XJ12 Series 3 - Noisy first gear around 2000 rpm

[Ken Briffa]

Hello all,

I have restored the mechanics of a perfectly original 1992 Daimler Double Six V12 which has done around 100k miles.
Before the restoration there was a vibration / small shudder / rumble / whine on first gear around 2000 rpm, after the restoration also.
This noise disappear as the revs go up and or the second or third gear engages.
The restoration is a £ 20k job and the car which was in excellent shape before the restoration is even better (of course) now.
No expense has been spared.
Car had and has no rust whatsoever.

The following have been done by a master Jaguar mechanic:
1) gearbox has been drained, checked, filter replaced and oil changed;
2) gearbox mount replaced;
3) drive shaft rebalanced and universal joints replaced with new;
4) differential drained, checked and oil replaced;
5) the whole rear end, dismantled, checked, re-assembled;
6) half shafts inspected and reassembles;
7) all wheel bearings replaced.

My mechanic and I after driving the car over the last few days are at a loss as to what is causing the vibration in first gear.
Ideas which have come to mind include a damaged (accident) half shaft.

Any ideas from the more learned among us?

Thank you in advance for your help.

[Ken Briffa]

Some photos of my car to get the jest of the refurb.

[mike020150]

Some nice looking restoration work. Since 2000 revs equates to different road speeds dependent upon throttle aggressiveness, it should be possible to eliminate the driveshafts, the prop shafts and associated transmission items from the equation by road testing different throttle openings to see if the vibration still occurs at the same revs. If it remains at the same revs (different road speeds), the problem is likely to be engine or possibly torque converter related. All this assumes that the gearbox oil level is correct having been checked hot with the engine running after moving the gear lever through its positions to ensure complete filling of all the hydraulic lines/valves etc. Mike.

[Ken Briffa]

Thank you so much for yours Mike.
I will discuss with my mechanic and get back.

The vibration only occours at the 1500 to 2000range in first gear.
No vibration in second or third gear.

[Ken Briffa]

All problems with my Daimler Double Six have resolved.
Interesting issue.
I Sent my gear box to Norfolk Automatics who refurbished the gearbox to as new.
Great professionals and sensible prices.
When I got the gearbox back the vibrations remained.
In desperation I purchased a used prop shaft to replace mine, which had been balanced, universal joints replaced and repainted!
My prop shaft was replaced with the used one without any work done to it.
All vibrations disappeared.

So that is the happy ending to a long story.
So in the end my mechanic was right that it did not seem to the gearbox BUT we had tried everything else.

Thank you for all your help.

[mike020150]

It's good to have solved the mystery problem. Presumably, you won't be using the prop shaft balancing company again! Mike.

[Ken Briffa]

Thank you for help Mike.
I have quizzed my mechanic regarding the balancing of the prop shaft which to him is a complete mystery.
He has concluded that the issue is to be found in the two concentric prop shaft parts which have some rubber in between.
I did not go further on the discussion.
The vibration, by the way existed, before and after the balancing.