Kubota L3400DT Hydraulic problem.

[Bill32]

I have a problem with my 2007 Kubota L3400 with std transmission. Occasionally, when operating front end loader under heavy load, I cannot get the transmission to shift out of gear after depressing the clutch without first lifting a rear wheel off the ground. The wheel turns and de-torques the differential. I can also relieve the torque by turning off the engine. Apparently the high pressure from the hydraulics is leaking back to the pump that is driven by the gear train, after the clutch, and tries to drive the tractor forward, thus a torque is created in the drive train that is not relieved by the clutch and it locks it in gear. It has had this problem since it was new, but the dealer didn't believe that the problem could occur and would not do anything for me. Note: This condition exist in 2 wheel drive so it is not a "4 wheel drive torque" problem.
Any Ideas?

 

[Gordon Gould]

That is a strange one. I would think that if your loader valve was in center position The hydraulic pump pressure would be close to zero. The high pressure holding the load is in the cylinder and locked thier by the closed valve. The pump doesn't see it. Sounds more like something in the clutch/transmission to me especially if letting the wheel turn frees things up. But I am not a mechanic and maybe I misunderstood what you were saying.

 

[crashz]

The hydraulic pump is engine driven, not transmission driven, therefore by releasing the clutch, you are only disconnecting the transmission.

Could the loader be applying enough force on the drive train that the wheels turn, slipping the gears out of sync? Like trying to shift while freewheeling?

 

[Bill32]

Thanks Gordon and Crashz.
I agree that rusty clutch splines is suspect except the problem never happens without hydraulic loading. Also it is unlikely that turning off the engine would relieve the problem. Their must be a leak back somewhere, but I don't know where. I was in hopes someone has experienced this problem and knew where the leak is occurring. Another clue is I have had the lock up happen while sub-soiling in hard dirt. The tractor still tries to move forward. Turning off the engine stopped it.

 

[Baby Grand]

I could see this leading to a potentially dangerous situation where you cannot get out of gear and stop the tractor from moving when you really need to in a hurry. I would escalate this a level if your dealer doesn't take it seriously. Luckily, you had exactly the right response - shut it down. But many people might respond by trying to use the brakes and panicking if that didn't stop the machine.

I'm sure Kubota (at some level) would see the potential for liability claims and be inclined to do something to help you (and get some good engineering design information in the process).

 

[Bill32]

I could see this leading to a potentially dangerous situation where you cannot get out of gear and stop the tractor from moving when you really need to in a hurry. I would escalate this a level if your dealer doesn't take it seriously. Luckily, you had exactly the right response - shut it down. But many people might respond by trying to use the brakes and panicking if that didn't stop the machine.

I'm sure Kubota (at some level) would see the potential for liability claims and be inclined to do something to help you (and get some good engineering design information in the process).

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Thanks Baby Grand, but I didn't mean to imply that the forward motion was strong. It just tended to move forward if on level ground with low load. It is easily overcome with the brake. The point is the gear train is torqued just enough to be impossible to shift to neutral until the pressure is relieved on the gear train. From the parts shown of a picture of the transmission there appears to be another pump inside of the transmission. This is acting as a small motor driven by back pressure I think.

 

[bullbreaker]

Just for starters have you tried checking hydro flow with wet guage to see what its reading ?

Boone

 

[Bill32]

Just for starters have you tried checking hydro flow with wet guage to see what its reading ?

Boone

No, I haven't found a flow diagram or any other info about the 3400 hydraulics. Would a service or repair manual help me with the information on all the elements involved to isolate the leak path?

 

[bullbreaker]

No, I haven't found a flow diagram or any other info about the 3400 hydraulics. Would a service or repair manual help me with the information on all the elements involved to isolate the leak path?

Don't know but I would be curios to know what wet guage reads hooked up. Someone(s) here (TBN) will know,be patient I 'am sure good advise/experience comeing.

Boone

 

[Bill32]

Thanks Bullbreaker. I may resort to getting a new tractor rather than rely on a dealer doing more harm than good.