Hi guys

I‘m new here in this forum. My name us Stefan and I come from Switzerland.

As allways, the first post is about problems.

I recently bought a 1969 350 coupe. After a few days driving around corners there were more or les vibrations in the car at about 50 mph/2000 rpm.

Now idea what is wrong. Tires are new and balanced.

Any ideas aoute here?

Thanks for advising.

Stefan

New tires don't mean that they are good. how old are they check the date on the sidewall. the tires could have been sitting stacked on top of each other for 2 years and could be bad.
also check
bent drive shaft or bad u joints
bent rim?
bent axle flange?

I agree with Big Chief's advice. I have a similar issue with my 57 Tbird at 45mph. I've narrowed it down to a bent axel or flange and since that's more than I am interested in messing with, I'm living with it for now. The way I narrowed it down was to swap the wheels around first to see if that changed anything. Next I had the driveshaft balanced and installed new U-Joints. When none of this worked I figured since I don't drive the car much I'll deal with it. If you want to drive it often I would jack it up and remove the rear wheels. Then have a friend start it up and put it in drive and get it up to where it should be vibrating. Watch the drums and see if everything runs out smoothly. Also it is possible a balancing weight came off the drum. A good machine shop should be able to check balance on the drums.
Hope this helps.

Bad idea running the speed up to 55 MPH with nothing holding the drum on the car.

Thanks guys

Thanks. I‘sure that the issue doesn‘t come from the tires.m because the vibrations were there with the old ones.

Will check your ideas.

Stefan

Welcome to the site Stefan.
Maybe check the wheel bearing play front and rear.
Another way to check for runout at the axle flange would be to remove the drums and use a dial indicator to see how many thou the total is. One would have to clean all the rust off and get the correct indicator, If you wanted to check the flange while in gear and the engine running it my be a bit easier to see runout with the brake drum off.
One can have the tires and wheels balanced and still not know if the wheel itself is bent, maybe your tire shop can check the wheels for true.

Welcome!

A few questions:

Does the vibration stop over 2000 rpm? Can you “drive through” it?
Is it speed related?... or RPM related?
Do you feel the vibration in your butt?... or Steering wheel?

I’ve done this more than once. Just use 3 of the lug nuts, backwards, to hold the drums in place.

Hi again

I‘m going to drive on a new highway this week. No chance to feel it correctly on old roads. first impression: it is a speed thing. we will see i a few days. will keep you informed.

Wondering if you ever found it? My vibrations come and go at highway speeds. Tires are only things I know are good. lol But I know everything is worn and loose. The list includes... everything. I don't drive on the highway much and if I keep it under 70 don't have too many issues. If it was happening at lower speeds I would certainly need to address it.

Hi folks

I‘ve found the time to go the shop. The problem is clear now. The wheels! I‘m driving (old) cragars. They were on the car when I bought it. the hole of the wheels looked very bad. So we tried cheva rallys. no vibrations!
So , i‘m gonna buy some Pontiac Rally 2 and the issues should bern solved.
Thanks guys
Stefan