4020 Powershift PTO brake and Trans Pressure

This is a long post, but I hope the details help to get to a conclusion or some good direction:

Working on my 1967 4020 diesel powershift. It has ~11000 hours on all original transmission hardware. It still shifts great and does not slip in any gear. It is only sluggish in 6-7 and 7-8 under full throttle, but I usually shift those at 1500 rpm anyway then throttle up in 8th. At 1500 RPM they are snappy shifts. As far as I can tell, everything still works with no failures.

I have the SM-2039 service manual. That is how I have gotten this far. I was doing these pressure readings today with oil that I got warmed up to 140F after an hour of running around but cooled down to 105F after hooking up gauges and turning the machine on and off a few times.

I think I have three semi-related issues; PTO is always spinning, the dash pressure gauge drops too low with hot oil (but the test gauge port holds steady), and the 3 point is leaking oil internally when not fully up or down.

One of the current issues is that the PTO is spinning 99% of the time when disengaged. I have checked and shimmed the transmission pressure to now run between 145-160 psi (160psi at 1900 rpm), as it was running 140-145psi before today. The only way the PTO will stop spinning is if I put the 3 point halfway raised and lower rpm to an idle. With the 3 point there, I can hear the hydraulics constantly pumping, I can see hydraulic oil dripping down when looking in the bung hole behind the remote on the back of the transmission case, and the trans pressure gauge goes all the way to the low side. The rockshaft seems to be heavily leaking oil internally. With that, I can get the PTO to stop spinning. Once I raise the 3 point all the way up and the dash gauge goes back up, PTO start spinning again. PTO clutch is dropping to 0 psi when disengaged, and when the PTO is hooked to a load but disengaged, it won t spin. It will however spin an empty small auger if there is no grain in it. When engaged it runs strong.

This 2 minute video shows the trans pressure (left gauge) and PTO clutch pressure (right gauge) and how when I set the 3 point halfway raised you can hear the engine load under the hydraulics and see the dash gauge drop. Also can get the PTO to stop spinning.
Trans Pressure and PTO

This 2 minute video just shows the 3 point operation some more. If left at the halfway point and idling, it will begin to shudder badly after about 10 seconds. In my mind, the internal hydraulic leakage in the rockshaft is exceeding the ability of the transmission pump to supply the high pressure front pump, which is constantly sending oil to the rockshaft circuit to keep it at the halfway point. Draft control lever is all the law down in the D position. Above 1500 rpm the shuddering stops.
3 point pressure loss and shudder

Is my dash gauge hot oil pressure loss likely related to how much oil this three point might always be bypassing? Could it still be internally leaking some even when all the way up?

Other than likely needing the new PTO brake hardware, anything stand out about the PTO operation? Would warped disks explain why it spins in addition to the brake being shot?
Where do I start on the rockshaft leak?

There is a chance I simply have too many questions in one post. It just is all in the transmission, and I thought that is might all need to all be addressed in context with each other.

While disengaged . Is the PTO spinning with enough torque to spin a load ? Or just whirring along with the hydraulic oil and won t spin a pto load ?

IIRC, gauge in dash reads transmission LUBE pressure, NOT clutch operating pressure. (I can't find anything quickly in the manual to back this up, someone correct me if I'm wrong.)

High pressure leaks to sump cause a constant flow of oil from the transmission pump to the main pump, "stealing" lube flow and lowering lube pressure and not clutch operating pressure, (as the gauge at the test port and the gauge in the dash are indicating).

The PTO clutch plates are slathered with lube from passages in the shafts inside them, so less lube pressure/flow would equal less PTO clutch drag. (As a side note, some newer synchro tractors have a "lube reduction valve" that decreases lube oil flow through the flywheel clutch plates when the pedal is fully depressed for easier shifting, showing that the clutch lube oil flowing between the plates definitely affects drag.

I didn't see where you posted PTO brake pressure, have you been monitoring that?

As to the 3-point, the first thing I would do is check the piston seal, and the bore for scratches and any other pitting or damage.

Had it on a little grain cart this fall. It would slowly spin the unload auger when empty. As soon as any grain was in it it would not spin it. It stops as soon as there s any resistance but engages cleanly otherwise.

My valve block there by the clutch pedal didn t have a brake test port, just the PTO one. My tractor didn t match the picture in the service manual that had both ports. Is that possible or am I missing something?

(quoted from post at 18:30:57 02/02/20)
My valve block there by the clutch pedal didn t have a brake test port, just the PTO one. My tractor didn t match the picture in the service manual that had both ports. Is that possible or am I missing something?

Click to expand...

I don't know, all the ones I've ever worked with had both ports.

Since you mention SM-2039, I assume you are working with a pre-serial# 201,000 unit?

jdparts list a whole bunch of clutch control valve casting part numbers, so the were changed an number of times over production.

"MARKED R33155, R33161, R41153, R41668, R44164 OR R67484"

1 Dollar How long has PTO been spinning ? Sounds like a ANCHOR PIN for PTO brake has broken off .& Free wheeling in bore of trans case. The o-ring may still be holding PSI from major oil leak?? I m working On a P.S. that lost a Anchor pin mess up bore & sent housing out to sleeve bore & That did NOT work.Ended up with buying a other trans case.So ending upside down is not all bad.I M still learning. Tim S. Can walk you through it if needs repair. He ll probably be chiming in shortly.