Webster Hydraulic Fan Motor

[pgchin]

Tommy,
I'm not an 8v guy so here are some general suggestions when you have a situation such as yours with repeated attempts to fix an issue:
1) Inexperienced installers, don't know your shop but I presume you do and they are good to go but it was worth mentioning as it has been a root cause for others in the past and I am sure a retired lawyer such as you has already thought about this and vetted this one! Teehee :-)
2) I agree with David, root cause of initial failure not found yet. Have you posted this issue on the yahoo Detroit diesels forum yet to get some more feedback? Those guys over there have decades of OLD DD engine experience and have probably seen everything.
3) The new pump actually was defective, binding causing low pressure due to the binding shaft and the shaft broke. You are dealing with .001 & .0001 tolerances and we are after all only human and make mistakes on assembly occasionally .
4) I'm hoping a more experienced guy like Leroy will weigh in here but until he does here goes... A solenoid valve either turns something full on, full off, or can vary pressure incrementally depending on design. Not sure what your is but if parts are loose or broken in it, then theoretically it can restrict pressure enough to give you slow fan speed and back the pump up until the shaft breaks. Pics of the gears here would go a long way to see if that was root cause. Since you started the thread with a guess here trust your instincts, you still got it ole bean!!!!! :-)
Try and keep a positive attitude, yes birds are very challenging but very rewarding and the challenge part it the price we pay for our reward, good luck!
PS the yahoo diesels forum may be able to source the valve for you, you never know what one of those old guys has stashed in NOS!!!!!