XJ12 -86 Limited Slip?

As topic, seems very difficult to find out if this car will have a limited slip in the diff…
Car is Europen sold.


Jack the rear of the car up, trans/gearbox in neutral, turn a wheel, if the opposite wheel turns in the same direction then its a LS, if it contra rotates then its open.
The other (more fun way) find a road with a loose shoulder and have one wheel on the hard and one on the loose. From a dead stop accelerate hard and it will either go in a straight line or the wheel on the loose will break traction :smiling_imp:

Just a loose IRS from a car beeing scrapped, the guy selling not very technical LOL

What Ive heard is that all XJS and XJ12 with inboard brakes are with LSD !?

That the prevailing wisdom, backed by Jaguar documents, and I’ve never seen or heard anything to discredit it


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Correcf. All V12s = LSD. Test is even easier off the car ;no need to jack up or put in neutral.

I have an 88 XJ-S V12 with the Dana instead of the Salisbury. Still not sure if I have LSD.
When I peel out, the car fish tails to the left.

I believe that is true.

Shouldn’t do that. With a live axle and LSD, it should break both tires loose and swerve hard to one side. With a live axle without LSD, it should break one tire loose and go straight. With an IRS, it should go straight either way.

BTW, you have LSD – unless someone removed it for some reason.

The LSD may be faulty, Greg…?

Fishtailing may imply that only one wheel is slipping, which is wrong - either neither or both with the LSD. One way is to have someone look when you ‘peel out’.

Or you can check with one wheel off the ground to see if either can be turned - box in ‘neutral’.

And if you are on a side slope, or road camber, rear end will slip. And with different grip on the rear wheels, the car will veer - LSD just locks the wheels, it cannot alter actual tire grip…

xj6 85 Sov Europe (UK/NZ)

Thanks for all replies, I have given the guy a simple instruction how to chek this.
Lets see what he finds out during the day, will report back with the result.


I’ve owned and driven many high powered cars with limited slip/posi-traction/locking differentials.

It is very common for the car to slew to the right as a result of wild/aggressive wheel spin.

This doesn’t doesn’t happen with a conventional differential because the rear tire that still has traction keeps the tail of the car in place.

My XJR would break 'em loose to the point where a full quarter turn of the steering wheel was needed to compensate for the slewing. Corvettes and other real bruisers sometimes need even more :slight_smile:


That’s what it does. I guess I meant a little fish tail?

Just my luck… not the origional IRS in the car… 2:88 ratio and no LSD.

Just to keep on looking


You don’t have a live axle, Greg.

Not entirely sure this is true. These LSD’s work by tightening up the clutches when torque is applied from the drive shaft. With no torque, there is some friction between sides, but it may not be enough to stop you from turning one wheel.

In principle; the clutches should lock up with independent spin on of a wheel, Kirbert - a standard test. If the clutch offers no resistance it has failed…?

As an aside; LSD does not prevent wheel spin with enough power input - with fishtailing as a consequence, direction depending on other factors. The point of the LSD is that if one wheel is on ice and the other not - power is transferred to wheel with grip. Gently getting out of trouble…

xj6 85 Sov Europe (UK/NZ)
xj6 85 Sov Europe (UK/NZ)

One black stripe = "one legged burn out. Unless too many blew the clutches…

Tale of something like that. There is a strip of bare ground dividing my drive from the neighbor’s drive. For a couple of years, he tilled it and planted veggies. shared with me. Yum… Nothing like a home grown tomatoe. Usually added richer soil to the base black clay. Then he got the idea of using hs big Toyota SUV to churn the soil. Put both passenger wheels in the wet ground. Applied power in 4wd. Churned nicely. But, hopelessly stuck! The wheels on the hard pan did not move. Clear, no LSD!!! His brother hooked up another critter and pulled him free… Says later, he asked me why? I explained differential action…


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So… found my IRS 2.88 and Power lock.
All good… almost… I want a much higher gear ratio…
So found a diff from a 2.8L XJ6 with the 4:11 gear in it, no Power Lock though.

Question: will the 4:11 gear set fit on the 2.88 gear carrier?

There are about 10000x10000 threads about this but no answer…
Anyone that really knows???


I think the answer is no and I have given the facts as I know them in many threads.

There are three LSD carriers. There is on for very low speed/high ratio gearing - say 4.10:1 and beyond. There in another carrier for very high speed/low numeric ratio gearing - say 2.88:1 and lower.

The commonest carrier is the middle one that supports 3.54 and others out to 3.07. If your proposed gearing is not in the group of ratios supported by whichever diff you already have (which it seems not to be), you’ll have to pay extra to find the parts or pay a rebuilder to strip two diffs and transfer the required parts into your keeper.

My understanding is that the inner diameter of the crown wheel and bolt count is the same on all ratios. The difference will be the offset between the carrier and the pinion… the lower the gear ratio the larger diameter of the pinion and vice versa.
This will make it possible to fit a 4.10 gear on a carrier made for the 2.88 gear with the use of a spacer between the crown wheel and carrier making it reaching in to the pinion gear. This is also why some gear manufactures like Yukon makes gear sets with “thick” ring gears making it possible to fit a high ratio on a gear carrier made for a low ratio.

Going in the other direction will not be easy…

As I can get the whole IRS with the 4.10 ratio for only USD100 I¨ll have a go and see what I can make out of the two differntials… 2.88 LSD fitting a non LSD 4.10 gear :slight_smile: