80's Hyster S50F Transmission stops moving when warm

I pulled the engine to replace the timing gears. The original cam gear is fiber, not metal. While it was apart, I dicovered a leaking torque converter. My forklift parts vendor was weeks out on a replacement torque converter. So I went to a local transmission shop and found an exact match, according to them. Put it on and installed the freshened up engine. The thing had leaks that I had to solve first, then it ran for like a week. It stopped moving. I changed out the main solenoid valve. Still nothing. Pull the engine back out. I got a seal kit for the trans, so I pulled the front open. Everything looks new, and in place. The fluid looks and smells ok. Only thing I found was some wear, on the seat of the torque converter. Seems like a tight fit. Torque converter must have failed. Right? Warranty replace the torque converter. Put the engine back in. Thing runs for another week, then stops moving. And I mean, no movement when warm. Must be wrong torque converter. Right? So I order the torque converter from the industry, that takes 5+ weeks to get here. Attach it to the engine and put it back in. Runs 2 weeks and stops moving when warm again. I really thought I had it. So here I am. Any ideas?



This question is for master mechanics, as this forklift design is one for the record books. The transmission torque converter is attached to the flywheel plate, which sits in front/behind a timing chain, that drives a gear that drives both the transmission pump and the hydraulic pump. Yea, I said it. The transmission pump does not reside inside the front of the transmission, where the torque converter plugs in, like every other transmission I've personally seen.

80's Hyster S50F Transmission stops moving when warm