PTO on M35A3 tranny

Gents, I searched for PTO on the A3 and discover one may have been driven off of the air compressor, but I cannot find information about taking one off the tranny.

We have an Allison AT1545 apart and I see the access plate (6 screws) that appears to be for a PTO. Not sure on the presence of gearing to drive the PTO (yet), but I would hope the military had it.

Does anyone know of a PTO off the AT 1545 Allison? What it might look like or some numbers? Or give me a hint for a search, I come up empty so far.

I'm still searching for information about taking a PTO off of the Allison auto AT1545 on an A3.

From what I have found, the AT1545 is the same as the 545, mechanically, except with a locking torque converter. Along with the locking torque converter, there is a different seal and an upgraded PTFE clutch sealing ring but mechanically the same...well not the valve body.

Parts for the 545 are readily available. I bought a seal overhaul kit and then the other seals for the locking converter, all frictions, 4th and reverse plates and a new piston. The old one was destroyed.

Since we received this tranny in a box, entirely apart, I can see there is a PTO driver spur gear. I found the Allison reference to the 545, which says it's 55 tooth (I'll confirm at the shop), 6-bolt.

I want a PTO for making the bed dump.

I won a GL bid with several of the PTO's that fit the 939 series (including A2), manual shift, 6-bolts and wondered if it would fit.

I'm sure the spur gear that drives the MT654CR has more teeth (is larger diameter) but the teeth may be the same. While I haven't located the information on the 939 series tranny driver gear, it appears the pitch dia. to face may be the same.

The 545 specs say that it is R.H., gear forward of center line, 55 teeth spur, with a pitch line to aperature face of 1.085".

When I get my PTO's, I'll see how close they are.

I just looked up the MT654 and other than having 64 teeth, is identical including the pitch line to aperature face of 1.085".

Okay, I have the NOS Chelsea PTO's and the same one that fits the 939 series does fit the A3. It does require a small floor modification, but that's not a problem, the frame is NOT in the way or near as tight as the 939 series. The speed will be 55/64ths of a 939, so will rotate the pump slower.

Direction...haven't figured that out yet and hope someone with a 939 will tell me. I think the PTO rotates the same direction as the engine, but have to confirm that.

Mounting of pump. It appears the pump would be better coming off of the PTO (bracket-like a log splitter with gas engine). The pump does not have to be as large as what is on the 939, I'm thinking 12-16 GPM gear, perhaps 2 stage. There is not enough room for a variable displacement piston...tried that.

Since my rebuilt tranny is out, I'll be mounting the PTO the easy way...out of the vehicle...and putting the entire unit up and in.

My M925a2 PTO rotates the same direction as the engine. And just going off memory I believe there are only a couple a different bolt patterns and gear pitches of PTOs. However I do believe you have to set the gear lash by shimming the PTO out if necessary.

Jbulach said:

My M925a2 PTO rotates the same direction as the engine. And just going off memory I believe there are only a couple a different bolt patterns and gear pitches of PTOs. However I do believe you have to set the gear lash by shimming the PTO out if necessary.

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Thanks Jbulach. Your right about the gear lash. I put it on without any gasket and the gear would not move over to engage...it hit the drive gear. So I started holding it out and at about the distance of the gasket, it began engaging fine. If you know how to do it in a more professional method, please let me know. I have not mounted it with the screws yet, just visual, putting the unit into and out of engaged.

I only found one pattern for Allison on the 654 or 545...6 bolt...and they have the same pitch lines. Inspecting the teeth, they appear the same, just different numbers of them.

tobyS said:

Okay, I have the NOS Chelsea PTO's and the same one that fits the 939 series does fit the A3. It does require a small floor modification, but that's not a problem, the frame is NOT in the way or near as tight as the 939 series. The speed will be 55/64ths of a 939, so will rotate the pump slower.

Direction...haven't figured that out yet and hope someone with a 939 will tell me. I think the PTO rotates the same direction as the engine, but have to confirm that.

Mounting of pump. It appears the pump would be better coming off of the PTO (bracket-like a log splitter with gas engine). The pump does not have to be as large as what is on the 939, I'm thinking 12-16 GPM gear, perhaps 2 stage. There is not enough room for a variable displacement piston...tried that.

Since my rebuilt tranny is out, I'll be mounting the PTO the easy way...out of the vehicle...and putting the entire unit up and in.

Click to expand...

If you get a chance, post some photos of the pto mounted to transmission.
What is the Chelsea pto model number?
I have an A3 that I would like to add pto to.
Thanks

It's Chelsea PTO 308594-1. I'm working on the proper pump and pump mount to the output shaft now. Sure, I'll take a couple of pictures soon. Put into ebay: "Military PTO" and one will come up (not mine but same thing), painted green.

Since I bought 17 of the PTO's, I'll have a few to sell. I have an ad in the SS classified for just the PTO but when this PTO-pump combo is worked out, I'll sell a few complete set-ups. It won't make the volume of flow that the OEM pump makes (not as large physically), but will be capable of more pressure.

I have 2 of Toby's ptos if anyone close needs one.

I just read that the M916 can use the same 6 bolt PTO as the M923 when they have the Allison transmission. I'd have to do more research to make a definitive statement, but that would mean the same PTO that fits the 923 Allison also fits the M916 Allison and the M35A3 Allison.

I read a good target RPM on a 939 series is 1000 engine rpm. But there was talk that confused me about the ratio from tranny to PTO output. It ranged from a reduction to an overdrive so I went and counted the teeth of the PTO. The tranny mesh gear is 25 tooth, which drives an intermediate shaft that has 14 teeth, driving the output shaft with 29 teeth. Thus there are 2 ratios, that of the transmission to drive gear and the intermediate shaft to the output shaft.

For every engine revolution, on the 939 series, 64 teeth will pass and on the M35A3, 55 teeth will pass, both contacting the 25 tooth engagement gear. So at 1000 engine rpm, the larger Allison will turn the intermediate shaft at a ratio of 64/25 or 2708 rpm. Then the intermediate gear reduces the speed on the output shaft at the ratio of 14/29 or 1307 rpm.

On the A3 with 55 teeth and 1000 engine rpm, the intermediate shaft will turn 55/25 or 2200 rpm and the output will turn 14/29 of that, or 1062 rpm PTO output.

Thus the Chelsea that I have, when running the engine at 1000 rpm on either vehicle, will turn the output of the PTO on the M939 series at 1307 rpm and 1062 rpm PTO output rpm on the M35A3. Thus both are overdrives, not reductions. Sizing the pump can be made from these rpm's.

Subsribed.. I have Brad's A3 w/w parked on the other farm, I can crawl under it and get a picture of the trans/PTO configuration. Give me a day or so .
JC

That will be great.
Thanks

Scar59 said:

Subsribed.. I have Brad's A3 w/w parked on the other farm, I can crawl under it and get a picture of the trans/PTO configuration. Give me a day or so .
JC

Click to expand...

Are you sure it has a PTO off the tranny or does it come off the back of the air compressor?

tobyS said:

Are you sure it has a PTO off the tranny or does it come off the back of the air compressor?

Click to expand...

I'll have to look tonight, I'll get some pictures.

I'll bring this up to date and add some pictures when the parts ordered come in. I have not put the rebuilt tranny in this A3 yet and am taking the opportunity to install the PTO with it out.

I bought a GL lot of PTO's that fit the M939 series, same as OEM on dumps and winch trucks and found they do fit the Allison AT1545 also. The only difference between the 5 ton Alison and the A3 Deuce Allison is the number of teeth that is driving the PTO. (55 on A3 and 77 on 5T).

I contacted technical support for Parker/Chelsea and found that these PTO's are considered obsolete. New ones that replace them are 1/2" wider....and the new model can have a frame interference problem on M(939)A2's.

On the M35A3, the (tranny mount) PTO appears to have a lot of clearance to the frame but is limited to the rear by the big transfer case, thus a shaft drive pump seems impossible. A direct mount pump does appear to have room

The Chelsea representative told me that the new model PTO and our version have interchangeable shafts and output flanges for direct mounted pumps. Thus, our PTO, that does fit the A2 5 tons and the Deuce A3, appears to have parts available for direct mounting an SAE A or B pump with a variety of input shafts.

I'm purchasing a rotatable SAE B 2 bolt with a 7/8"-13t internal spline that I will retrofit to direct mount on my NOS PTO. I bought a Prince 3.18 cu in/r gear pump. When I get the parts, I'll post results (of assembled unit) and pictures.

I expect some floor modification in the truck, but it appears to fit otherwise...giving the A3 a compact option and no open driveshaft.

The pump came yesterday and the direct mount flange should be here tomorrow. Pump is a Prince SP25A52A9HI-L.

http://www.princehyd.com/Portals/0/pumps/pumpssp2025.pdf

At 1000 rpm it can pump about 13 gal (@ 2500 psi is 22hp) and at 1500 it is about 20 gpm (@ 2500 psi is 32 hp) and at 2000 rpm is is 26.4 gpm (@2500 psi is 44 hp). I read someplace that Allison recommends no more than 45 hp from the PTO.

A second pump, a Muncie showed up after being lost in the mail.

My mistake. I bought a new Prince pump that is left hand or counterclockwise and see I'm backward for my PTO. Dam. It's going up for sale in classified as changing to right hand drive is cost prohibitive. Sell at my cost. SAE "B" mount with 13 tooth spline. Specs above.

gone

Got the flange kit today and took apart the PTO to see how to change out the shaft and pump mount. First I made sure they were mating parts, the flange to pump, flange to PTO and shaft to shaft. It has to come completely apart and has 2 tight fit bearings that prevent it. To take the shaft out, one has to use a puller that reaches down in, and apply heat....too much heat. Heating the bearing cone quickly became ruining the bearing temper.

So both bearings ordered. In addition to ordering the shaft and flange kit (Chelsea 328591-30x) when doing this, order 2 new bearing cones, Chelsea # 550532 and 550397. Note the race for the drive end is new and included in the flange.

I have sat at that table!

Nice work, sounds like a pita though.

Yes you have Chris! The sun was great today. Let us know when your headed this way.

Yea, two pressed on bearings was a PITA, but now I know to use new bearings.

I got word today that the flange kit I bought first and was lost in the mail had actually not been sent and they went ahead and put it in the USPS. So the real PITA has been a flange kit ordered and claimed to been shipped....but not, and a pump that was sent USPS and rolled around the post office for 2 weeks, then delivered. And there was a second pump that was left hand drive...a mistake. What a cluster...

I can't see an alternative for an A3, unless one comes off the back of the compressor. I don't like pulling power there. I'll probably sell this one when done and use a smaller pump, now that the other mount kit is coming. I don't need the flow (this one has a rather large pump) but be great for a 20K winch.

Update. The new bearings came in and I'm putting the PTO back together. I will be installing on the tranny (that is out of the truck, rebuilt).
Here is a picture of the female spline (1"-15t) and 2 or 4 bolt (SAE B) adapter, together and installed in the PTO. Then there is a picture of the PTO and pump together.

This pump is a big nearly 4.0 cu. in./revolution. Will work great for a high volume winch or crane.