Broke Hydrostat twice? Why?

[Bob Christensen]

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

 

[HEC]

To bad Jordon couldn't give you a heads up with what is going on . It is beyond me for sure , but others may jump in and offer some help .

Good Luck

 

[Raincoast]

It would be great if you could get a teardown report when the unit goes in for repair or overhaul. It would be worth asking the dealer if they could send you a copy... That is, IF the unit is going to be repaired. They might just toss it in the scrap bin.
Good luck. I hope third time is the charm for you!

 

[Billrog]

Jordan can't say this is a problem but are you running at to low of an rpm ? If this is the case you could be starving the pump of oil which could lead to damage. This is often the case with the hydraulic drive motors on skid steers when run at low rpm.

 

[Bob Christensen]

Jordan can't say this is a problem but are you running at to low of an rpm ? If this is the case you could be starving the pump of oil which could lead to damage. This is often the case with the hydraulic drive motors on skid steers when run at low rpm.

I have often wondered what the proper RPM is.

I almost always run at about 1800 RPM. Red line is 2700.

This time of year Jordan is pretty busy. They say that since they're curious too they may rip into it this winter, and if so they will tell me what they find.

 

[Bob Christensen]

The above is not to mean that I really expect Jordan to solve the problem any time soon or even at all.
I'm relying on someone here to hopefully recognize the problem and tell me if I' doing anything wrong.

Thanks, Bob

 

[SweBota]

Is your hydraulic oil cooler working correctly? Put an oil temp meter in the return path somewhere and monitor the temp. I have had a hydro pump failure after 400 hrs in a smaller machine due to high temps.

/Marcus

 

[Billrog]

I think running at 1800 is fine my case 20hp has 3700 hrs. and I ran it any where from 1200 to 2000 most of the time plowing snow and higher when splitting wood, tilling or running a flail. It still works just fine and never a trans. prob.

 

[Bob Christensen]

Marcus, Hmmmm...
I do a lot of compost turning. My engine has never overheated according to the dashboard gauge, so I haven't been concerned about heat.
I blow the radiators out from time to time when they seem encrusted with compost or dirt but now it occurs to me that the tranny cooler is small and sits in front of the main radiator and gets covered first.

So there may be a time when it is clogged but the engine radiator is only partially blocked and in my cool climate this does not show up on my engine temp guage.

I'll never know now,of course, because thanks to you this will never happen again.

Anyone want to chime in on whether this was likely the culprit? I might add that since the other main task for the poor beast is clearing and maintaining paths in a forest, random sticks have long since destroyed the front grill, making easy access for mulch dust, etc.

Plus turning over a,say, thirty ton pile of manure would perhaps make the tranny want to heat up without perfect cooling?

 

[Grandad4]

I'd pay attention to what Marcus has noted. There have been a few times when I have worked the tractor hard enough that the hydraulic fluid got pretty hot. On mine it took intense heavy FEL work on a 95 deg. day to get to that point. Began to smell a whiff of hot fluid - it has a unique aroma - and touching one of the FEL lines confirmed it was too hot to touch. Backed off the pace of work and it cooled down to more normal temperatures, no harm done and I learned to watch for overheating the hydraulic fluid in extreme conditions. While it's normal for the fluid to get good and hot as the tractor works - 180-220 deg is probably typical, when it gets well beyond that there's the potential for harm. Every situation is different of course but heat seems like a real possibility in setting up the conditions for your HST breakdowns.

 

[paulfun9]

I have thought about this a bit since you posted. My final thought is that if you cant find a clear cut answer to why I would sell it before blowing an other one and replace it with something else. If temps really were the problem I would suggest that you would have noticed it running/working differently as well as smelled the fluid overheating which gives me the indication it could well happen again without you realizing it.

 

[MHarryE]

Usually if the problem is heat the oil viscosity drops too low to prevent metal to metal contact and things start to wear. I tried taking a picture of 2 hydrostatic transmission pistons from an overheated transmission but my iPad camera sucks at getting the detail. Anyway the result is often slowly degrading performance due to internal leakage. Yours have been sudden catastrophic failures. Even more unusual is that with your latest failure the tractor went fine in reverse but wouldn't pull itself forward. I don't know your particular hydro and it is much lighter duty than the ones with which I am familiar so it's hard to really define a likely failure point but if it were one of the ones I am familiar with the first failure would likely be a blown piston due to a material defect and the second one either a failed high pressure relief in the forward side or a plugged control/ other control failure. Any idea why the dealer happened to have a used hydro available? Seems unusual unless he rebuilds failed hydros during the winter to be available for customers like you who need one immediately during the peak season.

 

[Gregster613]

Bob, I, also, have a TYM273 and have not had any transmission troubles as of yet...knock on wood! I have 500 hours of mostly trouble-free operations. I have experienced several (numerous) times of engine overheating -- noticed through spitting out of the radiator overflow tube -- NOT via the temperature gauge!! The gauge "always" stays within the normal operation range?!? I have come to realize that I need to blow off (via air) the radiator "each and every" time I put it away after operating it!! I also "flush" out the radiator fins with water and I "always" include the oil cooler each time!! With both air and water -- as it is directly in front of the radiator -- it is covered with debris first!! This has been my normal ops procedure for quite awhile now and has thus been successful. It is a PITA bothersome task, but one that I gladly partake of rather than having $$$ breakdowns. Has worked so far -- again -- knock on wood!! I await any results you may learn of as to your 2 transmission failures!
Good luck. Greg

 

[Bob Christensen]

Thanks for your reply, paulfun9.
Selling is not a first option for me because my best dealer option is in Idaho, alooong drive for me.
Plus I couldn't get much in trade for mine.
I almost have to stay with TYM because I have a backhoe that wouldn't fit any other brand.
And the size/ power is perfect for me.
And my wife won't let me.

 

[Bob Christensen]

MHarryE,
I' not clear just how quickly the problem developed. I don't remember smelling hot oil but I don't know if I would recognize it anyway.

It can' have been the forward relief valve because I took it out and switched it with the reverse one and there was no difference. Reverse but almost no forward.

The dealer had a near new hydro because someone else burnt their tractor and traded what was left for a new one. There was no singed paint on it and I payed less than half new. It wasn't entirely a coincidence because I checked around and this was one thing that influenced me to go to Jordan.

 

[Bob Christensen]

Greg.
I've always wondered about the temp guage. After a brief warm up period it goes to the half way point and stays there no matter what. I will now surely adopt your cleaning regimen!

 

[dfkrug]

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.

Interesting problem, Bob. It is no secret that I love working on HSTs.

I never had a TYM, but would love to get a broken one. My initial thoughts:

Sounds like you have done some good initial analysis. Do you have the service manual?

The charge pump pressure of 125psi sounds about right, but the HST relief pressure
should be more like 4000-5000psi. To get that measurement, you need to put the
HST in high range, and drive it up against an immovable object. In reverse, since
you say that still works fine. What did you do to get the 500psi measurement? And
the 2500psi spec...is that from the manual?

Since REV still seems to work OK, your HST valve plate and slippers are OK.
Does your HST use a direct-acting swash plate-to-pedal connection, or a
servo?

 

[paulfun9]

Thanks for your reply, paulfun9.
Selling is not a first option for me because my best dealer option is in Idaho, alooong drive for me.
Plus I couldn't get much in trade for mine.
I almost have to stay with TYM because I have a backhoe that wouldn't fit any other brand.
And the size/ power is perfect for me.
And my wife won't let me.

I can understand that, so my next train of thought would be to find out exactly what went wrong with the old one even if it means paying for the place you had the repair done to tear into it and find the exact cause. Myself I just couldn't feel right about not knowing and having the potential for an other breakdown to happen. We use our tractors all year long and simply put I couldn't rest not knowing especially if it can be avoided or if its maybe even a simple fix. Many folks would be surprised at how simple the fixes were for some known problems with machines/cars /trucks over the years.
Good luck and I hope you don't have anymore problems with it.

 

[Bob Christensen]

dfkrug -

I do have a service manual (not that I'm a good mechanic and can actually understand all of it) it says:
"The hydrostatic system is a closed loop fluid power system that consists of a charge pump and a THI piston pump/motor assembly, which is driven by a flexible coupler. Attached to the flywheel. Fluid flow is controlled by changing the angle of the cam plate. This angle is controlled by the operator through a mechanical linkage"
Does this even answer your question?

I tested the pressure at the rear remotes, but I soon after gave up and brought it to a local mechanic/engineer who I have used previously.
He tested the hydro at the test ports and got about 500 psi.
I believe he followed the manual which states:
"Place range transmission shift lever in neutral. Start engine and run at full throttle. Slowly depress forward directional pedal. Gauge should slowly rise to approx. 130-170Kgf/cm2, 1848-2417 psi and relief valve will open with an audible squealing noise if the pressure rises to over 350Kgf/cm2. Repeat with reverse"

They go on to say that if charge pressure is good (it was) and you can't reach relief pressure, the hydro static pump is worn or damaged (but remember I got 1800 psi at the rear remotes).

So, I believe my local mechanic got about 500 psi at 2700rpm and expected about 18-2500psi and never tried to reach relief pressure of about 5000 psi.

Jordan was expecting something simple like linkage, driveshaft or such and were forced by their examination and tests to agree that the Hydrostat was shot.

One thing I forgot to mention was that in forward the tractor would make a noise like a pig killing a cat.
Now it is as quiet as I can ever remember.

Thank you for your interest.
Bob

 

[MHarryE]

Your transcribing from the shop manual proves it is a regular piston pump and motor hydro. Forget the rest of the hydraulics - steering, 3 point, any auxiliaries. They are powered by completely different pumps. In neutral, the swash plate controlling piston displacement is straight up and down - no fluid pumped. As you increase forward or reverse the swash plate is tilted to a degree equivalent to how far you push your pedal. Since the same major components are driving forward and reverse, it doesn't follow that you have normal reverse and no forward. That's why I suggested a problem in the control section. Now that you described the noise in forward, that does sound bad.

My engineering basic reference on hydrostatic transmission design is to use 30% of available power as the amount of heat needed to be rejected by the oil cooling system. Some of this is transferred directly from the reservoir (transmission case) to the air and the rest by the oil cooler. When we have tried downsizing in order to reduce cooling package size we always regretted the decision. That's why I have this sack of failed pistons here to remind me penny wise, pound foolish.