Broke Hydrostat twice? Why?

[crashz]

Whether opening the relief or bypassing through the open loop, the fluid is still flowing. And even though that supplied by a separate pump, its the same fluid as the HST. So if its getting hot while working, and the remote lever is accidentally activated and dead-headed for 10 hrs of hard use, that fluid will get extra hot!

But..

I'd expect that the fluid would show some degradation. Overheated ATF smells burnt. What does overheated Kubota UDT smell like?

 

[dfkrug]

I have a frame mounted backhoe. It is usually not attached. There is a lever that comes out from under the front of my seat that operates the rear remotes. The lever moves either way sideways and has a detent position at its full travel point. It is possible when entering or leaving the tractor to brush up against the lever and if you do it hard enough, it will stay at its full side detent position. I've noticed this before and I just re center the lever. There is no strange sound or any thing.

If you are causing your system relief valve (prob on the FEL valve) to be activated for extended
periods of time, then that would indeed heat up the fluid, without even driving the tractor. I do
not know if TYM uses a separate system RV for OEM AUX valves. Kioti does not, and they also
power their hoes off a detented AUX valve.

Note that SUPER-UDT is a lower-viscosity THF intended primarily for colder climates, like Idaho.
Tho I think that SUDT is a semi-synthetic THF like Kubota's UDT, lower viscosity will generally give less fluid film
protection at higher temps. Esp for the HST slippers.

I use Kubota UDT and its equivalent THF products from Chevron and Conoco. The largest Kubota dealer
in NorCal sells little SUDT, pushing all their customers toward UDT. Semi-synthetic THF products are specifically
designed to work well with HSTs and wet brakes. I do not know of a full synthetic THF (tractor-hyd-fluid).

 

[Bob Christensen]

If you are causing your system relief valve (prob on the FEL valve) to be activated for extended
periods of time, then that would indeed heat up the fluid, without even driving the tractor. I do
not know if TYM uses a separate system RV for OEM AUX valves. Kioti does not, and they also
power their hoes off a detented AUX valve.

Note that SUPER-UDT is a lower-viscosity THF intended primarily for colder climates, like Idaho.
Tho I think that SUDT is a semi-synthetic THF like Kubota's UDT, lower viscosity will generally give less fluid film
protection at higher temps. Esp for the HST slippers.

I use Kubota UDT and its equivalent THF products from Chevron and Conoco. The largest Kubota dealer
in NorCal sells little SUDT, pushing all their customers toward UDT. Semi-synthetic THF products are specifically
designed to work well with HSTs and wet brakes. I do not know of a full synthetic THF (tractor-hyd-fluid).

I did not know that the Kubota super UDT and UDT were made for colder climates. So another possible contributing cause.

For what it's worth, Amsoil tractor hydraulic oil is fully synthetic and has a higher vis than Super UDT2 and even a little higher than Chevron's tractor hydraulic oil.

But it retails for over $200 per 5 gallon bucket. But they advertise it for 'extended use'.

 

[dfkrug]

I did not know that the Kubota super UDT and UDT were made for colder
climates.

Super-UDT is for colder climates, not UDT.

 

[Coyote machine]

Bob, I think a distinct possibility is your HST's have been failing related to excessive heat over time. Though the fluid in each trans may have not shown visible or smell test issues/signs, upon lab analysis of it's condition it might well fail to pass viscosity or other testing.

Anyway, I know my Kioti dealer and I discussed the possibility of an operator being able to bump the detented rear remote lever into position without knowing it had been done and causing a no flow condition when no backhoe or other hydraulic demand was present at the rear remote. This would, and to my knowledge, HAS caused the hydro pump to fail.
The solution, remove the detent from the remote lever, OR, in my estimation, add a hose with male QDs when the hoe is not present. This is what I had made up by my dealer, and whenever the hoe comes off the hose loop goes in it's place. This also allows one to use the detented lever for items like log splitters, etc.

I would suggest this might be the easiest solution to your detented lever 'fix'.

P.S. Don't forget to add it to your checklist.:thumbsup:

We're getting there! This thread may lead to fewer HST failures for many brands - not that they're prone to failing; they're not. However, the more we all are aware of potential causes the better able we are to prevent same.

P.P.S. Amsoil is good/great product, BUT is it worth $200/ 5 gallon pail?! Who knows. I suggest that you might just scope out some other tractor brand name fluids, including Kioti's label HST. I don't know if it is synthetic a blend or just their own dino mix, but I know it too is way more expensive than TSC Traveller's universal fluid. I'm not saying it's better or worse, just pricier. I've got two 5 gal pails awaiting me changing it for the first and to date only fluid change in over 785 hours on the clock.

 

[Bob Christensen]

Bob, I think a distinct possibility is your HST's have been failing related to excessive heat over time. Though the fluid in each trans may have not shown visible or smell test issues/signs, upon lab analysis of it's condition it might well fail to pass viscosity or other testing.

Anyway, I know my Kioti dealer and I discussed the possibility of an operator being able to bump the detented rear remote lever into position without knowing it had been done and causing a no flow condition when no backhoe or other hydraulic demand was present at the rear remote. This would, and to my knowledge, HAS caused the hydro pump to fail.
The solution, remove the detent from the remote lever, OR, in my estimation, add a hose with male QDs when the hoe is not present. This is what I had made up by my dealer, and whenever the hoe comes off the hose loop goes in it's place. This also allows one to use the detented lever for items like log splitters, etc.

I would suggest this might be the easiest solution to your detented lever 'fix'.

P.S. Don't forget to add it to your checklist.:thumbsup:

We're getting there! This thread may lead to fewer HST failures for many brands - not that they're prone to failing; they're not. However, the more we all are aware of potential causes the better able we are to prevent same.

P.P.S. Amsoil is good/great product, BUT is it worth $200/ 5 gallon pail?! Who knows. I suggest that you might just scope out some other tractor brand name fluids, including Kioti's label HST. I don't know if it is synthetic a blend or just their own dino mix, but I know it too is way more expensive than TSC Traveller's universal fluid. I'm not saying it's better or worse, just pricier. I've got two 5 gal pails awaiting me changing it for the first and to date only fluid change in over 785 hours on the clock.

I agree with you. There are just too many issues uncovered in this thread that indicate high temps or low viscosity.

The good news is that inside of a week, if all goes well, we'll get to the bottom of this thanks to Dkrug, and a report will be forthcoming.

The position of the detent lever is such that it will be easy to tie it in the neutral position and release it when I have the backhoe on. I have no other hydraulic rear attachments.

Oil in future? Well, I'll await the postmortem, but I use Amsoil or Mobil 1 for all my other machines, several of which I bought decades ago and never had any oil related issues. The extended change intervals that I do use pays or almost pays for the extra cost. And my TYM only uses one pail per change.

 

[Fluid]

Hi Folks,

Haven't been on here for years now, but about 8 years ago you were super helpful in getting a tractor when I knew nothing and then keeping me alive while I learned.
I wound up with a TYM 273-27 HP CUT with all the attachments. Now 8 years and 1300 hrs old I love it.
My issue here now is that at about 400 hours the Hydrostat broke - tractor wouldn't move at all. It was replaced under full warranty and was fine again.
A few weeks ago, almost all forward motion stopped. Reverse was fine. Implements were fine.
I reversed the relief valves and still no forward.
Checked pressures:
Rear (backhoe) 1800 lbs - this is correct.
2 check valves at Hydrostat - 500 lbs each - should be 2500 lbs.
Feed pump check point - 125 lbs - correct.
I have no nearby dealer so I hauled it to Jordan in Post Falls, Idaho. Can't say enough good about these guys.
They diagnosed faulty Hydrostat. Had a low hrs. used one on the shelf! Replaced and all is again well.
My question is that since everyone says there is rarely a problem with these Hydrostats, how did I break 2 of them? and how do I keep from breaking another?
Background:
10 acres of mostly old growth forest. Path building. Lots of bucket and grapple work.
Hard work - 1300 hrs now but oil and filters always changed with the best - Mobil 1 and Kubota Super UDT transmission fluid.

I am putting this in Owning/Operating instead of the TYM section because of the lack of traffic there and I think this could have happened to any tractor.
I have always received lots of help from this site and I thank you in advance for any advice you can give me now.

Bob

8 years old with 1300 hours, two broken hydrostat units and you love it. You did not tell us how much it cost to fix it this last time, parts, labor, fuel hauling it and time. And you love it? I can not understand people sometimes. The best thing you could do for yourself is sell it now that it moves under its own power and buy a John Deere. You will be able to give the JD to your grandkids or great grandkids.

 

[Fluid]

Hi Folks,
My question is that since everyone says there is rarely a problem with these Hydrostats, how did I break 2 of them? and how do I keep from breaking another?
Bob

Two answers to your questions, answer #1 You bought a TYM. answer #2 Sell it and buy a John Deere.

8 years old 1300 hours two broken hydrostats and you love it. HOW and WHY?

 

[Bob Christensen]

Well Fluid,

The purpose of this thread is to determine how this happened.

If it turns out that the fault is inherent to the tractor, or TYM in general, then I'll have to agree with you although buying a new tractor has multiple issues for me.

But what if the damage is found to have been my fault- through ignorance or whatever? The tractor is otherwise perfect for me and with the kind of help I am finding here, I could easily change my habits. I know I can do this; I've been married 40 years.

 

[TSO]

Fluid ... You're an idiot.

Bob ...I'm sorry, but I don't think that excessive heat due to fluid quality had anything to do with your failures. Many many people use store brand fluid without failures. And, like Coyote mentioned, HST's are not prone to failing.

I'm leaning towards your detent issue, or, something else internal that's leading to the failures.

 

[Bob Christensen]

Fluid ... You're an idiot.

Bob ...I'm sorry, but I don't think that excessive heat due to fluid quality had anything to do with your failures. Many many people use store brand fluid without failures. And, like Coyote mentioned, HST's are not prone to failing.

No, I don't think the oil 'caused' the problem.

But there seem to be a half dozen things, perhaps the worst being the detent thing and sometimes crudded up oil cooler that maybe caused the problem, and if so, starting with thinner oil could have contributed to the problem.

Or from the other side if we're seeing damage caused by 5 years of elevated temperature, perhaps thicker, synthetic oil might have extended the life.

But no ,this is surely not the meat of the issue.

 

[oldnslo]

HST operation:
ALL HST's require some form of of make up flow to compensate for leakage loss. This is done with designated charge pumps on most models but some like the Kubota BX series use oil from the implement/ steering pump for this function. This flow is typically around 20% of the HST pumps displacement.

If the RPM's of the engine are to low the charge pump system may not have enough flow to compensate for the leakage losses. As the oil / HST temperature rises the leakage increases and depending on the condition of the charge pump the charge flow may decrease. This is part of the reason for running at higher RPM's.

Typically if there is not enough charge flow the HST will be noisy. If you are right on the edge of loosing charge pressure from insufficient charge flow this could cause some cavitation. Cavitation is death to all pumps and motors.

I frequently use high range on my HST for doing loader work but I also do not allow the HST to "stall" for an extended period of time. "Stalling" an HST will send the fluid over the cross port relief and right back into the pump inlet and over heat the pump in a very short time.

definition of stalling: Point at which the tractor tires are not spinning and the HST is going over relief. You may or may not hear the relief valve function over the diesel engine.

From what you have described I would be surprised if over heating was the only issue since it worked in one direction and not the other.

Hope you can find the root cause since odd things do happen in mechanical equipment.

 

[Bob Christensen]

HST operation:
ALL HST's require some form of of make up flow to compensate for leakage loss. This is done with designated charge pumps on most models but some like the Kubota BX series use oil from the implement/ steering pump for this function. This flow is typically around 20% of the HST pumps displacement.

If the RPM's of the engine are to low the charge pump system may not have enough flow to compensate for the leakage losses. As the oil / HST temperature rises the leakage increases and depending on the condition of the charge pump the charge flow may decrease. This is part of the reason for running at higher RPM's.

Typically if there is not enough charge flow the HST will be noisy. If you are right on the edge of loosing charge pressure from insufficient charge flow this could cause some cavitation. Cavitation is death to all pumps and motors.

I frequently use high range on my HST for doing loader work but I also do not allow the HST to "stall" for an extended period of time. "Stalling" an HST will send the fluid over the cross port relief and right back into the pump inlet and over heat the pump in a very short time.

definition of stalling: Point at which the tractor tires are not spinning and the HST is going over relief. You may or may not hear the relief valve function over the diesel engine.

From what you have described I would be surprised if over heating was the only issue since it worked in one direction and not the other.

Hope you can find the root cause since odd things do happen in mechanical equipment.

Thanks for that really goodexplanation, oldnslo. It makes it much easier to visualize what's going on in that hydrostat.

 

[Coyote machine]

I agree with TSO and Murph, what's his name is clearly an idiot.

Now back to business. TYM's aren't noted for HST failures, IIRC what Bob said earlier in this thread. BUT two failures on one machine is a possible indicator of an operator that may have unknowingly killed them through ignorance of what conditions of use were doing to their life expectancy. I'm NOT saying Bob is ignorant; rather I'm saying, ignorance/lack of needed knowledge of cause and effect, for which he is no longer ignorant of how to prevent future mishaps, might have led to the unfortunate outcomes leading him/us to where we are in the learning curve.

 

[MHarryE]

This thread has been interesting but also has lost civility. People bad mouthing each other over Bob's broken hydro - how about donations to Bob so he can drop everything and tear the hydro apart taking pictures of everything he finds, including the locking pin that somebody failed to install properly.

Cavitation - a silent killer - but wait, not so silent. With my L3710 my dealer gave me a paper printed by Kubota showing why Super UDT (in those days) helps cut down hydro noise in colder weather. It didn't give an in depth technical description but instead printed out flow rates at given temperatures showing how much improved Super UDT was at cold temps. Users on here have confirmed that by found. Actually the increased noise level using UDT is due to the suction filter restricting cold oil flow to the hydraulic pump which in turn feeds the charge pump. The charge pump in turn provides oil to the hydro high pressure and control circuits. John Deere supplies their low viscosity oil for the same reason in their hydros. Of course there are even better oils out there but selecting them is the challenge. Companies publish their viscosities at 100 and 40 (Celsius) but what is the viscosity at -20 Celsius when you start? What is the viscosity when the oil reaches 120 when brush hogging and the cooler plugs? Makes you want a gear transmission hut I haven't shown you my failed gearbox pictures yet.

 

[Bob Christensen]

This thread has been interesting but also has lost civility. People bad mouthing each other over Bob's broken hydro - how about donations to Bob so he can drop everything and tear the hydro apart taking pictures of everything he finds, including the locking pin that somebody failed to install properly.

Cavitation - a silent killer - but wait, not so silent. With my L3710 my dealer gave me a paper printed by Kubota showing why Super UDT (in those days) helps cut down hydro noise in colder weather. It didn't give an in depth technical description but instead printed out flow rates at given temperatures showing how much improved Super UDT was at cold temps. Users on here have confirmed that by found. Actually the increased noise level using UDT is due to the suction filter restricting cold oil flow to the hydraulic pump which in turn feeds the charge pump. The charge pump in turn provides oil to the hydro high pressure and control circuits. John Deere supplies their low viscosity oil for the same reason in their hydros. Of course there are even better oils out there but selecting them is the challenge. Companies publish their viscosities at 100 and 40 (Celsius) but what is the viscosity at -20 Celsius when you start? What is the viscosity when the oil reaches 120 when brush hogging and the cooler plugs? Makes you want a gear transmission hut I haven't shown you my failed gearbox pictures yet.

MHE, I appreciate your concern, but I don't think the thread has lost civility. Ten pages , a hundred comments almost all helpful and kind. No, this problem touches on several issues on which people hold fervent beliefs, and only one person forgets himself. That might be a record

Anyway, no donations needed. I have received the HST back from Jordan and dafter tomorrow we're heading down to Cali to take advantage of Dkrug's offer to take it apart. And we are bringing a camera!

All this running around may look goofy to some, but there are reasons.

The trip to Idaho put me together with a dealer known to this board to be one of the good ones and I can confirm that whole heartedly. I also knew they had a lo Hours HST sitting on the shelf.

Plus, after they fixed it I was able to go visit my older sister who lives in northern Idaho bringing a tractor, box blade and FEL plus a pickup full of horse manure compost - I'm really getting good at making that stuff. Spent two days working around her place. Got more satisfaction out of that...

The trip to California will be 1,000 miles each way on the Coast Highway. I really love to drive and we'll be taking our new to us car that is a joy to drive.

Oils.
I think you meant to say 220 degrees which is close to 100 centigrade. And as for -20, well pour point would perhaps be more interesting than vis.

I can't even find Super UDT around here anymore. When I went to buy some recently I got Super UDT2
Which Kubota makes sound like full syn, but is actually a blend. At unknown proportions.

Gotta go. The firewood guy just drove up. I'm wholesaling about 10 cords of logs to him and I have to pull the last of it out of the woods with my tractor that I love.

 

[SweBota]

I think you meant to say 220 degrees which is close to 100 centigrade.

I think he meant 120 Celsius which is the point where most oil temp meters start showing red. Some don't until 140, and some start at 100, but in any case it's now my believe that HSTs prefer oil considerably cooler and on the machine where we added a lacking oil cooler (and a temp gauge) we now rarely see temps over 75, which feels good. I don't think HSTs should be compared to engine oils when it comes to acceptable temperature, but I have no hard data confirming this. All my temps are in Celsius, of course.

BTW, please don't use "centigrade" for Celsius, that use was officially abandoned in 1948 due to disambiguity. A centigrade is actually a measure of angle, 1/100th of a gradian (or gon). As the gradian is 1/400th of a turn, a centigrade is 1/40000th of a turn. Related to the milliradian which is 1/1000 of a radian, another angle measure which approximates to the "mil" for those who have worked with rangefinding in artillery....


/Marcus

 

[Jkott]

No one should actually be paying $200 for a 5 gallon Paul of Amsoil synthetic. Throw a $10 preferred customer membership in your cart and it's only $139. It was cheaper than the F200 I prices at my New Holland dealer earlier this year.