Hello!

My 02 XJR with 70,000 miles has developed a clunk when stopping. It's worse when I stop quickly. If I stop slowly, I don't feel it at all. If I stop semi-slowly, I feel it but it's not as noticible as when I come to a quick stop. At first, I thought it was the transmission shifting down hard into first or second gear because that's exactly what it feels like. But when I rode in the backseat, it seemed to be coming more from the rear of the car rather than the middle of the car.

I had the transmission fluid changed about six months ago but the clunk didn't start immediately after that. I also had the fluid in the differential checked and it looked clean.

Could this be a rear transmission mount? Any ideas would be greatly appreciated. Thank you!

 

Transmission mount?....mmmm, possibly. But I would be more suspect of a more common problem, the rear shock dampers. Its a large foam bushing that seats on the top of the rear shocks and is known for breaking down (as mine did). While your at it, check your front shock towers. Look for tiny rubber granules from the tower bushings breaking down, they tend to deteriorate at roughly the same time.
If not those then I would be looking at the driveline.

 

Does it make any difference whether you're in sport mode or not? In sport mode, the transmission is shifting to 1st as you stop. In normal mode, it only shifts to 2nd.

If the sport mode doesn't make much difference, it's probably not the transmission.

 

I have tried it in both sport and regular modes and it's the same. There's no difference. But I didn't know the transmission was shifting to first rather than second in sport mode. Good to know! Thank you!

 

What does the car do in "N" -- if it makes the noise/ sound/ feeling in N it's not the driveline.

Do you get any change in any sounds as you add /subtract power on level ground at 45mph.

I would make sure the transmission is properly filled .. what fluid did they use?

 

I haven't tried putting it in neutral but I will try that tomorrow when I drive it. Good idea!

Regarding the fluid they used, my receipt says they put in five quarts of Pentosin Jaguar synthetic fluid. I don't think they completely drained the fluid before they added new.

I had the fluid changed last July and this issue only started a couple months ago so I don't think it's related.

 

Pentosin? Could they have used CF11S hydraulic top fluid? I believe Pentosin also makes ATF, didn't know it was approved substitute.

 

Two things that I thought of...
#1, either of the driveshaft couplers on the transmission side or differential side. They're made out of rubber and can come apart either due to time and/mileage. I suspect this is what you have going on.

#2, Where the 2 piece driveshaft meets in the middle has splines. The metal splines sometimes weaken and cause what you say you have.To diagnose this is really tricky. You just would need to replace the driveshaft.

 

The symptoms sound like:

a) front subframe vee mounts have separated

or,

b) body bushes at the front of the rear a-frame are toast

Either one will allow a separating motion during braking
and then come back together with a clunk when you let
go of the brakes.

If you say it sounds like it is coming from the rear, then
check (b) first. They are between the rear jacking point
and the rear tire.

 

I'm sorry for reporting back so late.

My mechanic couldn't find anything wrong with the car other than the rear sway bar end links. I was sceptical about the problem being fixed when they told me that was all they could find wrong and that was all they replaced. I've driven the car more than a month now and I no longer feel the clunk. I should say, I may have felt something once or twice but maybe it was my imagination. It used to do it all the time and I don't think I've felt anything at all in over a month. So I'm happy to report my problem is fixed!

Thank you to everyone for your help and advice.