[swedishsteel]

Had exact same problem with tranny I got with a boat load of parts. PO had "rebuilt" it with all new or like new parts--looked brand new. But when rear bearing holder was tightened down it locked up. After MUCH searching and head scratching, on page 298 of the Green Bible at the bottom of the page there is a footnote to not use 81A-7071 thrust washer with main shaft 51A-7061. That was the problem, the washer was on the shaft, took it out and it spins freely like it should. Check all your parts, this very well could be your problem if you have used a collection of parts to assemble your tranny. Good luck.