Back story - I broke my ankle and haven't been able to drive anything fun since November. A about a month ago a friend needed to borrow a car and I needed them to be driven, so I let him drive the XKR.


On the way to a meeting that night, I was riding along, there came a weird thumping, bumping thing, felt like a flat tire. We pulled over to take a look and nothing, all was good. Drove on and bump bump bump. Decided to speed up a little and BUMP BUMP BUMP, faster and louder, the whole car shook. We were only dong 40mph. Figured it might be a flat spot seeing as it had been sitting and it had gotten really cold for a couple nights.


Got her home safe and took a slow drive around the neighborhood with the windows down and could hear some kind of metal crunchy noice from the rear driver side. I pulled the wheels, they rolled fine, nothing noticeable. Drove the XK8 and all was good so I decided to swap wheels and see what happens. Now both cars run like nothing's wrong. I haven't swapped the wheels back yet, as what I expected to happen didn't and now I want to pound some tequila.


No excessive play in the hubs, everything looks ok but of course you can't see everything that might be wrong. I suspected wheel bearings but now I don't know. BTW if you want a little rush put some 255's on the back of your XKR romp on it, it's like Christmas.

 

I would recommend that you check the universal joints associated with the rear axle you have 2 for each side. They are often overlooked and not lubricated and go dry.

 

Feel at the back of the tire for a big lump and the tread area.


Wayne

 

This is a diagram if you need it

Link http://www.jagrepair.com/images/Auto.../Halfshaft.jpg

 

The XKR has 48k on it, XK8 124k. XKR tires look ok, though they do need to be replaced, tread is getting a bit thin. The XK8 tires are almost brand new.


I was expecting the XK8 to start bouncing around if the tires were bad, and the XKR to keep bouncing around if the tires were good. I didn't expect both cars to drive like nothing's wrong.

I did take a look at the universal joints and they appear to be ok. More inspections and wheel swapping tomorrow. yay

 

Loose lug nuts (fixed when swapping wheels)? Raised pavement markers (fixed by changing drivers/roads)?

 

Not sure if your Ok was just a visual but to further check the universal joints jack one rear tire up and try to rotate the tire at the same time look at the universal joint and see if you see or feel excessive movement in the joint between the drives. This is a common problem resulting in the lack of proper lubrication.

 

Only 1 lug nut was loose, it was stripped on the XK8 so not the problem. Same road is being driven for the test drives.


I'll see if I can get a video loaded of the universal joints. But if it's the universal joints then swapping wheels would have no effect.

 

Took a longer test drive today with the rear wheels still swapped out. Drove a little harder, added some weaves and some hard starts. Nothing wrong with either car, though the XKR will light the world up on 255's and the XK8 launches like a beast on 275's. Still no bumping, thumping, shaking or noises. Maybe there was a cat hiding in the wheels.

 

Now I just give up. Swapped the wheels back to where they belong. Went for a quick test drive in both cars, having a little fun as well, and nothing. All is right with the world.


Drove the XKR for about an hour and a half today and it's running like it should. The bumping thumping thing just went away. U-joints are fine, no play, no excessive play in the hubs either. Lug nuts were all tight when I took them off. No metallic crunching noise either. I guess if you wait long enough the problem just goes away.


Gave her a bath and went shooting, VICTORY

 

I would take Gus's advice and have the half shalt joints lubricated. My 03 XKR had a crunching sound at low speed, I had to tell the dealer to lubricate them on my next oil change. This was on my third oil change at the same dealer. No noise afterwards.
It's possible that the act of jacking the car to change the tires unloaded the shaft joints allowing them to move w/o sound.