# HONDA HS928 Drives Fine For 20-30 Minutes and Then Slows and Then Stops?



## orangputeh (Nov 24, 2016)

There is a guy about 50 miles from me that has a HS ( not HSS ) 928 that says his machine drives great for 20-30 minutes and then slows down and eventually stops.
If he lets it sit for awhile he will try again and it works fine for about 5 minutes and then slows and then stops. When it is slowing down he says reverse does not work at all.
Reverse goes out before forward. If he lets it set overnight it will work great for 20-30 minutes and then eventually slow again and stop. 

I asked him to check fluid in reservoir and he says there is fluid. I havent had a chance to look at machine yet but I am suspecting an air bubble in system .
Or could it be something worse? I'm hoping @JnC sees this as he has rebuilt these.

I also asked him to check belt operation for slipping and that may be a longshot. He said the belt is okay. If he brings it to me I'll check that myself. I really suspect the hydro from the symptoms he is reporting. 

After checking belt I will put the machine on nose and remove the hydro drain plug to see if oil is low. Wondering if oil could be full and still have an air bubble in there? I have bled about half a dozen systems successfully in the past when the oil leaked out due to a pushed out seal.

The owner reported that the seals are flush with case. Another thing I will check for myself or the hose ends. But he said there is oil in reservoir. 

He wants to keep using it 20 minutes at a time and then letting it set but I advised he could do further damage and destroy the hydro altogether. Just guessing.

Best case is there is an air bubble and I can bleed the system.
Worse case? I'm not sure so that is why I am asking. Perhaps a more comprehensive hydro rebuild or replacement ?

Thanks you fellow Honda maniacs.


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## orangputeh (Nov 24, 2016)

@JnC rereading your sticky on servicing these hydros refer to post #51 where a member had no reverse and he did something with a ball from a check valve? dose this maybe sound like the issue?
I'm not sure what he us talking about. Where is this on the hydro?

it may be my solution if there is no air bubble in system.


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## tabora (Mar 1, 2017)

orangputeh said:


> a member had no reverse and he did something with a ball from a check valve? dose this maybe sound like the issue?


It could be that the relief valve spring #25 25431-VD6-851 is weak and isn't holding the ball bearing #83 tightly against the relief valve seat #26?


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## orangputeh (Nov 24, 2016)

tabora said:


> It could be that the relief valve spring #25 25431-VD6-851 is weak and isn't holding the ball bearing #83 tightly against the relief valve seat #26?


thanks. will have to check all the check valves. never played with one of these before. the shop manual cautions that the hydro needs to be put in a specific position or the ball can fall in somewhere and then the case would need to be opened.
wunderful wunderful.


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## JayzAuto1 (Jul 25, 2016)

That sounds like a time/temperature cycle...if indeed the same symptoms happen at the same amount of drive time. 20 minutes is long enough for warmup and things to expand, and tighten up. Then things return to normal after cool down?? Maybe check the rubber hose from reservoir to hydro.... sounds like maybe sucking air in there??? Loose clamp? Hose has hardened up, allowing air in?? Is it the original fluid?? Dirty?? IDK, some things to check. Maybe ask him if it was making Any noises during use.... Ask if he's running it at full throttle during problem??
Tough until you see or experience it yourself.

GLuck, Jay


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## orangputeh (Nov 24, 2016)

JayzAuto1 said:


> That sounds like a time/temperature cycle...if indeed the same symptoms happen at the same amount of drive time. 20 minutes is long enough for warmup and things to expand, and tighten up. Then things return to normal after cool down?? Maybe check the rubber hose from reservoir to hydro.... sounds like maybe sucking air in there??? Loose clamp? Hose has hardened up, allowing air in?? Is it the original fluid?? Dirty?? IDK, some things to check. Maybe ask him if it was making Any noises during use.... Ask if he's running it at full throttle during problem??
> Tough until you see or experience it yourself.
> 
> GLuck, Jay


Thank you . Will check these variables.


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## JnC (Feb 21, 2014)

Keep us posted, this is an issue that has me intrigued as well as I have never seen an HS series HST act this way. I know you mentioned that it has been drained/refilled/bled so contaminated HST fluid is out as a cause, may be a pesky bubble somewhere? Bench bleed?


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## groomerz (Feb 7, 2015)

It may be one of these sn

 https://www.snowblowerforum.com/th...tin-intermittent-ground-speed-slowing.131610/

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## tabora (Mar 1, 2017)

groomerz said:


> It may be one of these


No, he has a HS928, not an HSS928.


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## orangputeh (Nov 24, 2016)

JnC said:


> Keep us posted, this is an issue that has me intrigued as well as I have never seen an HS series HST act this way. I know you mentioned that it has been drained/refilled/bled so contaminated HST fluid is out as a cause, may be a pesky bubble somewhere? Bench bleed?


i will. the owner had surgery so he is going to bring machine when can.


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## orangputeh (Nov 24, 2016)

I now have the machine. Anyone know where @ST1100A is? he may have some experience with this.

HS model , not the HSS model.


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## orangputeh (Nov 24, 2016)

The main clue is that it works for 20-30 minutes and the slows and fails. The oil warms up , thins out perhaps and leaks or bypasses something? I looked in shop manual. page 14-4 on exploded view and do not see any seals? Waht powers the tranny into forward and reverse? those small pistons?

Does anyone know the purpose of these 3 check valves?

I do have an old junk hydro that I can take apart and learn from. I just don't know what to look for. The solution/defect could be staring me in the face and I may not know it.


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## ST1100A (Feb 7, 2015)

#8-9-16-17 are wearing. The pistons fit lose in the cylinders and when hot the cylinder starts to expand and hydraulic pressure is lost causing the slowdown and stopping.
That is very common on Hydro-gear and other units but also happens on Honda built transmissions. Honda generally last a lot longer before they wear out due to higher quality materials used in manufacture.
The parts are expensive and there is labor work involved in the repair.
#8 is the pump cylinder #9 is the motor cylinder #16-17 are the springs and pistons for them. All those parts should be replaced with new.
It might only be the pump causing the problem, or just the motor, but if it is apart, replace both of them because if one is worn the other will soon so do them both when disassembled.
The check valves are what recirculate the oil back and forth between the pump and motor and act as a pressure relief if there is a problem plus 1 acts to unload pressure so it can be 'Free-wheeled' or 'Release' so it wont drive. They also help aid in bleeding air out of the hydraulics in the valve body.


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## ST1100A (Feb 7, 2015)

orangputeh said:


> The main clue is that it works for 20-30 minutes and the slows and fails. The oil warms up , thins out perhaps and leaks or bypasses something? I looked in shop manual. page 14-4 on exploded view and do not see any seals? Waht powers the tranny into forward and reverse? those small pistons?
> 
> Does anyone know the purpose of these 3 check valves?
> 
> I do have an old junk hydro that I can take apart and learn from. I just don't know what to look for. The solution/defect could be staring me in the face and I may not know it.


Orangeputeh, yes its those tiny little pistons that power the machine forward and reverse.
Honda didn't offer good literature to the public on the technical how to's of the transmission and how it works. They did have it available to their authorized dealerships with their training books, service literature and videos plus when they used to have their own training centers and dealer seminars.
Honda kept a lot of their technology secret from the public due to 'Copyright' and didn't want their secrets stolen, until they started having some of their engines made in China where it was stolen and that's how you now have all those 'Honda Clone' engines today. Honda realized they made a big mistake but it was too late, their trade secrets got out on their engine designs. They tried to sue the Chinese companies for Copyright infringement but they lost because China wasn't obligated to abide by them like America was.
I remember when all of that happened very well and what that did to American Honda Corp.
O.P. when you have the transmission apart check to see if the pistons are the slightest bit loose in their cylinders on both the pump and motor cylinder blocks. Remember the pistons have to go back in the same exact cylinder holes they came out of. The pistons are 'Lapped' into their respective cylinders, each and every one of them so don't mix them up.


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## orangputeh (Nov 24, 2016)

ST1100A said:


> Orangeputeh, yes its those tiny little pistons that power the machine forward and reverse.
> Honda didn't offer good literature to the public on the technical how to's of the transmission and how it works. They did have it available to their authorized dealerships with their training books, service literature and videos plus when they used to have their own training centers and dealer seminars.
> Honda kept a lot of their technology secret from the public due to 'Copyright' and didn't want their secrets stolen, until they started having some of their engines made in China where it was stolen and that's how you now have all those 'Honda Clone' engines today. Honda realized they made a big mistake but it was too late, their trade secrets got out on their engine designs. They tried to sue the Chinese companies for Copyright infringement but they lost because China wasn't obligated to abide by them like America was.
> I remember when all of that happened very well and what that did to American Honda Corp.
> O.P. when you have the transmission apart check to see if the pistons are the slightest bit loose in their cylinders on both the pump and motor cylinder blocks. Remember the pistons have to go back in the same exact cylinder holes they came out of. The pistons are 'Lapped' into their respective cylinders, each and every one of them so don't mix them up.


Thanks. I did drain the oil and it's a dark greenish. Unless something deteriated in there it may not even be Honda hydro oil? In a previous discussion members were recoomending synthetic 5w-30 oil and other hydraulic oils that were much cheaper and I wonder if this is the case here.

BTW, what do you recommend to flush out this system before I install new Honda hydrostatic oil and bleed the system? In your experience I imagine using the wrong oil can damage the tranny beyond repair? I would have no idea on rebuilding this tranny if it comes to that. I'm advising the owner we may have to replace with new. I'm skittish about used. This is a lot of work to R/R these units. 

thanks again. glad you're back.


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## JnC (Feb 21, 2014)

The damage to the pistons/cylinders could be caused by any one of the variables. Time, usage, misuse, contaminated or wrong oil etc etc. I'd advise on replacing the HST with a good used unit, then opening this one up for further inspection.

BTW here is a picture of the actual internals.


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## groomerz (Feb 7, 2015)

Any scoring on plates of pump or motor. Have rebuilt hydro gear pumps and scores on the plates or on the cylinder body where it contacts the plate will release pressure also besides worn pistons

Think of the plates as a cylinder head and any scores will leak pressure

As far as forward reversthe pump side cylinder gets angled and changes piston strokes which changes pump flow direction











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## orangputeh (Nov 24, 2016)

thanks people. just got back from dealer and spoke to head mechanic with 30 years experience. He told me some of the same stuff you guys mentioned. When the fluid heats up it causes frothing and bubbles perhaps from a bad seal.

He also said Honda does not even rebuild these. They just replace. Recommended I dont even try. Some parts are inaccessible? he said or it's too complicated for a novice to try. I kinda agree. I can change oil and bleed system and give it a go. He showed me on blow up diagram where seals are but if i changed them and THEN IT DIDNT WORK???

Many wasted hours. The dealer did not have any good used units. 

thanks for the help. i'll check back soon.


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## groomerz (Feb 7, 2015)

Dark green hydro ? 
Exmark and toro 500 hydro oils are green 



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## ST1100A (Feb 7, 2015)

They probably changed the oil and if they used the wrong oil or didn't bleed it properly the first time they would do some damage to it.
I always use the Honda oil that is recommended for it. Honda built them with very tight close tolerances so you need the proper oil for them that Honda recommends.
They can be rebuilt if you know what you are doing with them. They can be tricky and for the cost of parts sometimes you are better off just replacing the complete transmission assembly then you know everything is new inside of them.
We've had very few of them fail and had to be rebuilt. Most of the time the failures were caused by abuse or a customer changing the oil improperly by not bleeding it correctly before they started the engine or they used the wrong -Non Honda- oil in them.
If you start and run them before they are bled properly first you will cause damage immediately to the pistons, cylinders and cylinder block to plate surfaces.
Another thing that can wear is the tiny 'Charge Pump' but that usually only happens if it is ever run low or out of oil.
The Genuine Honda HST oil is very clear with a light 'Beer' color, a slight goldish look.
I don't flush them out with anything, I just let them drain out and replace if I was only doing an oil change, but if the trans was disassembled then everything would be cleaned in the parts washer before reassembly then add new Honda HST oil.
I can imagine most dealers won't rebuild them anymore because not too many of them have the experienced people to do that anymore and the costs of the job, it's easier to just replace the unit with a new one and put it back together to give back to the customer. Then when times are slow a tech might want to play with them and try their luck with a rebuild to get the experience of them unless they went to an official Honda training school to learn to rebuild them, which Honda no longer has anymore as they did in the past.


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## JnC (Feb 21, 2014)

^^ Thats exactly what I think happened, the previous owner probably proactively changed the HST oil and replaced it with non OE oil and caused the damage. 

BTW I have opened a couple of these, one in detail and one only to swap the wheel driveshaft to a track driveshaft, they arent that complicated. The one you see in the picture above was disassembled even further, cleaned, put back together, filled, bench bled and put into service without an issue. So take a gander at it once it off of the machine, no harm in exploring and opening it up, I am sure at that point its written off anyway.


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## orangputeh (Nov 24, 2016)

ST1100A said:


> They probably changed the oil and if they used the wrong oil or didn't bleed it properly the first time they would do some damage to it.
> I always use the Honda oil that is recommended for it. Honda built them with very tight close tolerances so you need the proper oil for them that Honda recommends.
> They can be rebuilt if you know what you are doing with them. They can be tricky and for the cost of parts sometimes you are better off just replacing the complete transmission assembly then you know everything is new inside of them.
> We've had very few of them fail and had to be rebuilt. Most of the time the failures were caused by abuse or a customer changing the oil improperly by not bleeding it correctly before they started the engine or they used the wrong -Non Honda- oil in them.
> ...



update.

change the oil , bled the system and it worked great for about 30 minutes. was doing out of town neighbors drive. after 30 minutes it started slowing and tranny started making noise . Let it set for 10 minutes and then worked perfect for 10 minutes or so and then same thing. The longer i let it set and cool the longer it would work fine and then start making a whining like grinding noise and then stop.

probably damaging it more by using it this way. dont think the owner wants to use it 20-30 minutes at a time.

agree that a replace with new may be best course of action. I don't like doing things twice. I may try a rebuild if MY machine . If it ddnt work I have about 6 used ones from 828's and 928's. But the risk of using a used one , a known good one even . would make me nervous. ( for someone else's machine )

The R/R time is maybe just several hours ( I did a replacemnet a couple months ago ) . It's just a PITA to me. Even while listening to the Beatles.

Wuth thanks to @rod330 I have been buying Milwaukee tools which cuts repair times quite a bit.........zip zip zip and parts are removed lickety split.
Makes work fun actually.


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## ST1100A (Feb 7, 2015)

Sounds like a good chance the oil in it 'Frothed up' like shaking a can of warm beer and pouring it into a glass. All of the air bubbles in the oil would cause metal to metal contact and the air would compress, the oil would not, causing a stop in the motion of the drive. That would also cause the noise you described, almost like a cars power steering pump when they get low in oil.
The Honda HST oil has special additives in it to help prevent the oil from 'Frothing up', 'Anti Aeration additives' that other oils don't have, especially synthetic automobile oils. 
Special 'Small Engine Oil' usually contains the Anti Aeration additives in them along with most hydraulic oils.


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## orangputeh (Nov 24, 2016)

ST1100A said:


> Sounds like a good chance the oil in it 'Frothed up' like shaking a can of warm beer and pouring it into a glass. All of the air bubbles in the oil would cause metal to metal contact and the air would compress, the oil would not, causing a stop in the motion of the drive. That would also cause the noise you described, almost like a cars power steering pump when they get low in oil.
> The Honda HST oil has special additives in it to help prevent the oil from 'Frothing up', 'Anti Aeration additives' that other oils don't have, especially synthetic automobile oils.
> Special 'Small Engine Oil' usually contains the Anti Aeration additives in them along with most hydraulic oils.


Yes , That is exactly what the Honda tech said. This is an excellent machine otherwise and I'm gonna advise the owner to replace with new.


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## JnC (Feb 21, 2014)

orangputeh said:


> Yes , That is exactly what the Honda tech said. This is an excellent machine otherwise and I'm gonna advise the owner to replace with new.



Excellent condition? Yeah that further proves the notion that the owner might have been proactively keeping up with maintenance etc, a bit too proactively I'd say :/ and could have opted to get a synthetic or comparable HST fluid to be used in the unit. I have seen a few threads on bob the oil guy forums questioning what can be used instead of Honda HST in the old Honda ride on lawn mowers etc that use the Honda HST fluid, thats no bueno. 


That frothing fact is so true with oil, I once rebuilt a GX340, put it into service with oil at proper level, went to check the oil on the motor after it was used for 10 minutes and couldnt believe how much poured right out of the fill hole. I was in shock and disbelief that I might have overfilled the unit only to realize it a minute later that it was due to the frothing, since then I only check the oil level when the machine is cold.


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## orangputeh (Nov 24, 2016)

JnC said:


> Excellent condition? Yeah that further proves the notion that the owner might have been proactively keeping up with maintenance etc, a bit too proactively I'd say :/ and could have opted to get a synthetic or comparable HST fluid to be used in the unit. I have seen a few threads on bob the oil guy forums questioning what can be used instead of Honda HST in the old Honda ride on lawn mowers etc that use the Honda HST fluid, thats no bueno.
> 
> 
> That frothing fact is so true with oil, I once rebuilt a GX340, put it into service with oil at proper level, went to check the oil on the motor after it was used for 10 minutes and couldnt believe how much poured right out of the fill hole. I was in shock and disbelief that I might have overfilled the unit only to realize it a minute later that it was due to the frothing, since then I only check the oil level when the machine is cold.


yes. the hydro oil didnt look like hydro oil. it felt like hydro oil but with the greenish tint? I had it in a glass container and ahould have taken a picture but it is already disposed .

one member here in my research swears by using cheaper synthetic 5w-30 in his 2 honda's and says the trannies have worked fine for 2 years now.

I don't likr to gamble like that ona $600 part and a couple hundred in labor. My Honda hydro oil cost about $17 to change . Cheap compared to the alternative.

Thanks for your input.


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