Convert M817 PTO to air actuated?

TurboJoe · Apr 2, 2018

My M817 like many has seen mostly short run dump duty in its lifetime. The linkages for dumping/engaging the PTO are pretty well clapped out. Mostly on the PTO side probably by trying to jam it in with the transmission input shaft still spinning.

So I could pull everything apart and build new linkages... or I'm thinking about just fabricating a dual acting air cylinder.

A small bracket, dual acting cylinder, a PTO switch and some air lines I think will work. Has anyone done this before? It seems way easier then the whole linkage set up currently on the truck.

simp5782 · Apr 2, 2018

TurboJoe said:
My M817 like many has seen mostly short run dump duty in its lifetime. The linkages for dumping/engaging the PTO are pretty well clapped out. Mostly on the PTO side probably by trying to jam it in with the transmission input shaft still spinning.

So I could pull everything apart and build new linkages... or I'm thinking about just fabricating a dual acting air cylinder.

A small bracket, dual acting cylinder, a PTO switch and some air lines I think will work. Has anyone done this before? It seems way easier then the whole linkage set up currently on the truck.

It has been mentioned on a deuce. Would be easy to find an air actuated pto for a Spicer transmission though

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tobyS · Apr 2, 2018

Yes, a manual valve and a small double action cylinder. It would be nice to have the same stroke length, especially if directly in line instead of an arm.

snowtrac nome · Apr 2, 2018

The best solution would be a hot shift pto they should be easy to find for a spicer trans. With the hot shift, you don't even have to push in the clutch to activate the pto we use them all the time on fuel trucks.

Floridianson · Apr 2, 2018

Does not the linkage behind the seat also control the PTO, up, down and hold for the hoist. Seems like it would be easer / cheaper to replace what you need. I did have a 817 with cable Chelsea PTO control and pump but the seat linkage was still hooked up to control the hoist. They made some kind of plate to go over the hoist control to control the hoist. Wish I would have taken a pic and numbers off the Chelsea PTO / pump and the plate they built.

gringeltaube · Apr 2, 2018

TurboJoe said:
...... or I'm thinking about just fabricating a dual acting air cylinder.
A small bracket, dual acting cylinder, a PTO switch and some air lines I think will work. Has anyone done this before? It seems way easier then the whole linkage set up currently on the truck.

Yes, it has been done, although it was on a Deuce. But both share the same aux. PTO, so I know it works well.

You don't need a double acting cylinder; just modify one single action with a Ø1"- piston, by adding a coil spring strong enough to overcome the force of the poppet spring on the shift shaft. As soon as you released the air the PTO will disengage.

topo · Apr 2, 2018

This air cylinder set has worked well easer then setting up linkage .

162tcat · Apr 3, 2018

I struggle with the same issue. Mine is a winch truck which causes more difficulty. I've considered switching to an engine driven clutch pump and putting a hydraulic motor on the winch to get rid of the PTO. Would make winching easier and solve my PTO linkage problem.

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Floridianson · Apr 3, 2018

I have five 817 parts trucks. Maybe the linkage would be faster and cheaper.

tobyS · Apr 3, 2018

Tell me the stroke length....I have a supply of air cylinders with short throw, 1 1/2" dia. or so.

gringeltaube · Apr 3, 2018

Stroke length is only 1/2". And even with a sound poppet spring & ball it doesn't take much more than 20 lbs to engage/disengage it. Add another 30 lbs if you included a return spring for a single action air cylinder. Which means that a tiny-shorty cylinder with 1"-piston @ 60psi is more than sufficient for the task - even if you had to mount it at a certain angle (= not perfectly aligned with the shift shaft's axis.)

tobyS · Apr 3, 2018

I use 1" stroke in high security jail locks and have a few that could be made shorter, might have a 1" dia but most are 1 1/2" dia....I'm headed to my little bus where they are stored. Thanks for the drawing.

tobyS · Apr 3, 2018

Here is the smallestthatI have.....1 1/2" x 1" stroke. Cut the spacers and cylinder for 1/2" stroke. The other piece is for angular misalignment.

gringeltaube · Apr 3, 2018

Unless the air supply came from a pres.reducing valve, a piston too large may react too violent, at 120 psi. Keep in mind this is not a large dog clutch like in the air-shift T-case...

A longer cylinder would be more desirable because then you can install the return spring inside, and still limit the stroke via spacers.

tobyS said:
......The other piece is for angular misalignment.

Or use this, a short piece of hydraulic hose and two strong hose clamps...

tobyS · Apr 3, 2018

Here is a flow control. This one meters in one direction and is free flow in the other. I'd probabably want two of meter in both directions, one on push and one on the pull side. That would slow it down. Normally I meter out, but on such short stroke, meter in and out.

Sure...the stiff tube would work and so would putting a return spring inside with Stroke limit sleeve.

TurboJoe · Apr 3, 2018

Thanks for the info!

As far as rebuilding/re-using what I have, this whole linkage is archaic. I bet it was designed so that it was one less step for soldiers.

I don't see that big of an issue using air. I like the idea of spring so that way I don't have to have air holding it out the whole time... But i think the commonly available civi switches are for double acting cylinders.

I plan to keep the stock lever to use for up/down. I'll get under there and see if I can build a bracket easily.

162tcat · Apr 4, 2018

I'd like to do the exact same thing. Keep the lever to control dump and find a new way to engage the PTO. I've been looking at a standard cable setup to engage. Air would be nice but cable is simple and cheap. I'd love to go full hydro to make winching a 1 man operation but fixing the pto engagement issue would be great for now.

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TurboJoe · Apr 4, 2018

I suppose a cable would work, but routing and fixing a cable might be more work than running air lines. With the cable we would still need brackets on both sides, and much more restrictions on bend radius's
.

162tcat · Apr 4, 2018

TurboJoe said:
I suppose a cable would work, but routing and fixing a cable might be more work than running air lines. With the cable we would still need brackets on both sides, and much more restrictions on bend radius's
.

That is all true but the cable thing can be accomplished for well under $100 and less than 2 hours work. Don't have to worry about adjustments or anything like that.

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TurboJoe · Apr 4, 2018

162tcat said:
That is all true but the cable thing can be accomplished for well under $100 and less than 2 hours work. Don't have to worry about adjustments or anything like that.

I'm actually leaning more towards the cable as I research. McMaster has a knob operated push/pull cable in 10 or 15' for 27 or 29 dollars. Then its just a matter of a a bracket and cable end. Ok, you sold me! I'm going to measure tonight and order up some parts. Will post pictures.

Convert M817 PTO to air actuated?

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