"...... I am beginning to wonder if it is my thrust bushing on my tail shaft of my trans.....


Ryans comment triggered a memory for me. My 57 Plymouth always had a drive line vibration above 75 MPH, not horrible but noticeable.. When I was getting it ready to drive back to Illinois a few years ago I decided to address it........figured it was an out of balance drive shaft (it was an unmodified factory drive shaft from some MOPAR). The 57 Plymouth had 4.10 gears and an OD 4 speed so the drive shaft is spinning pretty good at 75 MPH).

Anyway when I went to pull the driveshaft I noticed a slight leak at the tail tail shaft seal and the the yolk had noticeable play. Put a new tail shaft bushing, new yolk and seal and the vibration was gone.

Not saying that's your problem, but it might be something to look at.


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