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Efficient transfer cases in 2WD

real_psyence

Member
Joined
Feb 1, 2022
Member Number
4764
Messages
7
Alright so hear me out. Trying to build a new tow rig with a Cummins to replace my D250 that got clobbered by a tree this past winter.
The D250 has the D70 rear, open diff, and got stuck on soft shoulders more than I liked.
I want to have the option to have 4WD on the new rig, which will have an LSD in the rear.
Thing is, the D250 got 22mpg and I know that would only go down if I'm driving the fronts all the time. Plan to use locking front hubs so in 2WD the front driveshafts will be static.
So I'm looking for a transfer case:
  • 2HI is a must, will be in 2WD probably 75% of the time (towing, driving in normal conditions)
  • 4LO is a must, getting out of places, deep snow, etc.

Nice to haves:
  • 4HI (aka AWD mode, snow, poor traction)
  • LSD center diff - see above
  • manual shifting, I can do electronics but prefer not to

I've found a couple candidates:
LT230 w/ Ashcroft ATB & 2WD kit
VF4** (VF4B might be able to be made selectable 2/4, else VF4AM if I figure out electronics)
NP242 but open center diff

But what I don't know is which ones disconnect 4WD on the primary shaft - for example, the NP205 in 2WD is still turning the gears and disconnects on the front output shaft.
I want 2WD to be passthrough - no gears or chains spinning when not needed.
I think the Toyota cases do this, not sure about the LT230 or NP242.

Anyone know? Source for power diagrams on random tcases?
 
well, i'll say it again. add a full locker to what you have now or a limited slip if you want, and get a winch for it.

you are going to lose a good bit due to the added weight and resistance of going 4wd, even if you keep a low drag t-case and freewheeling hubs.

what little drag you get from spinning the chain with the front output disconnected is going to be inconsequential because you are already going to be moving enough of the train to keep the main shaft lubricated.

chain drives are lower drag than gear drive, which is part of why so many more of them were made during the fuel efficient era
 
Vf4 in a fullsize diesel is retarded

Do you really need awd? Most get by just fine with regular 4hi all winter.

Also, it's not a fucking 1.3L, a 6bt is not going to significantly use more fuel spinning a few gears that are barely bigger than its timing gear set :laughing:

Spending extra money to over complicate a build chasing a mpg number almost never pencils out. Either accept loosing a bit of fuel mileage going to 4wd, or accept the limits of 2wd.
 
Ran a w250 for a while. On 33" tires. It had no trouble getting 22-23 mpg, even running 85mph highways.
 
You have 2 variant drive systems, gear and counter shaft and planetary, both have residule friction and drag in 2wd.

Unless youre going to wholely design a new drive system those are your options.

Youre nit picking tcases based on drive options a d not paying any attention to compatability or strength. Youre going to gut everyone of those with a trailer and mild power.
 
"I want to spend 1000s to save 100s" is all I read in the first post.

My dads 96 7.3 5 speed 4x4 dually got 22+ mpg when it was newer. No idea now. Driving style dictates a lot
 
Some good points being made but also a bunch of assumptions.
posford said:
"I want to spend 1000s to save 100s" is all I read in the first post.
Click to expand...
I'm not taking a W250 and trying to swap out a functioning tcase for a more efficient one. Right now I have a 2WD rig that got totalled by a tree falling on it. It still runs and drives and I might add a locker to it, but it's still 2WD, the door doesn't close, it was pretty rough to begin with.
I liked the engine, have another 6BT, want to build a new 4WD rig around it and don't want to shoot myself in the foot adding a bunch of drag to it.
MPG for me is only partially about $$$ - the bigger advantage is how often I have to stop on a long trip, especially when I'm pulling an awkward trailer.

Provience said:
well, i'll say it again. add a full locker to what you have now or a limited slip if you want, and get a winch for it.

you are going to lose a good bit due to the added weight and resistance of going 4wd, even if you keep a low drag t-case and freewheeling hubs.

what little drag you get from spinning the chain with the front output disconnected is going to be inconsequential because you are already going to be moving enough of the train to keep the main shaft lubricated.

chain drives are lower drag than gear drive, which is part of why so many more of them were made during the fuel efficient era
Click to expand...
Good points and I was headed down this route (locker + winch) before a tree fell on it.
But 2WD w/ a locker is good for soft shoulders, not so much for snow.
Thanks for the bit about chain drives - that's what I had been guessing, a lot of them also seem to disconnect on the input shaft.

YotaAtieToo said:
Vf4 in a fullsize diesel is retarded

Do you really need awd? Most get by just fine with regular 4hi all winter.
Click to expand...
Yeah, that's the weakest one I was looking at for sure, there's a newer similar one - JF3A or something that came in Sequoias apparently but I don't know much about it.
AWD is a nice to have not a hard requirement.

total newb said:
Youre nit picking tcases based on drive options a d not paying any attention to compatability or strength. Youre going to gut everyone of those with a trailer and mild power.
Click to expand...
True - I'm trying to see what's out there to see if I can have my cake and eat it too. Gut them as in break a chain or snap the input splines off? The NP242 I was thinking of is the HD one or the one from the H1 - both have wider chains than the J.
Maybe a better way to put this is which tcases give me the option to run 4WD while still behaving the most like a simple/strong driveshaft in 2WD.

The easiest options are probably a NV273 or whatever came in the recent rams or, for ease of implementation with a random trans and chassis, something divorced like the NP205.

I never said this is going in the D250 - plan is to keep that as is, as a salvage title backup truck, and I have an AWD wagon for a daily/snow car, this is me trying to figure out what driveline to build an all-purpose tow-capable vehicle around.
 
Since i have a W250 and several D250s....

  • the 4wd cummins truck is ~5" taller than a 2wd; stock
  • 2wd with a locker has been great for me; something i can drive year-round
  • the ride of the 2wd is much better than the 4wd

That said, with auto trans and driver-drop diff, a np242 swap should be cake. Most are 23 spline. Theres a number of different rear output styles though; i.e. skip past the early XJ variant (small).
 
total newb said:
post #1, line #2.
Click to expand...
I wrote replace, not modify - what are you saying?

Still want to know how you see these cases failing with a trailer attached - do the input shafts twist up or just the chain if I'm trying to tow in 4hi?
 
You wrote that you are building a new tow rig with a cummins, to replace your detroyed one.

The new rig will have a cummins.
Cummins make torque not rpm.
High load breaks shit.
Trailer adds load to your high torque motor.
You talking about adding toyota/rover/jeep tcases to a high torque, high load drive platform.

Youll be lucky if you just bust the front output off those pos because then you can keep driving on rwd for a bit. But outputs and planetary failures are in the future of all those cases.

You completely fail to recognise the distinction of your "requirements" to reality. No existing tcase doesnt spin the counter gear or chain through drag, friction or physical contact.

Youre wanting "awd" high, have you ever driven in snow wich a locked 4wd? I do 30mi a day in the winter time with a 205. The only time you notice is tight turns in parking lots.


but you do you and some people have to learn the hard way. What ever pos you buy, get 2 and keep it handy.
 
I do lots of snow driving in the winter, 4runner, F150 and F550 pulling over 20k lbs, as mentioned, 4 hi works fine and is only noticeable when turning full lock. On all of them I will pop back and forth from 2 to 4 on the fly as needed. I was semi curious about swapping an awd tcase into the 4runner when one popped up locally, but when I found it wasn't bolt in, I lost interest :laughing:
 
real_psyence said:
I'm not taking a W250 and trying to swap out a functioning tcase for a more efficient one. Right now I have a 2WD rig that got totalled by a tree falling on it. It still runs and drives and I might add a locker to it, but it's still 2WD, the door doesn't close, it was pretty rough to begin with.
I liked the engine, have another 6BT, want to build a new 4WD rig around it and don't want to shoot myself in the foot adding a bunch of drag to it.
MPG for me is only partially about $$$ - the bigger advantage is how often I have to stop on a long trip, especially when I'm pulling an awkward trailer.
Click to expand...
Neat. Buying an obscure transfer case and adapters is dumb. Buy a 4x4 trans and transfer case and move on with your life
 
My next tow rig build will be a 96 ppump 6bt. Zf6 with nv271 Ford super duty 3.42 axles elocker rear and a milder tire in the 34" range

Lower rpms is the biggest thing, then drag

From there I'll spend a little money on turbo/ pump/ injector to make more power/ efficient to roll over the little hills in 6th
 
Projectjunkie said:
My next tow rig build will be a 96 ppump 6bt. Zf6 with nv271 Ford super duty 3.42 axles elocker rear and a milder tire in the 34" range

Lower rpms is the biggest thing, then drag

From there I'll spend a little money on turbo/ pump/ injector to make more power/ efficient to roll over the little hills in 6th
Click to expand...
3.42?
 
Yeah 3.31s


He hasn't mentioned tranny, so if this isn't a manual or full lockup auto with overdrive, this is all mental masturbation



Rpms is biggest factor on cummins
 
Projectjunkie said:
Yeah 3.31s


He hasn't mentioned tranny, so if this isn't a manual or full lockup auto with overdrive, this is all mental masturbation



Rpms is biggest factor on cummins
Click to expand...
I don't think anybody has even thought of swapping a non lock up no. Od trans into anything on the road for at least 40 years :flipoff2:
 
Projectjunkie said:
My next tow rig build will be a 96 ppump 6bt. Zf6 with nv271 Ford super duty 3.42 axles elocker rear and a milder tire in the 34" range

Lower rpms is the biggest thing, then drag

From there I'll spend a little money on turbo/ pump/ injector to make more power/ efficient to roll over the little hills in 6th
Click to expand...
This is the closest to what I had in mind - had a donor truck with a blown 6.0 lined up then the guy backed out saying he was gonna try and fix the motor. Hard to find complete donor trucks for reasonable money, plus the hassle of parting out the remainder, which led me down the path of piecing stuff together. 6-speed, low ratio axles.

For the initial intent of this thread, I misunderstood the LT230 diagram I had looked at - thought it was a pass-through in 2WD, I was looking at the driven countershaft (with diff) - so that's out on merit.

Looking like the NV271 is my best bet, maybe I can get away with the NV242HD (maybe with the 6-gear planetary from the H1 case?)
 
real_psyence said:
This is the closest to what I had in mind - had a donor truck with a blown 6.0 lined up then the guy backed out saying he was gonna try and fix the motor. Hard to find complete donor trucks for reasonable money, plus the hassle of parting out the remainder, which led me down the path of piecing stuff together. 6-speed, low ratio axles.

For the initial intent of this thread, I misunderstood the LT230 diagram I had looked at - thought it was a pass-through in 2WD, I was looking at the driven countershaft (with diff) - so that's out on merit.

Looking like the NV271 is my best bet, maybe I can get away with the NV242HD (maybe with the 6-gear planetary from the H1 case?)
Click to expand...
Don't reinvent the wheel, find a manual tranny that will bolt to the cummins, and get one with a t case attached and rock out

The less custom pieces on a tow rig, the better
 
1. Manual hubs might get you 1/4 mpg. Much less hubs and awd is idiotic.

2. None of the awd cases you mention have the strength to go behind a 6BT.

3. LT230? Really? Not strong enough and offset rear output. Do you plan on swapping the rear axle?

Sounds like you want to step over hundred dollar bills to pick up pennies
 
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Great mental exercise, but I think the complexity will far outweigh the .04 mpg increase you might see.
 
Just to throw op a bone, I had a 2wd 1st gen 12v/5spd. I never drove it on the highway enough to see what mpg was, but I wonder what that engine and transmission would do for fuel mileage in a different platform. If you have 2 engines, maybe throw one in a regular 4wd truck and save the fuel mileage chase for a different project. I like the 12v swapped full-size cars personally :laughing:
 
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