Rear diff noise on 2015 Jaguar XF / Seal replaced 4 years ago

[MJG50 7]

I've bought a 2015 X250 Jaguar XF 3.0D S from BCA that had an advisory for a rear differential fluid leak on its first MoT in 2018 at 15,000 miles. I phoned the Jaguar dealer that serviced the car from new before buying it and a new seal was fitted by the Jaguar dealer in 2018 and I assumed the problem was fully resolved. However, I took the car in for a pre-sale PDi & service today at 40,000 miles and was told there is a noise coming from the differential and that rear diff pinion seal is moist. The noise is very slight and I can only hear it from the passenger seat, it just sounds like the air conditioning fan is on at a very low setting speed. The car still drives 100% fine.

I've read lots of horror stories online about XF rear diffs failing and it costing a fortune to replace them. I've found a transmission/differential specialist not too far away and I was thinking they should be able change the diff oil and put a new seal on. However, if the diff is already making a noise is it already damaged to an extent that a diff oil change won't improve things?

Also, I've heard that changing the diff oil and seal involves rebalancing the diff and this is a tricky job and that the diff won't be as smooth afterwards. 

In the very worst case scenario, if the diff fails in the 6 month CRA period, I have seen a few second hand diffs on eBay for around £250 - how much would it cost to get a used diff fitted and is it possible to fit a used diff without losing the smoothness of power delivery associated with the XF? I've read online that it can cost several thousand pounds to replace the diff but as I say there are always quite a few used diffs on eBay and I can't imagine that the labour would be thousands of pounds at an independent garage.

I've never had any diff problems with Jags before but I've had a quick look online and it seems diff issues are relatively common with XF s and S-types.

[Halfpenny 114]

Diff issues are quite common on the Jags.  The problem is that most dealer/repairer mechanics don't have the knowledge and experience to repair diffs - you need a specialist diff rebuilder.

I am an old-school mechanic and have rebuilt plenty of diffs in the past. Its a black art to get them quiet. Mostly the dealers will replace the oil seal and just torque the pinion nut up to factory spec.  That is NOT the way to do it, because it takes no account of the fact that the collapsible spacer (which sits between the pinion bearings and provides preload) has already been crushed when originally tightened.  Re-tightening to factory spec actually crushes the spacer a bit more and puts too much preload on the bearings. They make noise, and furthermore the gear teeth get out alignment and also make a noise. Eventually the bearings fail.

The best way to replace the seal is to use the original nut and mark it. On reassembly use so Loctite and return it to the exact same marked position. The tightening torque will be way below factory spec.

In your case the damage is already done. The diff will need stripping, new collapsible spacer, then tooth contact setting with new shims. It will be expensive (labour).

If you find a good used diff then go that route. But you won't know how good it is until its installed and been driven. You could be back to square one.

Inadequate spec on the original seals in the problem here. Bloody JLR lack of development/testing/QC !

[MJG50 7]

Thanks for your help Halfpenny, it does seem quite a common problem with Jags but it's the first one I've had with this issue. I've seen a few used diffs for about £300 but how much would the labour be to fit it and would it need a diff specialist to fit it?

It probably is worth risking a used diff - there is a legal case between Dana Axle and JLR in connection with diff seals made from 2013 and 2016 so if I can get a pre-2013 diff to fit it might be ok. That said, I've heard that the early XF also suffered with diffs but I've never had any trouble with 2008 and 2009 XFs

Edited March 12, 2022 by MJG50

[Halfpenny 114]

You don't need a diff specialist to fit it. Its not a technically difficult job, just a lot of work. I reckon it would be 4-5 hours labour on an XF.

[MJG50 7]

Thanks Halfpenny, I've used the same workshops for nearly 30 years but quite a few of their mechanics have retired over the years so I'm not sure I'd trust a diff job with the younger ones! It's good to hear it's not technically a difficult job though. Is there a risk of losing the smoothness of the power delivery by fitting a replacement diff?

[Halfpenny 114]

11 hours ago, MJG50 said:

Thanks Halfpenny, I've used the same workshops for nearly 30 years but quite a few of their mechanics have retired over the years so I'm not sure I'd trust a diff job with the younger ones! It's good to hear it's not technically a difficult job though. Is there a risk of losing the smoothness of the power delivery by fitting a replacement diff?

The diff is basically a sealed unit. Your mechanic will remove propshaft, driveshafts etc and various rear suspension and subframe components. Unbolt the old diff. Bolt in the new diff and refit all the external parts. It 'relatively' straightfoward.  Assuming you can get hold of a servicable diff then it will have no impact at all on power delivery.

[MJG50 7]

That's great, thanks again Halfpenny, I've seen new, supposedly genuine JLR diffs on eBay for £575 but they are for the 2.2 litre - I'm pretty sure the diff is the same for all XFs apart from the XFR with the e-diff.

I can see why I'm leaning towards mainstream stuff these days though! 

Talking of diffs and Jags, I remember about 20 years ago selling an X300 XJ6 that was about 7 years old at the time and the guy who bought it reckoned his mechanic said the diff was leaking but he ran that car for another 5 or 6 years/30,000 miles without doing anything about the diff before rust got the better of it. Total diff failure on the XF seems quite common though so I won't be driving this one very far before it's sorted.

[Halfpenny 114]

There are various different part numbers for these diffs. I don't know how they vary, probably best to consult a specialist.

I must say that JLR are one of the brands on my 'no buy' list. Too many problems.