Transmission Tailstock Bearing Play

I bought the car about three months ago and was aware that there was a vibration. So far I have had tires spin balanced (off the car). In doing this we found two rims and one tire that had runout. I replaced the rims and tire, but vibration is still there.

This week, I'll have the tail shaft bearing replaced as there is noticeable play.

The vibration kicks in at approx 45 MPH and stays there up to to 70, i haven't taken it faster. The vibration stays when I shift to neutral and let engine return to idle.

I'm not sure on the driveshaft whether its original or aftermarket. I've asked PO for more history, but so far not much has come. The car was used as a drag strip vehicle, but, I know that rear axle is 1973 or later as it has 5 * 4 1/2" BC axles and disc brakes up front.

When the car is in for the tailshaft bushing; I'll check for U joint phasing. There was no noticeable play in the U joints.

I have developed a sheet to go through more vibration analysis after the tail shaft bearing.

Have you had experience with the steel beads that are supposed to dynamically balance tires?

I have also read that some people suggest drilling the drive shaft and adding ATF and welding hole back up.