Will an 8.3 cummins create too much torque for the M35 driveline?

Title says it all. The 3208T deuce has been fun but I'm looking to build a truck with more power. The hills in Colorado are sizeable enough to make 500-600 ft lbs in this truck seem like a mouse motor. My truck would be a screaming flatland truck but unfortunately I've learned (the hard way) that I need more power and, on the tranny side, more splits.

I'm leaning towards the reputable and somewhat bomb-able Cummins 6CT 8.3 (mechanical). This truck will allow torque numbers into the low 1200's. My 13 speed will accomodate 1400 ft lb input.

I would love to put one of these into a deuce, but I'm concerned about strength of the driveline. Especially at the driveshaft speeds we see when wrapped up to 60MPH (my calculations is about 3200 rpm with 42" rubber), even the larger size (1550) ujoints will be about 400 ft lbs (see graph on page 5 of the below PDF):

http://www.pirate4x4.com/tech/billavista/Driveshafts/Spicer Driveshaft engineering data - IJ900-02[1].pdf

Any thoughts here? Should I sell my deuce and start over with a 5 ton, and single the rear? I think that would be a great way to go.

So many questions....

Best,
Bob

well, the way i see it is the driveline will only see as much torque as there is load. meaning, sending 1000ft-lbs down the driveline in an empty 13k# truck is a whole-lot more forgiving than a truck at 23k#. when the load or other force binds the driveline (heavy load on pavement, extreme offroad terrain, etc.), that's when ultimate torque is experienced and the driveline will eventually see all of the engine's torque - whether that be 330ft-lbs or 1000ft-lbs. another thing to remember, too, is that the deuce drivetrain is rated for 18.5k# offroad, or basically, the worst conditions imaginable.

so, this doesn't answer your question directly, but here's my point: it will depend how it's driven. if your deuce is often loaded heavy and accelerated hard, then maybe. full throttle in LL gear and L transfer and good traction may piss off something down-stream, but that could happen with a stock setup, too, and should be avoided.

the obvious weak-link IMO is the transmission - but you're replacing this. so, really you have the transfer and axle assemblies. it seems that few transfer failures are seen, so, likely the transfer is stout enough. driveshaft failures aren't too common either, because of the advantage of the double-reduction in the axles. then there's the axles themselves and the shafts.

i personally don't believe there are 'ratings' on any of these components.

i'd say out of anything, the shafts are most subject to breakage - we know a stock deuce can break axle shafts. the axle third member can deflect (under hi-hp mud boggers), so there are trusses available to strengthen the diff. and 16-spline replacement alloy shafts are relatively inexpensive.

if it were my truck, it'd be relatively empty a lot of it's life. so i'd repower with a 6CTA as you mentioned, or a DT466 (which is truely bomb-proof ). if i broke a shaft, i'd replace w/ an alloy. and if i broke that, well, i'd consider 5T's or 2" OEM shafts. rather, if you weren't hammering on it mercilessly and only give as much go-pedal as needed, i don't think you'll see catastrophic failure or excessive wear.

there's a lot of OTR trucks on the road today with engines that slightly exceed the torque ratings of the driveline (many trans have higher OD input ratings than in the lower gears); but driven smartly, everything survives just fine.

all my opinion, of course...

i say do it.

agreed the trans is the weak link my friend put a cat motor in his with 1200ft lb of torque first time he got it out and gave it full throttle on dry ground he twisted the input shaft off. durabilty is in the foot of the driver..i have friends of mine that will brake anything no matter what.i tell them a tennis ball will fix it.they look at me like i'm crazy then i put it under thier go pedal problem fixed

Travis and TM america - Thanks so much for your insight and feedback. I like the cummins motors and I'm pretty enthusiastic about the project.

I think I've found my next project, and the base is 5 ton. As much as I like the deuce platform, there's a lot more preferences for the 5 ton platform.

So, my 3208-powered deuce is in the classifieds.

Best
Bob

sounds like fun. though, in my opinion, a 5T is just about literally twice the truck as the deuce. so, a 6CTA might be an upgrade for the deuce, i think you'll be wanting some big cubes for 'upgrading' a 5T.

i'm thinking 14L Cummins, 3406, 8v92TTA, DD60 series... you know, big power-makers.

Buy an M809 and add a turbo, or ante up and buy an M939A2 and turn up the fuel. There are guys on this list who have done both with success in CO.

The air shift transfer case and lockouts are nice on a deuce or 939 series. If your building a serious truck think about going with a 939a2(engine,trans,airshift trans case,airbrakes too) The only downside to the 939 is if youre pulling a heavy load on soft ground you might have to go low range to get it moving.

Interesting - I wasn't sure if the airshift was only on the 920/930 series - guess so. Thanks for the heads up.

I'll learn more about what the current options are tonight, and go from there.

That said, I am pretty confident that the 8.3, this 13 speed tranny I have, and 5 ton mil axles are in my future. I'm not sure if I want to pair it with a commercial truck cap for creature comforts, or the vintage 5 ton cap (which would be pretty cool).

2.5 ton driveline will handle the power just fine as long as you dont get crazy with it (hauling heavy loads, rock crawling, etc) Those components are way under rated and will take a beating. If you are concerned you could always get new 16 spline shafts from Ouverson or RCV. The old shafts could be brittle depending on age and condition. If you are really concerned you can get 47 spline shafts and i believe 16 splines in 300M.

If your transmission is rated at 1400 foot pounds (again very conservatively and probably for a much heavier truck) you should be fine there too.

No reason to go off and put this engine and trans in a heavier larger truck, you are just putting yourself in the same situation again.

I have seen CTA motors make 700hp and over 2000 pound feet of torque with injectors, minor pump mods, upgraded turbos, and better intake and exhaust, so your numbers should be easily achievable by any good diesel shop who knows that motor. If you are in doubt call Scheid Diesel.

Hey guys,


Thanks again for the thoughts. If I stick with the deuce, I have enough spare shafts to make that not a concern (the easiest thing I could break would be an axle shaft!).

I see two options:

1. Put 8.3 and etc into the deuce body. Relocate xfer case, split braking circuit, maybe make a crew cab.
Pros:
-Already have the truck, with its myriad little upgrades
Cons:
-Still 2.5T drivetrain and axles. Not enough confidence in a single rear axle to single the rear end.
-Have to find a buyer for the oddball 3208 and tranny, unless I could sell it specifically as a deuce repower.

I'm really torn on what I should do..... I think you're right - if I put the 8.3 in a larger truck, I'm at a power/weight issue again. But, I consider option #2:

Option #2:
Body and frame on Option #2:
8.3 into a new frame (technically, the frame it's already in, along with radiator intercooler etc).
5 ton cab, hood and fenders (longer sheetmetal fits the engine better)
Possibly crew cab, and shorten the bed (or fabricate dropsides at the same time?).

Drivetrain Brakes/Axles on Option #2:
I definitely want to split the braking circuit.
I do have the complete air-over-hydraulic brake setup from a COE Hino. I could use all or part of this in a split circuit juice breaks setup
-And-
Run 5 ton M5x or M8xx series axles, possibly with air conversion (I have/can get the parts, even maxis on the rear)
Run either the old or a M900 series tcase with the air disco

And brakes are either juice or air.

Option #2 Pros and cons:
Pros:
- New frame
- Less BS trying to get the 8.3 and 13 speed in place
- Engine and accessories are already snug in that frame
- Get to sell the deuce complete
- 5T axles, singled rear
- Could possibly put together air brakes for everything.
- Already have the 14x20 tires out back I could use

Cons:
- Time, alot of time
- The unknown (truly, I don't know what I don't know about this platform, especially the brakes)



Thoughts? Should I put a modern truck cap on the 5 ton, or could I use 5 ton sheetmetal up front, and a modern cab behind it?

I have a line on most of these parts, and have all of the big daddy fab tools (frame driller etc) to help with the conversion.


Either of these would allow me to keep the GVW under 15k, and if I kept the majority of the cap (and title) military and vintage, I could keep collector tags and avoid the every-year emissions hassle with newer trucks. ...

Tough decisions.

I'm just super torn. I am fairly sure that I could build the 5 ton 4x4 truck for an amount within my budget - I'm just wondering if it's going to kill me on the time and unknown detail aspect.

Best
Bob

In reviewing how much time is available....

I think now that my play will be as follows:

Reutilize my existing truck.

Brakes:
Juice brakes. Still air over hydraulic, split the circuit.
Option 1: Maybe use only air - maybe use the stock M/C for the front, and then put an additional airpack on for the rear end
Option 2: .... or perhaps just convert to an entirely new pedal. to entirely new civvy style airpacks.

Relocate xfer case back, run new drivelines. I might have to clock the tcase to accomodate the increased depth and girth of the tranny.

Keep your eyes peeled for a cheap-ish 3208T powerpack and radiator made to fit the deuce.

Thanks everyone for the brainstorming.

Ok guys, back to the drawing board.

Found another platform (c8000 cabover truck) with the 8.3 already in it, and air brakes. I'll put my 13 speed and a military tcase behind it. Military 5 ton Cap.

Axles will be 5 ton units (single screw rear), converted to S-cam brakes (already have the parts).

Big project, but my only deadline is finish by hunting season in September.

take lots of pictures!!!

I'll definitely put together a flickr account, and I'll post the address when I get started, which will be after ski season here in Colorado. :thumbsup:

What ever happened to this build/project?

Flat Black said:

What ever happened to this build/project?

Click to expand...

I just found this post. Flat Black, if you're still on here, here's the answer!

I built the truck. It is a hoot to drive, and scoots.

M35A2 cab
M809 sheetmetal fore of the cab, sourced from a member here. Also, airfilter and grille.
C8000 Ford frame
Ross power steering
70's Ford F600 rear leafs
Cummins 8.3 6CTA
RTOO-14613 transmission
Deuce t-case
M54 axles, converted to airbrakes


This build was mostly done in 2011, and I spent some time in the past 2 years to finish the nagging aesthetic issues with the body and also get the 13 speed to shift correctly. It's finally to a place where I'd consider it "done".

It *hums* now, and is basically a military looking restomod. Purists may decry some aspects, but it looks great and is mechanically very sound.

Oh, I still have that Braden winch and also a 12 foot plow I'd like to put on some day, along with all of the requisite hydraulics. But, no rush!

Trango said:

I just found this post. Flat Black, if you're still on here, here's the answer!

I built the truck. It is a hoot to drive, and scoots.

M35A2 cab
M809 sheetmetal fore of the cab, sourced from a member here. Also, airfilter and grille.
C8000 Ford frame
Ross power steering
70's Ford F600 rear leafs
Cummins 8.3 6CTA
RTOO-14613 transmission
Deuce t-case
M54 axles, converted to airbrakes


This build was mostly done in 2011, and I spent some time in the past 2 years to finish the nagging aesthetic issues with the body and also get the 13 speed to shift correctly. It's finally to a place where I'd consider it "done".

It *hums* now, and is basically a military looking restomod. Purists may decry some aspects, but it looks great and is mechanically very sound.

Click to expand...

Perfect running 8.3L from my 5 ton listed in classified if anybody really wants to do this. I've seen them in M35's before.

Any photos of a converted 8.3 in a duece?