Still Vibrating... Options

[MikeM]

Hello all...I recently posted about a vibration I'm having at 30 and 60mph.
I have some new information to share and some more questions.
I purchased the hub centering rings from Chris Foley and they made no difference.
Today I took the car to my mechanic's shop and we put it on a hoist and I ran it up to 70mph. The shake/vibration was still there!! So, it's obviously NOT in the front end. Mechanice says he's pretty sure the shaking stopped when I put the trans in neutral and turned off the engine. Although that could be a function of the speed reducing also.
So, where to look now? Flywheel? CV joints/axles?
Car is a 74 2.0 liter.

Thanks as always...
Mike

[76-914]

Jack it up with one rear wheel on the ground and the other above the ground. Doesn't matter which one. Put it in gear. The wheel above the ground should turn and the one on the ground should remain motionless. I say should because if it was modified then both could turn but check carefully in first gear. As long as it is still in first gear and the wheel is turning slowly, you can check the tire/wheel combo for out of round. I place a 2x4 next to the tire for a visual reference. Don't place it in front of the tire or it could get pulled under and fired out the rear. (IMG:style_emoticons/default/headbang.gif) Then run your speed test at 30 & 60. If we get a vibration from one side and not the other, I'm looking at CV's and/or their shafts. If there is no difference start working your way thru the tranny. BTW, you have had a 4 wheel alignment by someone that knows these cars, right?