Funny vibration in a '78 308

Recently I've had a vibration that has occurred several times when first driving my 308.

1. It occurs after a couple of miles of driving and feels like a tire with a bulge.
2. It starts with a little vibration and gets worse, independent of speed and gear, the longer you drive.
3. I've stopped and felt around all 4 tires, moved the car a little (in case a bulge ends up on the pavement) and felt again. Never felt anything.
4. After starting again, the problem is gone and usually doesn't reoccur on that drive.
5. Only once has it reoccurred immediately. Even then, no vibration for a mile or so and then progressively got worse.
6. I've had the car on the lift and checked out that the suspension is tight, nothing loose and the CV joints feel fine. All wheel weights are still under their racer tape.
7. The problem feels like the right rear and definitely from the rear since there is no steering wheel vibration.
8. The other day this happened and I noticed that the RR tire was a little low, so I brought it up to the correct pressure. No reoccurrance when I left a few minutes later even though I drove 250 miles with a couple of stops.
9. Today, it happened within a few minutes of starting. I just stopped by the side of the road, engine on for 2 minutes. Starting off again, no vibrations for the 250 miles and three stops home.
10. This gets so bad that at 50 MPH, the mirrors are shaking so much you can't use them and I have to stop the car.

I'm really stumped. This has the classic symptoms of a tire bulge, but it seems to be intermittent and goes away immediately after stopping. At least I can't feel anything by the time I get stopped and out of the car. When slowing down you can feel the thump thump acting just like a bulge to the point of thumping on each revolution of the tire at very slow speeds.

I can't really put the spare on since I have QV 16" wheels and the spare is 14". Besides, with the intermittent nature, I'm not sure that the lack of reoccurrance would mean anything. The tires are P-Zeros Asimmetrico so I can't even swap them side to side. I did have a side-wall bulge on the LR and replaced that tire about two years ago. The rest are 4 years old.

Any comments or suggestions welcomed.

Regards, Kerry

 

Sure sounds like tires. If it wasn't so intermittent I'd lean more towards suspension or drivetrain. If you want a professional opinion take it down to the guys at Group 2. I took my 308 there after having vibration problems and it turned out to be wheel balance (I had just had old tires mounted on new wheels). The place I had do the mounting didn't do a very good job of balancing I guess! Good bunch of guys to deal with too.

http://www.group2inc.com/

 

With regards to your comments that you can't put the spare on; don't you still have the old wheels? Everyone on Fchat always says to save your old wheels! I wouldn't worry about running the tires backwards for a little while to see if it feels like it's different. Sounds like a tricky problem good luck & report back.

 

My two cents: check the lug nuts and then wheel studs. You may have a couple broken studs on a wheel, or loose lug nuts.

Also, did you check for play in the half shafts? Jack the rear and grab the wheel at the 12/6 o'clock position and pull and push; do the same at 9/3 o'clock. My car should have like .005" of play; it should not be dead tight. You should see what yours should have. Just a thought.

Ken

 

The mirrors are supposed to shake like that. LOL

 

Intermittant problem that rotates at the same speed as the wheels/tires. Only thing I can imagine is that the right side axle has a cv joint binding up. If that happens, it could put the axle off plane and cause a wobble you could feel. That's my guess.