M-900 series failures

[Jones]

We've had several posts on the M-900 series transfer cases cracking when in low range and reverse gear is used. Our own Joaquin Suave gets the credit for determining why. In shopping for an Allison for his project truck he ran across some specs. for the Allisons in the 900s. He sez that those Allisons have a reverse that's almost 11 to 1 while most other transmissions are about 5 to 1. With that much gear reduction, coupled with the fact that; with an automatic you can shift into reverse at higher than idle speeds-- it's no wonder that the t-cases will occasionally grenade on you. The military's fix is a positive shift linkage lock-out that keeps the driver from shifting the transmission into reverse unless the t-case is in high range. For trucks without the mod. kit, just remember to let everything settle down before reaching for reverse; then back up carefully if you have to do the move in low range.
Thanks again, Jack.

 

[spicergear]

Excellent post! Those big Allison's sure aren't selling dime a dozen yet...or looking like anytime soon-

 

[ARMYMAN30YearsPlus]

I will take at least two when they get cheap

 

[Joaquin Suave]

Adelmens has "take-out" Allison MT 654CR Transmission for $900.

Here is the link to their PDF flyer

http://www.rockanddirt.com/dispads/0000667874.pdf

I am going to go with the MT 653DR in my LMTV

Here are the specs of the 2 transmissions:

MT 653DR
250 HP
640 lb ft

1st: 8.05
2nd: 3.58
3rd: 2.09
4th: 1.39
5th: 1.00
R: 5.67
****
MT 654
300 hp
950 lbft

1st: 4.17
2nd: 2.21
3rd: 1.66
4th: 1.27
5th: 1.00
R: 10.76 !!!!!

 

[emr]

Im going to say the 900 is getting a bad rap , Due to driver error. With that much torque, and a bunch of drivers that have never even driven a stick before, get in a real truck and destroy it, well that's what it sounds like to me. Ive been pushing mine alittle and it is fine, also never heard of one going at the local units, and ive been asking. I dont even turn the front wheels on any vehicle without the vehicle in some sort of motion,wear and tear.it costs money and shortens the life of the vehicle. I always let all my auto's finish shifting before i move out, from U joints to tranny's and all moving parts, I say feel the truck U got to feel it, and then one wont be ruining it before its time is up! Randy

 

[CUCVFAN]

Agreed. They are good trucks, but when not driven properly, they can break things. Those trannies are stout, but not when they are overloaded. Never shift unless fully stopped to be safe.