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.
A transmission with an external pump is not unusual, Clark used this design for years as did others. Now to your problem, have you checked any pressures after or before it quits operating? It seems strange that the problem "seems" cured for a week or so only to reappear. Does the truck have "Monotrol" or hand lever directional control (they made them both ways). When it quits do you have any sensation of the transmission changing direction such as a slight decrease in engine speed? Does the inching seem to be operating correctly?
Hyster Trans It does have a monotrol pedal that I have rebuilt. To answer your movement question, it has no movement until completely cool, like overnight. It doesn't even grab at all. Doesn't seem to try. I have no manual to help me with what pressure ports go to what, but I can see the one after the activation solenoid, connected to the e-brake switch. And when it's clonked out, there is still pressure going thru that solenoid. Which is the only thing that I've seen that cuts movement like this. I'm trying to figure out which port is from the pump, so I can test it before pulling the engine again, to rebuild the transmission. But I've got like 6 test ports and can't tell which one goes to the pump.
I don't have any pictures for test port identification but if I were you and keeping the machine I would purchase a service manual. The manual will give port locations and pressures along with a schematic so you can do a proper test. Just my opinion, but it could save you time and money in the long run.
I'm the repair company. This is not my forklift, it's a customers. This was an engine repair, that started a transmission problem. I'm too far in the hole, to go spending $500, on a service manual for a 30 year old truck, that I won't touch again after this repair. I will avoid this model like the plague. I put this up, to see if I was missing some trick to this trans. Since nobody has any real tricks, I'm pulling the trans, for rebuild, on Saturday. What would have been nice, is if somebody with experience with this truck, knew what port tests the pump pressure. Because I don't have to pull the engine, to replace the pump.