Cummins and t-case doublers do they get along?

[jeep9867]

So i'm putting together some options for my M715 build coming this late spring summer. To give an idea of what i'm going for is to use my M715 boday on a first gen dodge cummins chasis and run 40 inch tires prolly mt/r's. Heres the dilemma gearing shouldnt be much of an issue with the 5 speed granny low but i'm also leaning towards an automatic for ease offroad but the first gear in the automatics is crap. My thought is to run a 203-205 doubler are these stout enough for the power and for towing??

[COcummins]

if you go with a 5spd, will it be the getrag or new venture tranny?

from my research the 203/205 doubler won't mate to the nv4500 without an input shaft adaptor. i'm opting for the "Black Box" & 205 for my build, it's like the klune v goliath only with an extra bearing race to support the shaft.

from what i've gathered, the 203/205 combo and the underdrive boxes should be fine as long as you don't have your reduction box in low range and your t-case in high range, this will result in way too much torque for the t-case input shaft.

[Mobcore911]

I think the doubler would hold up fine however I'd worry about even 1 tons when you're sending 4800+ ft lbs to them spinning 40" tires...

[COcummins]

that's why man made chromolly axle shafts

[jeep9867]

well for the 5 speed its looking like the getrag i know not the best but i figure i will run it till it quits, as for axle strengh it could be questionable but i'm looking to make it more of a road worthy truck rather than all out rock crawler other wise rocks or unimogs would go in. i want to still be able to do highway speeds at a low rpm...hence the low gearing options so i can keep around 4.10's or so

[COcummins]

i would recomend going with a little higher gearing if you're going to run 40's, i was running 37's with 3.54's and it wasn't bad on the street but the motor was working to turn those tires which was getting my egt's up there, i sure wouldn't have wanted to tow anything with this setup. with the numbers i was crunching, 4.88's and 42's would have brought me pretty close to 3.54's and 285/75r16's, so i would guess that 4.56's would work best for your setup, just my $.02 though.

[jeep9867]

if i'm towing i can just run 4th gear its direct drive and generates the less heat that way but i agree if i end up towing alot i will change. i thought of running smaller tires too but with the huge wheel wells the 37's may look small