4V K bikes have a two piece drive shaft with a U-joint at each end.  It is not uncommon for one of these U-joints to fail and 'splode after about 90-100,000 miles of use, leaving you stranded by the side of the road.

The original drive shafts used to be available either as a set or front (part 26111458480) or rear (part 26112312851) half.  These have since been superceded by a newer (possibly better?) drive shaft that includes both front and rear halves - part 26112325746.

What Can You Do To Prevent U-joint Failure:

Since the U-joints are sealed at the time of manufacture, without having them rebuilt ($$$), there is no good way repack the U-joint bearings with fresh grease to prevent them from failing.

However, when reassembling the swing arm, drive shaft and final drive, you can minimize the strain on the U-joints by properly phasing the drive shaft.

Also, once the bike has reached 75,000 miles or so then it's probably not a bad idea to check the condition of the drive shaft U-joints when performing a spline lube or installing a new rear tire.  If any "lumpiness" is detected in either axis of rotation then that's probably a sign of impending doom and an indicator that the drive shaft should be replaced in the near future.

© 2013 Drake Smith - Please do not use or reproduce this elsewhere.  Feel free to link to it though.