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Old 07-18-2017, 06:18 PM   #1 (permalink)
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Dodge Cummins 2WD/4WD mechanical efficiency questions...

Good day, all!

Our Dakota Diesel + 5th Wheel streamliner plans have been expanded a bit; we're now likely to be full-timing, so the trailer got a foot wider and a hair taller, and tankage and gear requirements for full-time living took the weight past what I am willing to relegate to the Dakota/OM617 combo.

Therefore....

We are in the market for a 1996-98 5.9L 12v Diesel 5-spd. extended cab Dodge Ram 2500, as it has the capacity we would prefer with the fuel economy we want. I occasionally find one out there in 2WD, and there are loads of them available in 4WD. On our recent trip from South Florida to Idaho and back, I had a couple opportunities to ponder whether 4WD is really as unnecessary as I have always thought it to be. I also will be installing a Torsen differential in the Sonoma as soon as practical....

I would like experiences and opinions regarding the 2WD/4WD question, and the best setup for 4WD efficiency.

My thought is that if we are running the 4WD truck in 2WD most of the time, with manual front hub locks, we will be as close as we can get to the drivetrain efficiency of the 2WD drivetrain, while retaining 4H and 4L for getting out of problems.

I am curious about how much mileage is going to be lost in this sort of setup.

The other, more laborious (to use), option is to install a recovery winch on the 2WD truck and hope there is something appropriate to tie out to when needed. This doesn't help out with sketchy roads, but will get us out of an emergency.

Thoughts?

ThomCat316

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Old 07-18-2017, 06:33 PM   #2 (permalink)
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Remember that a 2WD setup is really a 1WD setup and a 4WD setup is normally a 1 x rear + 1 x front drive, without something like a thorsen lsd.

My old Celica with the permanent Toyota AWD system didn't suck fuel at all for some reason.

It really just depends on how efficient the system is and things like optimising the lubrication can make a big difference.

Most 4WD owners of the older systems are disappointed with the off-road capabilities and go to install things like diff-lockers to reach 3WD status for their vehicles.

So if you have an idea about installing a thorsen on the rear, I'd really try that first and see how good it is. I've seen a lot of VW kombi's in stupid places with big tyres and wheels so now I take the '4WD Only' signs with a grain of salt.
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Old 07-18-2017, 09:27 PM   #3 (permalink)
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little jona - '91 Dodge D 250 first gen cummins LE
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Bigest question is are you going to be in snow country during winter?
Then 4x4 is good for DD. For interstate towing chains are required for towing. 2or 4wd don't mater.
Installing the free spin kit, like Skyking did ,will help with rolling resistance 5%@70 but dose nothing for the "tall truck" aero penalties 95% @70 (he saw a cupola mpg improvement) .. if this will be a highway only setup(4x4 is for snow/muck only) then consider lowering. You can maintain your tow capacity with airbags /solid /overload springs . Drop it as low as possible. With my 91 D250 1wd eaves a lot to be desired on ice. Underway it sticks to the ice vary well, geting moving now thats the sore spot, Ive had to put on chains to get out of a flat(albeit 6" of crusty frozen snow) parking spot.
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Old 07-19-2017, 12:02 AM   #4 (permalink)
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I'd certainly avoid the automatic trannys, so the 5-speed is a good choice.

2 wheel vs 4 wheel is a trade-off. My truck with low rolling resistance tires (narrow width) designed for the highway can't drive on flat, wet grass in 4WD, let alone 2WD. With higher rolling resistance tires designed for offroad use, I can drive around in 2WD on flat grass, and more difficult terrain in 4WD.

The trade-off is more weight/cost/complexity vs lower fuel economy due to running tires with more off-road traction.
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Old 07-19-2017, 12:32 AM   #5 (permalink)
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We did an insane 10 mile jeep trail and only put it in 4wd twice as a precaution... that was downhill. Up hill we wouldn't have made it in 4wd. The uphill road was 20 miles and didn't really ever need 4wd either but it was bone dry. That was our stock suspension 2004 long bed crew cab with stock 2015 Ram highway 33" tires on factory 18" wheels. We were about dying on both roads with 75 psi in all the tires and 50 psi in the rear airbags. At the bottom of the shortcut was a sign that said basically Jeeps only. Little late on that warning, had we broken something up there it would have had to be fixed in place as no recovery truck could have gotten it out. In the end it was a blast because nothing bad did happen and it was beautiful.
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Old 07-19-2017, 03:04 PM   #6 (permalink)
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I have lived in snow country (Wisconsin and the UP) for all but 4 years of my life. I have never owned, or even needed, four wheel drive. My truck does have the GMC locking rear end.

I do carry tire chains in my truck, and expect to use them once every year or two. It's not a big problem because it only takes 2 or 3 minutes to put them on.
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Old 07-19-2017, 05:17 PM   #7 (permalink)
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the option of 2wd low is enough for me to have a 4wd and tow larger trailers.
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Old 07-20-2017, 12:48 PM   #8 (permalink)
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So, it looks like the General Consensus (SIR!) is that a 2WD with a Torsen rear carrier will be the best overall answer (simple, efficient, low maintenance, positive 2WD), as we are not trail-crawling enthusiasts, and plan on staying out of the snow and ice.

Does this sound good considering the following rig?

Dodge 2500 Cummins 12V ext cab, bed replaced with skirted flatbed, low profile 5th wheel hitch.
Not planning on lowering, as there will be boondocking and really bad roads in the future, but will be belly-panning and otherwise enhancing the truck.
32ft. ultralight (3-4K lb.) streamliner trailer, built to the truck for aero.

One other question for those who have done this - if we aren't carrying spare off-road specific rear wheels, would cable-type chains be a good substitute in time of need?
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Old 07-20-2017, 03:52 PM   #9 (permalink)
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Cable chains are good for traction on hard pack snow and ice, for deeper snow and slush link chains are better. The link chains will last longer as well but will ride rougher and mean lower speeds. If it's really bad out and you are towing you wouldn't want to go faster with cable chains anyway. I spend weeks if not months on end delivering mail in an old 2wd mail truck. We use link style hardened chains and they need repair every week even driving only 20 miles a day. We are at the disadvantage of having to run them sometimes on perfectly clear and dry paved roads because around the corner we will be back in the drifts.
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Old 07-20-2017, 03:57 PM   #10 (permalink)
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cable chains will work in sand too.
Sounds a lot like my 96 Maybe we should talk a deal. It is an auto but I know of a 5 speed kit nearby.
IT has a custom air ride 5th wheel system in it too.

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