Help needed PTO won’t disengage

[customcarswy]

So long time lurker and first time poster, I have a 72 m818 nhc250, 5speed that has been turned into an m817 dump. It has the dual output PTO for the front winch and rear dump. I’ve have spent hours reading my service manuals and this site but cannot for the life of me get a solid answer to my question.

Does the rear output run constant while the clutch pedal is up? I never looked before I finally
decided to play with my dump box and that’s when I went to disengage it and it would not disengage. The PTO lever seems to have 3 detents. All the way back for the rear output(I assume) middle For neutral(I assume) and forward I know engages and disengages the front output. But no matter what I do I can’t get the rear output to shut off.

side note does anyone know what modern fluid I should use in the hydraulic system since I had a line crack im going to need to replace that and fill and bleed the system.

Thanks guys!
Ben

 

[INFChief]

So long time lurker and first time poster, I have a 72 m818 nhc250, 5speed that has been turned into an m817 dump. It has the dual output PTO for the front winch and rear dump. I’ve have spent hours reading my service manuals and this site but cannot for the life of me get a solid answer to my question.

Does the rear output run constant while the clutch pedal is up? I never looked before I finally
decided to play with my dump box and that’s when I went to disengage it and it would not disengage. The PTO lever seems to have 3 detents. All the way back for the rear output(I assume) middle For neutral(I assume) and forward I know engages and disengages the front output. But no matter what I do I can’t get the rear output to shut off.

side note does anyone know what modern fluid I should use in the hydraulic system since I had a line crack im going to need to replace that and fill and bleed the system.

Thanks guys!
Ben

My first instinct is to say that only one shaft should turn at a time when the PTO is engaged - either front or back. However, your set up could be such that the engagement is at the winch or the dump gear box.

I ran a M54 & a M800 series wrecker a LONG time ago. I may be lying to you but that’s not my intention. If my memory is correct, the transfer went in to neutral and the PTO lever was engaged. The transmission was put in to gear and the clutch applied. The transmission is what I believe drove the PTO gear box.

Once the PTO was engaged and my throttle set I could separately run the boom, rear winch, or front winch with the controls on those components.

Do you need to put your transfer in neutral and put the transmission in to gear operate your PTO?

I do remember that at times shifting the transfer, PTO, or component control levers were a PITA. I don’t recall why.

I know there was a “Sprague” unit that helped engage the 6x6 and sometimes they would load up causing all kinds of binding problems. God help the poor bastard who jacked up a front wheel to unload that Sprague unit and didn’t keep clear of that tire letting loose!

After all of that, go back and double check how you disengaged everything. Take a look at what actually controls what - I physically raised my eyebrow when you wrote “it’s been converting” because who knows what someone did to convert it.

Just use caution.

 

[customcarswy]

My first instinct is to say that only one shaft should turn at a time when the PTO is engaged - either front or back. However, your set up could be such that the engagement is at the winch or the dump gear box.

I ran a M54 & a M800 series wrecker a LONG time ago. I may be lying to you but that’s not my intention. If my memory is correct, the transfer went in to neutral and the PTO lever was engaged. The transmission was put in to gear and the clutch applied. The transmission is what I believe drove the PTO gear box.

Once the PTO was engaged and my throttle set I could separately run the boom, rear winch, or front winch with the controls on those components.

Do you need to put your transfer in neutral and put the transmission in to gear operate your PTO?

I do remember that at times shifting the transfer, PTO, or component control levers were a PITA. I don’t recall why.

I know there was a “Sprague” unit that helped engage the 6x6 and sometimes they would load up causing all kinds of binding problems. God help the poor bastard who jacked up a front wheel to unload that Sprague unit and didn’t keep clear of that tire letting loose!

After all of that, go back and double check how you disengaged everything. Take a look at what actually controls what - I physically raised my eyebrow when you wrote “it’s been converting” because who knows what someone did to convert it.

Just use caution.

 

[customcarswy]

so as best I can tell the conversion used all oem parts from an m817 I believe the prior owner had a place that specifically sells these trucks do the swap. So to my knowledge and from scouring my service manuals everything looks to be original and correct…this is where it gets Weird. When he showed me how the dump box works originally he did what you said, put the transfer case in neutral and the truck in 4th gear. I have determined through playing with things that I have the transfer case back in gear and the transmission in neutral and the PTO is still running and I can raise and lower the bed. And I did make sure the transfer case was in gear by moving the truck to verify. Sounds like an exciting time to unload the sprague! Lol

 

[INFChief]

so as best I can tell the conversion used all oem parts from an m817 I believe the prior owner had a place that specifically sells these trucks do the swap. So to my knowledge and from scouring my service manuals everything looks to be original and correct…this is where it gets Weird. When he showed me how the dump box works originally he did what you said, put the transfer case in neutral and the truck in 4th gear. I have determined through playing with things that I have the transfer case back in gear and the transmission in neutral and the PTO is still running and I can raise and lower the bed. And I did make sure the transfer case was in gear by moving the truck to verify. Sounds like an exciting time to unload the sprague! Lol

Are the dump box & winch controls back in a neutral position?

 

[customcarswy]

Are the dump box & winch controls back in a neutral position?

That is correct, there are 3 positions I can feel Forward(winch) middle(I assume neutral) and rear(I assume pto) I can crawl under the truck and visually see the rod that the lever is attached to that sticks out of both sides of the PTO and it is going back and forth. The forward shaft for the winch only engages when I push the lever forward. As soon as i pull it to the middle or back the winch shaft stops spinning.

 

[customcarswy]

Not sure if these images will help in anyway but this is what it looks like.

 

[gimpyrobb]

You should have 2 controls for that pto. One should be on the floor by the transmission tunnel, the other should be on your left, between the cab and the seat. The one on the floor should control the winch only. It has (i believe) two speeds and reverse. The one on the left should be on (up position) and off (down position).

 

[customcarswy]

You should have 2 controls for that pto. One should be on the floor by the transmission tunnel, the other should be on your left, between the cab and the seat. The one on the floor should control the winch only. It has (i believe) two speeds and reverse. The one on the left should be on (up position) and off (down position).

So if what you’re saying is correct the rear output of the PTO for the hydraulic pump is running at all times? And the floor lever only affects the PTO drive for the front mounted winch. And the lever by the seat is the up and down for the dump box but it just controls the hydraulic output and not the pto itself.

side note I have no clue how the front winch works either? If anyone with knowledge wants To shed some light on that that would be cool.

 

[Mullaney]

So if what you’re saying is correct the rear output of the PTO for the hydraulic pump is running at all times? And the floor lever only affects the PTO drive for the front mounted winch. And the lever by the seat is the up and down for the dump box but it just controls the hydraulic output and not the pto itself.

side note I have no clue how the front winch works either? If anyone with knowledge wants To shed some light on that that would be cool.

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Generally the PTO on any truck is OFF (should be turned off) unless there a reason to engage the hydraulics to lift the bed on a Tipper, or the winch to pull yourself out of a sticky situation. It shouldn't be on at highway speeds for sure.

 

[customcarswy]

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Generally the PTO on any truck is OFF (should be turned off) unless there a reason to engage the hydraulics to lift the bed on a Tipper, or the winch to pull yourself out of a sticky situation. It shouldn't be on at highway speeds for sure.

That is my understanding as well. But the rear output shaft that runs the hydraulic pump does not shut off no matter what position any of the levers are in…hence my concern that something in the PTO is stuck engaged…

 

[Mullaney]

That is my understanding as well. But the rear output shaft that runs the hydraulic pump does not shut off no matter what position any of the levers are in…hence my concern that something in the PTO is stuck engaged…

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Silly as it sounds - wonder if the linkage is bent? If you pull the pin, you should be able to push the lever forward and backward. Just to see if you can try pushing the lever all the way one way or the other and see of the truck cranks without engaging the PTO? Might be that when you pull the pin the lever will jump one way or the other and show you something is bent maybe?

 

[customcarswy]

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Silly as it sounds - wonder if the linkage is bent? If you pull the pin, you should be able to push the lever forward and backward. Just to see if you can try pushing the lever all the way one way or the other and see of the truck cranks without engaging the PTO? Might be that when you pull the pin the lever will jump one way or the other and show you something is bent maybe?

Not a bad idea. I’m going to go mess with it shortly just to freshen my memory to make s

 

[customcarswy]

I fixed it! Sorta. I still don’t have a clue how it’s supposed to function but the yellow rod above the rear output shaft is what engages and disengages the rear output shaft. The floor lever does appear to only be for the winch…I’m still confused on what operates the yellow rod…I suspect it is the lever bedside the seat and that putting it in the down position should disengage the pto but I suspect my linkages are mucked up just enough that it doesn’t do that! But I’m learning!

 

[customcarswy]

Upon really hammering that lever beside the seat towards the back of the cab it does just exactly that and disengaged the PTO! Thanks for helping me guys. I guess I need to adjust some linkages a little. And any tips on the winch would be appreciated!

 

[G744]

The winch PTO has three speeds: Low, high, and reverse. Neutrals between all of them.

BTW, it is a sprag, not sprague.

It is found in the transfer, and controls the front drive. It is a one-way deal, depending on if you are in forward or reverse gear, controlled by an air switch on the transmission.

It senses when the rears slip 6% relative to the fronts, and automatically engages the front drive. It will release when it senses things are in unison and not carrying torque.

DG

 

[Mullaney]

I fixed it! Sorta. I still don’t have a clue how it’s supposed to function but the yellow rod above the rear output shaft is what engages and disengages the rear output shaft. The floor lever does appear to only be for the winch…I’m still confused on what operates the yellow rod…I suspect it is the lever bedside the seat and that putting it in the down position should disengage the pto but I suspect my linkages are mucked up just enough that it doesn’t do that! But I’m learning!

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@customcarswy , That really is good news!

So, if I remember correctly the Tipper PTO is what was running all the time? If so, all we gotta do is figure out if something bent the linkage or if maybe a a "jam nut" came loose and let the rod turn possibly. Definitely shoot some pictures if it isn't obvious and maybe the group here can help figure it out. Maybe a picture or two of the handle in the cab. Maybe something there got bent...

Glad you made good progress today!
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