Kubota L4701 Sometimes Stalls When Moving Forward with HST Pedal

[josiahgarber]

This winter I've been having a problem with the tractor where it starts fine, and then when I press the HST pedal to move forward it stalls. If I leave off the pedal quickly it will not stall and RPMs will come back up. Interestingly, when pressing the pedal for reverse it does not stall.

Is that typical of a seat switch problem? I would have thought that it would prevent me from going forward and reverse not just forward.

 

[jeff9366]

This winter I've been having a problem with the tractor. It starts fine, then when I press the HST pedal to move forward it stalls.

1) In cold temps when you first start the tractor the engine oil is very heavy/thick.

2) When you try to move forward you connect secondary resistance of the cold/heavy/thick hydraulic oil which links the HST pump to the wheels and resistance of cold transmission/wheel bearing oil and grease.



If you increase tractor rpms 10% after the engine has warmed, does the engine still stall? You should not run a L4701 DPF equipped tractor at minimum rpms during cold weather. Increase hand throttle power a tad during cold weather.



Seat switch on all tractors I have operated will kill the tractor engine if not closed. Engine on or off, nothing between.

 

[josiahgarber]

This winter I've been having a problem with the tractor. It starts fine, then when I press the HST pedal to move forward it stalls.

1) In cold temps when you first start the tractor the engine oil is very heavy/thick.

2) When you try to move forward you connect secondary resistance of the cold/heavy/thick hydraulic oil which links the HST pump to the wheels and resistance of cold transmission/wheel bearing oil and grease.



If you increase tractor rpms 10% after the engine has warmed, does the engine still stall? You should not run a L4701 DPF equipped tractor at minimum rpms during cold weather. Increase hand throttle power a tad during cold weather.



Seat switch on all tractors I have operated will kill the tractor engine if not closed. Engine on or off, nothing between.

Thanks. I will check this. What RPMs would be high enough to operate the L4701 in the winter?

 

[Fxfymn413]

It will stumble if the seat switch gets momentarily activated; like hitting a bump for example.

The previous reply is probably correct. I never try to move my L4060 when it is below freezing until it has warmed up for at least 10 minutes at about 1000 rpms. And even then I can tell the hydraulic fluid is more viscous than usual.

 

[jeff9366]

All I can recommend is experiment.

You are in cold winter PA. I am in temperate-winter north Florida. I experience only one or two nights of frost per winter.

 

[Fxfymn413]

What RPMs would be high enough to operate the L4701 in the winter?

My dealer encouraged me to run my 4060 at 2000 rpms or higher to avoid frequent regens.

 

[Fallon]

This winter I've been having a problem with the tractor where it starts fine, and then when I press the HST pedal to move forward it stalls. If I leave off the pedal quickly it will not stall and RPMs will come back up. Interestingly, when pressing the pedal for reverse it does not stall.

Is that typical of a seat switch problem? I would have thought that it would prevent me from going forward and reverse not just forward.

Yes, sounds like typical safety switch issues, but it could be other things. Easy check would be stand up briefly while moving. If it cuts out & back in (if you can sit fast enough) that's a good sign you are on the right track.

Pushing the machine cold isn't great, but shouldn't stall it if it's had a minute or so to warm up. I usually give mine a couple minutes to start to warm up before moving. Oil won't thin out much at that point, but it does get everything lubed up properly. I run them easy for 10 minutes or so before going hard. A working machine generates a LOT more heat than one idling, even at a higher RPM.

 

[nybirdman]

Are you using Kubota branded HST fluids(Super UDt)?

 

[whitetiger]

This winter I've been having a problem with the tractor where it starts fine, and then when I press the HST pedal to move forward it stalls. If I leave off the pedal quickly it will not stall and RPMs will come back up. Interestingly, when pressing the pedal for reverse it does not stall.

Is that typical of a seat switch problem? I would have thought that it would prevent me from going forward and reverse not just forward.

The seat switch appears to be doing its job, but the complaint you have is that the Hydro pedal safety switch is out of adjustment. it is located under the LH running board and just ahead of the LH rear axle housing. You need to unplug the wiring connector from the switch, loosen the jam nut holding the switch, turn the switch in one turn. Tighten the jam nut, plug in the wiring connector and go play.

Edited to correct a typo.

 

[Grandad4]

Very likely it is one of the safety switches or the wiring thereto needing adjustment or something. Probably the one at the foot pedal from your description. Even when cold the engine should have ample power to move forward.

 

[mikester]

This winter I've been having a problem with the tractor where it starts fine, and then when I press the HST pedal to move forward it stalls. If I leave off the pedal quickly it will not stall and RPMs will come back up. Interestingly, when pressing the pedal for reverse it does not stall.

Is that typical of a seat switch problem? I would have thought that it would prevent me from going forward and reverse not just forward.

I ran into the same problem before christmas. The engine would lug to the point of stalling in fwd or rev with auto-throttle and stall-guard active. Going to full throttle and putting the HST pedal to the floor would get past the stall point and it would drive me back to the shop.

I was near my next major service interval and I went to the dealer to pick up parts and fluids. I talked with the service manager - he said they were booked solid for the next 2 weeks, but after describing the issue he said the issue sounded electrical to him. On the models with the drive-by-wire servo actuated HST, he said the only failures he's seen are with the actual fwd/rev servo mechanisms. He said it typically happens around snow clearing season, especially with guys who operate along salt covered roads.

I told him I've been operating a lot in the rain and deep mud recently.

He told me that if there was a hydraulic pump issue I would be hearing bad noises and the engine wouldn't stall. The likely issue was that both fwd and rev hydraulic circuits were trying to be active at the same time and acting as an engine brake. If my pump was bad oil would simply blow by. He said these hydraulic pumps on the M59 are robustly built and he's never seen one fail.

He suggested checking and cleaning all the electrical contacts to start with, sometimes salt gets in and corrodes the contacts. At worst he said I may need to change out the servos, they had them in stock and they were only a couple hundred bucks. He gave me the parts diagrams and suggested I give it a try before booking a service call.

I bought some contact cleaner spray and cleaned the harness contacts from the servos and to the HST pedal. On the M59 the servo harness clips are a SOB to get at unless you have alien long skinny hands and fingers. I could only get at the top one off with a set of 18" forceps and a straw on the contact cleaner spray.

I let everything dry thoroughly, re-assembled and am driving around without any problems for over a month now.

 

[Fallon]

On the economy Ls (3000 series at least) its a mechanical HST pedal, not electronic like in the Grand Ls or bigger machines.

 

[josiahgarber]

The seat switch appears to be doing its job, but the complaint you have is that the Hydro pedal safety switch is out of adjustment. it is located under the LF running board and just ahead of the LH rear axle housing. You need to unplug the wiring connector from the switch, loosen the jam nut holding the switch, turn the switch in one turn. Tighten the jam nut, plug in the wiring connector and go play.

Thanks. I'll check that. What does LF and LH stand for?

 

[whitetiger]

Thanks. I'll check that. What does LF and LH stand for?

The "LF" was a typo, should have been "LH" or Left Hand".
The "LF" actually means "Left Front".

 

[josiahgarber]

Went out to troubleshoot the problem today. It was warmer in the 40s and I let the tractor warm up for a while. Did not encounter the problem at all except when getting off the seat. I did notice that the lever for the seat switch sprung back easily, whereas last time I checked it did not.

 

[whitetiger]

Went out to troubleshoot the problem today. It was warmer in the 40s and I let the tractor warm up for a while. Did not encounter the problem at all except when getting off the seat. I did notice that the lever for the seat switch sprung back easily, whereas last time I checked it did not.

Next time it starts acting up, leave the hydrostat pedal in neutral and engage the PTO. If the seat switch is causing the problem, the engine will die in about 1 to 2 seconds.
If engaging the PTO does not shut the engine off, step on the hydrostat pedal leaving the PTO ON. If it dies in about 1 to 2 seconds, the failure is the hydro pedal safety switch.

 

[josiahgarber]

Next time it starts acting up, leave the hydrostat pedal in neutral and engage the PTO. If the seat switch is causing the problem, the engine will die in about 1 to 2 seconds.
If engaging the PTO does not shut the engine off, step on the hydrostat pedal leaving the PTO ON. If it dies in about 1 to 2 seconds, the failure is the hydro pedal safety switch.

Thank you. I will certainly try that.

 

[s219]

Went out to troubleshoot the problem today. It was warmer in the 40s and I let the tractor warm up for a while. Did not encounter the problem at all except when getting off the seat. I did notice that the lever for the seat switch sprung back easily, whereas last time I checked it did not.

In the past, several people have reported issues with safety switches sticking in freezing weather. Is the tractor stored outdoors where it can get rain/snow on it?

 

[josiahgarber]

In the past, several people have reported issues with safety switches sticking in freezing weather. Is the tractor stored outdoors where it can get rain/snow on it?

It is stored in a barn. It was definitely sticking in the cold weather, though I'm not sure how it would be sticking up when I'm in the seat. Not sure.

 

[PlasterProspector]

I had the same issue. Found out the foam seat froze and wouldn't activate or maintain pressure on the switch if motion occurred. Pulled it out, checked the connections, they were all fine and so I zip tied that switch down.

Warranty and liability are always a concern when bypassing safety equipment. So now I'll occasionally ask my wife what to do if there's ever a tractor accident, once everybody is safe of course, and she always answers, "flip the seat and cut the zip ties" haha.