What issues can you think would cause drive line vibes in my 56K mile 95' XJS 4.0?

I have replaced all the tires with new, balanced etc...
I have replaced the bushings in the transmission mount...
I have greased all the u-Joints
All the brakes/rotors look new.
The engine mounts look solid.

I am thinking the u-joints in either the rear axle half shafts or the driveshaft are the culprits..

Would an alignment or worn out bushings cause a drive line vibe? Bad Shocks?

Any ideas of where to start?

 

Could you provide a little detail as to the vibration? Is it road speed sensitive? RPM sensitive? Do you feel it the steering wheel? Or more through the body of the car?

"Drive line" would be engine, transmission, driveshaft, differential, axle shafts. A drive line vibration is a different beast from a tire/wheel/suspension vibration....but often no easier to solve :-)

But, yes, U-joints are a possible culprit for a driveline vibration. If a u-joint is moments away from death it'll have obvious free play when you check it. Otherwise you'll have to disconnect the driveshaft or axle shaft to feel the action of the joints....which, of course, should be butter smooth. If it is stiff (starting to seize up) it'll certainly cause a vibration... but may not yet have reached the point of having obvious free play.


Cheers
DD

 

its more a whole body vibration above 50mph.

 

how do all your rear bushings look?? I don't think it would be that tbh because when rear bushing go it is really obviously from the back of the car especially under acceleration and the rear feels loose and squirrely.
I don't know anything about u-joints but it seems to be one of the only things you haven't taken care of.

From my little experience its exactly what unbalanced wheels do, but you said you took care of it so i don't know.

I would try checking the u-joints like doug here said, sorry if its the ones on the halfshaft those will be annoying to replace.
Good luck!