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West Central Nebraska - Sandhills | I have an M925 military 6 x 6 that I put a twin screw vertical mixer on the back of. It’s been a great truck but has always felt like it’s been too much for the transmission. Is incredibly difficult to shift PTO out of gear or back in gear when the truck is loaded. Well, after two years, the transmission finally went out.
The engine is an NHC Cummins 250. The transmission is an Allison MT 645 CR I talked to a feed truck company who recommended I have my local Allison switch to a New World 3000 series Allison or Weller transmission. He said “if that’s possible“. Anyone ever done it? Any other thoughts? The twin screw mixer holds about 5k lbs of feed and runs directly of transmissions PTO. Thanks in advance!
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| It would be a good idea to know what the horsepower requirements of your mixer are? And compare that to your current transmission and then the pto outputs. Isvyour transmission bad or just the pto? You might just need to get a pto with a lower ratio? I wouldn't put a new world allison in that truck if it were me. I would just have that one rebuilt with heavy specs. |
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SW MN | I agree, check the specs. Then decide. Maybe the Military surplus would have a transmission.. I think you'll be doing a little info digging.. |
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Michigan | An Allison 643 would be an upgrade and is still a completely mechanical trans so no need to mess with computers and wiring. 643s are good for close to 70k GVWR. |
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West Central Nebraska - Sandhills | Thanks for your response.
The segue mixer requires 100hp from a tractor
This is mounted on a truck now so I don’t know if that changes anything.
The truck has an NHC 250 which is 250hp
The transmission is Allison MT645CR which is rated for 266hp
The PTO is a Chelsea PTO that is 1:1 gear ratio but I have not been able to find HP on it. It does come directly off torque converter which is what my mechanic cited as the problem for it being so difficult to shift the PTO in and out when the truck is loaded. And that’s why he recommended switching to new world 3000 series as he said that clutch shifting PTO directly off engine instead of torque converter would make it smoother. But he said he needed me to find more info if it was possible to switch to the new world transmission and I’m not sure where to turn.
The transmission is blown, it won’t go into any forward gears.
I had originally planned on having Allison rebuild transmission but then the concern is it will still be difficult
To shift in and out of PTO when truck is loaded. Thoughts? |
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West Central Nebraska - Sandhills | How is the PTO structured on that transmission? Still off torque converter? Is it a hot shift?
The PTO is the big issue |
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Parker, SD | If memory serves the PTO is main shaft driven with a lockup control, PTO only runs in neutral or driving. In gear parked it does not run. It should have a hot shift, if it does not you should be putting it in gear to stop the main shaft, then back to neutral after shifting. Can't believe how many Allison's I've seen with pto complaints and manual coble operated PTO....It can be done, on some, but you need to shift it correctly.
As far as 3000 conversion, to do it right open your pocket book. We did an Eaton Fuller to 4k conversion on a sterling for a local construction company some years back. I think that bill was north of 40k P&L. But I know it was done as well or better than the factory could have done it. Being you already have an MT trans the adaptation hardware should all be correct I believe, or closer than a fuller would be. SAE #2 housing. Getting a properly functioning calibration will be the biggest battle. If you found a donor chassis would be your best option. But I'm not familiar with what military trucks are what and what years, probably aren't going to find a 3000 behind a 250. Bu tif oyu found one with an L10 or similar with mechanical fuel system, it would be the most compatible. You'll need a TPS or cable sensor off the throttle linkage. I worked on a couple retired FL120 military trucks with big cam 400s and 3000s
Weller is just a reman company, its still an Allison transmission, just cheaper, quality is hit or miss.
Edited by dodgetruck2 6/30/2025 18:42
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Callao Missouri | Well your kind of behind the 8 ball here. You should have started with a cement mixer truck and used the front drive hydrostatic drive to run the mixer via the hydraulic motor that rotates the drum.
Your not going to be able to get enough horsepower out of a truck pto to make your system work reliably.
I wouldn't spend a nickel on a world 3000 upgrade because of the horsepower requirement. Yes you can get a hot shift pto for them but your going to smoke it in short order drawing that much horse power through it.
One thing you can do is find a wet bell housing with an auxiliary drive off the side. Then run that to a clutch and some sort of transmission to get your gearing right.
What I would do is get a DT466 and a 5,9. or 10speed on the back of that truck and run the mixer off the transmission driveshaft of that engine. You will have plenty of horsepower and independent pto that way. |
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| Are you sure you don’t have a MT654CR transmission? I’ve never heard of a MT645. If so a MT643 would not be an upgrade. You’d be getting a smaller torque converter with basically the same size transmission. You could solve your shifting problem by simply installing a hot shift pto onto the same model transmission you already have. However, I don’t think you can get a pto for any of those small Allisons that is rated at 100 hp. Have you considered putting an auxiliary transmission behind the Allison with a power tower to run your pto? That would be a much more robust setup. I’m not sure you’d have room for it though. |
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| All you need is a hot shift pto and i would call Chelsea and give them the horsepower pto requirements. You probably need a different ratio in your pto to match the requirements. |
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| The 645 has a lower gear that the 643 doesn't have. I would just get a heavy duty rebuild and get the correct pto. |
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| Your transmission is sufficient for the hp requirements of your mixer. Seague ssys 100 hp min but thats the engine hp of the tractor so i guess you need much less actually at the pto. If you talk to Allison about your application they can recommend the correct torque converter ratio for your needs and match it up with the correct hotshift pto with the correct ratio and youl love it. And i would run 15w40 oil in it also. |
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Allison MT645CR->”new world” 3000 series?
