Broke Hydrostat twice? Why?

[Raincoast]

As mentioned before, I would REALLY want to see a teardown report on that unit. Paulfun9 suggested paying for it & I agree wholeheartedly! If you are gonna keep that tractor, the peace of mind (if nothing else) would be worth every penny spent. It would likely take less than an hour of shop time. You probably don't need a formal, written report. Many shops are reluctant to put such things in writing, for liability reasons. If you ask for a verbal report, that may overcome any reluctance you might encounter.
My history is in the aircraft industry, where premature failures are routinely assessed to discover the cause & prevent future occurrences. A quality teardown report is worth it's weight in $$$.

 

[Leejohn]

You state the manual said.

"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"

I don't see how it can build pressure if there is no load on it. For sure the relief couldn't open when the tractor is in neutral. The transmission has to be doing work to build pressure. What am I missing?

 

[RandyT]

Just thinking outside the box here. Could it be possible that the bypass valves are getting sticky when they get hot from the oil going through the system. Leading to shock loading which lifts the pump off of the mating surface and then slams down when pressure drops to normal levels, like when you ram into a pile of dirt and suddenly stop or change directions.

 

[Bob Christensen]

Leejohn
I think you hit about 2000 psi in neutral at redline and about 5000 psi as you push the go pedal while pushing against a wall or something.

 

[Bob Christensen]

OK, I just called Jordan in Post Falls, Idaho.
They agreed to pull the old hydro apart though it might be a couple of weeks before they can get to it.
I offered - then insisted on paying, but they refused. Said they were curious too.

Did I tell you that while they were working on the hydro they unilaterally decided that my tractor body was ratty looking after 8 years of hard use, so they replaced it with an almost new one they had because they had replaced one under warranty cause it had a tiny bit of paint peeling? No charge.

So I'll keep the radiators clean from now on and will report back when I hear from Jordan.

 

[Bob Christensen]

Oh, and another thing Jordan reminded me of.
They removed the tranny strainer to see if there was any shrapnel in it and there wasn't.
And the oil was clean and looked good.

 

[Sysop]

I have often wondered what the proper RPM is.

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

I agree with everyone that finding a resulting cause to your issues is a high priority, in the mean time I would say that while 1800RPM should be fine in most instances for most machines; after having two failures I would use a higher RPM. HSTs love flow. They run cooler and last longer the more you fluid you feed them. They are designed for and tested at PTO speeds as a minimum as the most common tasks generally work best at full PTO speeds. Generally if you closely examine the speed charts provided with newer HST tractors, the speeds are rated at RPMs higher than the PTO RPM, and in many cases they are rated at the governed RPM redline.

I have never heard of such a thing as running the engine too hard for the HST to handle, but there are many documented cases of not having enough flow and wearing/overheating/ruining the HST. Till you get it figured out I'd operate at an RPM you know it is spec'd to run at such as PTO speed.

 

[dfkrug]

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?

Yes. You have a mechanically controlled HST, as expected. What TYM calls a "cam plate"
is known in the industry as a swash plate. The photo shows one kind of swash plate,
from a McCormick HST unit. The lever arm tilts the plate to change the volume and
direction of the HST pump flow.

 

[dfkrug]

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"

Given that the test was done in a no-load situation, I would expect something less than 500psi. The
test procedure looks plain wrong. With range shifter in neutral, the HST pump in FWD or REV is only
driving the internal gears and other parts. I few hundred PSI max, IMO.

Kudos to LEEJOHN for also seeing the mistake. My main tractor is also Korean, and the manual has
lots of errors. BTW, my Kioti CK30HST uses 2 independent RVs for the FWD and REV directions,
while the newer HST on the CK35H uses only one shared relief.

Here is another photo of an HST's guts, this time a Kubota B21.

I would do a post-mortem on your HST for the postage, Bob, if your mechanic does not
get to it.

 

[Bob Christensen]

I think I was making an assumption about how my local guy did the test based on my interpretation of the service manual and since either or both of those things have been shown here to be wrong, I will try to find out from my local guy just how he did do the pressure test.

Dfkrug, that is a very generous offer and if Jordan fails me (they really are very busy) I'll take you up on it.

Back tomorrow with more info on the testing.