M939 and M915A1 PTO info

[LanceRobson]

jatonka and I have been discussing this for our M915A1 tractors for some time so I spent some time this week checking into this. I'm not a PTO guru so much of what I am relating here is from folks who are gurus and I'm a bit like a 6'4" sock puppet on the subject. Mostly, I'm just passing on info from others.

All of the HT-754 CRD transmissions in the M915A1 and the HT-654 CR transmissions in the M939 series will accept a PTO.

The 6 bolt PTO port for the M915A1 is over the torque converter at about the 11 o'clock position as viewed from the rear of the transmission. It is a PITA to reach and you may need to drop the transmission to install the PTO and pump. I don't yet know if there are any clearance issues but the linkage for the shifter and a couple of hoses are in the general area where the PTO would sit and they may need addressed, especially the shift cable.

The Allison MT-654 CR in the M939 series trucks will take the same PTOs they just mount on the right side at about the 3-4 o'clock position as viewed from the rear.

I'm most familiar with Muncie products but other makers have similar PTOs available. Cross referencing them should be easy. There is a Chelsea cross reference on Muncie's site

Clutch shift PTOs seem to be favored for automatic transmissions and the Muncie CS ones are constant mesh and pressure lubricated. They can be engaged while the engine is running and even while the truck is in motion as long as the engine RPMs are below 1000 RPM. They are more forgiving of operator carelessness than some other PTOs and can be had with RPM limiters to prevent over speed damage to the PTO or transmission. It has another advantage in that there is no fooling with checking backlash. Just bolt it on and go. This could a big plus since just reaching the M915A1 PTO cover without dropping the transmission from the truck is tough and it might save you removing the transmission.

There are also TG and SH series PTOs that will work. I know the TG series needs to have the lash adjusted with gaskets as shims and that pressure lubrication is an option but do not know about the SH series. PTO output shaft rotation on all of the recommended CS, TG and SH PTOs is the same as the crankshaft. Some automatic transmission PTOs reverse the rotation so be sure whatever PTO you wind up with will work with your pump.

Depending on the PTO the output available at 1000 RPM in either truck will be from 51 to 76 HP and 285 to 400 pounds of torque. The PTO output speeds for the M915A1 range from 108% to 154% of engine speed. The M939 PTO output shaft speed is from 96% to 126% of engine RPM and the torque and output HP remain the same as for the M915A1.

You have a wide range of choices for pumps based on your flow rate and pressure requirements. These PTOs are designed for use at 1000 engine RPM so that the torque converter is locked. I think all are rated for 1000 RPM max.

Here's the link to the specific PTOs with specs Muncie has available for the HT-754 CRD:

http://www.munciepower.com/clientuploads/QRSectionns/ALLI-03.pdf

And for the HT-654 CR:

http://www.munciepower.com/clientuploads/QRSections/ALLI-02.pdf

When researching the subject be sure you are looking for PTOs for an HT-754 CRD (close ratio) or HT-654 CR since they are the exact transmission in your truck.

I hope this helps someone else and please post your thoughts and any other info you find since we are feeling our way into this. If anyone spots incorrect info in this please let me know so I can change it.

Thanks

Lance

 

[Danl]

Danl M915A1

the tranny shop called me back its the weekend and he is not sure monday when the boss comes in he'll call me I gave this guy all the info that he needed but he is one of those not sure guys

 

[m16ty]

The only thing I'd add is if you mount the PTO to a M915, you'll want it pressure lubed. Mounted at the 11 o'clock position it won't get enough lube otherwise. The M939 won't need the pressure lubricated option.

The clutch shifted PTOs sure are nice but they are expensive.

 

[LanceRobson]

I haven't checked the overhead clearance height above the M915A1 PTO opening but since the opening is clocked at about 11 o'clock I'm hopeful that there is enough room to fit a PTO with out cutting into the cab floor. Since the driver's seat sits on a tool box cutting the floor and boxing around the PTO doesn't seem to be all that big of a deal though.

I talked to someone in the Muncie tech department a couple of times last week but wasn't smart enough to get the dimensions of the various PTOs.

I'll look at the clearances today and try to get a rough idea of how much room there is over the PTO opening. I also want to look at where the nearest cross member or other obstruction is behind the PTO opening to see whether the pump can be directly mounted to the PTO or if a drive shaft will be needed to work around any obstructions.

When I get some dimensions on the PTOs I'll post them along with my best guess as to available space and whether it looks like there is room to snake the PTO and pump up into place without dropping the transmission.

Lance

 

[Danl]

Danl M915A

Lance there is plenty of room for the pto and pump, I did have a tranny filter line in the way. I tuned the line end for end, so I had a 90% fitting on top. you are going to need a 4 foot shift cable the stock cable will be to short to run over the top of the PTO and back down to the tranny shift port . I did post pictures and work on converting a tractor to a dumptruck Thread. All is running Now and the truck came around real well. I do have to haul useing the tranny as a Hygro matic. The auto matic is or only seems to be the two lower gears. when I'm frated with 22 ton I start in 2nd the tranny goes to low low. it sift up to like 0-1 to 1-1 than goes to 2-1 than to 2-2than at 21oo rpm I slide it to 3 and again at 2100 I slibe it ti 4 and at 21 00 to 5th the truck will be rolling 50 mph 40 to 45 mph the tranny is in 4th if you hit a hill you have to keep the motor in its power band of 2000 rpms run your tack and all is great. the tranny slide in any gear you need if the hill slows 4th gear to 1950 slide it to third and she will slide in smooth and not jerk the truck at all, you see the rpm go to 21 and the truck will slowly gain speed you hit 2150 slide it up one or hold it at 2150 untill the hill climb is compleat. A little pratice and you will like the heavy hauler. run it like a hygro matic. Because that is what it is. you run it like this ,and you will find that this hauler is unreal fast try and run it like a full auto and it is a dog, I really like this truck now. Let me know how you make out Dan

 

[Danl]

Danl M915A1

I for got to say I really think this tranny is a 7 speed frate the truck and check it out

 

[Hasbeen]

constant mesh backlash

I would verify with the Muncie or Chelsea guys about the requirement or lack of,
shimming or adjusting the backlash just because it is a constant mesh PTO.

The majority of all pto applications are CM as opposed to "Sliding Input Gear", but I believe they all need something like .008" to .012" clearance between the Drive gear in the transmission, and the driven gear in the pto.

Also actually checking the backlash on most of the clutch shift or "Hot Shift" pto`s is more difficult because typically they do not use a "shift top" on the pto that you can remove in order to set up a dial indicator on, but are engaged via an oil pressure line. This reduces you to removing a large plug and dial indicating thru the hole.

I was in the pto business (distribution/sales/installation) a L O N G time ago, but generally if you install a pto with 2 gaskets/shims 1 thin .010" and 1 thick .020", your backlash will be close to the required range. Crank the engine and if it`s too tight it will "whine", and too loose will rattle slightly (.030" will almost never be too loose)

Like i stated....it has been a long time since I have been involved, so I would suggest verifying the requirement with the manufacturers.

Hope this helps, and Good Luck.

Hasbeen

 

[spicergear]

Well timed thread and posts guys, thanks! I'm soon to install PTO/pump combo on my 931A2 for the K-boom and ...possibly other...attachment.

 

[Danl]

Danl M915A1

I would verify with the Muncie or Chelsea guys about the requirement or lack of,
shimming or adjusting the backlash just because it is a constant mesh PTO.

The majority of all pto applications are CM as opposed to "Sliding Input Gear", but I believe they all need something like .008" to .012" clearance between the Drive gear in the transmission, and the driven gear in the pto.

Also actually checking the backlash on most of the clutch shift or "Hot Shift" pto`s is more difficult because typically they do not use a "shift top" on the pto that you can remove in order to set up a dial indicator on, but are engaged via an oil pressure line. This reduces you to removing a large plug and dial indicating thru the hole.

I was in the pto business (distribution/sales/installation) a L O N G time ago, but generally if you install a pto with 2 gaskets/shims 1 thin .010" and 1 thick .020", your backlash will be close to the required range. Crank the engine and if it`s too tight it will "whine", and too loose will rattle slightly (.030" will almost never be too loose)

Like i stated....it has been a long time since I have been involved, so I would suggest verifying the requirement with the manufacturers.

Hope this helps, and Good Luck.

Hasbeen

my pto whines if I rev up , and it will whine at the end of the lift. If I'm to tight on the gaskit is damage being done if I run it easy for I'm two weeks away from getting back in there and changing it ?

 

[Danl]

Danl M915A

Also I was told that no shims was needed for this set up, the pto shop didn't give me a gaskit I reused the gaskit that was on the cover plate. There was also talk of a oil line needed because there was not enought oil up there to lub the gear. My truck has a tranny filter I think added to it. its a spin on and the return line dumps right there on the pto gear, I had to ajust the return line inorder the get the pto to fit

 

[LanceRobson]

I don't know about Muncie but Chelsea clearly states that their constant mesh PTOs for the Allison transmissions we're talking about here do NOT need shimming and claim that fact as a benefit that makes for easy installation. Still, if you are concerned then that's why they have technical support folks so call them.

Dan, the torque converter lock-up can be very harsh under some conditions, especially in 1st and second gear and can easily fool an operator into thinking there are extra gears since when it locks the RPMs will drop and everything will sound and feel like downshift.

Here's a link to the operators manual for the transmission;

http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM1334EN.pdf

You are correct about keeping the engine high in the power band when climbing with a heavy load. It's usually going to take a manual down shift to keep it there since with only 5 gears to work with the tranny valve body often won't downshift until your RPMs are well under the best power band in the next lower gear. I suspect that's why the -10 TM lists such a slow speed at such a shallow grade when climbing at max weight. No manual downshift=painfully slow climbs with a heavy load. If haven't yet had the issue so hopefully Wreckerman or somebody with more experience than I have running heavy can chime in.

The tranny operators manual states that if you try a manual downshift at too high an engine RPM the tranny will downshift only when the RPMs drop to a safe level so I suspect that the best way to be at the top of the fourth gear RPM range is to manually downshift while the fifth gear RPMs are still high but I'd check with Allison before trying it.

My thought is that the RPM limiter in the tranny would downshift at the very top of the fourth gear engine RPM band and you'd be better able to hold speed then as opposed to downshifting later manually or waiting for the tranny to do it on its own.

Another quirk of the tranny to be aware of is if the engine is at risk of being run into an over speed condition the transmission will up shift to protect it so especially when running a manually selected lower gear down hill be aware that the thing will up shift without warning to protect the engine.

Lastly, the Jake brake is most effective at high RPM so a manual downshift may be needed for best braking. If you try to downshift when the RPM is still too high the tranny will downshift only when the RPMs drop to a safe level.

Hope this helps.

Lance

 

[Danl]

Danl M915A1

Thanks Lance One thing that was wrong was the shift cable was not set good enought . I fixed that. but when I start in 2nd or slow down for a stop and jest rolling forward the tranny goes to frist . I don't beleave the down shift I feel is a lock up. it will shift three times befor I shift it to 3rd one might be lock up or maybe terbo kick in I'll keep reading the TM and playing with it, other than the hard down shift or lock up at a very slow speed all seems to be good. hauling 20 thousand plus pounds. I have to shift this truck up and down. Or she will lug and be a pokey. I do tend to slow the rpms down befor I down shift. I kinda of run it Like I 'm running a roadranger, and the tranny slides in gear real well no over rev or lug jest run nice and smooth, Jest that real slow to a stop down shift or lockup. It is kinda like putting a four speed standed in frist when the thing is still rolling a bit. this is the only thing I'm uneasy with

 

[Danl]

Danl M915A1

I reread your post yes it is very harsh this lock up I gest all is ok. I'm really not thinking much wrong with the pto shim mesh, The whineing I get is from the pump. I'm running dextron in it and I need to go to a 20 wh oil I think

 

[spicergear]

I can have mine in 2nd around the farm and get on the brakes and it will feel like it down shifts to first then slows down and down shifts again. The converter lock up on the 931A2 is strong and definitely feel like a another gear.

My Mitsubishi 3000GT (over 373,000mi stock engine) splits gears with the converter lock up. I can be going up a hill and it will feel like a downshift which you would think would be simply dropping the over drive. But, I can then flip off the overdrive and will down shift again. Splitting gears with converter lock up is a decent way to add driveability to a vehicle as opposed to just 3 or 4 main auto gears.

 

[LanceRobson]

Danl, if you look at the side of the tranny behind the battery box cover you'll see the data plate. It will confirm or deny what tranny it is. I've never heard of an M915A1 with anything but an HT-754 CRD but who knows what could have been done over the years.

Lance

 

[markmontana]

I read here on SS that there was a USMC version of the 915A1--- that had a 7 speed Allison. Nope. After searching around, I think it was an M916. Oh well...

 

[Danl]

Danl M915A1

Danl, if you look at the side of the tranny behind the battery box cover you'll see the data plate. It will confirm or deny what tranny it is. I've never heard of an M915A1 with anything but an HT-754 CRD but who knows what could have been done over the years.

Lance

I will check out the date plate in the AM. with my pretrip and will get back to you. My truck was Overhauld in 07 in Texas, I now have 40 thousand miles on it.

 

[Jmm1980]

I have a mt654 cr transmission in my 90 model m939a1 am general and got a Chelsea model 221 pto does anyone know if there is a different model that will fit as the way they set up my pto it won't fit between the frame and the transmission thanks for any info

 

[Postman515]

Did u try taking the step strap bolt out that goes through the frame. I had to fix the pto on my 929 and the only way I could get it to fit is slide it in the frame from the back then I still couldn't get it over the studs until I took that one bolt out of the step strap

 

[Jmm1980]

I will give that a try thanks for the info