Hello. I have posted before and received good help regarding the lighting on the climate control cover panel. Thanks to the good people on this forum.


I have a 93 XJS convertible with 189K miles. The car has had a vibration in the front end at 65 mph for the past 100+ K miles. I have been through 2-3 sets of tires, wheel balancing, alignments, front end replacement of ball joints and struts but no one can fix the problem. The vibration seems to be diminished when I drive with the convertible top down. I have been asked if the vibration is in the seat or the wheel. I feel it in both places. One mechanic thought it may be the drive train axle. He said possibly the balancing weights on it may have fallen off and it should be checked for balancing. Any suggestions? Thank you.

 

My sympathy, it took me a year to track down a slight vibration, which had, in the end, two causes. Here are some suggestions for possible causes, particularly as you have a high mileage car:

I know you posted that you replaced the balljoints, but test them again, all of them. One of my problems was a set of new balljoints, three of the four failed in 6 months.
Have the wheels carefully tested for runout, as well as balanced.
Ensure steering arms and stub axles are all attached properly.
Check float on wheelbearings.
Ensure the upper and lower wishbone bushes are in good condition, better still change them (lowers a big job on an XJS).
The gearbox output bearing could be shot, so the shaft that attaches the gearbox to the propshaft is wobbling about. Equally the clutch could be out of balance and semi-shot, or one of the bearings involved with it.
The propshaft itself could have gone home. It could be the universal joints, but on the 6 cylinder cars there is a central fixed bearing attached to the car which often fails and is easy to replace. Actually your symptoms sound as if this could be the trouble, certainly replace this first.
The diff could be loose where it is fixed to the rear cage top, or even the diff input bearing could be a problem.

Basically you have to work through the system methodically to find it. Good luck.
Greg

 

Greg will know, but if the prop shaft is the same arrangement as the
X300, check the alignment. Also check that the two pieces have not
been separated at some point and put back together out of phase.

Basically, the furthest front and rear u-joint ears have to be perpendicular
to each other when the driveshaft is assembled. If not, there *will* be a
vibration. Some shaft spline arrangements have markings or a odd spline
to aid in proper assembly and some do not.

On the other hand, if you have flexible Jurid style couplings, they could
be falling apart internally.