In something of a surprise, the local dealer today diagnosed a failed rear diff on my 2017 XF 3.0 RWD. It has led a very sheltered life, driven pretty gently by my wife. I have never had a diff failure in any car, no matter how hard I've thrashed them. The tech daid it was noisy. He drained the fluid. It was a mucky brown and was thin as water! Replacing the fluid did not quieten it. He said it looks like water ingress, and there are some metal shavings. It went in to diagnose a vibration. I didn't realise a diff could cause vibration. Noise, clunking, yes, but vibration?

Anyway, this is one expensive failure! I'm inclined to swap it out myself to save the labour cost.

I don't have a workshop manual, as I've never needed it! The biggest job I've had to do on the XF was a front bearing/hub replacement. That was a lot easier than I expected. How big a job is a diff swap? I can't find any guide or YouTube videos on the procedure.

If it isn't a huge job, I might try a used part. I've seen them from c. $300 to $700. More so if this is not a common failure.

All advice welcome!

Jim M.

 

Has the rear diff been serviced since your at 67K miles?
I have the E-Diff in my XJ but change rear diff fluid about every 30K miles or so.
The metal shavings sound like it was a factory problem but that was only reported on the earlier models.
Any chance you still have a warranty?
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No warranty, unfortunately. The car was serviced according to the schedule by the dealer until the 5 year period was up, but I didn't pay attention to what was in each service, TBH. I've done the oil and filter changes annually since, but never touched the diff.

I find it very strange that water could get in. The seals would have to be absolutely knackered to allow that. I read that there were seal problems with some earlier diffs, but not this late in production.

Found a manual... the diff swap looks pretty simple. Just not sure if a used one is a good idea.

 

One thing I forgot to mention... the service advisor is adamant that the diff is the major source of the vibration. The transmission mount is also worn, however. She says that will only be apparent at stop and start, not while driving. I'll swap that out anyway to see what the vibration does.

 

Yes I can't see how the water can get in past those seals? One outside chance is the rear diff has a vent and if the the entire diff gets submerged in water maybe water could enter that way?
If changing the transmission mount be sure and check the engine mounts too.
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This is exactly what the shop supervisor said. I can absolutely guarantee that the diff has never been submerged, however. He just looked at me blankly when i said that :-)

It is very strange indeed.

He did agree that a used diff was the best way ahead. It is a 6 hour job, by the book, which seems a lot, but entirely doable on axle stands at home. transmission mount is easy. Haven't looked at engine mounts myself but that was on the list of items for the dealer to check.