My 1990 XJS went in for a trip-worthiness check today and the
mechanic told me that the diff pinion bearings were starting to
cause noise. He recommended against driving the car from
California to Texas based only on that, as everything else was
pretty ship shape.

I'm wondering now, is this something that is doable? I've fixed my
cars before, doing as much as a clutch change, but I've never
messed with a differential.

If it is doable, what else beside the pinion bearings should I
replace while I'm doing it?

I'd have about a month to do it in and I have the Service Manual
for the car.

Am I crazy for thinking about this?

Thank in advance.

 

Dain, if all that you are doing is the pinion bearing, then that should be doable by you. But, at the same time, replacing the carrier bearings would probably be a good idea too. But, that would involve a lot more work to access those. It would also require a lot more specialized tools. For just the pinion bearing, you will need your normal assortment of hand tools, but also a torque wrench for applying the proper amount of pre-load on the pinion bearing. If you do the carrier bearings, then you are going to need an assortment of micrometers and depth indicators. Also, you will need to set stuff to within 0.003". So, if you are looking to do the whole 9 yards to the rear differential, a shop to do the work for you will be advantageous.

Hopefully this gives you what you are after.

 

That's not a likely fault with your 1990 XJS, although certainly not impossible. Worn pinion bearings induce a misalignment of the ring and pinion: this normally produces a growl or whine that clearly changes in pitch when you go on and off the throttle at highway speed.

If you have had the car for a while, or owned other similarly equipped Jaguars (the IRS/diff layout is basically identical 1962-1992, and quite similar afterwards) you should have noticed any significant rear end noise as it got progressively worse.

So long as the unit is holding oil and it is topped up, there is virtually no chance of it sticking you by the side of the road. If the pinion bearings are in fact badly worn, you most likely have a significant leak from the pinion oil seal. A noisey, leaking diff is a good one to replace before a long road trip.

You cannot overhaul the differential yourself, and it is a major task to remove/ refit the differntial unit from the rear suspension. If you think you can accomplish that much, have a blast. Then find a good used diff, or find a rebuilt (I'm guessing $700 for the latter).

XJ40 and X300 diffs eat up output shaft bearings, and the contamination from particulates can ruin the pinion bearings as well. Alot of diffs get screwed up by guys changing the pinion seal and over-torqueing the pinion flange nut: this puts more preload on the bearings, and increases the ring and pinion backlash. If those terms are not common knowledge to you, leave your diff alone.

XJS do not eat output shaft bearings, and it is not common for them to have pinion bearings fail either. If the diff is in fact whining a little, top up or change the fluid and forget about it. If it's really noisey, change it.

If your guy knows what he is talking about, ask him if there is a collapsable spacer in the diff. If he doen't say "yes" right away, then he shouldn't be getting his hand inside your diff, or your wallet. I'd opt for installing a rebuilt from a remanufacturer who is familiar with this procedure and will guaranty the result.
And I'd also expect you don't need one.

 

The noise that I hear now is usually around 35 mph and will increase in pitch as I go faster. I was going down a hill with no help from the engine and it was also present. It sounds basically like the noise you described. The mechanic said that the pinion bearings were not to the point that the ring was misaligned yet. However, he said that a long road trip could bring about the heat that could induce this condition.

Unfortunately, I've only had the car for about seven or eight weeks. It existed when I bought it.

So, basically, this guy only works on Jaguars and Saabs and he is known in the area for being the guy to go to if you have an old Jag. I got his name through word of mouth. He explained the whole situation to me and had several pinion bearings that were worn to show me what the situation was.

Overall, I tend to trust his judgment, as he was giving me detailed instructions on how to take the stuff apart.

As far as it being good as long as it holds oil, the mechanic said that even with oil, it could eventually seize, leading to a loss of power. Is this true?

Sorry, I'm so new, I'm really just trying to find out what I need to do. If it's replace the diff with a rebuilt one, great, I'll get started. If it's nothing, fine, that's easy. I just need to know what to do.

 

So I answered the questions you asked, and you like his answers better.

To answer the only question you asked in this post: I have been working on Jaguars exclusively since 1982. I have seen exactly one differential suffer a catastrophic failure: the pinion snapped inside the diff. That's a stress fracture induced by a damaged component or a warped driver. Good luck with your car.

 

Not sure what you finally chose to do but I have pulled a couple of these rear ends without much difficulty and I am certainly not a Jaguar mechanic. Hot Rodders are very fond of these and I am installing one that I pulled from an 86 XJS under a 1950 Ford F1 P/U that I am modifying somewhat.

It didn't take more than a couple of hours at most and if I did them regularly it would probably be less than an hour with a competent helper.

I agree with JagTech that these units are rather robust. I'd rank them second only to the "gold standard" Ford 9" in a car.

Might I suggest that you consider as JagTech did that you try changing the differential fluid first if that hasn't been done already. That alone may fix the problem if the original gear oil is still in there. Also check for leaks.


As far as price, last one I bought the whole car for $350.00

 

Hey Tex,

As for pulling the complete rear suspension assy, I agree with you. Disassembly to remove the differential afterward is a fair bit more work.