Sorry don't know where is got that 18mm from. I still have my old sway bar and measured it @ 32mm. The XJR bar is slightly thicker and does not effect the drive comfort, but does give flatter cornering and improved steering response.

OEM Sway bar non XJR 32MM

 

Thanks, this just added to the confusion. Lol maybe my reading is jacked up. I don’t want to dismantle the car to get a reading. I thought it would be an easier task.

 

Ended up having to check my vin for these as even the Jaguar parts guy could not figure it out. Ended up being C2P13649 for my 5.0SC Portfolio. I will assume you had 31.5MM on the SportSpeed and the XJR has 32.5MM, there is probably a smaller bar for the 3.0 and NA5.0 cause I was hoping to have the $25 dollar units and not these that go for $45each. Anyways the old ones are hard like poly but likely not clamping they bar tight enough, the fabric is smooth. Let’s how it gets it done, engine heat kills these.

 

When you torque down the sway bar bushings, the car weight needs to be on the wheels, so on a flat, drive on lift, not with the wheels hanging in the air. This eliminates the soft clunk that you are trying to get rid of.

 

A trick I use is to wrap the bar with Teflon tape where it rides on the bushing.
Seems to help with the noise.
.
.
.

 

So the saga continues, I have replaced the sway bar bushings and while temperatures were warmer it had appeared to alleviate, cold weather came in clunk was back with a vengeance. During my last oil change I poked around with a crow bar and felt bushings were mushy and the torsional arm seemed suspicious. so I just replaced them, which I was happy about after removing them. These were aftermarket unsure how long on the car, maybe 50k idk. Previous owner repairs. I replaced it with well the same aftermarket ones. They were distorted and off centered, the rubber came lose from the middle aluminum sleeve. Also while these were off the steel lower control arm inner bushing separated from the inner sleeve, but bushing appears ok still. I don’t believe it’s the cause.

But the clunk is still present!!!!! Next on the list is upper shock mounts. And if that’s not it gotta find a river to drive off into, wait maybe I’ll try upper control arms before dumping in the river.

 

Keep at it!!
I think it might be upper strut mounts now although they tend to squeak rather than clunk?
.
.
.