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I had gone down this path when I had a M55A2 and a MK17 unit. I was to the point where I had all the numbers worked out to make it work with the sprag unit but I still was afraid to try it. But with a M939 series truck the t-case still worries me (weakness).
That said, as I recall, the numbers worked out that a 16.00 tire up front and 395/85R20's on the rear would make everything happy.
The MK axles are worth keeping. They have air lockers.
The other side of the coin would be to swap the front axle in the M939 series chassis to a front axle from a MK48 or a HEMTT. But that'd be a lot of fab work to make it happen. I'd love to take my SEMTT and swap in a MK48 front end and MK1* tandem set for the air lockers. Most likely I'll just find one more detroit locker axle and swap out the rears.
That said, as I recall, the numbers worked out that a 16.00 tire up front and 395/85R20's on the rear would make everything happy.
The MK axles are worth keeping. They have air lockers.
The other side of the coin would be to swap the front axle in the M939 series chassis to a front axle from a MK48 or a HEMTT. But that'd be a lot of fab work to make it happen. I'd love to take my SEMTT and swap in a MK48 front end and MK1* tandem set for the air lockers. Most likely I'll just find one more detroit locker axle and swap out the rears.