Getting highway speed vibrations between 55 and 70+ mph. Feels more centered in the car if that makes any sense. Steering wheel itself has slight shimmy, but not enough for me to think it’s in the front suspension. I took both rear tires off and looked over half shafts and suspension bushings at a glance. Nothing stood out as obviously worn or damaged. With a vibration occurring, are the odds more so a u joint problem, or bushing problems? I can’t get under the car enough to inspect the actual drive shaft itself. I ruled out transmission by putting the car in neutral when it was vibrating. No changes in vibration, so it has to be in the suspension. New tires put on it that were road force balanced and within specs. Any thoughts?

1987 Corvette

 

I hate vibrations unless it comes from the audio system. If you had new tires installed and balanced it should not be that, They usually start vibrating at 45mph on up. You can have them rebalanced at a last resort. Did it start vibrating after new tires? I would try raising up the rear of the car or put it on a lift, tires on, tires 2 to 3 inches off the ground start car and see if it vibrates above 55 mph. If it does remove the wheels turn the lug nuts over and snug them against the rotors and try 55+again that way, if the vibration is still there, let it idle in drive (with wheel chocks or blocks) and visually check the shafts for running off center. If shafts look ok, turn off the car place in neutral and physically try to move the ends of the shafts. Check the rear transmission bushing,(should be very little) differential input bearing and diff side output bearings for slop. it's easier to check wheel bearings with wheels on off the ground for excessive play. Inspect shafts for recently lost balance weights and slop in the u joints. That should get you started..

 

Thanks for the info. Yeah, the car vibrated even worse actually when I first got it. Took it to a tire shop to start with the basics. They found spacers on the car that were not hub centric and tires that were twenty years old. Replaced tires and bought hub centric spacers. Vibration calmed down some but still exists in the 55+ speed. It’s not easy at the moment to find a shop that will take on the car. They either don’t have lifts designed to not damage a low sitting car or can’t duplicate the vibration while on a lift verses driving highway speeds.

 

I would be curious to know what the car would do with a floor jack and some jack stands. Rear tires off and 60 mph in the air. If you don't have a jack and stands and no friends that do. You can go to a rental store and rent some unless you don't feel comfortable doing that. There must be something else causing the vibration than the old tires. They will check your driveline with new tires with an alignment when you buy new tires most of the time, unless you put the wheels on yourself.

 

Even with the transmission in neutral, bad u-joints could still cause a vibration. Can you tell any difference between when you're accelerating versus decelerating with it in gear?

I forgot to mention that if the car is on jack stands with the wheels off the ground, the half shaft u-joints will not be at their normal angle which might affect what's causing the vibration.

 

Raised the car and noticed the driver rear tire has play up and down; None side to side. Passenger rear tire also has play up and down; none side to side. There is no give in any of the bushings when moving the tire up and down. Play seems to be at or around the wheel bearings. I’m leaning towards a bad driver side wheel hub assembly. I’m going to replace both rear hub assemblies and replace the u joints on both half shafts. I’ll keep you posted on the driving results after parts replacements.

 

Hope that takes care of the problem.