The 1981 GLT wagon "project car" suddenly developed a nasty vibration, which I suspect is due to a frozen U-joint at the differential. It's the only part on the car with a grease nipple, so is probably not original equipmemt. (And has probably never seen fresh grease since whenever it was installed.) When I applied grease, the vibration decreased noticably, but is still too much to ignore.

Now comes the tricky part - finding the right replacement part. The drive-shaft diameter and span of the yoke don't seem to match any of the three listed on the IPD website (http://www.ipdusa.com/ProductsCat.aspx?CategoryID=91&NodeID=1255&RootID=629). In fact, the rear section of the shaft seems odd, the front half is 2" diameter, which "nests" inside the rear half, which is 2.5" diameter. IPD lists 2 5/8, 3, and 3 3/16" shafts with yokes at 2 3/4", 3 1/4", and 3 1/2". The yoke on my joint is 3 3/16".

Any suggestions, or do I need to take the old one off and carry it into a parts store to find a match?