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.
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: