I have had a vibration for several thousand miles now, that is getting worse by the week and I'm hoping for some direction to find the source.

It's related to wheel rotation and more noticeable (louder too) as speed increases.

What I've done so far to eliminate possible sources is changed tires,wheels, and rotors.

I've also driven at a speed where the vibration is very noticeable and shifted to neutral and had no change, so it's not related to engine speed.

It does feel/sound slightly more intense when rounding a curve, under load, and coasting. i.e. everything except steady throttle on level roads.

I've checked temperatures of several components with a laser thermometer and found no significant differences from front to back or side to side.

At one point I was thinking tranny/diff, but I'm not sure how to check that.

I thought about running on a dyno to verify which end of the car (front or rear) is the source.

The one thing that bothers me most is the increase that came when I swapped from my base rotors back to the larger F55/Z51 rotors.

Any ideas of what to check next?

 

Bad clutch pack?

Have you changed your differential fluid? Gm additive, royal purple fluid is what I did when I started hearing grinding while backing and turning at slow speeds, solved the problem.

Possibly a tire out of balance or bent rim?

Those are my guesses.

 

As a rule if you feel it in the steering wheel the problem is in the front. If it's in your seat the problem is in the rear.

 

Sounds like it could be a wheel bearing. Try zig zagging the car back and forth while driving down the road and see if the noise/feel changes more in one direction Vs the other. If it is louder on the left turn then the sound/vibration is coming from the right side. Excessive run out in the bearing would be more noticeable with the larger brake rotors.

Bill

 

Wheel bearings, probably front. Symptoms sound "similar" to my DD (not a Vette) that ended up needing new wheel bearings on both front wheels. Hope it's that simple for you.

 

I know this is not a Vette, but I chased a vibration that was speed related on a 84 Buick La Sabre rear wheel drive. Turned out to be a U joint on the drive shaft. I know the torque tube drive shaft doesn't have U joints, but the half shafts each have 2 (4 total) CV joints.

 

Push the clutch in at speed, give it a few revs. Still there?

 

Well a front wheel bearing was my guess too. I do feel vibration in the steering wheel, but I feel it in the rest of the car too, even if I'm in the passenger seat.

I checked both front spindles without rotors and again on the rotors (lugnuts added) and again on the rims with a dial indicator and found nothing out of factory specs. I also did the push/pull on top/bottom to take up any slack and still nothing. There is no temperature difference from one side to the other after an extended 100 mile drive on any component. I'm planning on checking the rears in the same method in a couple of days if I can get started early morning while it's only 90 degrees in the garage.

On a 20 mile trip today, it started out noisy for the first mile or so then quieted down. About 15 miles later it became it's normal loud self. It repeated the same sequence on the way home, but didn't take as long to get quiet.

At speeds up to 40-50 I can definately tell it's wheel rotation as it make the same type of noise/vibration as a warped rotor. I can't hear it over the wind and exhaust with the window down, so it's not that loud yet. By the time I'm up to 60+ it becomes more like a shudder that cycles on an every other wheel rotation frequency.

I may change the front bearings anyway if I don't find a problem on the rear, just because I have 85K on the clock and I have a 6K+ road trip next month.

Thanks for your help so far. If something else comes to mind, post it up.

 

Already well past the wheel/tire check and have no grinding diff noise, but the clutch packs do have me a little concerned. If I'm reading the tranny sequencing correctly, slipping into neutral at speed does a disconnect with everything except the output shaft. Does that sound right?

If the rear bearings check out good, I should probably spin the rollers somewhere before changing the front bearings (the easy ones ). so far I haven't found any heat indication on any CV joints, although I was suprised that the half-shaft itself (both sides equal) was warmer than the wheel bearings or the CV joints.

It's an A6 and I've basically done that and found no change.

 

I had a loud sound on my 97 and it turned out it was due to all 4 bearings needing replacement. The sound just kept getting less as the bearings were replaced one at a time. The bearings didn't have any free play and the only way to tell they were bad was to hold them in your hand and turn them. Then you could feel the roughness.

Bill

 

Nothing to add but wish you good luck, I have been through this type of thing before.

 

Thanks Bill. I'll keep this in mind as I continue. I've never been real comfortable with the so-called lifetime products. The only one that really meets that criteria is a casket.

 

Ive heard of something similar from the torque tube bearings going bad on A6 cars...hopefully not it but maybe worth a check.

 

Why don't you put the back end up on jackstands (or on a lift) and run the car at the speed the noise is most noticeable. If it's gone, it's probably a front bearing.

You can also listen to each wheel bearing with a stethoscope while spinning the front wheels by hand. You will hear a difference if one is going bad.

 

I was experiencing a similar issue and it was my passenger rear bearing. A quick test will be to get the car up on stands (or a lift) and hold the tire and 12-6 and wiggle (vertically) to see if you get any play, then at 3-9 (horizontally). If you feel almost any slack really, that bearing is either on its way out or gone.