shake/vibration

1981 Corvette rebuilt/restored. 35+ mph. steering wheel shakes/vibrates. Higher speed, depress clutch, smooth ride. HELP!
Taken to mechanic recently, test driven to acknowledge, lift done twice, no clue.
Tim

So you are saying while the steering wheel is shaking, depressing the clutch causes it to stop, this isn't happening because the car then slows down?

So you are saying while the steering wheel is shaking, depressing the clutch causes it to stop, this isn't happening because the car then slows down?
It is happening, the vibration is not a side to side, it is an up and down. Yes, the vibration goes away when the clutch is depressed, yes the car slows but no vibration!
Tim

If the vibration quits suddenly when depressing the clutch then check eng,trans mounts and driveline. I'd also give a look at the crankshaft vibration damper.

What I remember at the shop, they did check engine mounts and claim trans. was OK.
Crank ?
Where do I check!
It is very hard for me to understand shake/vibration, but all responses are learned and appreciated.
Tim

Basically, from your description, the vibration issue is engine and/or clutch related. You should be able to duplicate it in the driveway with the tranny in neutral and the clutch out. Get the motor up to the rpm's where the vibration occurred on the road.

You say this motor was just rebuilt. Was it internally or externally balanced? Is it a small block or big block? Is the motor original to the '81?