Intermittent High Speed Vibration

[gorilla1969]

Hello,

I have a '00 Pontiac Bonneville which has an intermittent vibration at speeds above 65mph. I've had the brakes inspected, all the wheels balanced, and had an alignment performed. Although the car now rides better overall, the root problem still exists.

The vibration comes and goes in 5 or 6 second intervals and is felt moreso through the seat/inside panels rather than the steering wheel. I had the had the brakes inspected since it sometimes felt more pronounced during braking but the mechanic said the brakes checked out fine.

Any ideas?

[golfyeti]

This is known as the mysterious 65 MPH shimmy. There have been numerous suggestions to get your tires 'road force' balanced, and some have said getting new rotors did the trick.

I have tried everything and still get the shimmy at that speed. I still think there's an aero-dynamic component to this effect as I have noticed that the shimmy happens at lower speeds when heading into the wind and at higher speeds with a tailwind. Once I get over 73 MPH I never get the shimmy.

The next area I am investigating is the rear suspension as I know this is a weak area on my car. I am replacing the shock mounts this weekend and may look at getting new bushing if this doesn't correct the problem.

[Archon]

Mine showed up when my driver's side tie rod end was worn. As is was time, I also replaced my struts, and mounts. The vibration was still there until I had the alignment done.

[gorilla1969]

The vibration is the strangest thing. And the car seems to drive smooth as glass above 80-85mph - just as golfyeti mentioned.

I did have the front wheel bearing/hub assembly replaced and the left front tie rod replaced as the mechanic said they should be replace after looking for the vibration problem. This took care of a rubbing sound I was hearing but the vibration still remains. I have had someone else recommend the Road Force balancing and also suggest there might be a tire defect (seperating tread, etc). I just hate to randomly throw money at it with no promises. That's the nature of the beast when it comes to cars (and women).

[imidazol97]

A good set of round tires helps, and then have them road force balanced by someone used to troubleshooting problems like this one. I'd recommend a good GM dealer.

I'm a big fan of Michelins for being round and staying round.

Also an alignment that s right on the perfect settings helps--not just "within the tolerance amounts." My leSabre 03 reacted to toe setting on the rears when new. At 12000 miles the dealer service manager had done the 3rd road force and test driving a newly paved hot asphalt road to find the source.

That might explain why wind seems to more easily affect the feel. Also if you've watched cars on the road some seem to have rear wheels bouncing slightly and the drivers don't seem to notice. They can be acting up and give a feeling but it's not definite like the fronts will feel.

Also check for a dragging caliper on the fronts.

Just replaced the original tires Symmetry by Michelin when they got down to 5/32 with Harmony by Michelin and the road force balance made them next to perfect. The first tire store in the chain didn't have road force and used a standard balancer--good, but no brass ring. Three of the wheels were .50 ounce off; but they had been driven 4-5000 since the rebalance at the first store. Another store in the chain has road force balancer so I went there for my balance check included in purchase price.