Kubota L3940 HST Hydraulics overheated

[Frankl3940]

When I was mowing the pasture in 100 degs temp, the radiator became
plugged with debris and the tractor overheated. When I noticed the problem,
I let the tractor idle for a half hour before shutting it down. But apparently
it had been overheating for several hours before I caught it.
The next day when I went to use the tractor, the hydraulics are now
very weak. I have to run the engine at 2000 rpm just to lift the front
loader bucket up plus it stutters. And the hydraulic power steering
also has the same stuttering and weakness. The hydraulics worked just fine
even at idle speeds previously. I could even steer it just fine at idle previously.
Now it has to be running at 2000 rpm just to begin to be able to
turn the wheels and lifting the bucket is very labored with the same stuttering.
Had anyone worked on the hydraulics for the Kubota L3940HST?

It was time to replace the fluids on the tractor anyway so I replaced all
of the fluids --- engine, radiator, front axle, 11 gallons super UDT in the hydraulics.
All with no helps at all. Its still very weak hydraulics.
There is only 420 hours on this L3940HST with never a
problem previously. Anyone have an idea
as to what the overheating might have caused? Is it possible for both hydraulic
pumps to become defective from overheating or is this more of a problem with
the hydraulic valves? I've never worked on hydraulics before.

Frank

 

[Leejohn]

If your engine oil level is same after running awhile, then check the hyd intake hose. It is real close to engine and could have messed it up. Also there has been some trouble with the intake hose. Like pin holes and small cracks.

 

[J_J]

I think I would install a hyd pressure gage and check some pressures.

This will tell you if the pump and cyl can develop the pressure up to the setting of the relief valve.

The excessive heat could have damage your seals in the cyl.

As a test, hold the FEL lever full fwd or back and see if the relief will activate. If you do this with a gage installed, you will see the max pressure.

 

[Frankl3940]

Well, the cooling fins for the hydraulic fluid sit at the very bottom
in front of the radiator. The mower had thrown plant debris --- which
was sucked up by the flow of air through the radiator. And that allowed
the plant debris to collect all around the lower position of the hydraulic
fluid cooling fins. So its a design issue with the placement of the cooling fins
at the very bottom front of the radiator. The cooling fins for the hydraulic
fluid should have been placed up higher so the plant debris couldnt collect
around it. The engine radiator did cool down when I let it ldle for
a half hour but the hydraulic fluid wasnt allowed to cool since its cooling fins
had been totally plugged up with plant matter.

I checked the inlet hose to the power steering pump (on the engine) and sure
enough, there are small fracture stress pin holes in it due to the overheating.
Causing a slow leak of fluid. The way that inlet hose is set up with a jog
in it is a point of stress to begin with. So its a hose that needs to be replaced
as a regular maintenance issue due to the stress its under.

Since both the power steering and the front loader hydraulics are bad, that
would indicate to me that its far more than just an issue with some pin holes
in the hydraulic steering pump. Is there an easy way to attach a hydraulic
pressure guage to see whats going on? Like some fittings that are designed
to have a gauge attached for testing? I dont have a gauge but looks like I'll
have to find one!!!

Frank

 

[J_J]

If you only have one pump, you can can install a tee in the pump OUT hose before it gets to the hyd splitter if that is what is installed.

If you are using the FEL, the gage will reflect the pressure developed.

If you are steering, you will see the steering pressure.

If you are doing both at the same time, you will probably see the higher of the two.

I believe the steering pressure is at a lower pressure than the FEL.

Your steering flow is 4.9 GPM. It also says Hydrostatic power steering, and that might mean that your steering fluid is from the Hydrostatic pump on the transmission. If not, then you will have another pump for the steering.

Your valve flow is 9.8 GPM

http://www.tractordata.com/farm-tractors/001/8/3/1833-kubota-l3940.html

If you do have two pumps, then install a tee and a male QD in the each tee.

Then make up a hyd test set, with a 3000 psi hyd gage with a female QD on it and just plug into which circuit you want to measure.

 

[Leejohn]

He has 1 pump housing with 2 pumps in it.

 

[Frankl3940]

The short length of hose that brings low pressure hydraulic fluid to the steering
pump does have pin holes in it. It was OK before so it was the overheating
that caused the pin holes in the 9" inlet hose. Do you know the proper procedure
to replace that hose? It has a hose clamp at each end but there dosnt appear to
be any way to get the hose off other than cut it off. I'm assuming in order to
place the new hose would require removing the incoming metal line from the
oil filter? Has anyone replaced that short length of hose going onto the steering
hydraulic pump?

Frank

 

[Leejohn]

On my 4240 there is a bracket that covers the hose, remove it and then you can get the hose off.

 

[PHILIP8N]

I am sorry to hear about your problems, but how did you over heat tractor? You have a temperature gauge, an idiot light, plus the screen on the intelli-panel that reads 'OVER HEAT - STOP ENGINE'. How could you miss all 3 things telling your engine was getting hot? I understand your problems. When I mow this on a 100F degree day I have to stop about every 30 minutes to blow my coolers and screen clean, plugs up in no time at all. I keep a close eye on the temperature gauge, don't want to overheat a good tractor. Good luck. Philip.

 

[madmax12]

I am sorry to hear about your problems, but how did you over heat tractor? You have a temperature gauge, an idiot light, plus the screen on the intelli-panel that reads 'OVER HEAT - STOP ENGINE'. How could you miss all 3 things telling your engine was getting hot?

Ouch!

We don't need to kick a man when he's down, do we???

Giving him the benefit of the doubt, a 100 degree day was probably very bright and sunny. It was probably very glarey (if that's not a word, it should be). He was probably dripping sweat in his eyes and could barely breathe. And probably just wanted to get all his hard work done.