Broke Hydrostat twice? Why?

[dfkrug]

The transmission on my Kubota BX2200 just died and when I get it fixed (probably
by the local Kubota dealer), I'd like to install a temperature sensor.

If you add a temp gauge, I suggest putting it in a low pressure return-to-tank line. Maybe a mechanic at
your dealer can suggest a place.

Good luck, Dan

 

[texasranger556]

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

Interesting thread even 2 years after the fact. As others have pointed out, I agree the manual is incorrect. Transmission neutral at full HST pedal is useful to check charge pressure since you would have the additional fluid loss introduced by the motor rotating instead of just the pump. Then put it in gear and stall the HST to check the forward and reverse high side pressures.

As far as the postmortem photos, I'd attempt fixing it. What is the depth of the erosion? If it's not all the way through the brass/copper colored coating, my father an I have resurfaced those plates by wet lapping by hand starting around 150-200 grit emery cloth and slowly working up to 2000 grit crocus cloth until smooth again. Need a very flat surface and even pressure, but aside from a few dollars for emery/crocus cloth the only investment is time. My 4400 was done that way 2 years ago and my grandfather's 400 garden tractor about 20 years ago. I've got about 75 hours on my tractor, his had several hundred last I checked, both running fine.

 

[dan268]

Update

I brought my tractor to the dealer and they replaced the hydrostatic transmission. The part was $2000 and the labor was another $2000. My tractor is now working great. I took some pictures of the broken transmission in various states of disassembly in case anyone is interested. Kubota BX2200 hydrostatic transmission - Google Photos

The damage was pretty obvious. The end of one of the pistons on the pump side had worn completely through and the spring was poking through it. The housing holding that piston was severely worn. There was also one other piston with a slightly worn housing. I'm planning to keep the old transmission for parts. If anyone is interested in buying some of the working parts, send me a private message.

Suggestions for how to test a transmssion when buying a used tractor:
1. Connect the tractor to an immovable object and slowly press the HST pedal in low gear. The tires should spin. If the pedal vibrates and/or the tires don't spin, it could indicate internal leakage in the HST
2. Drain a bit of the transmission fluid from the bottom of the tractor (half a shot-glass or so). The thing you're looking for is fine metal particles. It will give the oil an opalescent sheen. These particles settle to the bottom, so you won't see them if you just look at the dipstick. When I changed the transmission oil before I brought it to the dealer, the first 1/3 was full of particles, but the last 2/3 was pretty clear.

-Dan

 

[dfkrug]

When I changed the transmission oil before I brought it to the dealer, the first 1/3
was full of particles, but the last 2/3 was pretty clear.

That's quite a failure, Dan. Any idea what caused it?

Nice photos.

 

[ultrarunner]

Don't know how I missed this thread...

Great analysis and pictorial!

 

[wheelsofsteele]

Hi all... this is a great post. I recently bought one of these tractors, thinking it was a drive shaft problem, it turns out that it's doing the same thing as Bob's tractor did and ,after hours of surfing the internet i found this article and its a good one!! I've gone as far as tearing it down as y'all did and it turns out that mine has the valve plate that is worn like Bob's unit did, so my next question is can that valve plate be ordered some somewhere or be made a made in a shop? The dealer in Michigan tells me that they are a non serviceable pumps is this true? Does anybody know ? I just don't want to buy a $3100 pump if that valve plate is all thats wrong with mine. Thanks in advance!!

 

[oldnslo]

If you can determine who made the transmission for Kubota and get the correct model number then you can maybe buy the valve plate. Otherwise these are probably considered throw away items in most cases.

I would suspect loss of charge pressure was one of the causes of failure. My BX 1850 had a priority flow control that was supposed to ensure that there was charge flow at all times. If this valve fails or a steering hose breaks you loose charge flow which would start the pump on the path of self destruction.

 

[texasranger556]

Hi all... this is a great post. I recently bought one of these tractors, thinking it was a drive shaft problem, it turns out that it's doing the same thing as Bob's tractor did and ,after hours of surfing the internet i found this article and its a good one!! I've gone as far as tearing it down as y'all did and it turns out that mine has the valve plate that is worn like Bob's unit did, so my next question is can that valve plate be ordered some somewhere or be made a made in a shop? The dealer in Michigan tells me that they are a non serviceable pumps is this true? Does anybody know ? I just don't want to buy a $3100 pump if that valve plate is all thats wrong with mine. Thanks in advance!!

As I mentioned a few posts up, if the plate isn't too bad, lap it and reinstall. Post some pictures, would help to determine how bad it is.

 

[wheelsofsteele]

I

 

[wheelsofsteele]