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You could also look into dual speed differentials - Rockwell makes diff-carriers with planetary reducers for an extra low, if you're lucky you can just drop them in. This way you can set the ring/pinion and tire size for highway speeds in your high gears and you still get another level of low when you want to crawl. You'd also get the benefit of the last reduction being done as close to the wheels as possible reducing the load on the rest of your drive-train (next most expensive step would be to get planetary hub axles).
I also second the idea of a 5.9L Cummins 6BT and perhaps an Allison auto, or another more modern manual transmission that can get you more gears. The 6BT is adaptable to any transmission so the sky is the limit (well actually, space and cost is your practical limit).
I'd encourage you to check that torque input for the engine output in your application and do a full work up of the drive-train ratings (all the manufacturer documents can be found). In the XM1027 Crew Cab CUCV build I'm doing, the 350HP Cummins 6BT I'm building will get me a peak torque of about 1060ft-lbs of torque (@1750RPM). You want to make sure whatever you do with your modifications you won't have to do again due to catastrophic failure (better to spend $500 extra on a more durable transmission than buy two $1200 transmissions), or injure/kill anyone - as a vehicle modifier you take full responsibility for the outcome. Research the input torque ratings of all of your components, and find out what gearing combinations will get you into trouble and where your weak points are, look at duty cycles and vehicle loads in addition to road speeds - it would be good practice if you're trying to get into the automotive engineering world, and if nothing else it would be a good academic exercise.
For all the modification bashing that goes on for those who wish to keep it stupid simple (KISS), there is something to be said for advancing your parts list about 40 years up for spares availabili
Rockwell made a series of Double Reduction 2 Speed Differentials in the 1960's. I've rebuilt quite a few of them. The only problem is they are much heavier and are not top loaders like ours are. Plus you would need the larger axle housing as the smallest was installed in a 5 ton truck. Even if you could find one, it would probably need rebuilding, and the cost for just the main shaft bearings was $500.00 each ! That was back in the early 1980's . One plus was that the high reduction was 6:1 just like our deuces and the low reduction was 8:1. So you could use a high reving engine like a 350 Chevy for highway speeds and still have the low end power for messing around in the woods and muck. Of course if you went that route you eliminate the whole reason for having a Multifuel engine or any diesel in a 6X6 truck.
A quick google search pulled up a couple results for double reduction 2 speed differentials, so it might be possible. This is getting to the point though where it might be easier to put a deuce cab on a commercial pickup, or take an unrunning deuce and put in a full powerplant and drive system from a pickup in itYou could also look into dual speed differentials - Rockwell makes diff-carriers with planetary reducers for an extra low, if you're lucky you can just drop them in. This way you can set the ring/pinion and tire size for highway speeds in your high gears and you still get another level of low when you want to crawl. You'd also get the benefit of the last reduction being done as close to the wheels as possible reducing the load on the rest of your drive-train (next most expensive step would be to get planetary hub axles).
I also second the idea of a 5.9L Cummins 6BT and perhaps an Allison auto, or another more modern manual transmission that can get you more gears. The 6BT is adaptable to any transmission so the sky is the limit (well actually, space and cost is your practical limit).
I'd encourage you to check that torque input for the engine output in your application and do a full work up of the drive-train ratings (all the manufacturer documents can be found). In the XM1027 Crew Cab CUCV build I'm doing, the 350HP Cummins 6BT I'm building will get me a peak torque of about 1060ft-lbs of torque (@1750RPM). You want to make sure whatever you do with your modifications you won't have to do again due to catastrophic failure (better to spend $500 extra on a more durable transmission than buy two $1200 transmissions), or injure/kill anyone - as a vehicle modifier you take full responsibility for the outcome. Research the input torque ratings of all of your components, and find out what gearing combinations will get you into trouble and where your weak points are, look at duty cycles and vehicle loads in addition to road speeds - it would be good practice if you're trying to get into the automotive engineering world, and if nothing else it would be a good academic exercise
For all the modification bashing that goes on for those who wish to keep it stupid simple (KISS), there is something to be said for advancing your parts list about 40 years up for spares availabiliView attachment 526953
Rockwell made a series of Double Reduction 2 Speed Differentials in the 1960's. I've rebuilt quite a few of them. The only problem is they are much heavier and are not top loaders like ours are. Plus you would need the larger axle housing as the smallest was installed in a 5 ton truck. Even if you could find one, it would probably need rebuilding, and the cost for just the main shaft bearings was $500.00 each ! That was back in the early 1980's . One plus was that the high reduction was 6:1 just like our deuces and the low reduction was 8:1. So you could use a high reving engine like a 350 Chevy for highway speeds and still have the low end power for messing around in the woods and muck. Of course if you went that route you eliminate the whole reason for having a Multifuel engine or any diesel in a 6X6 truck.
I totally agree ! Nothing beats a good drivers seat ! After most trips now I can barely walk for about 1/2 hour afterwards.
