I have a 68 SS 396 with 325hp. I have had it for about a year. The problem is i get a big vibration if i go over 60mph or above. I have changed the u joints thinking they were the problem. Still there. At 60 i have put it into neutral and gunned the engine. It vibrates while gunning. The motor mounts seem ok by visual and i poked them to see if they are solid. Seem to be normal, the rubber gives. When i bought the 68 i was told it has a radical cam. It does lope abit in park. Is the motor out of balance? Its hard to drive under these conditions... Any suggestions to what i should look for?

to me it still sounds like it might be the tires, have you had them balanced? might be the drive shaft too. specialy if someone did a tranny transplant and cut down the drive shaft before you got it.

if it was the motor i think you should be able to feel the vibration while in park at the given rpm at which you turn to run 60 plus mph.

you could try and hold second gear and run it past 60 mph to see if the vibration is still there.........this will let the engine rpm higher........and if the vibration is still the same then i would lean towards the chassis part........

but it does sound like tires or drive shaft because since you put it in nutrual and gunned the motor the frequency of the vibration should have changed along with the rpms of the motor.

and since you said it was still there im sure its not the motor.

also i have seen tires that have broken cords inside that cause a lump in the tire and makes the car vibrate at given speeds. something to look into.

Kevin,

I also had vibrations at 60+ mph and it turned out that the mechanic had not torqued down one of the A arms. It is easy to determine if yur problem is a front suspension problem. Lift the front of the car and shake each wheel *hard* (up down and forward back). One of my wheels moved a lot... It might also be a front wheel bearing problem or worn out shocks.

Does your car still vibrates if you are doing 60mph but you are at a lower or higher gear? If it still does, it is not your engine.

Good luck,
Theo.

Check the transmission tailshaft bushing if it is worn you will get a vibe.

I had a similar problem with a 68, so one day my buddy says "speed up and see if it goes away" so i did and the vibe went away at 70mph(when all the studs broke off and the wheel departed) seems that I had a bent wheel and from driving it like that for about 2 months it fatugued the studs to the point that when i sped up they let loose. luckily we just slid off the road (it was late no traffic thank god) my point is be careful when you are acting as a "test pilot" trying to find these problems you can hurt yourself or someone else graemlins/clonk.gif

Thanks everyone for your input. It turned out that the shop who did my brake job did not tighten the front wheels correctly when they repacked the wheel bearings. They where both loose! Lucky no damage to the bearings.

Again thanks.

Lucky there was no damage to YOU !