Weird vibration

[Zippyworld]

I originally posted this on the general forum under technical and caught no luck.

I have received my 98 XJR back after a Dinitrol treatment and it has a drive issue, it definitely was not like this before it went in.
It was up on a ramp and the wheels have been off.

At 45 mph and especially at 50mph there is a deep trembling / vibration feeling from the car, it doesnt feel like front end.
I have done the pressures and balanced all four but its still there. Tyres look fine.

Its really difficult to describe, it could be a diff issue.....I have never felt anything like this before. Its doing my head in though. It doesn't affect the steering wheel and still does this in Neutral.

Is there anything that anyone can think of that could cause this ?

[Zippyworld]

Thanks for your comment, Is there a way to check for this ?

[Zippyworld]

Concise and helpful as ever JS. Will take your advice (again) Thankyou
Will teport back

[Zippyworld]

Update : I thought I'd get the car back to the garage that completed the Dinitrol treatment and I asked them to remove the treatment from both drive shafts, propshaft and UJ's.

It worked, the vibration has gone.

The garage were very helpful and had never come across this before.

I thought I was in for a long pain in the arse fault diagnosis time !!

[Zippyworld]

Jaguar steve said:

Good news. I guess they'd got a strip of treatment fluid along the prop. Shows it only takes a few grams to throw the balance out.

Certainly surprised me, I was wondering if maybe the old Dinitrol was not properly removed and there was a build up.....