I've got a vibration on my 72 Supreme that comes and goes at around 60-65. It lasts a few seconds and goes away a few seconds. Not in the steering wheel but the whole car. I just had the rear u-joint replaced but I also put the wheels - which I had balanced last year with new tires - off my 66 on it at the same time. I didn't drive it on the highway until about a week after the change and that's when I noticed it. I'm thinking the rear wheels weren't balanced correctly or the u-joint is defective. Any thoughts?

 

It could be any of a number of things. You're just going to have to troubleshoot until you find it.

 

Is the rear u-joint correctly seated in the pinion flange?
I replaced a u-joint in a 72 and had to slightly squish the ends of the u-joint with a c-clamp to get the u-joint to correctly seat in the flange.

Try jacking the car up and grab the rear (and front) of the drive shaft and try to shake it. If there's any play at all that needs to be addressed.

 

If light throttle pressure can vary it, look at the u-joint for binding/stickiness.

Good luck!!!

 

Is the car lowered? Stock rear control arms?

 

It's not lowered and the rear control arms are stock. Going to double check the new u-joint tomorrow.

 

So I had the wheels balanced today and the culprit seems to be a slightly bent back rim. The guy who mounted them last year didn't catch it. Now I have to go to my rim pile and clean and paint another rim. At least I know what the problem is.

 

Good news.