I have a 64 Fleetside with an extremely bad vibration that starts at around 65 mph. The vibration is in the drivetrain. Up to 65 the ride is smooth and rattle free. At 70 it's worse and at 80 (or more) it's unbearable (noise-wise). The truck has a floor Hurst shifter and on a couple of occasions the vibration has worked the screw that holds the shifter to the tranny completely loose. I've heard that the problem may be a bad u-joint. Any suggestions?
