Vibration

[cadillac512]

Originally Posted by 47jailbar

I doubt it’s wheel/tire related as there is no vibration at low speeds and seems to be more dependent on engine RPM; at shift points and above 45 mph in third. No tach installed at this time however by my calculations 275 60 15 tires with a 4:11 gear would produce a driveshaft rotation in the neighborhood of 2220 rpm at 45 mph which would also correspond to a reasonable shift point.

This is a clue. It appears the vibration may be engine, flywheel or clutch related since the above statement indicates it occurs both at shift points and above 45mph in third (which would be another shift point if there was another gear). This would likely rule out anything to the rear of the clutch.