Hello,

My 86 XJ12 shakes under hard acceleration only. Under moderate acceleration, it is smooth at all speeds. I noticed the fan shroud had knicks, and since the transmission seemed to sit low and loose, I thought it could be time to replace the transmission mounts. A local Jag mechanic did the same assessment. After I changed the parts, I ended up more confused.

Please see pics attached.

Questions:

1) Did the previous owner put an XJS transmission (and therefore wrong pin) on my vehicle? The transmission mount pin doesn't seem right.

2) If I DO have the wrong pin, is the XJS type so different dimensionally that it would explain my shake?

3) If not, what should I check next?

The motor mounts did not seem worn, but now I might need to revisit that possibility.

Thanks,

ROD

 

Since nobody else has answered....

Interestingly...or maybe not.... my Ser III V12 catalog shows the pin with the ring.....the one you think you should have. However, my XJS catalog (which doesn't cover all years) shows the "no ring" pin but with no mention or illustration of the spacer and washer.

I dont know that's significant in any way.

My gut feeling, and that's all it is, is that either type you've shown would be OK....just a design change thing with no operational difference.

I'll mull other possible causes. U-joints comes to mind.

Cheers
DD

 

There was a TSB on this subject a long, long, time ago, and it related to the middle bearing mount on the propshaft. I think this is also in the Workshop Manual for the Series 3.

The middle mount has slotted mounting holes allowing it to be positioned laterally. Instruction was to position mount fully to the right-hand side of the car and road test. Then if syndrome still present, move laterally in increments, (with road test each time), until syndrome had disappeared.

I had what you describe and it worked for me. Of course this assumes everything else is in order, like UJs of the drive shafts, etc.

 

Great point, Fraser. Certainly worth investigating. Those propshaft bearings are known to give trouble and the side to side adjustment really does make a difference...as I found out when I "lost" the factory-set location on my X300 :-)

Cheers
DD

 

Hello,

Thanks for all the quick answers. When I swapped out the parts, I noticed the driveshaft seemed to be pushed towards the passenger side. I didn't notice any signs of vibration against the body (which was close) so I left it. After reading some of your comments, I guess it might be factory setting, but next time I have it on a hoist, I'll try different positions.

 

Normal to be biased towards the right. Make sure to mark the original position !

Cheers
DD