Between about 60 and 65 mph, my car used to make a deep, pulsing rumble that resonated through the cabin, similar to when being passed by an old semi or dump truck under load. It was pretty loud and I was sure something was wrong, and that it was road speed-related. There was some vibration along with it, but it was heard more than felt, maybe like a strong subwoofer.

I found some play in the differential pinion bearing caused by a loose pinion yoke nut. After tightening the nut enough to get about 15 in-lbs preload on the bearing (with diff assembled and wheels off the ground), the noise is greatly diminished, but I still hear it.

Now I’m thinking about the other end of the driveshaft. How much play in the tail shaft bushing is permissible? If I cannot find evidence of lost driveshaft weights, can I assume driveshaft balance is probably acceptable?

Ujoints are new. Rear wheel bearings and tightened pinion bearings feel smooth.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive