My Series III recently had the diff and cage over-hauled but there is now a knock on acceleration that feels like the propeller shaft is not aligned. How does one align the shaft ? Is there a tool or technique ?
Rob
Rob,
Welcome to Jag-Lovers!
The procedure for aligning the propeller shaft is covered on page 47-3 of the Jaguar Series III Service Manual. (a very worthwhile document to own if you don’t already have a copy). I have done this alignment a few times over the past 22 years of XJ6/XJ12 ownership primarily when I removed and replaced failed center bearings. Often it was a trial and error process of setting the alignment and then taking a test drive looking for vibration. If there was a vibration on brisk acceleration, then I would make a slight change in the center bearing location and then try it again. The final locations were always closer to the right side of the tunnel than the left side.
Are you certain that your center bearing and universal joints are OK?
BTW, there are probably dozens of posts in the archives discussing this. Search for “center bearing” or “propeller shaft vibration”.
Paul
Don’t forget to check exhaust system-to-body clearances.
And transmission mounts.
IMO these are more likely causes of your knock. In any case, easy to check
Cheers
DD
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A misalignment would cause vibration, generally or during acceleration, Rob - which you do no mention…
Doug’s advice is good as a first step. As Paul says; aligning the propshaft is a trial and error, fractionally move center bearing and test drive - repeat as required…
And welcome on board!
Frank
xj6 85 Sov Europe (UK/NZ)
Welcome Rob,
If it’s just one knock I would look for play at the lower hub bearing shaft, u-joints (there are many), hub spline play, or even a loose/bad diff.
If it’s a series of knocks check if your prop shaft is touching something, burt most probably it’s your gearbox rear mount as Doug mentioned.
Rob,
Attached is a picture from beneath showing the location of the transmission mount, circled in red, in my former 1984 XJ6 Vanden Plas. There are two larger rubber mounts and a rubber bushing that support the transmission and isolate vibrations when these parts are in good shape. The rubber in these parts all perished in my former 1984 XJ6 Vanden Plas and former 1987 XJ6 Vanden Plas resulting in noticeable clunks when driving. I removed and replaced them and was rewarded with much more enjoyable rides. The large mounts all sagged considerably and the bushings had turned to dust.
As Doug and Aristides mentioned, the transmission mounts are another possible source of knocking sounds on acceleration. A visual inspection from below while the car is on the lift is needed. If these rubber parts in your car are original, they are well over 30 years old and should be replaced.
Paul
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Thanks Doug.
Yes, clearances are tight.
I will keep an eye on the exhaust system.
Rob
Robert Wilson,
CPA, B.Com. Chartered Secretary, JP.
Financial Management.
The contents of this email, and attachments, are confidential and may not be forwarded, copied or provided to any third party without the written permission of Robert Wilson.
Thanks Frank.
Yes, the knock coincides with acceleration from a standing position, particularly on a right-hand uphill turn.
I assume that the whole system, from engine mounts to cage, is tested at that point.
Thank you for your advice and for not pointing out my spelling error.
Rob
Robert Wilson,
CPA, B.Com. Chartered Secretary, JP.
Financial Management.
The contents of this email, and attachments, are confidential and may not be forwarded, copied or provided to any third party without the written permission of Robert Wilson.
**
Heaven forbid, Rob - spelling is not what we look for…
Just one initial knock at take-off is not associated with center bearing or its alignment. Look elsewhere, as others indicate…
Frank
xj6 85 Sov Europe (UK/NZ)
This is my experience on our XJ6. Standing start - inital high torque - to get going - caused a vibration that remained for a few seconds. Could amost feel the loading cause eccentric running at the centre bearing. As discussed the workshop manual deals this pretty well.
A single knock only and I might be looking for something simpler as well Frank.
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Is a single knock slack being taken up in a sloppy propshaft UJ, perhaps?
Thank you guys.
I discovered that one of my engine mounts is moving - so that might be the culprit. I will fix that and then assess.