'66 4000 SOS PTO issue

I've been reading these forums a lot since picking up a '66 4000 with SOS a month or so ago. It's in rather good shape, the only real issues are the dripping CAV injection pump, and inoperative PTO.

I have the rebuild kit for the CAV and it looks straightforward from the videos I've seen. It starts and runs great so not too pressing, I'll rebuild it when I get a chance.

The PTO issue is more pressing. It operates in the ground speed mode which of course is a completely different drive.

The T handle was missing and I found the pot metal housing for the handle had stripped out threads on the flare connection at the back so I fabricobbled a replacement assemble from stainless which is working well. The actual cable was fine so it's re-lubed and in use.

Testing with control handle out (ground speed selector off of course) and a brush hog sitting in light brush for some resistance there is no PTO movement. Lifted off the brush there is slow rotation which seems to indicate the PTO clutch is in reasonable shape.

The SOS transmission operates fine with or without the PTO handle out so it would seem there is no hydraulic issue or leak in the PTO side of things. There is also no detectable change in engine load either way.

If I move the ground speed selector to ON, the PTO handle movement stops / is blocked after about 1/4" of travel so that seems to prove the cable connection is working properly.

Looking at the manuals it would seem the sheet metal linkage between the incoming cable and the link down to the control valve would be the prime suspect and I read they have been known to get bent.

Thoughts on my diagnosis or anything I'm missing before I pull the cover to investigate further?

Thanks,

Pete





This post was edited by wp6529 on 10/23/2022 at 12:50 pm.

There should be two levers on the left side. The forward one switches between 540 and 1000 rpm, with a center position that is neither. To use ground speed, you put that front lever in the middle position and then the second lever toward the rear actually engages the ground speed PTO. When the forward lever is in either of the 540 or 1000 rpm positions, I believe that the rear lever for the ground speed is locked out and you cannot move it into the engaged position. If you turned off the ground speed, maybe that front lever is still in the middle position?

It doesn't appear that there is any interlock related to the PTO speed selection and I don't see in the service or operator manuals any indication that the speed selector needs to be in off for ground speed mode. I've tested with both 540 and 1000 selected with the same results.

Thanks,

Pete

There is an interlock device inside the transmission that prevents you from engaging the ground speed
lever when the t-handle on the dash is pulled out, or vice versa. Sounds to me like that is operating as
it should. This interlock has nothing to do with the 2-speed lever on the lower LH front side of the case.

Before you pull the top cover off, I'd do some pressure testing first. I know you said it shifted fine,
however there could be a hydraulic issue with the PTO control valve and/or clutch that might be detected
with a pressure test.

The fact that the PTO spins with no load does not mean that the clutch pack is OK. It could either not be
receiving any pressure due to a cable misadjustment, or else the clutch pack itself could be shot.
Hopefully it's not the latter, because if it is, the PTO clutch is the last part to come out of that
transmission.

There doesn't seem to be a test port for the PTO clutch, it appears all you can do is watch the pressures for the trans servos and see if there is any drop when the PTO control is shifted.

Certainly I'd like to avoid digging in any further than necessary since most everything else seems to be working well and I have several other projects in-progress.

I haven't actually tried all the gears, but R1, N and 1-5 all seem to work fine so the transmission seems in decent shape. Given my expected usage, those are all the gears I'm likely to need anyway

You're correct, there is no pressure test port for the PTO, however you can still see a leak indirectly at
the 3 servo ports if the leak is bad enough.

An even more accurate way to test for leakage is via lube pressure at one of the cooler fittings. You'd have
to drill and tap a lube fitting banjo bolt to pull that off. Lube pressure is the first to drop when there's
an internal leak upstream. This is because the lube circuit is at the tail end of anything that comes out of
the pump.

That sheet metal link on mine was bent when I got my 971.