I have a vibration that starts around 50, gets real bad around 55-60, then goes away. Doesn't do it with the clutch in. U-joints are new, checked that they are centered in the yokes. No noticeable slop in trans yoke, has new bushing and oil seal. Checked pinion angle when it first started and it was OK, don't remember the numbers now. Had driveshaft balanced. Also checked the pinion was tight.

Just replaced the tranny mount tonight. The old mount wasn't real bad but it was missing the nut that holds it to the mount, basically the trans could lift off the mount. I'm guessing this could cause the vibration? Car is a 70 bee with 4 speed.