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Any further updates on the noise ? Mine is going into my local specialist this Thursday, so it would be good to be able to give them some pointers if you've had a result.

Thanks
 

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Discussion Starter #22
Any further updates on the noise ? Mine is going into my local specialist this Thursday, so it would be good to be able to give them some pointers if you've had a result.

Thanks

I had all the rear upper and lower suspension arms replaced and shock bushes as they were shot. Had the diff oil changed for good measure but still can hear the knock sound! He also checked over the prop and drive shafts and said all was ok, a bit of lash in the diff but nothing major. So tbh I’m back at square one. I’m starting to wonder if it’s the sc but reading up on various forums that seems to display a rattle rather than a dull clonk unless someone can correct me?
 

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S/c coupling gives a rattling at tickover I think, maybe a knock at startup. But not when taking up drive.
 

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Discussion Starter #24
S/c coupling gives a rattling at tickover I think, maybe a knock at startup. But not when taking up drive.


That’s cleared that up, thanks wilf! Just wondering if a transmission flush and oil change would help? I know some have said it solved the gear selector clunk which my car does occasionally
 

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Discussion Starter #25
Any further updates on the noise ? Mine is going into my local specialist this Thursday, so it would be good to be able to give them some pointers if you've had a result.

Thanks
Good luck with the specialist Manaray, let me know if he finds anything!
 

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That’s cleared that up, thanks wilf! Just wondering if a transmission flush and oil change would help? I know some have said it solved the gear selector clunk which my car does occasionally
How many miles on your car? If 50k +, then a gearbox oil change is a very good idea anyway.
 

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Thanks for the update Archive.

I had the gearbox oil changed at the last service, and the Diff oil was changed when I had a new E-diff motor fitted. The drive shafts seemed fine to me and also the propshaft.

The noise definitely comes from the rear of the car as I apply throttle or back-off the throttle so I'm pretty sure it's going to be a bit of play in the diff or a knackered bush somewhere in the suspension.

I have history with hearing transmission noises (Mercedes S500 and a VW Phaeton V8) and it has been unfounded on a couple of occasions - maybe I should just turn the stereo up and wait for something to fall off !

I'll report back after it's been looked at.

Martin
 

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So the guys spent a while under the car yesterday investigating everything that could possibly making this noise, and they've pinpointed the differential as the most probable cause.

There's no play in the propshaft as it exits the gearbox, there's no play in the drive shafts as they enter the hubs, there's nothing worn enough in the suspension bushes to make such a deep clunk, and as I reported earlier I'd noticed a small amount of play in the differential between the wheels moving and the propshaft turning.

The opinion of the two guys (who have over 25 years of Jag dealer experience between them and numerous years of independent experience) is that there is slightly more noise than they'd expect but it's certainly not a 'bad' noise yet. They could fit a new diff for around £2600 but they said this was a large amount of cash for something that they would probably ignore if it was one of their cars. I could run the car for another 10,000 miles and the noise might not get any worse so the choice is mine.

I have days where I don't notice the noise at all, but then I'll notice it once and start thinking about it, and then I'll notice it for the rest of the journey or until I get distracted ... ooo, doughnuts ...
 

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I rather think this might fall into the "if it ain't broke don't fix it" area.

I had a similar knock from a Jag (old XJ) diff in my old Cobra that was transmitting 500 BHP and lbs ft (regularly, lol) and it never gave any other issues, although I did change it when I wanted to alter the diff ratio.

Not the same diff I know, but essentially similar.
 

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Wait until it goes bang.

£2600 is a little less than mine cost, but that was main dealer pricing and under warranty, fortunately.


Sent from my iPhone using Tapatalk
 

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I rather think this might fall into the "if it ain't broke don't fix it" area.

I had a similar knock from a Jag (old XJ) diff in my old Cobra that was transmitting 500 BHP and lbs ft (regularly, lol) and it never gave any other issues, although I did change it when I wanted to alter the diff ratio.

Not the same diff I know, but essentially similar.
Wait until it goes bang.

£2600 is a little less than mine cost, but that was main dealer pricing and under warranty, fortunately.


Sent from my iPhone using Tapatalk
Yep, this is the way I'm leaning now too.

One more complication is that there's a parts guy on Ebay (who seems legit with 1200+ feedback at 100%) who is selling a number of these diffs for £750 brand new. So I could get mine replaced now for around £1200 or risk paying the full price when/if it goes kaput .... dilemma

:D
 

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If you have the spare moolah, might be worth buying a diff now at that price and holding it? You could always resell it if it turns out to not be needed.
 

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Discussion Starter #33
So the guys spent a while under the car yesterday investigating everything that could possibly making this noise, and they've pinpointed the differential as the most probable cause.

There's no play in the propshaft as it exits the gearbox, there's no play in the drive shafts as they enter the hubs, there's nothing worn enough in the suspension bushes to make such a deep clunk, and as I reported earlier I'd noticed a small amount of play in the differential between the wheels moving and the propshaft turning.

The opinion of the two guys (who have over 25 years of Jag dealer experience between them and numerous years of independent experience) is that there is slightly more noise than they'd expect but it's certainly not a 'bad' noise yet. They could fit a new diff for around £2600 but they said this was a large amount of cash for something that they would probably ignore if it was one of their cars. I could run the car for another 10,000 miles and the noise might not get any worse so the choice is mine.

I have days where I don't notice the noise at all, but then I'll notice it once and start thinking about it, and then I'll notice it for the rest of the journey or until I get distracted ... ooo, doughnuts ...
Thanks for the info mate! Probably the same issue with my car so will forget about it unless it gets worse. I also looked at those diffs on eBay when I first suspected it could be the diff, seems a reasonable price. I wonder if he would discount if we both bought one 🤔
 

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Am I right in thinking xj xk and Xfr 5l s/c all share the same diff?
AFAIK all 5.0 SC Jags have the e-diff, so that would include the later model XJR, XKR and of course XFR (and XFR-S).
 

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Anyone have updates on this as I believe I have the same symptoms.

Slight clunk/thud with light throttle on/off applications generally 30mph and below.

Diff seems fine, only a few mm play In the crown/pinion when rotated back and forth by hand.

Gearbox output has a bit more play and clunking when rotated by hand but I don't have another 6hp26 to check against for normal back and forth rotation play.
 

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If you're sure it's not the diff' then two other things occur to me.
1. A suspension element - worn bush somewhere.
2. Gearbox. How many miles on the car? And has the gearbox/transmission oil ever been renewed?
 

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It sounds further up the driveline, I'd almost say the gearbox mount had torn if I didn't know any better. The movement at the diff seems to be minimal. You can feel a slight amount of backlash in the crown and pinion, but nothing that I'd say is excessive.

Its on 55k, and I plan to sevice the gearbox at 60k.

I replaced the diff oil a few weeks ago and pretty much the correct amount came out, with no signs of seals leaking so I would assume the diff bearings to be ok???

I've cracked a rib so getting under it again isn't likely any time soon.
 
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