kubota L4740 hydraulic pump problems.

[jonsstihl]

Here is a run down of what is going on. tractor is new to me since february. no problems when running the snowblower. I checked hydraulic pressure at the rear remotes when I bought it and I seem to remember it being on the low end of the spec but not out of spec. It was cold when I tested it but the tractor had been inside so hydro oil was probably around room temperature.

All filters are OEM and I have no reason to believe the previous owner did not use SUDT2. The tractor has been very well taken care of and is in near showroom condition. tractor has 550 hrs now 516 when I bought it and last hydro fluid change was at 480hrs. In theory the tractor has only had 2 hydro fluid changes, 50hrs and 480 (a little late) and the latest one at 547 hrs after the third function install.


the problems started when my pto would not disengage after mowing for several hours in hot conditions. Started by checking the pto solenoid pressure and found 300 psi (below spec. 363-413). could not adjust past 320 psi (ran out of threads)

sent it in to adjust all hydraulic pressures and install third function kit.

So they tell me my hydraulic pump is tired and cannot generate enough pressure to meet spec. 2500 psi versus min spec of 2630. other pressures were brought back into spec. pto solenoid 390 psi HST charge 380 psi.

their excuse is that maybe the previous owner did not actuate the hydraulics after a fluid change and ran the pump dry since pump is above oil level and may not have primed without running loader or power steering immediately after starting.


Is it really that easy to damage the hydro pump?

my problem now is that even with the pto solenoid pressure up to 390psi at PTO rpm. I am still getting the PTO does not dis engage problem so now I am looking at replacing the PTO clutch pack and I might as well replace the pump while it is in the shop and get all the pressures back into spec.

I'm just worried that I will be repeating the same repairs in another 500 hrs if I don't find out why the pump went bad in the first place.

 

[hawkeye08]

IIRC, the first hydraulic oil change is 400hrs, only filters at 50hr. So it had only one change at 480hrs.

 

[moship]

Your PTO problems make not be an issue of max pressure initially, but at what RPMs the previous operator used when PTO engaged.

A few forum members have had issues because they ran at lower RPMs not knowing the pressure is also lower, thus reducing clamp pressure on the clutch pack.

Kubota also changed the specs in the workshop manual at some point to the values you stated.

From manual:
3. Start the engine and set the engine speed to maximum.
4. Turn on the PTO switch (3) and measure the oil pressure.
5. If only the pressure in PTO clutch engaged position is low,
check the hydraulic PTO clutch system.
6. If the measurement is not within the factory specifications,
measure the system pressure, and adjust the system pressure
with regulator valve (4) if necessary.

If your system pressure is OK, it sounds like repairing clutch pack may resolve, but if it is also too low the pump may be bad. At least that is how I interpret the WSM.

Are you testing pressures with hydraulic fluid between the recommended temperatures (40C to 60C)?

Keep us posted on what you find.

 

[jonsstihl]

I tested the pressures when it was hot. the main system pressure feeds the pto solenoid valve through the pto regulating valve. I now know that the main system pressure is down about 100 psi from the min spec and that is as high as it will go, so the pump is technically bad but still functioning. Dealer suggested I run it like that. I checked the pto circuit pressure after having mowed for a few hours so oil was hot. at idle i got 340psi, at pto rpm i got 390 when brought back down to idle from pto rpm i got 360.

I did have a weird buzzing noise at start up that lasted a few seconds then went away but since the dealer worked on it that is gone. I'm thinking they tightened up the clamps on the suction line now it is no longer sucking air.

when the pto would not disengage I revved it up and it disengaged but the second time i tried to disengage it revving it up did not help even shutting off the tractor and restarting did not help. I shut it down and checked the oil and hydro fluid levels and restarted after a few minutes and the pto was disengaged

 

[jonsstihl]

I don't mind running it like that but I need a tractor that I can shut off the pto. otherwise it is quite dangerous, atleast the clutch always works to shut off the pto. good thing I got a 40 series

If I do the clutch pack I will probably do the pump as well so they can adjust the pressures back to normal. what are the chances my prop shaft seal will go out right after this repair is all buttoned up.