Hi All,

My car is an early 1993 V12 with the 5.3 engine and I think it will have the GM Power lock limited slip diff. The car has done 60,000 miles. Whilst I had the IRS out of the car I changed the diff oil using the correct LSD type.

Can anyone please tell me how the LSD should behave as I am not sure mine is working as well as it should.

My symptoms

If I pull out of a junction quickly, it will spin up the inside wheel. The wheel will spin quite fast before the diff locks up and because of this the transition of power to the other wheel is fairly brutal which can cause that wheel to break traction and the car will then go into a power slide.

I think the diff should lock earlier so there is a smooth transition to both wheels and therefore a more controllable slide.

I had a similar problem with a Caterham Seven, the diff preload had dropped so it had the same characteristics as my XJS does now. I had the diff rebuilt with new pressure plates which then made it far more controllable and smiles all round!

Cheers
Richard

 

You car will have the traditional Sailsbury Powr Lok (TM) type limited slip, the same as all other classic Jaguars back to the E Type. In theory, it is locked until it needs to unlock, such as cornering. I think in your case the wheel is spinning because it is locked, not because it is unlocked.

There are two ways to assemble the pressure plates in the differential, the earlier way gave more clamping force and the later way gives less locking force. Based on the various service manuals I have seen, it changes sometime in the 80's.

I have a 1994 6.0 and I can squeal the tyres on a tight turn if I am generous with the throttle. I have rebuilt the differential and I assembled it with the "less clamping" style, and I made sure all the clearances and preloads were absolutely correct. I think it's simply the nature of the design combined with the power of the V12. I have never chirped the tyres in my 1966 S Type with the original diff and the "more clamping" style of plates, but it also has less power than the V12.

 

are they the same basic designs , one made in UK, other made in USA, both are Basic GM engineering?
ron

 

Neither. Nothing to do with GM. Chrysler did use the same design in the 60's in the C body cars up to about 1967, I believe under licence from Sailsbury in the UK. GM ( and Ford) have used very different styles of limited slip axles.

 

MY 1978 Jaguar XJS POwerlok has 1959 Corvette Bellville spring clutch plates in it! its a little tight so you drive it with that knowledge! in slippery weather!
a simple bolt in!, all my XJS Diff parts are the same as early Corvette parts?
i also use a GM HD u-joint pinion yoke , that mates up to my aluminum drivshaft!


NO problem for kickin the rear out for showoff drifting!
ron

 

Hi, thank you for your reply.

I am not sure the diff would be 'locked' in normal operation? The whole point of an LSD is that is allows some slip, i.e you are making a normal turn, before it starts to transition power to the other wheel.

 

The whole idea of limited slip is to provide some locking under normal conditions - hence the "limited slip" condition, as a normal open differential has unlimited motion between the wheels. Here is the description of how it works from the service manual:

 

Thanks for this, I think I understand it now.

It operates in two ways;

1. Under acceleration, where there is high torque through the drive train the diff locks up as the cross shafts move up the bevel.

2. Where there is wheel spin the clutches then come into effect, transitioning the power to the other wheel.

It's the clutch bit that I don't think is working optimally on my car.

I'll have a go at measuring the preload.

 

just read the Salisbury use of the Bellville clutch plate, my 1978 Powerlok had NO bellville clutch plate , i installed some from a 1959 Corvette ,fit perfect!
so where do you think Salisbury got the knowledge for using them?
GM/Dana/Spicer.