If the driveline is straight then then only angles that change are the up and down angles of the pinion and the trans yoke. If not, then there is a compound angle that would throw some vibrations into the mix.
I have a strange resonating vibration around 80 that is still there when I push in my clutch, eliminating the engine. I've also changed out all of my wheels and tires. Its like on for a second, off for a second, on for a second, etc.
I'm thinking that I need to do an alignment check with the mains all the way to the rear-end yoke's center to see if they line up. I've been to Jerry Bickel's and Jerry Haas's race cars shops in the early 90s , when I used to drag race and I noticed that when they lined up the engine and rear end, they would use a solid bar, bolted to the mains, that went all the way to the rear end to center everything up.
I might try to use some kind of laser to shoot a beam to somehow check alignment. Maybe hang some plumb bobs from the crank front snout, then the trans' output shaft to see if they point straight to the rear end's yoke. My car was in a left front wreck sometime in it's life causing me to change my left front frame rail, when I restored it. I should have taken it to a frame shop to have it all laser aligned before paint.
If anyone knows of how others have checked this let me know.
