Got a vibration

[blown motor]

I've been noticing a vibration lately when I get up around 60mph. It's negligible at 50 mph. It wasn't like this last year as I recall so something is changing. I can roll the driveshaft back and forth a very small amount as if there is play in the gears. Is that normal or could it be causing the vibration. Also the vibration seems to have a bit of a drone to it. U-joints seem tight.

[brads70]

"Some play" is normal.  Any play in and out on the pinion?

[blown motor]

Never really checked it that way. There is a 'cap' on the shaft between the U-joint and the casing. It was dry but the casing itself wasn't. I looks like it's been leaking a bit. I assume there is a seal in there.

[DocMel]

Myself and others have had the same exact symptoms.  If the u joints are GTG and the DS is in balance, then the prob most likely lies within the dif.
Our difs are 40-50 years old, and no one likes the tome/expense to have them rebuilt.  Ill say most likely thats were your prob is.  It was on mine