I have a vibration in the rear of my car. It doesn't really start until I reach 70 mph and above. The vibration doesn't get worse with more speed. I have had the tires road force balanced at two different shops. My tires have about 8000 mi on them with no unusual wear. The wheels and tires have been checked for out-of-roundness and I have had the rear up on jacks placed under the shocks and run the car up to 90 mph with no vibrations. In my mind this kind of elminates drive shafts, wheel bearings, wheels, tires, and rotors. (i could be wrong) Another thing to add to this mix is that when I use the recommended tire pressure for the 17 in revolver wheels 32 F 34 R I have the vibratioin that I describe. If I reduce the tire pressure to "maximum comfort" 26 F 28 R the vibration is there but reduced in intensity. With regular city and country driving there is no noise or "clunks" in the suspension, car drives fine and tracks straight. I have done the shock test on all four corners and they seem fine. Also the vibration seems to be up and down...not side to side. If I am on a new piece of highway there is little to no vibration...the car seems to pick up on small variations in the road and magnify it.

I sure could use some advice on what to test or look for next. I suspect the lower shock bushings or torsion links but I would like to have a direction before I start tearing things apart. Thanks in advance for any advice.

 

If you can see the bushings you can usually see if it's going bad; squashed out, cracked, torn, etc. At 14 years old, anything rubber in the suspension is suspect. If you plan to keep the car a while you'll eventually change most all of them.

 

Rear shock bushings would be my first suspect. The upper mounts are usually fine in the rear, last much longer than the front.

Check your wheel bearings also for play, my right rear was out of spec, where my driver rear was just fine.

 

H20boy...you mentioned the wheel bearings. All 4 have a very small amount of play both at 12 - 6 and 3 - 9. All four wheels feel the same. what is the acceptable tolerance on the bearings? Thanks

 

ooooh, sorry don't know the tolerances. If you can make it move and it also creates a noise...that is obviously too much.

 

I have the same problem...vibration that seems to be coming from the back of the car. At slow speeds the vibration is less but at 80 it is extremely noticeable. Mine is a 2000 XKR with 45k miles. Always garaged and almost pristine. The back right needs a shim due to wear on the inner edge but I haven't yet read in a forum that would cause a problem. All of my suspension components look new...to my untrained eye. My tires are new, but not sure about the road force balance.
Let me know what you find!

 

My plan is to replace the shocks all the way around and replace outer tie rods. I'll probably tear into it sometime this winter. When I get it all replaced I'll get a 4 wheel alignment and see where it stands. On your problem I would make sure my tires have been road forced balanced before anything else. You can go to the Hunter web site and find tire dealers that have that equipment in your area.

 

Vibrations on these cars can drive many a folk insane. When the road force system came out, that helped but didn't cure.

What I think you may have is multiple concerns.

You mentioned play at 12:6 and 3:9.

12 and 6 can have a certain amount of movement. What is important is WHERE that movement is from. Two areas that could have movement and only one is normal. My test was to push the top (12 o'clock) and feel the output shaft of the diff of the side you are pushing on. There should be a small amount of movement there. The other area is the wheel bearing. Move the wheel 12 and 6 and feel the u-joint inside the hub carrier (the big piece of aluminum where the caliper bolts to. There should be zero movement there up and down. (I recently had to replace the left rear wheel bearing on my car, tedious if you know what you're doing, not so much fun if you don't)

3 and 9 should have ZERO movement. Two things control that movement. The wheel bearing is one, the testing of which I described above. The other is called the fulcrum bearings. These are small tapered bearings that do sometimes fail. The test for them is to move the wheel 3 and 9 and inspect where the hub carrier is held onto the big heavy lower control arm. There is also a rear toe adjustment at the bolt that keeps the fulcrum bearings and hub carrier in place.

I hope this helps next time you get a chance to look at the car. I didn't have a vibration or noise but my left rear wheel bearing had way too much movement in it. It's worth checking all those points mentioned above.