M923A1 motor swap (transmission input)

[poorman4x4]

Have a chance to get a nice rebuilt Cummins 400 Big Cam III, im just wondering if the gearing/power combo will be affected if i kept the 654 allison, it being a five-speed I dont want to "run out of gear", and prompt higher RPM's. Hence the cummins 400 came in 915's with those cat transmissions and civilian trucks around 13-18 speeds. Any input or schooling is accepted!

 

[nridr124]

im wondering the same thing bc my 923 has a bad motor and fills the oil pan with water after replacing the head i thot was bad its still fillling up so im cutting my losses and i have a good 915 that ahs a brand new motor in it bud truck is bad so im scared that the automatic trany is too small and will just break stuff but im sick of not having any power and im not having the 16 speed out o the 920 its too big to put in the truck i beleave but i need more power out of the 923 . any ideas?

 

[Bighurt]

IF I was to do a swap I'd choose neither the 654 or the 750, and find something that has OD. IMO the CAT is out based solly on the fact it's a pain to find parts and work on. Plenty of people have suggested alternate tranny's for either engine in other threads. I'd personally like a roadranger in my M915A1, but an Auto in the M923 would make offroading a bit easier.

 

[poorman4x4]

I'm not scared about breaking the 654 Allison, just the gears is my dilemma. I know two things to be facts, my buddys have mud trucks 1. The first truck has a 700-750HP 12v cummins with a stock Allison 545 behind it ran two seasons no problems. 2. The second truck has a 07 Duramax with basically a CP3 pump and a computer with a 230HP tune, his Allison 545 lasted one season, our 654 Allison's in our 923's are bigger and our motors wether 250 or 400 will never make as much power as these engines will (in my setup) so i dont worry about breaking anything i just putt with my truck anyways my 250 is fine i just cant pass up this great deal on a sweet engine


thanks,
john

 

[poorman4x4]

thanks big hurt, OD would be great, any allisons bigger than 5 speeds are so huge though

 

[Bighurt]

Yeah I wasn't worried about breaking them...

 

[Csm Davis]

Okay I thought the 915 had a Allison in it but I think it will be to long to fit in the 939 trucks and I would go with the 400 no question as speed will not be a problem unless you want to run 70 or more.