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And...[drumroll]...The flywheel side of the clutch looked fine. But there was zero friction material left on the other side. The flywheel looked great. The pressure plate had wear on only about 90degrees of the outer edge. I haven't looked closely yet, but it suggests that something got...

Well, looks like the main clutch... Thanks to @PoTreeBoy for suggesting. I took the starter off, and the top of it was covered in clutch fibers. I would have to say that I was fooled - because the clutch housing is sealed - meaning that any smoke or fumes from a hot clutch are trapped.

My last hope is taking the starter off. The flywheel looks to be very thick so I kinda doubt that I will be able to see anything. Might be able to spot debris in the bottom of the clutch housing. The machine is mostly apart right now anyway...I reconnected the wiring harness and hydraulics...

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...

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...

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...

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...

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...

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.

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.

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.

I have an L39 with the GST...and a similar issue. I expect to have a look at the GST itself tomorrow.

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.

I plan to check the GST pressure - looks like an 1/8" Pipe Thread port. I have a suitable gauge, so...

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...

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...

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...