I have an L39 that was being driven down the road, operator heard a snap or pop, and it went down on power. Engine runs fine, just not delivering the power to the wheels. Foot clutch feels fine. I am thinking pressure issues in the GST clutch. Looking at the manual, it could be the low pass valve, proportional reducing valve, or even the power steering unit that supplies the oil. Could also be the ECU but I think that less likely. Could the little filter in line with the PRV slow clutch engagement if it was plugged?
L39TLB GST Pressure - trans not fully engaging
- Thread starter Marty Jones
- Start date
So, I have a theory: Something has interfered with the operation of the PRV and is not allowing it to close fully. The steering feels fine, so the flow to the GST which comes from the power steering should be good. The low pass valve opens - which allows the GST clutch to fill with oil. The pressure switch that checks for a completed shift seems to be working because I don't get any error codes. The GST clutch gets some pressure, but not enough to fully lock it up - if I step on the brake while moving, the engine slows a little but doesn't stall. I don't feel, hear, or smell any of the usual signs that the foot operated clutch is slipping. That leaves the PRV or a structural failure in the wall or seal of the GST clutch that allows fluid to leak out. It is building some pressure, just not enough. I am going to pull the PRV and see what it looks like.
Just found out that the operator, my son-in-law, was driving down a hill, in 12th gear, clutch depressed, controlling speed with the brakes only. Going faster than the tractor can go under power. Makes it more likely that the system tried to push more fluid through the PRV than it was able to handle - which makes it more likely that something inside broke from overpressure. Which explains the noise.
I plan to check the GST pressure - looks like an 1/8" Pipe Thread port. I have a suitable gauge, so...
So, since my last post I built and am operating a sawmill... But time to get back to the Kubota. If anybody has any experience with such an overspeed condition, I would love to hear about it.
No experience with over speed, but here's a thread where someone had GST hydraulic clutch break. I think you can see it without splitting the tractor.
L4200 Need GST guru's
Hello all, hoping I can find some direction here with my new-to-me L4200. I picked it up for a bargain being told the "clutch was bad". Figured at worst I split the machine and pop a clutch in it. Well, I pick it up, and notice it does in fact act like there is no clutch engagement. I get it...
www.orangetractortalks.com
Thanks! I read through that thread and my issue seems similar. I have dropped the tractor frame to gain access to the GST valve and pressure port. I expect to pressure test it and remove the valve today to see what's going on with the GST clutch.No experience with over speed, but here's a thread where someone had GST hydraulic clutch break. I think you can see it without splitting the tractor.
L4200 Need GST guru's
Hello all, hoping I can find some direction here with my new-to-me L4200. I picked it up for a bargain being told the "clutch was bad". Figured at worst I split the machine and pop a clutch in it. Well, I pick it up, and notice it does in fact act like there is no clutch engagement. I get it...
So, I was unable to connect a pressure gauge to the port. The manual identified the port as 1/8 PT. But is that 1/8 NPT or 1/8 BSPT? Measuring it makes it look more like BSPT.
I am proceeding to remove the GST valve to see what lies behind.
I am proceeding to remove the GST valve to see what lies behind.
I remember someone saying BSPT, but he was able to teflon tape an NPT nipple good enough to get a reading.
Probably the other way around. NPT is slightly larger than BSPT and the threads won't start.
I have taken the GST valve off, and the clutch looks beautiful. No apparent damage whatsoever and it spins easily with finger pressure.
I have taken the GST valve off, and the clutch looks beautiful. No apparent damage whatsoever and it spins easily with finger pressure.
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I applied air pressure to the GST clutch via the in-line and the clutch operated as it should - so I replaced the GST valve and will focus on pressure testing the circuits - as soon as the BSPT to NPT adapter arrives.
Two basic alternatives remain - either fluid is not getting to the clutch, or fluid is draining out too fast.
Two basic alternatives remain - either fluid is not getting to the clutch, or fluid is draining out too fast.
I'm not sure you've ruled out the dry clutch.
Engage the PTO. Watch the shaft while you stall the tractor. If the shaft stalls, the dry clutch is the problem. Otherwise, the problem is elsewhere.
Engage the PTO. Watch the shaft while you stall the tractor. If the shaft stalls, the dry clutch is the problem. Otherwise, the problem is elsewhere.
My reasoning behind not suspecting the dry clutch is first, the abruptness of the onset of the problem. Full power to very little in seconds. Second, the problem arose while coasting downhill with the dry clutch pedal pushed in. And third, as the lack of power worsened, there was no smoking or smells that indicate a burned clutch.
Ordinarily, I can stall the tractor by depressing the brake while in gear. That requires both the dry clutch and the GST clutch to transmit torque, which is not happening.
And, BTW, I received the 1/8 BSPT to 1/8 NPT adapter and it fit perfectly.
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Having coasted a tractor before and having ripped the linings off a clutch before (not the same occurence), in my, ahem, younger years, I was thinking the 'operator' might have dropped the clutch, tearing the lining off. The time we (my Dad was trying to pull the other tractor out of a spring I sank it in) tore the clutch out, the linings stacked up under the pressure plate where it wouldn't disengage.
More testing. With the tractor still mostly disassembled, I am able to start it and operate the gears - the tractor being on jackstands. Pressure at the GST clutch started at 0psi then quickly rose to 340psi when a gear is engaged. It quickly drops to zero when changing gears, and then quickly rises again. Seems nomal. What does seem bizarre, is that the output at the wheel hubs slows down noticeably when the engine is speeded up - while in any gear. That goes back to suggesting the dry clutch. Maybe my son in law accidentally let the clutch out while overspeeding... and didn't say anything.
Can the dry clutch be inspected without splitting the tractor?
Can the dry clutch be inspected without splitting the tractor?
What's the PTO shaft doing when the wheels slow down? It's a solid path from the clutch to the PTO. I was going to make a rude comment about knowing how to engage it. I doubt mine has ever been used - the cover is still on it.
L39, according to the manual, has concentric drive shaft. The inner shaft splines to the flywheel and operates the PTO and the hydraulics. Hence you can do hydraulic operations with your foot on the clutch. The outer 'shaft' which is a tube, transmits torque to the transmission. The PTO has its own clutch which is electrically operated.
Ok, I take part of that back. The PTO is cable operated, with a couple switches to tell the CPU and the dash that it is on/off. But the PTO isn't connected to the engine through the dry clutch - it has its own shaft. So, it operates at increasing speed as the engine speeds up and the rear wheel flanges slow down.
Looks like an issue with the dry clutch.
I took out the drain plug and it was dry. You can't see anything because the front drive shaft goes right over the top of it. I guess I am about to remove the starter... I have an inspection camera that might be able to see something.
Looks like an issue with the dry clutch.
I took out the drain plug and it was dry. You can't see anything because the front drive shaft goes right over the top of it. I guess I am about to remove the starter... I have an inspection camera that might be able to see something.
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Excuse me a for moment while I get my foot out of my mouth
. I thought the L35 and L39 were more similar.Well, maybe @North Idaho Wolfman will see this and offer some help.
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Can you remove the drive shaft without splitting the transmission? Is there any access to the shifter gears, they're ahead of the hydraulic clutch? Anything to confirm where the problem is. As I'm sure you know, splitting that thing is no picnic.