C-6 tranny

I have a c-6 early 1970s transmission that I have used on 2other 460 engines.I bolted the tranny back into the truck with a fresh 1973 rebuilt engine and the tranny would not move or even attempt to go anywhere.I took it back out of the truck and pulled the torque converter then thefront pump.the small gear in the pump had been shattered into 3pieces wondering what may have caused this and if I should tear the whole tranny apart and start over get a new torque converter and pump then reassemble or what?Checked the torqueconverter pilot to the crank and the both have the big diamater.I cannot seem to understand what may have happened to cause the hardened stout gear to break?:confused:

Surprising to fail a C6 - I've had several vehicles with one(pickups, LTDs, station wagons) and have tortured the hell out of them without any sign of problems even after pulling large travel trailers and 5th wheels

'Twere me, I think that transmission would have to come apart if for no other reason then to make sure nothing else is broken or that there are no broken pieces "floating" around. When that gear broke, there was a shock transmitted to other parts that may also be ready to fail. And the torque converter - a good 'core' for trade in and might be the opportune time for a different stall speed if needed or wanted.