Sorry to chime in late on this post mortem, folks, but I don't think it takes very much to explain what has caused this to happen.
First of all, its a fast driveline. it runs at engine speed, not 540, nor is it a steering shaft that runs at 0+ rpm.
The shaft connects an engine to a transmission. They MAY be some elevation or sideshift between the crankshaft vector and the transmission input shaft. But, there's probably very little DIFFERENCE between the directions of these two shafts.
The key piece of the puzzle is the photo showing the splined joint from the two piece driveshaft. That joint is probably there for assembly of the connection, not because these is relative motion between the 2 assemblies. If so, then a flex coupling likely would be used instead (as on most other JD tractors that have a separately connected motor and transmission. Thats because the motor is rubber mounted but the transmission is hard mounted.
Your Honor, it seems to me (as a Professional Engineer familiar with driveline mechanics and 20+ years in the field) that this driveshaft was misasembled. If the splined pieces are not aligned such that the phase angle of the input yoke and the output yoke was NOT ZERO, then a rocking moment existed in the driveshaft which eventually cause the cross retention pieces and bearings to fail. When the cross fell out of the bearing cups, it soon caused the shaft to be mechanically unstable and this resulted in catastrophic failure(s) down the line.
While I can't PROVE it beyond a reasonable doubt, it would be helpful for other owners to report back as to what the phase angles on their driveshafts are. If there are ANY which are non-zero, then these are likely going to have some pending failure with the worst one(s) being a shaft whose angles are 90 degrees in error. The failure is common to all machines from cars to trucks to any power take off driven machinery with this type of geometry.
It is possible that the shafts were misbuilt, that they were assembled incorrectly, or that this particular machine was serviced in a manner that required removal of one end of the driveshaft. If so and the shaft were reassembled incorrectlly, then this was a probable cause of the failure.
What would help from all you owners with similar model machines, would be for you to report back (with pictures if possible as to what the input and output yoke positions are. It is possible that they are randomly assembled (meaning a JD problem or owner problem.
The grease situation as a contributor to failure is remote because there is so little movment in the cross of a properly designed and installed shaft when the input and output couplings are colinear and parallel as to make wear and tear on the yoke bearings miniscule.
However, a misphased powershaft causes there to be unexpected cyclic end pressure on the bearing caps of all the U-joint parts. In fact a knowledgeable owner can recognize the unexpected vibration level. If one of the C clips retaining a bearing cup became over stressed, it could jump out and compromise the integrity of the shaft.
In court, a JD expert would describe how they deliberately misphased a driveshaft in an experiment and it blew out after a few hours of 'gentle' operation and some power cycles.
A jury would want to know who did that, so where are all the service records...
In other words, let's see what a dozen or so other owners have for shaft angles in their tractors. All the same or different?
If different, then there is a problem there. If not, and the shaft can be misassembled via a spline index shift OR a yoke/cross misassembly, then we have a winner.
