Hi everyone. I’ve been an avid reader for a long time, but am now in need of your help. I’ve had my XJ8 for over 2 years now and so far it has been a good marriage. There has however been one problem that so far has not been solved. After about 6 months of ownership I started to notice a slight vibration after I would let it kick down on the highway and drag it to the redline. This however went away after some driving and I didn’t think much of it. After some time it got really annoying and I brought it to a Jaguar specialist. The previous owner had the rear end rebushed, but the garage apparently had made some mistakes that were promptly corrected (for example springs upside down). All in all u joints, rear wheel bearings, new flex discs, good used propshaft and a good used diff were fitted. This made some improvement, but it’s still there. The vibration is now constantly there and is still more noticeable after stepping on it on the highway. You start to feel it from about 80kph when the gearbox shifts into 5th and it gets worse from 120kph. It does become less noticeable from about 160 kph. Some have suggested to just always drive it at that speed, but that would be my final resort.

What also needs mentioning is that top the previous owner also had the gearbox rebuilt (50000 km ago) and that I’ve tried 3 different sets of wheels. The bushings of the front suspension look in okay state and the front and rear shocks have also been replaced at some point. Rear shocks are green Bilsteins and front shocks are Sachs. Suspension seems tight all in all. Engine also works flawlessly.

I’m very curious whether someone has something else that might have been overlooked so far.... thanks in advance!

 

Forgot to mention that a sticking front calliper was also replaced.

 

Welcome Elias..please take a moment to introduce yourself here please (site requirement, only takes a minute)... https://www.jaguarforums.com/forum/n...-intro-must-5/
Also, please list your car yr, model and engine in your signature. This way you don't have us asking for it and we have better reference for the yr and model we're dealing with. Euro is different than NA, which is different than AUS. This can be accomplished in the User CP, top task bar, left side.

..so, I have to ask, what kind of vibration and where? In the steering wheel, up through the seat, both....is it a sudden vibration or does it slowly come in as you increase speed and fade as you get out of the range?

Now the reason I ask this is because of these 2 threads, which are both from the How To section at the top of this forum....

https://www.jaguarforums.com/forum/x...g-info-188400/

https://www.jaguarforums.com/forum/x...pshaft-207717/

Your description of the what was done with the prop-shaft really points toward the second thread. But, I didn't see where the center bearing was replaced, thus the 1st thread.

 

Check and/or replace the engine & transmission mounts if they haven’t been. 20+ year old rubber looses its ability to absorb vibration because rubber turns hard over time. They can also sag which in turn changes the angle of the driveshaft up to the center support bearing and that will cause a vibration. This also includes the driveshaft center support bearing which is encapsulated in rubber.

I would also question a shops knowledge that install springs upside down. I don’t even know how that’s possible. (Head scratcher) I know it’s been corrected though.

You also mentioned 3 sets of wheels but were those with good tires already mounted on them and were they from cars that were vibration free? The sure way to rule out wheels is to have them mounted on a road force balancer tire machine to see how bad the up & down pressure of the tire on the road is.

 

As per the links from Highhorse:
From what I've read here on JF, I think that kind of vibration points to the u-joint of the prop shaft itself.
(Not the halfshaft u-joints.)
This is the one that's tucked away halfway down the car.

If it's a wheel based vibration, my understanding is that it should still exist in neutral at the same speed.

I have had a vibration that I found stemmed from a warped alloy wheel:
First step in isolation was to swap front wheels for rear to see if it came through the steering wheel.
Next step was to spin the wheels whilst jacked up - rear end is best as you let the engine tick over in gear - take a lot of care if doing so!
Check inside as well as outside as mine only presented itself on the inside edge.

 

Assuming you tried three separate sets of road wheels, and have replaced drive shaft components, including greasing the zerk fittings each side of the differential, the problem seems to be with internals in the transmission (not likely) or in the engine and transmission mounts (as mentioned above), the rubber components wear and dry out after twenty years and are no longer damping the engine vibrations.

 

the trans mount collapses and causes bad clunks/vibration

 

Lots of good suggestions re mounts, etc. So much can start going on at high speeds that many things can add up to create the vibration.....

One area I haven't seen discussed is the transmission / torque converter. Several years ago I was chasing a highway speed drive train vibration that I couldn't identify, but that came on only at higher speeds. In my reading I found many references to Torque Converter clutch issues that caused similar vibration symptoms in ZF equipped vehicles (Jag, Audi, BMW, Range Rover). The issues usually start to manifest at TC clutch lock up points - which matches your highway symptoms - esp if the Torque Converter is trying to modulate lock up if you have the pedal floored.

Not clear from your post what year your car is, so not sure which ZF box you have (5hp or 6HP), but I think the torque converter operation is similar in both. Lock up is initiated in both top gears. Top gear lock up starts at ~100 km/hr with full lock up happening at ~110-120. If lock operation is impaired that leads to the vibration and would certainly be a candidate at the speeds you reference.