I would do autopsy. I bet a drive Pin / key is sheared.The only good news in this bowl of crap is the cost of the pump. It came with the tractor NIB. I can't return it of course, but no out of pocket for this one.
I guess I'm shopping for a new pump. Any ideas?
I'm going to do an autopsy on this one just for grins and a need to know what failed.
where is your relief valve in the FEL circuit or pump circuit? does it have one? Could either have been stuck and pump pressure was to high to handle and shear the Pin / Key internally when you was deadheading to bleed air? It will shear fast with no sound or sign if pressure is not manage correctly.