OK, another quirk I am attempting to ensure does not end up costing big bucks...
When driving along and I let off the accelerator I hear a dull thump/clunk from what appears to be tranny or prop shaft. A similar noise is also heard when foot is applied back on the throttle. Almost like there is some slack that is in the tranny or prop shaft.

Any thoughts..?

Thanks,

 

I've got something similar in an 03 XKR which also happens when shifting from R to D.

I got under the car and turned the propshaft by hand to locate the source. There was near zero play in rear end or half shafts and the noise was coming from the output of the transmission.

There was a TSB for 2003MY for a clunk that called for changing the output flange with a revised part. I'm not really sure the differences in the old vs new flange, but your 08 should already have the newer one.

There is also a component in the transmission called a diode that locks into the case and only allows rotation in one direction. It has a little play in the case but has what is called an anti-clunk spring to keep the mechanism from lashing back and forth in the case as a function of load.

Based on what I understand of the transmission, neither of these would be fatal problems, although they are annoying. Next time I have the car in for an oil change, I plan to have them take a look and give an opinion.

There is one more option that I have heard of, that the rubber in the transmission mount goes bad and allows it to sort of thunk against the floorpan as it pitches up and down slightly with engine torque. This one usually only happens when getting on the throttle pretty hard and doesn't happen when getting off of it.

 

Thanks Charlie. Keep me in mind as and when you do get under to evaluate further. I was thinking prop shaft u-joints or something similar. I will try and take a quick gander myself in a week or so and see if there is anything obvious. I'll post the results (something or nothing) under this same thread.

 

You may need to have your tranny re-flashed/re-progamed. I had the same issue and thought it was a rear end or rubber donut (xjr tend to tear them up) but all it was a re-flash of the tranny hardware at the dealer and no more noise.

 

Do you have any noise when you make a tight and fast left turn? Under heavy acceleration do you experience a cluck or bang? Backing up do you fell a clunk or any thing weird? If you do it maybe motor mounts. I had all of the above to find that I had a failed left hand mount and a partially failed right.

Replacement fixed all the weirdness. Now to change sway bar bushing....

 

ooootis I don't have any noise under the scenarios you presented, but I will look at re-flashing the tranny next week and see if that cures this problem. Thanks, albert328gts.