honda pro hydrostatic HRH 536 transmission problem

Hi folks. New to this forum, so greetings from over the pond. I have spent several hours but now stuck. End of the input shaft broke on the hydro transmission. Stripped down the input part and replaced with a new shaft. Very careful to make sure everything went back as it should, all the little pistons and springs etc. Gasket fully intact. Lost most of the oil and replaced with hydraulic oil 46 (had nothing else). NO DRIVE. Took to bits again, everything as it should be. Would really appreciate some advice. Thanks Stu.

StuMetz2 said:

Hi folks. New to this forum, so greetings from over the pond. I have spent several hours but now stuck. End of the input shaft broke on the hydro transmission. Stripped down the input part and replaced with a new shaft. Very careful to make sure everything went back as it should, all the little pistons and springs etc. Gasket fully intact. Lost most of the oil and replaced with hydraulic oil 46 (had nothing else). NO DRIVE. Took to bits again, everything as it should be. Would really appreciate some advice. Thanks Stu.

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Honda is very picky about the fluid used in hydrostatic transmissions, and they say ONLY Honda HST fluid, period. Anything else, and you're risking anything from just not working to possible damage to internal parts. Best bet is to drain/clean out all the "hydraulic oil 46" and then fill/bleed using genuine Honda HST fluid.

The full procedure to completely overhaul the trans. and do a proper bench bleed is in the shop manual, but I understand from others these are generally not available to consumers in the U.K. It is possible the USA-version of this mower's shop manual would be close, if not identical, but hard to say for sure, as I don't have any HRH536 tech info from my desk here in the USA.

That said, here's a general bleeding procedure for HRC models:

Hi Robert. Thank you so much for taking the time to reply. I will get the proper fluid ordered and follow the procedures. What you said does make sense as the installation of the new input shaft went quite smoothly and I'm certain I did everything properly. I will keep you informed.
Thanks for the advice. Stu.

Hi again Robert. Drained the wrong fluid, put the new in. Bled the system as best I could. Topped back up. Still no drive. I've come to the conclusion I've messed up somewhere when putting back together. The schematic I have is very poor and difficult to understand. I'm guessing a very small part has dropped out somewhere. When I put the pump and housing back onto the main housing should there be a little needle sticking out of the centre of the plate set where the pump cylinder /input shaft meets the main housing? Or would that be out of site behind the plate set and unable to come out (without removing the plate set, which I didn't). Cheers Stu.

Stu, here are a couple of service bulletins and some shop manual details for the USA version of the HST...they might help a bit with your project sir.

Hi Again Robert. Thanks so much for these diagrams, looks exactly like my transmission. They are a great help. They have confirmed however, that I appear to have put the transmission back together properly. I was kinda hoping I had lost a little part that I could simply send for. Will keep scratching my head and keep you informed. Thanks Stu