Justin with ProShaft here. Another question that we get asked pretty often concerns wear on the transmission or transfer case slip yoke. A lot of times customers wonder why their driveshaft is always covered in transmission fluid. They've changed transmission output seals a few times, yet the leak persists.
The first place to check is the ground hub (also called the barrel) of the transmission/transfer case yoke. If the yoke is worn, you'll usually see an indented ring where the yoke has gradually degraded over many miles of driving. The output seal has a hard time sealing against this worn surface and it's probably time to change your transmission yoke.
Above is an illustration of a transmission yoke showing the ground hub and also the area where the yoke is typically worn. Keep in mind that the ground hub describes the entire round portion of the yoke that slides on to the transmission output shaft.
Another problem that often pops up with old yokes deals with the u-joint "eye" holes where the bearing caps are installed. If the universal joint bearing cap spins freely or is loose in this hole, it's time for a new yoke. These holes are precision machined for a press fit of the u-joint caps. The caps rely on this friction to keep from spinning in the holes and causing driveshaft vibration.
As always, if you guys have any questions regarding transmission or transfer case slip yoke and fitment for your drive shaft, don't hesitate to give us a call at 501-626-070 and we'll be happy to help you out. Have a good one!
Justin from ProShaft