertible
1980 XJ-S Pre-HE
Jaguar 4.2 Supercharged engine (but not with a Jaguar body..)
1980 XJ-S Pre-HE
Jaguar 4.2 Supercharged engine (but not with a Jaguar body..)
V12 Manual
Kev,
Unfortunately you will allways get a bit of tramlining with very low profile wide tyres, if its enough to make the car feel uncertain then there is some play in the bushes or bearings as mentioned above, but if it does not effect the handeling but merely feels a bit odd then its probably ok. Try adjusting tyre pressures 2psi at a time either way and see if the handeling improves (thats largely how manufacturers do it).
As for the judder, high performance brakes can be verry jittery when cold, again as mentioned above, do you notice a difference in judder under different conditions? Do you know what sort of pads and discs you have?
Sounds like you have a rather wonderfull car there, much fun.
Unfortunately you will allways get a bit of tramlining with very low profile wide tyres, if its enough to make the car feel uncertain then there is some play in the bushes or bearings as mentioned above, but if it does not effect the handeling but merely feels a bit odd then its probably ok. Try adjusting tyre pressures 2psi at a time either way and see if the handeling improves (thats largely how manufacturers do it).
As for the judder, high performance brakes can be verry jittery when cold, again as mentioned above, do you notice a difference in judder under different conditions? Do you know what sort of pads and discs you have?
Sounds like you have a rather wonderfull car there, much fun.
V12 Manual
Thanks for the information. I will certainly check out the problem possibilities you both mentioned.
I much appreciate your thoughts..I'll get back when/if I find something.
Kevin
I much appreciate your thoughts..I'll get back when/if I find something.
Kevin
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