M939 PTO information

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Entropy455

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Here’s some PTO information, for the M939 series trucks. Note: I’m posting this information because it was difficult to find, and it might be useful to others looking to convert their truck over to hydraulics. Please let me know if I’ve made any errors below.

The M939 series trucks utilize a MT-654CR Allison transmission. The transmission’s PTO drive gear (piece 11, of figure 187,of TM9-2320-272-24P-1) is a 64-tooth, 6” diametrical pitch, 20-degree pressure angle, straight-cut (non-helix), full-involute spur gear. The gear is downstream of the torque converter, thus it is powered whenever the engine is on, across all 5 forward gears, including neutral and reverse. Due to fluid-coupling within the converter, the transmission’s PTO gear turns at approximately 80% of crankshaft speed at low engine rpm, and approximately 1:1 at higher rpm.

Regardless of which PTO brand you select (stock or aftermarket) the input gear on the PTO itself must be a 6” diametrical pitch, 20-degree pressure angle, straight-cut (non-helix), involute spur gear.

The stock 5-ton PTO uses a 25-tooth input gear (piece 20, of figure 530, of TM9-2320-272-24P-2). The other two gears (piece 21 and piece 23, of figure 530, of TM9-2320-272-24P-2), combine for an overall PTO gearing of about 1.236:1 (overdrive with respect to crankshaft rpm). The Muncie TG6S series PTO, requires a U60 input gear for use with the MT-654CR Allison transmission, which is a 24-tooth gear. The TG6S-U6004 gears combine for an overall PTO gearing of about 0.963:1 (reduction with respect to crankshaft rpm). The TG6S-U6005 gears combine for an overall PTO gearing of about 1.255:1 (overdrive with respect to crankshaft rpm – which is similar to the stock 5-ton PTO).

For the purpose of sizing the hydraulic pump, assume the transmission PTO drive gear (piece 11, of figure 187, of TM9-2320-272-24P-1) is turning at 1000 rpm. This is a reasonable throttle setting for a PTO hydraulic application. Ensure your pump is safe to operate at the maximum engine rpm (max pump speed is 2100 rpm, times the PTO overall gear ratio).
 

monkster

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I am looking for such a system if the $'s are in my budget, PM if you want. Question for Entropy455 what is the gpa and working pressure for 900's. Good info.
 

jdknech

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I am looking for such a system if the $'s are in my budget, PM if you want. Question for Entropy455 what is the gpa and working pressure for 900's. Good info.
the stock 939 pump is 14gpm @ 1,000 rpm. The PTO turns right at 2,000 rpm at governed speed so that gives you right at 24-26gpm not sure on the psi.. let me do some looking.. i had all the specs a few weeks ago..
 
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Speedzilla

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Bringing back an old thread, I have read the front winch cannot be used while in anything but neutral. According to this the PTO is live in all gears. Anyone have the right info? Curious if you can assist the front winch while in forward gear.

Edit: After thinking about it, I guess the winch WOULD work in forward gears, but only if the drivetrain is spinning as otherwise the transmission (PTO) isn't spinnng.
 
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To my understanding the torque converter locks up in neutral to drive the pto. The pto is live in all gears but will turn when moving only,and not at full rpm because the torque converter will not be locked up. Here is a 221R ordered with air shift and direct pump mount , will be installed next week $1200 CanadianNahanni 8.JPGI believe some people are using the wrong PTO housing and that's why they are having problems installing them.
 
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Jbulach

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Bringing back an old thread, I have read the front winch cannot be used while in anything but neutral. According to this the PTO is live in all gears. Anyone have the right info? Curious if you can assist the front winch while in forward gear.

Edit: After thinking about it, I guess the winch WOULD work in forward gears, but only if the drivetrain is spinning as otherwise the transmission (PTO) isn't spinnng.
Your edit is correct. So if you’re stuck and able to spin the tires, you can power the winch at the same time, if the winch doesn’t have enough power, and/or you don’t have a snatch block. Low range, first gear work’s best for trying to keep everything in check, and not birds-nest the cable.
 

74M35A2

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Where does the recommended 1800rpm limit come from for operation of the M939 PTO/hydro pump?

Also I have stuck my 925a2 in 4’ of mud, and the winch pulled it out effortlessly in neutral only. I don’t see many cases of where one would have to spin the tires as well, though it may help? Have always wanted to try it as well, but never been stuck since.
 
To my understanding the torque converter locks up in neutral to drive the pto. The pto is live in all gears but will turn when moving only,and not at full rpm because the torque converter will not be locked up. Here is a 221R ordered with air shift and direct pump mount , will be installed next week $1200 CanadianView attachment 784455I believe some people are using the wrong PTO housing and that's why they are having problems installing them.
here is an installed picNahanni 15.JPG
 

M35A2-AZ

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All my M939's you have to have the truck in neutral to run the PTO, so you can not use the wheels to help the winch.
 

Jbulach

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Where does the recommended 1800rpm limit come from for operation of the M939 PTO/hydro pump?

Also I have stuck my 925a2 in 4’ of mud, and the winch pulled it out effortlessly in neutral only. I don’t see many cases of where one would have to spin the tires as well, though it may help? Have always wanted to try it as well, but never been stuck since.
Wheres Doghead when you need him? Found it for you!IMG_7995.jpgI’ve always assumed the pump was the limiting factor on the speed. I’ve inadvertently went over 1800 several times and it does get quite a bit louder, quickly. We had a discussion on here somewhere and I think it was Tobys figured out the pto ratio, and it put the pump at it’s max rpm of 2700 at 1800 engine rpm. I could be wrong on this though, I’ll see if I can dig it up.

If your winch pulled you out effortlessly, you weren’t that stuck. I’ve always been under impressed with mine, but I’m usually working on the outer layers of cable and have to double line.

Guess I need to do some experimenting on how many rpm the wheels turn in L-1 vs winch drum rpm. Always a couple guys that say it cant be done, and yes I realize it’s not very practical winching, but I run my pump all the time while driving and dumping.
 

Lukes_deuce

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here is an installed picView attachment 785110
How did the install go? That air shift unit is bigger than the stock unit. I had to loosen the motor mounts to lift up the trans enough to get the pto in. Im just happy I got it to work!

On another note, Ive seen 939 trucks use the winch and have the transmission in drive to winch themselves out of a mud hole. If your that stuck, you need to be using the winch along with the wheels to get out. I have used my dump hoist while moving around the yard as well. Once the PTO is on, then its being powered by the converter, which is moving when your in motion in gear. Its only stopped when your stopped in gear.
 
How did the install go? That air shift unit is bigger than the stock unit. I had to loosen the motor mounts to lift up the trans enough to get the pto in. Im just happy I got it to work!

On another note, Ive seen 939 trucks use the winch and have the transmission in drive to winch themselves out of a mud hole. If your that stuck, you need to be using the winch along with the wheels to get out. I have used my dump hoist while moving around the yard as well. Once the PTO is on, then its being powered by the converter, which is moving when your in motion in gear. Its only stopped when your stopped in gear.
My PTO went in no problem ,It's a stock housing with optional air shift fits great .Chelsea parker still makes them with 10 different shift options and 30 different outputs.I am thinking that people may be having problems installing the 221 ptos some people sell,The 221R is the original housing.
pto.jpg
 
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