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

Pitted tapered bearings and races in the rear comes to mind.  Without any more detail on this, I would put Pinion bearings at the top of the list with carrier bearings being right below that.

Lorena, Texas (South of Waco)

Is there any detail I could provide that would be helpful?

I had thought that damage in the pinion, carrier, or wheel bearings would be perceptible by hand when turning the yoke and wheels. Everything felt totally smooth. The needle on my in-lb torque wrench wasn’t very jumpy during rotation either.

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

Something else to consider is the drive shaft angle and/or the u-joint orientation on the drive shaft itself.  If the drive shaft is not original and has been fabricated or modified, then it’s important the u-joints be in phase with each other.  Likewise, if the rear end housing has been replaced with something else, the pinion angle needs to be verified.

Unfortunately having any oil in the rear end masks worn bearings if attempting to just turn the pinion by hand and thinking you are going to feel any roughness in the bearings.  A mechanics stethoscope could potentially help to identify bearing issues but that will require the vehicle on a lift and actually having the drive train in motion while performing that check.  Safety reasons keeps most shops from doing that.  I typically just test drive the vehicles and if there is a growl coming from the back, then the rear is the obvious place to start.  Making left and right turns while at speed will help to determine if the wheel bearings are the issue versus the rear end itself.  A metal analysis of the rear end oil is also another option as a prelude to actually disassembling the rear end.

Lorena, Texas (South of Waco)

2 Words ....Wheel balance 

I am not sure of the car’s history, but I think the axle and driveshaft are original. I have not checked drive shaft angle yet, but I can. I also want to inspect the driveshaft closely for potential sources of imbalance. I am not opposed to trying using the stethoscope on the rear with the car running on jack stands.

I snapped a shot of the driveshaft where it enters the transmission. Should the ujoint be closer to the tail shaft housing?

I measured 57.125” from the differential end of the driveshaft to the end of the transmission. As best I can glean from the Ford parts manuals on the Ford parts wiki, the original driveshaft assembly length would have been 59”, leaving only 2” of slip yoke inside the transmission. I may have to remove the driveshaft to verify because that doesn’t seem like enough at all.

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