# There is always a first time; dead HS series HST



## JnC (Feb 21, 2014)

I have been working on Honda snowblowers for a while now and have seen only a hand full of HSTs that have stopped working, usually the oil seals on the driveshaft pop out and oil leaks out. You put new seals on, fill the HST with HST fluid, bleed it and you are back in business.

I picked up this machine and was told that it doesnt move, usually that means that the driveshaft pin is broken and would need to be replaced, no big deal. I opened the gear case and everything was fine, in fact the inside of the gear case was very clean without any water damage. 

After the gear case rebuild I went to do the HST drain, fill, bleed procedure, while bleeding the HST the driveshaft was not moving, rotating the driveshaft manually (as per the bleed procedure) I could feel grinding gears within the HST. At this point I decided to open the transmission. Even though I have been working on these machines for close to 7 years I have never opened an HS series HST, a bit intimidating but I was able to open up the unit and I think I have have found out the issue. 


The conical final drive gear has wear on some of its teeth, I am going to replace that shaft/gear to see if it fixes the issue :fingerscrossed:


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## JnC (Feb 21, 2014)

That little gear is $140, yikes lol.


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## 140278 (Aug 27, 2020)

hear the $$ OUCH big time. first time anything is a intimidating experience for even a long seasoned mechanic . and 
thanks for bringing back memory's of doing my first hydrogear zt2800 on a zero turn. scary.


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## JnC (Feb 21, 2014)

After spending a couple of hours on the unit's inside I am pretty well antiquated with the workings of this particular HST. The pistons withing are fine with good compression seal and nothing else seems out of the norm, the pump works fine as well, just a few metal shavings which I believe are from the worn gear. I have a spare HST from a wheeled unit,rather than investing money in the new conical gearshaft I am just going to replace the driveshaft on the wheeled HST to the driveshaft from this track unit. Dont need to open the whole unit as the driveshaft pulls right out from the left side after doing three bolts. 

I can get used working HSTs from a local guy for as little as $80 so no point spending $150 on this unit just to see if it can be fixed (also realized that there is wear on the corresponding gear that the aforementioned conical gear transfers power to, good thing is that the above price is for the set of gears and one bearing not just the conical gear shown above).

At the same time I dont want the next owner to run into issues due to any damage that might have already been caused by the metal shavings so I'll just keep this unit as spare and get the machine up and running using the transplanted wheeled HST.


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## orangputeh (Nov 24, 2016)

WOW. looks intimindating to me. I have a bunch of good HST's lying around and would just do a transplant but I agree with you. Have yet to see a bad HS HST. yes. Have seen about 10 with blown seals or cracked seals and just replace or even just push in and fill the oil bleed the system and she's good to go. ( always in frame ) and have yet to have a problem with that .

On just about every Honda I work on for someone I put a label on the reservoir cap ( snug only ) since people love to tighten that cap . And I show them it is supposed to breathe with the slots in the rubber cup insert. 

It is kinda puzzling that this happened to this machine as you opened up the right side gearbox and said it was in pretty good shape. Was it serviced or rebuilt beforehand or original ? 

Also , what would cause this kind of wear on the gears in the HST? low oil or a worn bushing or washer that was causing improper gear alignment? If I had the time I would open up a good HST to see the differences between a worn one and good one.


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## JnC (Feb 21, 2014)

When doing the transplant all I have to do is open the left side and slide the driveshaft out to replace it with the one for the track unit. I'll be sure to inspect the splines on the good gears in the wheeled blower's HST. 

There is no extraordinary wear inside the transmission, at least non that I can notice, unless there is some tolerance somewhere that has gone out of the threshold. The only thing that perplexes me is that when I was trying to bleed the HST there was no movement or even a hint of any movement on the driveshaft. No movement would mean that some teeth on the gears are completely missing or the gear is broken. With the amount of meet that the gears still have on them you'd think the driveshaft would at least try to show some sign of movement where it'd move till the gears slip but there was nothing like that happening in this case. 

Once I have some more time and once I compare the two gears to the ones out of the good unit I'll be sure to share what I think might have gone wrong in this case. 

The wear/damage on the gears can only be attested to the tracks being stuck somewhere and the transmission trying to move the unit still, in that case you'd hope the shear pins on the drive cogs would shear and not let the transmission get damaged BUT to add to the mix the left side drive wheel/cog was seized onto the driveshaft hence deeming the shear clevis pin useless. 

It must have been a perfect storm (no pun intended) for the drive wheel to seize onto the driveshaft, the machine/tracks getting stuck in a position where they couldnt slip and had to transfer the force back to the HST, nothing else in the right gear case giving in and eventually leading the weakest point to slip and get damaged. Again this is just a theory with some substance behind it.


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## orangputeh (Nov 24, 2016)

good investigating work. I agree . with that drive wheel seized on shaft the torque or tension had to possibly damage those gears or splines. I shake my head when people use hardware bolts in place of shear pins anywhere; the augers, impeller, cam lock pins or the sprocket wheel shear pins. cheap insurance is what I tell owners.


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## ST1100A (Feb 7, 2015)

I have seen some gear teeth that were actually made that way to allow oil to pass/squeeze by easier with less resistance.
The worn area isn't in the spot were the actual tooth contact area is, that is on the shiny area on the side face of each tooth.
Some but not all bevel gears are made that way, some are flat or built with a straight edge, and some have the little curvature for oil to pass through with less resistance.
You will see that pattern in a lot of worm/screw drive type gears, and some bevel types.


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## JnC (Feb 21, 2014)

ST1100A said:


> I have seen some gear teeth that were actually made that way to allow oil to pass/squeeze by easier with less resistance.
> The worn area isn't in the spot were the actual tooth contact area is, that is on the shiny area on the side face of each tooth.
> Some but not all bevel gears are made that way, some are flat or built with a straight edge, and some have the little curvature for oil to pass through with less resistance.
> You will see that pattern in a lot of worm/screw drive type gears, and some bevel types.



Nailed it!

So I was closely examining the gears yesterday and couldnt fault the gears as if they were damaged it would be pretty evident, both the gears have the characteristics where some teeth are curved and some not, that unevenness is the reason why I thought that its extraordinary wear and cause of the issue. As it turns out that the gears are designed to be that way and as you mentioned they are designed so the oil can pass through and lubrication isnt hindered. 

I opened up the second HST today and inspected the gears and they were the same shape as the ones from this transmission. 

Non the less, I swapped the parts over to the wheeled HST i.e. driveshaft and the machine has a working HST now. I am going to open up the distributor plate next and see if the check valves are ok as I cant see anything else wrong with the faulty unit.


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## ST1100A (Feb 7, 2015)

Those transmissions are actually pretty simple to rebuild.
It is always interesting to take one apart and see how they are made, and operate.
The most likely cause of any damage to them is from either using the wrong type of oil, or running them low in oil, which can happen if you have a seal leak or "blow-out".
If one is run without being bled first, that can cause major damage quickly.
The parts that usually wear first, and the most common that causes the machine to slow its travel speed are the hydraulic pump and motor pistons, the round cylinder bodies and the area that the cylinder body meets the surface plates. If you have any leakage there, you will lose hydraulic pressure and the machine will slow itself down. That happens when it gets hot most times. That is an early indicator of impending transmission failure.
Hydro-Gear units are notorious for that problem because the material that they are made with is not that high of quality, and they wear out very quickly as compared to the Honda quality material, another reason Honda parts were so expensive, better quality materials used in manufacture.
Many times we see people having early transmission failures starting to happen, and they switch to a heavier weight oil in them. For example, they switch from a 5-30 weight to a 20-50 or a straight 30 to get them operating again for a little more time before the unit has to have the pump piston and cylinders replaced.
That is just a "Quick Fix" with using the heavier oil before an overhaul is required, but that quick fix might get them a few more years of service out of the unit before it needs a major overhaul.


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## JnC (Feb 21, 2014)

Indeed, this one was intimidating to open up due to the hundreds of parts within but once laid out in front the internals are pretty simple and you are right, I have never liked the hydrogear products especially after fixing a few of the transaxle type hydros they use for the john deere mowers that I have worked on in the past. 


When I was doing research on changing the oil in the honda HSTs for when I was to do my first drain/refill/bleed on these machines some people had mentioned using other products beside the honda recommended Honda HST fluid, for the peace of mind I stuck with the Honda recommendation and it hasnt failed me yet. 

The replacement HST that I swapped over the driveshaft onto had the seal pop out on it before the owner decided to sell the unit. After the swap, new seals, new fluid refill/bleed the unit is fully operational. 

One key point here though per the bleed instruction, when I was rotating the pulley counter clockwise and observing the drive shaft for movement, it took a while before the driveshaft starting rotation. I am thinking this due to the transmission loosing pretty much all its fluid.


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## orangputeh (Nov 24, 2016)

ST1100A said:


> Those transmissions are actually pretty simple to rebuild.
> It is always interesting to take one apart and see how they are made, and operate.
> The most likely cause of any damage to them is from either using the wrong type of oil, or running them low in oil, which can happen if you have a seal leak or "blow-out".
> If one is run without being bled first, that can cause major damage quickly.
> ...


Are you speaking of the HSS hydro trannies ? They use 5-30 weight? With the hydro trannies in the HS models I just use the Honda specific Hydro-static oil. ha. dont even know what weight it is.


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## ST1100A (Feb 7, 2015)

orangputeh said:


> Are you speaking of the HSS hydro trannies ? They use 5-30 weight? With the hydro trannies in the HS models I just use the Honda specific Hydro-static oil. ha. dont even know what weight it is.


With the Honda transmissions, you are better with the Honda specific oil. It is made specifically for hydraulic transmission use.
The HS trannies are not that hard to rebuild, the HSS trannies are easier.
Actually you don't rebuild the HSS trannies, you just scrap them and replace them with a new unit because the price is very cheap on them. They are cheaper to replace than trying to repair them when you figure you can get them for around $160 USD for the complete unit. You know what a HS Honda Hydro unit costs for just the hydro unit, multiply the Hydro-Gear price by almost ten.
The weight oil for winter cold weather operation is 5-30, warm weather usage is normally 20-50 in lawn tractor trannies. The Honda oil is a 5-30 weight, but different than an automotive oil.
A lot of Hydro-Gear repairs we do is specified at that weight automotive oil. When working on a Honda product, we use the specified Honda HST oil that is designed for that type of usage.
HST oil has some different ingredients in it, like pressure additives, shear additives, anti foaming additives, anti corrosion additives and a few others at higher levels not found in regular automotive oils.


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## Ralphy007 (Dec 29, 2018)

Maybe I missed something in the tread.. how do I re- stall the steel ball held in by the check valve bolt? The steel ball keeps falling in to the pressure fluid..

ty for all the reply’s..


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## orangputeh (Nov 24, 2016)

Ralphy007 said:


> Maybe I missed something in the tread.. how do I re- stall the steel ball held in by the check valve bolt? The steel ball keeps falling in to the pressure fluid..
> 
> ty for all the reply’s..


I read it here somewhere. the unit has to be tipped a certain way. These posts are too long to reread for me anyway. 
JnC takes the unit out of the chassis. I would see if I could remove the engine which only takes about 10-15 minutes and tip the chassis if you have enough room to work with.


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## JnC (Feb 21, 2014)

There is nothing in this thread that shows how to sort the issue you are having. This transmission was dead (or so I thought) after the I assembled it back together, topped it off, did the bleeding procedure it was back in service.

In your case, is the transmission still mounted on the chassis or is it on the work bench? 

If you dont already have it I would suggest getting a copy of the service manual, it goes in detail as to how to reassemble the whole thing. I'll dig in a bit more and see if I can find more info. 

Your best bet, if all else fails, is to open the transmission and diagnose/install the check valve/ball properly. The mid section of the unit is by itself (piece on the left next to the screwdriver in the first picture above). The Hydro looks intimidating but everything has its place and if you have the schematics you should be able to put it back together without any issue, there are no special tools required.


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## orangputeh (Nov 24, 2016)

JnC said:


> There is nothing in this thread that shows how to sort the issue you are having. This transmission was dead (or so I thought) after the I assembled it back together, topped it off, did the bleeding procedure it was back in service.
> 
> In your case, is the transmission still mounted on the chassis or is it on the work bench?
> 
> ...


I must have read it somewhere else then. I think the hydro unit has to facing up a certain way but your method here is the best way to do it right.


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