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

Transmission judder at take-off. 1985 Slll

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Old Oct 17, 2017 | 07:09 AM
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iramphal's Avatar
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Question Transmission judder at take-off. 1985 Slll

Morning folks,
I have a consistent slight judder when moving off from a stop. It disappears after a second. Straight line or at a turn - same thing. No noise, just a slight judder. I would not call it "slipping" as such, but??? Any thoughts - Once moving, smooth as silk. Ian
 
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Old Oct 17, 2017 | 07:25 AM
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My first thought is worn out transmission mounts.

Cheers
DD
 
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Old Oct 17, 2017 | 08:11 AM
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There's a driveshaft support bearing that is a common culprit. It eventually wears to the point where you'll feel it knocking. Reasonably straightforward fix and not too expensive a part as I recall. Jack up the car and find the support then grab the driveshaft and see if it rattles around. You shouldn't be able to move it side to side or up and down.
 
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Old Oct 17, 2017 | 11:09 AM
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Originally Posted by pjprofili
There's a driveshaft support bearing that is a common culprit. It eventually wears to the point where you'll feel it knocking. Reasonably straightforward fix and not too expensive a part as I recall. Jack up the car and find the support then grab the driveshaft and see if it rattles around. You shouldn't be able to move it side to side or up and down.
This is what mine was....
 
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Old Oct 17, 2017 | 03:59 PM
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A common problem on many cars and usually noticeable when the drive shaft comes under load, such as initial move off from a stop as you describe. I've just had the shaft support bearing bush replaced on another (non-Jag) car of mine which gave the same symptoms i.e. only the bush was bad, the actual bearing was fine.
 
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Old Oct 17, 2017 | 04:41 PM
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As I remember from my Series 3, the centre bearing on the prop-shaft needs moving across to the offside in stages until the shudder disappears. You'll find slotted holes in the mounting bracket for this. Once I had adjusted mine, all was well. I think this was in the original workshop manual, (the big green book)
 
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Old Oct 18, 2017 | 07:39 AM
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Thank you all for your responses. Would anyone have a description (or a page from the "Big Green Book") on how to "adjust this mount as described by Mr. Mitchell above?
 
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Old Oct 18, 2017 | 08:15 AM
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The procedure described in the workshop manual involves using a jig to correctly position the driveshaft/propeller shaft. Specs of making your own jig are given.

In practice it seems that everyone just moves the bearing all the way to one side and then moves it in the opposite direction in small increments...maybe 1/8" inch at a time....until the vibration is gone. Tedious work.

To state the obvious, no amount of adjusting will fix a worn out bearing.

All that being said....

I've owned three Series III cars and worked on several others over the years. In all cases the bearing adjustment was all the way over to the right. In assembling my present project car I put the bearing all the way to the right and there are no vibrations or judders. Coincidence? Luck? I dunno. Just a pattern I've observed.

Cheers
DD
 
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