MT654CR trans replacement for M923

[surfhacker]

Hello,

I have an M923A1 with 23k miles, I noticed the transfer case was running hot, so I changed the gear oil in the case, and then figured I'd change the oil in the transmission as well (used Dextron).

After towing an ammo trailer around for the day, I went back to park, and the truck won't reverse. The gear select lever no longer "bumps" and "settles" into gear range select, but shifts fairly smoothly between them.

So I assume I'll need to replace the transmission.

My question is... I've found a variety of MT654CR transmissions around. Do I need to buy one specifically refurbished or taken out of another M9**A1, or can I buy any old MT654CR that I find, even non military editions. Do they come in different gearings that I might need to worry about?

 

[simp5782]

Hello,

I have an M923A1 with 23k miles, I noticed the transfer case was running hot, so I changed the gear oil in the case, and then figured I'd change the oil in the transmission as well (used Dextron).

After towing an ammo trailer around for the day, I went back to park, and the truck won't reverse. The gear select lever no longer "bumps" and "settles" into gear range select, but shifts fairly smoothly between them.

So I assume I'll need to replace the transmission.

My question is... I've found a variety of MT654CR transmissions around. Do I need to buy one specifically refurbished or taken out of another M9**A1, or can I buy any old MT654CR that I find, even non military editions. Do they come in different gearings that I might need to worry about?

CR just means close ratio.

Transmissions for the A2 trucks have a different torque converter, converter ratio and front pump mounting.


I haven't dug into what ratios they differ on cause it hasn't been an issue to find any of the transmissions for the specific trucks. The parts TM doesn't specify a difference or a parts breakdown difference for the trucks seperately

 

[surfhacker]

Thank you. There are sites like Eastern Surplus that sell MT654CR transmissions, and their list of compatible truck models includes the A1 and A2.

Automatic Transmission Allison MT654 M939A1 M939A2

Automatic Transmission Allison MT654 for M939 5-Ton Trucks

www.easternsurplus.net

I assume, then, that they probably listed it incorrectly, and that I'll need to call to figure out the right MT654?

 

[simp5782]

Thank you. There are sites like Eastern Surplus that sell MT654CR transmissions, and their list of compatible truck models includes the A1 and A2.

Automatic Transmission Allison MT654 M939A1 M939A2

Automatic Transmission Allison MT654 for M939 5-Ton Trucks

www.easternsurplus.net

I assume, then, that they probably listed it incorrectly, and that I'll need to call to figure out the right MT654?

They aren't the same. Coffey ran into this problem years ago. I'll see it I can find the thread somewhere.

 

[DeMilitarized]

Hello,

I have an M923A1 with 23k miles, I noticed the transfer case was running hot, so I changed the gear oil in the case, and then figured I'd change the oil in the transmission as well (used Dextron).

After towing an ammo trailer around for the day, I went back to park, and the truck won't reverse. The gear select lever no longer "bumps" and "settles" into gear range select, but shifts fairly smoothly between them.

So I assume I'll need to replace the transmission.

My question is... I've found a variety of MT654CR transmissions around. Do I need to buy one specifically refurbished or taken out of another M9**A1, or can I buy any old MT654CR that I find, even non military editions. Do they come in different gearings that I might need to worry about?

Well your first problem was not running 15w40. I would drain it and throw some back in and see if it fixes the issue. IDK why people change it over then become amazed the trans fails and cant find out why. Seen multiple threads on it all the time.

 

[surfhacker]

Well your first problem was not running 15w40. I would drain it and throw some back in and see if it fixes the issue. IDK why people change it over then become amazed the trans fails and cant find out why. Seen multiple threads on it all the time.

I thought I'd read up on all of the most recent threads here, and figured the concensus was that Dextron was the way to go.

But I've found a few now that talk about overheating with Dextron.

I'll drain and go with 15w40 from now on.

 

[G744]

Dexron. No "T".

 

[simp5782]

I thought I'd read up on all of the most recent threads here, and figured the concensus was that Dextron was the way to go.

But I've found a few now that talk about overheating with Dextron.

I'll drain and go with 15w40 from now on.

There is no overheating with Dexron. The 5 ton transmission temp is maintained by the heat exchanger. If the transmission temp is going up that means the engine temp went up in order to rise the transmission temp

 

[juanprado]

many many threads on here about the fluid.
My m923 came with dexron already straight out of Ft. Polk. No issues and shifts great. If you are running 1000's of miles or heavy towing, weight carrying , working her like a rented mule; consensus is to use the motor oil.

Whatever you do, key is to change both filters and flush appropriately.