L3940 HST Overheating Problem

[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 plus 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 help at all. Its still very weak hydraulics that stutter.
There is only 420 hours on this 2009 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.
The nearest tractor service center is a 250 mi drive so I'm hoping to fix it myself.
The only thing I've seen out of the ordinary after it overheated is the short length of hose attaching to the inlet to the power steering hydraulic pump has a stress fracture and leaks a small amount of fluid. When I drained the fluids they all looked ok.


Anyone have any ideas what the overheating has caused to go bad?
I suspect the pumps are still good and that the problem is the control
valves. But I've never done any hydraulic work before.

The engine runs just fine. So the overheating has only effected
the hydraulics.

Frank

 

[Bluegill]

Overheating the engine should not effect the hydraulics, but I could be wrong.

The hose with the leaky crack could very well be your problem. As I believe the same pump runs the power steering and loader...

 

[birddogger]

Stuttering hydraulics often points to a blinded hydraulic fluid filter.

Unfortunately this is a bad way to find out to clean the seed-screen every time before starting. The little radiator is the hydraulic oil cooler, so is it was equally plugged the hydraulics overheated as well.

 

[Bluegill]

Stuttering hydraulics often points to a blinded hydraulic fluid filter.

Unfortunately this is a bad way to find out to clean the seed-screen every time before starting. The little radiator is the hydraulic oil cooler, so is it was equally plugged the hydraulics overheated as well.

Shuttering hydraulics is also caused from a leaky suction hose.

Good point about the HST oil cooler. I don't have HST so didn't think about it.

 

[frankl3940]

After changing all the fluids including the anti freeze, engine oil, front axle oil, 11 gallons of Super UDT, both hydraulic filters. The only thing I found wrong is the short 8" length of large diameter rubber hose that feeds hydraulic oil to the pump on the side of the engine has tiny pin holes in it. Which both leaks small amounts of hydraulic oil and would also allow the pump to suck air. And thats probably the reason for the stutter of both the power steering and the front loader bucket. Both must share the hydraulic pump oil at the side of the engine.

So the million dollar question is how to go about changing out that short length of large diameter rubber hose? I can easily cut it off but I dont see any easy way to attach the new rubber hose. Anyone have any ideas as to work it takes to place a new hose? If it wernt a 250 mile drive to the nearest dealer, I could gladly trailer it in. I dont want to cut the old hose out until I'm sure I can replace it. As its in drive-able condition presently. Frank

 

[Bluegill]

Yeah, that suction hose is your problem. You're goin to have to get under there and see if it can be fished into place. Looking at both mine, it can be done. But mine are not HST and are different models. You might have to remove the floor section?

 

[birddogger]

Looking at the parts pix, that tube goes on the inlet pipe, which then heads uphill a short bit then drops vertically. Along that vertical drop there's a stabilizing tab screwed to the side of the motor. If you can access that and remove the screw so you can move the pipe gently that should allow you to wriggle the tube into position, it only goes on the pipe about 14mm, so between flexing the tubing and jogging the pipe up a touch. Slobber up the tubing and pipe with some UDT and slip it on and set the clamps, replace the stabilizer screw. You may have to remove a fancy panel but they are usually 4 screws.

 

[frankl3940]

Thanks for the tips on the short 8" inlet hose that has fractured. Today I placed two
layers of Etherna Bond tape around the area where the inlet hose fractured. And now the L3940HST works just fine. So the problem was the hydraulic pump was sucking air in the fractured hose on the low pressure side of the pump.
When I install the new hose, I'm going to wrap a couple layers of Eterna Bond tape around it just for grins. Eterna Bond tape is used on commerical roofing projects.
Great tape for making quick repairs. Although expensive in large rolls.
I'll have the new hose by next week --- But in the mean time, now I can use the tractor and finish haying !!! Frank

 

[frankl3940]

Just a side note regarding the cooling for the Hydraulic fliud on this L HST series of hydro-static tractors: If you look at the front of the radiator where the tiny hydraulic fluid cooling fins are, you will notice that in front of the fins is the lead acid battery. The battery is almost flush right up to the cooling fins. Preventing air from circulating around the cooling fins. But the final insult is the fins are sitting at bottom area in front of the engine radiator. Where there is little or no movement of air to begin with. Plus when you are mowing a pasture, the crop debris is sucked into the area of the radiator... causing the debris to settle right onto the cooling fins.
So if your using the L3940HST, you should bring the tractor back to the shop every hour and use compressed air to blow the debris away from the cooling fins.
They should never have placed the lead acid battery right up to and blocking air from getting to the tranmission cooling fins. A serious design fault by Kubota. I'm looking into moving the battery back to the tractor seat area where its out of the way.
Shame on Kubota for such a poor cooling design. No wonder the hydrostatic drive overheats so readily.
Fortunately for me I use this L3940HST mainly in winter at high elevation for pushing snow ... and its below freezing all winter at this northern area of the US at high elevation. Frank

 

[Stubbyie]

Agree with poor placement of cooling parts in front behind battery.

On one machine found Previous Owner had never cleaned either cooling system radiator or hydraulic cooler.

Required much flushing with water and air and using HVAC fin comb to get everything right.

NOW we use an HVAC-type cheap blue (green, white) spun fiberglass gross contaminate particle catcher filter (box store, $1 each or less) in front of both cooling and hydraulic radiators.

Placement is in front of pull-up Kubota screen but behind battery. Wide variety of sizes can get close to fitting your engine compartment. Around this area these filters are known in the trade as (depending on speaker) "made of blue cat hair" or "made to catch cat hair". Now you know...

Some of these filters have thin metal grid of large-diameter holes supporting filter mesh. Because of proximity to battery I avoid these preferring to use least expensive types of fiberglass-only construction.

Can remove in field, shake clean, reinstall. Or carry spares in support truck. Cheap, fast, easy. In busy season haying we'll use a new one every day or two.

 

[kuboman]

I don't know if the L3940 has the identical grill as the L5740 but mine has air intakes on the grill that are on the side and behind the hydro cooler. I taped these off so that all the air the the engine fan drew in was forced through the cooler. Hard to tell but I think it did make some difference.

 

[birddogger]

A useful tool is a "radiator brush." Actually for old-fashioned steam radiators in homes. A long thin brush for narrow places.

Handy when you are far away from a hose or the shop compressor.

 

[frankl3940]

Thanks for the inside information !! I've decided to leave the battery as is and use an idea similar to what you mentioned. It dosnt take long mowing a pasture till the area both in front and behind the transmission cooler is plugged up with debris. So some additional screening to keep the material from getting into the area in the first place would certainly help. I'm hoping I can maneuver a new inlet hose onto the hydraulic pump without too much difficulty. The new hose might be here by this Friday. Frank

 

[TripleR]

A useful tool is a "radiator brush." Actually for old-fashioned steam radiators in homes. A long thin brush for narrow places.

Handy when you are far away from a hose or the shop compressor.

I have kept various brushes handy for a quick cleaning and they work pretty well, I also usually have a Stihl leaf blower in my truck.

 

[frankl3940]

I'll try & find one of those brushes. Here is some good news. The new inlet hose for the hyd pump showed up and it only took 20 mins to install it. Now the tractor runs like new The temporary repair I made with Etherna Bond tape wasnt the best. Thanks to everyone on this group for the generous help and tips. We are located in one of the most isolated areas of the US with no service shops avail. Plus I'm over 70 and getting on in yrs... So its great to have it all serviced and fixed up in time for winter at this high elevation area -- snow country near the Canadian border. Cheers

 

[Bluegill]

I'll try & find one of those brushes. Here is some good news. The new inlet hose for the hyd pump showed up and it only took 20 mins to install it. Now the tractor runs like new The temporary repair I made with Etherna Bond tape wasnt the best. Thanks to everyone on this group for the generous help and tips. We are located in one of the most isolated areas of the US with no service shops avail. Plus I'm over 70 and getting on in yrs... So its great to have it all serviced and fixed up in time for winter at this high elevation area -- snow country near the Canadian border. Cheers

That's good to hear! Good luck with it.

 

[cliffcren1973]

Thanks to guys and this site, I have a L3940 with the sluggish steering and i read your comments and found my problem , the short 8" hose was cracked , thanks a million guys