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Honda Mower Hydrostatic Transmission Issues

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Clive Foster16/06/2021 08:34:20
2990 forum posts
105 photos

Got involved with resurrecting a Honda 536HRD self propelled rotary mower after several years hibernation. Previous fiddlers were unable to get the hydrostatic drive going.

Filling the drive box with oil and bleeding the air out, a right pain getting all the air out too, got things moving but its clearly not working properly.

If the control cable is pulled up tight the beast will drive at a single, fixed, speed close to flat out. Drive engages with something of a jerk and the rear wheels generally lock against reversing so it can't be pulled back. The speed change lever also tends to spring back to the slow position when drive is engaged but it continues to run at the single speed.

By very careful adjustment its possible to get things set so the rear wheels are usually free to reverse and the drive usually operates. But only at either its preferred high speed or a very slow crawl. Sometimes a bit of manipulation of the controls is needed to get it moving at the higher speed.

Sounds like something deranged internally on the control side. I have a download of the workshop manual and disassembly doesn't look too horrible.

Can anybody advise as to what I should be looking for and how to fix things. Word on the street is that these things are generally treated as unrepairable by the trade and simply replaced.

Thanks

Clive

Oily Rag16/06/2021 08:52:01
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529 forum posts
172 photos

Clive,

Being a Hydrostatic drive system I would expect the speed control to be set by either the pump being a 'swash plate' type axial piston pump or a fixed feedrate pump with a variable bleed off pressure release valve. The former is expensive to manufacture (and may be the system used in the Honda seeing how much they sell for!) whereas the latter is liable to failure due to contamination of the oil system.

Sounds like you are half way there with re-filling the hydraulics and bleeding the system, that at least got it moving. Do you have a link to the system details or can you scan the relevant document?

My mate 'rescued' an Atco ride on mower at the weekend at the local tip. All it needed was a wash out with fresh petrol. Even the battery was good enough to get it started. The blades were in very poor condition though - looked like it had been mowing granite chippings. I am constantly amazed at how many mowers are junked because people don't know how to sharpen a blade.

Martin

Chris Evans 616/06/2021 09:16:49
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2006 forum posts

I have recently played around with a ride on with hydrostatic transmission. A change to a fully synthetic 10/60 oil was recommended and did work. An expensive oil at around £80. Now working we find the cutting deck is rotten and not cutting square, I will try a repair before £3,500 replacement mower, the mower came with a house my Daughter recently bought and money is still tight whilst house renovation is ongoing.

Clive Foster16/06/2021 10:59:47
2990 forum posts
105 photos

Thanks for the advice.

Judging by the pictures in the workshop manual it has a variable delivery swash plate axial delivery pump with springs to return the pistons.

Pressure relief valve appears to be fixed. Relief pressure set by valve needle length. Several needles available and the manual gives detailed instructions for selecting the right length one. Doesn't appear to be a spring on the relief valve.

Being a variable delivery swash plate pump its odd that it will only operated at, apparently, full or close to full delivery with the control yoke at what is most likely and improper "over maximum" position. As the pistons are spring return if the pump worked at all I'd expect them to follow the swash plate yoke at all intermediate positions and pump oil as appropriate. Only functioning at close to maximum stroke seems odd.

Time to unbutton I think. Job for when the rain gets here at the end of the week. Right now weeding the veggie plot is more important.

Clive

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