3.8 differential shim issue

Morning all,
I’ve been working on MIK’s IRS to replace the leaking output shaft seals only to find this:

It is one of the shims used to set the ‘free-play’ on the output shaft, closer inspection shows evidence of wear on the shim, in fact there are places where it has been warn through. The question in my mind is how could this happen? Is it because the free-play was set incorrectly, perhaps to loose allowing the inner bearing race to spin?
The bearings appear to be in good condition and no visable damage. I’ve ordered some new shims but thought I’d check with the brain trust to see if there is something I’m missing. If I get time I’ll disassemble the other output shaft and see what it looks like.
Thanks in advance for your input.
Kindest regards,

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Hi Lynn, with that damage t one side I think it prudent to pul the other side out just for peace of mind.
Just my 4c (inflation and all that)

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Your diff is a different version than mine, but both types use shims to set the free-play and I would think it was set incorrectly, or something was not set correctly. My free-play was supposed to be .001 to .003 after tightening the big nut. Are you sure the shim has spun? Or maybe it was too thick and was crushed by tightening the nut? I need to go look through my photos and refresh my memory.

@awg Tony, any thoughts on what might be going on with L.Lynn’s shim breaking?

How do the surfaces look like, on which the shim rubs? That’s going to determine your course of action.

@angelw… seen this before?

I have experienced some that likely had not been done correctly, and it does seem things can go wrong

One had a blue bearing… that side was very tight with the nut done up,
another busted the outer axle at the Jesus Nut (apparently a design flaw, so maybe not related)

afaic, the best way to do them properly is to make a “dummy” bearing
and do the setup that way.

A brand new bearing honed on the inner is best, the old one can be used if it can be removed without damage, is in good condition, and measures the same thickness with a micrometer (when compressed) as the new ones

I also note there should never be any need to change the factory “master” shim thickness, (unless they got it wrong back then)…or any shims…unless its been altered since

I dont think the bearings are expensive, got them over the counter locally for about $25 or maybe
40, have them forever now, as a “special” Jag tool Its difficult to get the old outer one off, as even a sharp edged puller tends to bear somewhat on the cage and distort it

outer oil seal can only go on goes on after everything is set, and the 1st thing, so you have to be certain its going to be right

heat the new bearing and freeze the old axle when time to unite

Hi Drew,
Sure looks like it has been spun rather than crushed. The remnant is about 4/1000ths thick but hard to tell if it was that thick originally. Without the damaged shim I could get just a bit less than 1/1000th so it may have been a bit loose. Didn’t notice anything on the bearing races but will look a bit closer tomorrow. Thanks for your thoughts.
Kindest regards,

Hi Paul,
I didn’t notice anything but will look again tomorrow.

Thanks Tony,
Right, the seal has been removed to allow me to check the freeplay. I wonder if the bearing is to loose on the shaft? Was thinking of putting a locktite product on the bearing race after I set the clearance just in case?
I know that Jerry had replaced the seals at some point but don’t know if he adjusted the free-play.
Thanks again for the insight!

I find a cheap set of plastic jewelers Loupe off Ebay works great for examining “witness marks”
on mechanical components, (can also be used for other household uses)

the bearings would be an interference fit on the shaft, its not easy to press them on and off

mate and myself mucked around for ages doing the first one by the book…after honing dummy bearings, which doesnt take long, we knocked over a few, and they were in spec 1st time

Hi LLynn I don’t think this is a big deal. The shims only come in 3 sizes - .003, .005, and .010. and seem to be readily available (SNG). If you think that the bearings are ok (I’d probably replace as they are not that expensive) you just need to set end float as described on page H18 of the 3.8l manual. Helpful to have a dial test indicator.

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I try to measure the freeplay before I dismantle it, if practical, as if it ok, theoretically the shims are correct

might be able to test my theory as the blued MKX diff which is still sitting around, one side tight and blue, the other seems ok. I supsect the the result to be the tight one will have zero endplay, but rather have been placed under excessive pre-load as a result of incorrect shimming

Thanks Terry, That begs the question though. Why did it destroy the shim? SNG only has the .005 and .010 but that shouldn’t be a problem. I probably should replace the bearings…

Thanks Tony, I will do that on the passenger side before I disassemble it. Will check that tomorrow.

Thank you,

I rebuilt the output shafts on my 3.8 years ago as part of the restoration and I think there should normally be several shims rather than just one. I have no idea why Llynn’s would have become worn so badly.

All four bearings on mine were very badly blued and neither side had any play. Shims weren’t easy to find back then although the Timken bearings were readily available from a local bearing supply house. I juggled the shims from both sides to get one side right and then made a custom spacer for the other side so it didn’t need any shims.

I set both sides to .0015" float. The totals were .590" one side and .591" on the other. I also managed to obtain OEM Jaguar seals.

I did this back around 1990 during the restoration and never had any problems later. I don’t remember having any particular difficulty doing the job just using my hydraulic press, a bearing separator and a dial gauge.


Jerry autocrosssed the car. I do the same with mine - it seems to be hard on differentials and hubs - it sure has been on mine. What appears to have happened is that the shims got “pounded out” as I’d put it, then when a bit loose ground out. I’d check the spacer with a micrometer to ensue it’s square. If the bearing has a bit less end float than that recommended that’s ok too. “Modern” Jaguar differentials went to preloaded bearings (negative end float) with collapsible spacers in the output hubs but that’s a whole other topic.

If the bearing has turned on the shaft you should be able to see that when you get the bearings off the shaft. Report back if that has happened.

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I’m starting to remember my rebuild from 2 1/2 years ago. That’s what I did, Clive. I had several shims on each side and adjusted between the two to get the right end float. I had .001 on one side and a little more on the other. My diff was a newer version and slightly different than yours and the one Lynn is working on.


Thanks Clive, reminds me to get the Vaseline out for the reassembly!

Thanks again Terry, makes sense. Funny thing was that this crossed my mind in the early morning hours too :wink: I’ll recheck the shims and bearings this morning.

I suspect yours was a bit more like Jennifer’s car that I had to replace the bearings in. I have ordered some new shims from William at SNG so between shifting them from side to side and the new ones I should be able to get close. From Terry’s comment, it sounds like it might be better/Ok to have a little preload but will aim for the .001-.003 as per the manual.

Thanks you to everyone who has offered their thoughts.

Hello LLynn,
As Terry points out, later Jaguars using opposing taper roller bearings used pre-load on the Output Shaft Bearing set up.

A different type of bearing, that had built in pre-load, was used in the differential for most S2 and all S3 E Types, as well as S1 XJ6 cars. This bearing was a Double Row, Angular Contact ball bearing race bearing that had a slit centre race. When the nut securing the bearing to the Output Shaft was tightened, the two halves of the inner race are drawn together and applies a build in amount of pre-load. This bearing has not been available for quite a number of years.

Later cars to the S3 E Type and S1 XJ6 reverted back to opposing Taper Roller Bearings and rather than have End Float, the specified set was for the bearings is preload. Taper Roller Bearings prefer to run in pre-load than End Float and Shortened Bearing Life is more easily induced with End Float than with Pre-Load (the step between acceptable and excessive End Float is small compared to correct and excessive Pre-load).

The appearance of the shims suggests that the bearings have been rotating against the spacer and shims. As Terry suggests, you should see evidence of this on the Output Shaft bearing journals. No torque figure is specified for the securing nut, but its important that its pulled up fairly tight to lock the centre races of the bearings solid to limit the chance of either spinning on the shaft.



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If you dont mind me inquiring, always enjoy your informative answers

are you able cast any illumination ?

All MKX and 420G I have seen have tapered roller bearings in the output shaft, but specify
.001" - .003’ Endfloat in the Factory Service Manual

If I check Timken (or any source) says to set tapered bearings with pre-load


Hello Tony,
I had a Typo in my previous Post, in that it should read “Later cars to the S3 E Type and S1 XJ6 reverted back to opposing Taper Roller Bearings.”

If you compare the diameter at any point of contact along the taper of the Cone and Cup of the bearing assembly when the Cone and Cup are in intimate contact (No End Float), the diameters are equal. Although minuscule, when there is End Float, the diameters of contact (each point along the taper) is different. This will vary between being equal to there being a variation (depending on the axial relationship of the two components of the bearing). Its somewhat like the self tightening aspect of the Knock Off Hubs, but without the thread that tightens the Hub. The more End Float, more the affect. This has an effect on bearing life.



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