New Holland 8670 PTO problem...

I have 500 bushels of corn in the cart behind the 8670 right now. I tried to unload the corn and the pto engaged normally, but as soon as I opened the slide on the cart and put some weight on the auger, the pto stopped turning. I revved the engine up and tried moving the hydraulic slide up and down and the pto did not respond. I closed the slide and dumped the corn from the bottom dump to get the weight off the auger and the pto would turn. As soon as I put the weight back on it, it stopped again.

I haven't had any problems with the PTO in the past, except I did replace the PTO brake on it in 2012 with bern's and other forum members' help. It was last used to run a 15 foot batwing mower with no problems. There is a fitting on top of the rear cover, like a small quick coupler that is marked PTO, and one on the side marked PTO BRAKE PRESS. I'd imagine I would need a female coupler and a gauge to measure the PTO pressure. I am going to take the fitting out, and to a local hydraulic shop to get a test gauge built.

What pressure should I have and how do I adjust it, if it is low?


All of the other hydraulic functions work just fine on the tractor and the transmission is not low on fluid. The filter was changed last year, or about 250 hours ago.

Any help would be appreciated. I wish I would have bought a service manual for this tractor. Darn thing has been so reliable, and low houred(4026 hrs), I figured I wouldn't need it. Go figure...

I got a test gauge made up with a 600 PSI gauge and double checked the fittings. the top fitting is marked PTO, and the side fitting is marked PTO CLUTCH PRESSURE.

So I got it backwards... Anyhow, on the PTO test fitting, when you start the engine, it goes to 200 PSI and holds steady. When the PTO is engaged, the pressure drops to 0 PSI, and the PTO spins. (There are no implements connected to the PTO shaft)

That, I assume, is the brake pressure. When connected to the PTO Clutch Pressure port, I get no reading when the tractor is started and running. When I engage the PTO, the needle barely moves off the pin, maybe a few PSI at best, and when the PTO is disengaged, the pressure drops back to 0 PSI.


That is all I know right now. I am not sure if there is an adjustment to increase the pressure without taking the tractor apart. If anyone has any ideas, I would love to hear them.
Thanks.

I had a 1996 8240 that had pretty much the same problem. It turned out to be a bad internal tubing leak. My 8240 had all of the control valves on the inside of a plate on the right side of the rear housing. A few months after mine was built they changed to mounting the valves on the outside. You may get lucky and the problem may be a valve there on the side.

Your PTO (top test port) pressure is acting normally.

When your tractor is running @ 1900 RPM with hydraulic system warmed at least 140F and you engage the PTO, this is what you should see at the PTO clutch test port on the side: pressure should rise from 0 to 120 psi within 1½ seconds. It should then go directly to 240 to 270 psi.

Since you're not seeing that, my guess is internal leak. Maybe remove the test port fitting and blow air to the passageway. see if you hear an evil hiss or a clunk. The hiss is not a good sign!

Of course, you might try swapping solenoids on the PTO valve, but I really don't believe this is your problem.

Thanks guys.

Larry,
Those are the numbers I was looking for. I assume the rise/jump in pressure after the 2 seconds is the PTO feathering? I will get it up to full operating temp and see what I have. I know the temp was cold when I went to unload and then when I went to test it. The last time I used the PTO, now that I think about it, was to unload soybeans and I had the tractor running for about an hour first, so the temp was up on everything. I will open the shed doors and let it idle for a while and then put the gauge back on it.

If you have to take the cover off the back it shouldn't be all that bad. you should be able to raise the back of the cab eight inches or so, and that should be enough to raise the cover with an engine lift and then pull it out. Your PTO clutch will be right there.

If you have to take the cover off the back it shouldn't be all that bad. you should be able to raise the back of the cab eight inches or so, and that should be enough to raise the cover with an engine lift and then pull it out. Your PTO clutch will be right there.

Showcrop,

On this tractor, I can take the entire PTO clutch assembly out by removing the rear cover above the PTO shaft. I have to drain the fluid, remove the PTO shaft, and both gears come out the bottom of the rear end. They are heavy and sharp. Then, the rear cover comes off the back, instead of removing a top cover. It is still a huge pain and since I have a cart with 500 bushels on the drawbar, I will have to figure out a safe way to unhitch the cart, because the drawbar has to come off to get the PTO gear out. The hydraulic lines that power the PTO come externally around the transmission from a place I can't see and they connect with flare fittings to the back cover, externally. I'm assuming that I have good pressure to the lines, since it gives the PTO brake 200 PSI, and the electric PTO solenoid (which is $700) has to be functioning since it applies the PTO brake, and releases it. So that leaves me to the PTO valve itself. It could have blown a seal on a piston, or cracked, or who knows what. Next step is to put air pressure to the test port and see if I can hear it hissing. That will have to wait until daylight tomorrow. My nerves are shot for tonight!

I almost forgot to mention...

I let it idle for an hour and got everything pretty warm. I have 20 PSI on the clutch pressure port when the PTO is engaged at 1900 RPM. It holds 20 PSI from idle up to operating speed. The needle drops to 0 PSI when the PTO is disengaged...

This doesn't look good for me.

(quoted from post at 16:49:26 11/14/15)
Thanks guys.

Larry,
Those are the numbers I was looking for. I assume the rise/jump in pressure after the 2 seconds is the PTO feathering?

Click to expand...

John,

You are correct. The first 1½ seconds are feathering. Then it should come full on @ 240 to 270.

I believe the pressures might be even higher if it's not up to operating temperature or near it.

Showcrop is in the wrong tractor . . . or something!

Blessings on your endeavors!