XJ6 & XJ12 Series I, II & III 1968-1992

Judder from rear on acceleration

 
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Old 12-29-2011, 04:34 AM
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Default Judder from rear on acceleration

I own a 1984 Sovereign XJ12 which I bought over a year ago now. After some expensive bills the motor has been ruinning sweet ever since. However recently there has been a juddering form the nearside rear on acceleration, this stops once cruising but I am obviously keen to get this sorted. The 'jaguar specialist' that I have been signing my salary over to doesn't think it a major problem, but I am not convinced. Does anyone have any ideas?

Thanks
DAKD
 
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Old 12-29-2011, 05:18 AM
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It is possible one or both of the UJs on the drive shaft is worn out. How many miles on the car ? These things are very long-lived, but don't last forever. They should be greased a regular intervals, along with a load of other greasing points.

Yes, this is a traditional car with traditional means of lubrication ! Most mechanics have long since thrown away their grease guns as modern cars dont have the points anymore. I had to search out mine from a dark corner of the garage when I bought a 1977 MG Midget last year !

Other thing that can cause juddering can be the propshaft is out of alignment. This is split with a central bearing. The bearing housing is on an adjustable mounting so it can be moved laterally. I had to adjust mine when I rebuilt an XJ6 in the early 90s, as I had the engine and transmission out.

Finally, one or more of the rear subframe 'V' mounts could have failed. There are four of these, and are of the silentbloc type. Eventually the rubber comes away from the metal. When this was the only Jaguar suspension, people could jack up the car and leave the subframe behind !

It sounds to me it's time to inspect the rear drive and subframe closely for wear and tear.
 
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Old 12-29-2011, 05:23 AM
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Obviously, he wants more of your salary, and is waiting for a big failure to sting you for it. I'd suspect a tailshaft universal bearing, or perhaps a bush and/or a crook shock absorber. Check for lateral movement in suspension components. Another possibilty (and I cannot recall for certain, but I think they have a two piece propellor shaft), check to see that the support between the two sections of the shaft hasn't died. If you can 'wobble' it up & down it is probably in need of replacement.

Whatever it is, it isn't supposed to be happening and the engine is quite powerful enough to quickly destroy such a faulty component under that sort of load. If it is a 'rythmic' (intensifies then reduces then intensifies again) it is probably a universal joint. Either way, you don't want it snapping under load. The results can be spoectacular.

cheers,

Languid
 
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Old 12-29-2011, 09:17 AM
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Thanks very much - thats certainly food for thought - the car has just over 94k on the clock but still pulls like a train and certainly has more power than I have nerve. I will investigate all the suggestions and let you know the outcome.
DAKD
 
 
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