MT654cr transmission replacement in"Joe" the 5 ton M923a1

[lindsey97]

Ok, so I finally got started today removing my bad transmission in Joe, my first M923 that I purchased in 2014. Joe is a 1990 M923A1 with NHC-250 engine.

Got everything unbolted except the 2 back bolts that secure the trans to the rear upper mount. Took about 6 hours to get everything unbolted. Currently brewing a plan to lower the old trans down safely, and then install a new one that I purchased from OKC GL.

Questions:
1) Has anyone got pics of how you completed the replacement without the correct transmission jack?

2) Are there any differences internally or otherwise in a transmission for a NHC-250 engine versus the 8.3l A2 variant?

3) Are the torque converters the same or different between the 2 types of trucks?

I have a large chain hoist, W20c wheel loader, and a few other machines to lift with. Pics to follow, and I will also post a list of tools and cheat sheet as to how I completed the repair. Any advice will be greatly appreciated. Also, anyone who is willing to help will be compensated.

 

[wrenchturner6238]

Is there someone local that you could rent or barrow a transmission jack? I have taken several in and out but had a jack and a box that fit the pan rail nice or used an overhead hoist on a deck engine. on a pickup automatic I have used just a floor jack but these transmission are to heavy and high up for that. I would be interested in seeing how you do this. I wish i was more help hopefully a good idea will chime in.

 

[adamsoffroadperformance]

we have used racet straps looped over the framerails on pickup trucks. if you use the big straps they are rated at 3300lbs each so they should handle it. though a borrowed or rented trans jack will be the ticket. if you had forks on the wheel loader you could slide the trans under and up most of the way with that then use straps from there to save some grunt work.

 

[lindsey97]

Also forgot to ask how to properly disconnect the transmission modulator cable at the transmission end. Would like to leave the cable on the truck and attached at the IP end for convenience. Do you remove the screws in the round can on the transmission end of the cable, and unhook the cable end inside of the round can?

 

[lindsey97]

Used 2 rachet straps to lower the bad transmission to the ground. Went well and didn't break anything or hurt anyone. Found the one 1/2" bolt that secures the modulator cable to the trans. Now I am on the hunt for a transmission jack.

 

[ghitch75]

i'm going to do this on my A2.....i was planning on using rachet straps too......

 

[SLOrazorsedge]

The torque converter for a NHC250 Vs 8.3 are dissimilar, I can't tell you how much...totally different torque ranges between the the two engines

 

[Lukes_deuce]

Im curious as to what failed? Normally the allisons have a good track record. I has to agree with SLOrazorsedge, I would bet money the torque converters are different. I would believe the stall speed has to be different for the different types of power bands in each engine. If you put a 8.3 torque converter in a 250, it will be a slug. But if you put a 250 torque converter in a 8.3, now that might produce some good results, especially if the 8.3 is turned up some.

 

[ghitch75]

mine 5th and reverse went out....so does the torque band on a 250 come in sooner than a 8.3?

 

[lindsey97]

Update: transmission is installed and went well. Very easy to do on a concrete floor and with the correct jack. Would like to say THANK YOU to bigrig379 for loaning and delivering to me a transmission jack. This is an awesome site and lots of good people on here. Jack is a Pittsburgh from harbor freight, item #60240. Worked great and lifts to 32.5" in height. My truck is a M923A1 with 14.00r20 tires(49") so I had about 3/4" extra height with this jack. So if you have hemtt tires, it will not be tall enough to change out the trans unless you mod the jack, or air down the tires.

Oil used: I settled on Orielly's premium green bucket oil, p/n 74209. It is 10wt, and has a Allison C-4 rating so for my climate I think this is the best pick for me. Another oil to consider is yellow bucket 303 from tractor supply, p/n SUS35. It is also a 10wt, but does not carry the correct Allison C-4 rating, so use at your own risk. Better than motor oil if you ask me though.

Tips and tricks for install: be sure and clean out your heat exchanger. I used motor oil and compressed air to blow out the lines and exchanger. Spin on filter is a Wix 51268. Be prepared to have a second 5 gallon pail of oil on hand, as I completely purged my system and installed a new trans. What I found was that mine held 5 gallons and 2 quarts, rather than the 17 quarts listed on the dash. Allison doesn't take into account for the filter, cooler lines, and heat exchanger capacity.

I also found that removing/installing the (12) 5/8" head torque converter bolts thru the starter drive hole was so much easier/quicker than trying to do it from the cover on the right side. I used a dewalt cordless impact reduced down to 3/8" drive with super short 5/8" socket to install them.

Be sure and use thread sealant on the dipstick to pan connection. I see quite a few truck with seeps in this area.

I cut down and used a small rachet strap to hold the transmission-to-transfer case jackshaft in place so I could get some bolts started and align it properly. That thing is a handful by yourself.

So I am pleased with shifting of the transmission overall, and am happy with my install, wasn't too bad and quite frankly I feel it was easier than doing the same task on a car. You have to have a great big jack........

 

[simp5782]

Update: transmission is installed and went well. Very easy to do on a concrete floor and with the correct jack. Would like to say THANK YOU to bigrig379 for loaning and delivering to me a transmission jack. This is an awesome site and lots of good people on here. Jack is a Pittsburgh from harbor freight, item #60240. Worked great and lifts to 32.5" in height. My truck is a M923A1 with 14.00r20 tires(49") so I had about 3/4" extra height with this jack. So if you have hemtt tires, it will not be tall enough to change out the trans unless you mod the jack, or air down the tires.

Oil used: I settled on Orielly's premium green bucket oil, p/n 74209. It is 10wt, and has a Allison C-4 rating so for my climate I think this is the best pick for me. Another oil to consider is yellow bucket 303 from tractor supply, p/n SUS35. It is also a 10wt, but does not carry the correct Allison C-4 rating, so use at your own risk. Better than motor oil if you ask me though.

Tips and tricks for install: be sure and clean out your heat exchanger. I used motor oil and compressed air to blow out the lines and exchanger. Spin on filter is a Wix 51268. Be prepared to have a second 5 gallon pail of oil on hand, as I completely purged my system and installed a new trans. What I found was that mine held 5 gallons and 2 quarts, rather than the 17 quarts listed on the dash. Allison doesn't take into account for the filter, cooler lines, and heat exchanger capacity.

I also found that removing/installing the (12) 5/8" head torque converter bolts thru the starter drive hole was so much easier/quicker than trying to do it from the cover on the right side. I used a dewalt cordless impact reduced down to 3/8" drive with super short 5/8" socket to install them.

Be sure and use thread sealant on the dipstick to pan connection. I see quite a few truck with seeps in this area.

I cut down and used a small rachet strap to hold the transmission-to-transfer case jackshaft in place so I could get some bolts started and align it properly. That thing is a handful by yourself.

So I am pleased with shifting of the transmission overall, and am happy with my install, wasn't too bad and quite frankly I feel it was easier than doing the same task on a car. You have to have a great big jack........

It is easier to bolt the caps on the transfer case side in. Bolt it up not snug And leave the transmission side caps off. Slide the caps on when it is centered in and then bolt em down. They are a pita i know

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