My 90 has a LSD verified by jacking the rear end up and spinning the tire by hand. The problem is I don't think it is locking under power. Could it be that there is no additive in the pumpkin? The car has under 100K.

 

The XJS LSD does not lock is has some slip, I am not sure how much slip it has but I would estimate 30-40% otherwise the inside wheel would shudder when you turn a tight corner.

You can check it by jacking up one wheel and leaving the other on the ground, use the tyre leaver and try and turn the wheel that is off the ground, it should be be quite difficult to turn.

 

My 88 XJS and my 88 BMW 535i both behaved the same. Around a normal corner under low to moderate loads the diff worked like an open diff (one wheel drive) but when heavy loads were applied i.e. heavy acceleration on the corner the diff would "lock up" (two wheel drive). My 90 will spin the inside tire and behaves like an open diff.

 

seems like its time to thow in s trakloc posi unit

 

I am hoping that the P/O installed standard fluid without the additive. If it is truly a bad diff then I don't see any advantage a different diff would give over rebuilding the stock unit. Am I missing something?

 

How are you checking for this?






I doubt it.

The additive doesn't add or enhance the "limited slip" effect. It is a friction modiier to eliminate LSD clutch chatter.

The LSD clutches can and do wear out, reducing or eventually nullifying the function.

Cheers
DD

 

Probably not.

There are many varieties of "limited slip" and some of the terminology is used loosely and confusingly :-)

Some LSDs are actually *locking* differentials which, depending on the type and actuation, can be a bit bothersome.

The Jag clutch-type LSD is probably as good as any other OEM clutch type LSD. Unless you have a particular desire or need for something else, I'd just have the Jag diff/LSD overhauled and call it good.

Cheers
DD

 

I'm checking for an LSD by jacking both rear wheels off the ground. In park I can't rotate either wheel. In neutral when I rotate one wheel in the forward direction, the other spins in the same direction.

 

Sorry, what I meant to ask is how are you checking for this:

"The problem is I don't think it is locking under power."


Cheers
DD

 

My '62 MK2 and '82 XJS, both have perfectly functioning LSD's, yet my 2001 XKR ($86 grand originally) does not have one. What a rip off!

 

Gotcha! 1 wheel in the grass and the other on the asphalt then punch it!

 

I think you'd go in the opposite direction with this. The differential could have too much additive. I've never seen it before, but in theory, too much additive could make the LSD slip too much.

Normally, people start with an LSD-friendly fluid (I used Mobil 1 synthetic gear oil) and take it from there. It is supposed to have enough limited slip additive for the LSD to function properly. If the rear end is a little too grabby (rear locks prematurely) then start adding friction modifier until it is smooth around bends and locks up when it is supposed to (one wheel spinning hard, the other not.)

 

You're not alone in feeling cheated. Presumably you have traction control? I'm sure the rationale was traction control obviates the need for LSD.

The old XJR/6 got both LSD and Trac Control. Lucky us

Cheers
DD