Took the 65 out for a long drive yesterday. I found that when I get up to 65MPH I'm getting a very slight rumble from under the car.
This car has a vibration dampening drive shaft from the factory and I have a feeling that the old rubber in the drive shaft is a hard as wood just like all the control arm bushing where, the U-Joints where in great shape when I rebuilt everything else.
Anyone have problems with there 50 year old vibration dampening driveshaft, I have visions of this thing taking a crap on me at 65MPH.

 

Might be just bad U-Joints

MOST road noise I have ever encountered is right from the tires. Have the tire store ck the tires for balance and bad spots?

 

Check the transmission mount.
If it has had fluid leaked onto it
unchecked for a few years, it
can get soft and gooey. It will
cause the tranny to move around some and not
be the stiffy it once was.

Also as Cris suggested, U-joints
could be a factor.

 

The only vibrations I've found from drive shafts has been when the cars have been off-roading and come down on something. Ended up with slightly bent driveshafts at times, and had to swap them.
My bad u-joints have given me more clunking than vibrating, but I'm sure they could cause both.
I've put the cars on the hoist and watched the shaft as the tires spun. Could see the bent shaft quite easily. Not sure about hardened rubber.

 

Yes, I've seen the rubber deteriorate on the old drive shafts. Check everything else first though, ujoints, tires, axle bearings, etc.