Meritor Transfer Case Into M939 Series Trucks

440Duster

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Has anyone attempted swapping a different transfer case into the M939 series trucks, specifically one of the Meritor units? While I have not had ant issues with my M925A2 unit, there has been a few times when the need to reverse arises and it is inconvenient to go back to high range in order to do so. Do the Meritor units have the same issue? The Meritor website doesn't offer up much info. I am tempted to obtain one and investigate the concept. Thanks
 
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73m819

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The problem with the 939 transfer cases is not so much the transfer but the DRIVER, the military had YOUNG drivers who believe the only way to drive is to drive pedal to the metal, so they shift to reverse in low, not remembering that going into low also shifts the front engage, and floor it, all the sudden extra traction (torque) will break something, the military found it cheaper and easier just to put a data plate saying "DO NOT USE REVERSE IN LOW RANGE" then it was train these Honda driving kids how to drive a big truck.

If you drive a vehicle like you own it and have to pay the repair bill INSTEAD of you stole it or your dad bought it and pays the bills, the vehicle will have just the normal maintenance, on the other hand, You make for a good living for the people that fix vehicles that are driven like they are stolen or dad is footing the bill.
 

Scar59

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De-activate the front auto engage switch/feature that engages the from axle when transfer case is placed in low. Now the truck will only drive the rear axles in low. This releives a lot of stress on the t case. But as Ron states, you still need to drive it like you own it. Abuse it and you'll have to fix it.
 

Swamp Donkey

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What actually causes the T-case to break? Is it the internal pressure on the gear train that busts the bottom out or is it an external force like a lack bottom support on the outside? I understand a lead foot is a factor in the failure but what is the actual point of failure?
 

bluehorse

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M939 transfer case problems.

What actually causes the T-case to break? Is it the internal pressure on the gear train that busts the bottom out or is it an external force like a lack bottom support on the outside? I understand a lead foot is a factor in the failure but what is the actual point of failure?

I would like to know what breaks too. I'm wondering if a fix can be made for the transfer case to make it hold up to full throttle in reverse in low range? I had wondered if another bigger transfer case would fit without too much modification too?
 

simp5782

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I would like to know what breaks too. I'm wondering if a fix can be made for the transfer case to make it hold up to full throttle in reverse in low range? I had wondered if another bigger transfer case would fit without too much modification too?
You can use a T138 case.

Or

https://www.steelsoldiers.com/showthread.php?t=175976

But you will lose the overdrive. So you would want to get an OD transmission

Sent from my SM-G935P using Tapatalk
 

moparrob

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Your transfer case is probably fine, the issue is the mega low reverse gear that your transmission has. Reverse puts out a lot more torque than first gear does, and there goes your transfer case. Im following the transmission swap thread and curious to see how the reverse ratios differ and if that will be easier on the tcase.
 

simp5782

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Your transfer case is probably fine, the issue is the mega low reverse gear that your transmission has. Reverse puts out a lot more torque than first gear does, and there goes your transfer case. Im following the transmission swap thread and curious to see how the reverse ratios differ and if that will be easier on the tcase.
The issue with the transfer case is going to be the 450+ hp and 1350ft lbs from a big cam going thru it coupled with the CAT 7155. The transfer case is not going to hold together very long with the hauling I do with it. I use R1 which is 14.77 : 1 all day long when backing up heavy and the case is fine. But we are talking under 800ftlbs of torque. My R1 and F1 are the same ratio along with R2 and F4.

I am going to swap to the HEMTT case simply because the down low torque if I need it I don't want to have to worry about babying the T1138 case when I need the power or anything else. It should be something I don't have to worry about.
 

74M35A2

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MRAP case seems well built, and was behind a 400hp ISL, but from the little I understand is AWD, not selectable for rear/front output.

Allison M654CR first gear ratio is 4.xx, but reverse is 10.xx. In most automotive applications, reverse ratio is usually between first and second.
 

simp5782

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MRAP case seems well built, and was behind a 400hp ISL, but from the little I understand is AWD, not selectable for rear/front output.

Allison M654CR first gear ratio is 4.xx, but reverse is 10.xx. In most automotive applications, reverse ratio is usually between first and second.
Most if not all cases are direct drive or numerically higher high range or singlespeed. Relying on the newer Allison double overdrive transmissions

Sent from my SM-G935P using Tapatalk
 
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