Greetings everyone,
It seems like I have a new question every day with this newly acquired XJS. I am extremely grateful to everyone for your assistance so far.
This morning on the way to work I put a recorder in the boot; we have a roundabout at work that gets very little traffic so I thought I could isolate the noise by driving around it quickly and decelerating. I did.
The knock only appears going around the round about left to right; it only appears when my foot is taken off the accelerator pedal.
So, I am thinking this is a rear differential issue.
Please listen and let me know what you think.
If so, is this rebuild or replace (if possible) territory?
Best wishes,
Charles

 

I do not believe that is the diff. it sounds more like a driveshaft or propshaft rotating against something. The rear axle is quite flexibly mounted, and its movement on a corner can easily make the propshaft touch something. get it on a ramp and look for witness marks.

 

I had a similar noise and it was the darn exhaust mount on the overaxle pipe that had let go although I can't recall if it was that regular.

 

You were asking about the trans mount a few days ago.

Have you done that yet??, if not, I suggest doing so, and then revisit this noise.

I did send that PDF from memory.

That small mount fiasco has been the root cause of knocking in all my Jags, from the MK X onwards.

Do that repair wrong, and that knock will haunt you, trust me, hence that PDF.

 

Forgot, it happens a lot.

The LH engine mount on the V12 takes a beating.

The LH side of the engine LIFTS a lot when accelerating, open the bonnet, put it in D, STAND on the brakes, STAB the gas pedal and watch the engine climb up on the LH side.
DO NOT HOLD THE REVS, JUST A QUICK STAB.

My reasons for mentioning:

That engine mount may be delaminated, most are, and the engine settles "oddly" when decelerating around a corner, gravity is a mongrel.

Beer time, see ya.

 

Dear Greg, Grant, and Ben,

Thank you so much!

Honestly, I have a long list of cheap aftermarket stuff to remove from this car. The list grows as I drive it. The transmission mount (which I don't believe has ever been replaced) is on the list. So are the engine mounts and all four rear subframe mounts. When the rear mounts are done, I will definitely start looking at the over axle area (the rear exhaust mounting brackets are on the list too).

It has become quite a project car, but I must admit I am loving it. I did the same when I got my Daimler Double Six for a dime and the upfront work with quality parts really paid off in the long run.

I will keep you posted.

Many thanks again, you are real stars!
Charles

 

I will watch this thread as I swear I have the same problem! I have taken it to multiple places, sometime they don't charge me anything because they can't find anything. Others charge me something because they tightened a shield, or removed a loose piece of something or other.

I did replace the diff fluid, no change. Replaced the rear mounts, no change. Replaced the motor mounts...you guess it, no change.

No obvious signs of rubbing or wear. No alignment issues, no obvious signs of wheel bearing issues....

Applying the gas doesn't affect the sound. You might not hear it though. It does occur, like you, when making left turns.

 

Dear Vee,

Greetings. I will keep everyone posted. It will take some time, I believe, to get to the bottom of this.

What has struck me is this: it only happens going around a roundabout. I never hear this with regular road driving, even making a right hand turn from the stop position. When going around a roundabout, the sound is not there when I have my foot on the accelerator, only when I remove it. The sound starts almost immediately once I remove my foot. The interval between knocks seems to get slightly longer as the car slows down.

This is definitely not a heat shield clanging on the second silencer, this is a real knock.

Really quite a mystery.

Charles

 

Vee, I forgot to ask: how long have you had this knock?

 

Charles
Very sensible to do the cage mounts, gearbox mount and engine mounts. Cage and engine mounts MUST be genuine metalastik brand. These are getting rare and are NLA from Jaguar Classic parts. David Manners still have some.
It is also possible that the knock could be the exhaust boxes in the tunnel under the boot each side against the tunnel sides, even with perfect mountings this happens on my car occasionally on very hard slow tight cornering under power.

 

Probably at least a year, maybe two.