4WD transfer case in a 2WD vehicle for low ratio?

[stillsearching]

I had kind of a dumbsmart idea while responding in another thread... maybe not 100% right on since this is ecomodder not performance modder but its for an mpg-aware hot rod and there's lots of smart people here so here goes.. it's for an eventually proposed hot rod type project i'd like to do I wanted it to get good mileage when on the highway (the super low RPM big engine thread is related to this, i'd like to get 30mpg with 500cid) but be capable of accelerating fast on the weekend drag strip. And to do it without an excessive budget. (cheapness is more expensive then absolute weight savings I mean)

So I was thinking, why not use one of those 4x4 transfer cases behind the transmission? Turn the 2.29 highway gears (even higher in overdrive) into a 4.56 or lower when in "4Lo", except there's no 4WD going on, just the range selection, unless there's some danger having a nonconnected part of the shaft just capped off by a metal tube or something covering it. It would act like a two speed axle. Maybe even parts could be stripped to use just the range selector ignoring the transfer case function entirely and saving more weight? (having never torn one apart i've no clue how hard it would be to stick it inline and fabricate up a lever to actuate it, or whether it's normally integrated into the case but I thought some 70's transfer case modifications used "double range boxes" so I assume some of them have a detachable unit you could use in this fashion)

Sure you can do the same thing with a modern six speed transmission, like the 6L80 going from 4.03:1 first gears to 0.67 overdrive or something about that. Price one out sometime. :P

This is a little clunky, adds weight, but all I would care is that it works. Is there any reason it wouldn't? Could maybe a 4x4'er more familiar with how the transfer cases even hook up under there comment on the feasibility of this?

PS - there's a secondary mileage related issue in that this could also solve my tow vehicle problem. Stick this in the Caprice, keep the 2.29 highway ratio, yet use it for 7000lbs towing unless there's a reason it cant run highway speeds in "4lo" to just one axle.

[drmiller100]

it could work. you want to run straight for mpg - so that would be "high range".

Low range for more acceleration.

Also available is the gear vendors overdrive unit. they can be found used.

[thomason2wheels]

Now that is really slick idea! Never does a day go by since signing on here that i dont read something that makes me look at things from a fresh viewpoint...god i love this place!

[shovel]

You could gut a transfer case, so that the chain and front output shaft aren't there... if you're ambitious you could cut the whole bottom of the case off and fabricate a cover, then make up the difference in gear ratios by using a numerically low rear axle ratio. You could "clock" the transfer case up so lubricant still makes its way to the gears..

Transfer cases common to Chevy and Jeep vehicles like NP231, etc are 2.72:1 in low range.

An important consideration is that transfer cases aren't intended to be shifted between ranges while driving, there is no clutch between them and the transmission so even when you are in neutral on a manual transmission, there's the (gear-enhanced) inertia of the transmission's spinning parts to fight against with no synchromesh.

Old Monteros have 1.91:1 low range, which might be more fit for this sort of idea. Several Borg-Warner transfer cases (often found in Fords) are 2.48:1 . Nissan 4x4's are generally 2.59:1 and I think there was one 2.02:1 but I don't recall which model. NP203 and NP205 transfer cases, on some Chevy trucks are 2.01:1 and 1.96:1 respectively. There are several aftermarket transfer cases (Atlas,Marlin for example) but they're $$$ and also several aftermarket add-on overdrive units intended for highway MPG on old, non-overdrive vehicles - also $$$

In the off-road world, some guys have frankensteined up multiple transmissions, or multiple transfer cases stacked end to end to get a broader spread of ratios.. but anything like that is adding complexity and weight and rotating mass and friction... none of those sound like a good idea for efficiency.

I think the basic concept starts off with merit, but there's probably no cost-effective measure for simply using a transfer case in this way. My opinion is the juice won't be worth the squeeze, and there'd be a lot of squeeze just to get there.

Early Colt/Champ models (1980ish) had a 2 range transaxle, so you had 4 forward gears and 1 reverse gear, but a "power" and "econ" stick next to that which allowed the driver to select something like 10% different ratios, remember this was on a carbureted 1.5 or 1.6L engine so there wasn't a ton of engine torque available to offer a vast difference between the high and lower ratio. I left mine in "power" mode all the time unless I was exclusively going to be on the highway.

These user-adjustable controls of course are vanishing from all cars because the engineering attitude is "make the most features available to the most users" - i.e. there are actually (MANY) 4x4 owners who don't know what that extra lever is for, and while the best option for mankind's viability on this planet would be to neuter those people so they don't pollute the future with their inobservant, oblivious DNA, that doesn't sell cars so the manufacturers replaced the lever with a button... and then with full-time AWD or one-size-fits-all software voodoo that is neither as fuel efficient nor rugged as conventional 4x4 with manual hubs on the older generations, but lets ignorant operators reap the benefits without undertaking any effort to understand the 2-ton tool they're piloting. Idiot proofing is nothing more than a race to bigger idiots, but that's another topic entirely. The point here as it relates to this thread is that the economy-minded underdrive DID exist once on OEM cars, and then became that "OD OFF" switch on auto levers, and is approaching extinction today. If you want to put one in a modern car, it'll be some Marco Polo action for sure!

[oil pan 4]

Toyota guys have been doing this since the 1980s.
Their transfe cases just happen to have the same bolt pattern on both ends and for some reason they are stackable.
They run 2 low ranges. Its the cheapest way to build a rock crawer that you can still drive on the highway just by changing tires.

[MGB=MPG]

ya gotta be pretty slick to shift out of low range on the fly ..
i always like small engines and lots gears .. Not available any more .. not because they can not build them its because the buying public wont buy them ..

.......think about 2 speed air operated or electric axles , think about 3 speed auxiliary transmissions

nothing quite like 2 sticks and 15 forward gears

[stillsearching]

Originally Posted by thomason2wheels

Now that is really slick idea! Never does a day go by since signing on here that i dont read something that makes me look at things from a fresh viewpoint...god i love this place!

So hit the thanks so I get social points. If I do it you'll hear about it here.

Originally Posted by shovel

You could gut a transfer case, so that the chain and front output shaft aren't there...

I could but was hoping for even simpler - as far as I can tell the NP203 rangebox is divorced from the transfer case, that's why they can bolt it to another box, often an NP205 (which isn't divorced but I think is a better 4x4 box or something) although other combinations exist. Except i'm not a 4x4 expert - only viewing from afar. Although I think the box is iron, at least I dont have the weight of an unused transfer case on top of it, it's just the range box. Unless you know of another transfer case with a divorced range box...

Sample ORD Doubler 4:1 Dual Transfer Case, NP205-NP203 - Fullsize 4x4 Parts - if i'm not mistaken the NP203 rangebox is on the right going to your transmission, whereas the NP205 transfer case (with it's own built in rangebox) is on the left. What I want to do is that minus the rear transfer case really. The front should bolt to common transmissions including the TH400, TH700-R4, and various manual boxes, sometimes with adapters. What i'm not sure about is what the output shaft is and how hard it would be to have that go to a U-joint, since it normally expects to bolt to the transfer case piece behind it. Too much money spent on custom machining and it sorta kills the money saving aspect.

But as mentioned, would there be any other problems with oiling and anything else that anyone can figure out... or would the box overheat left in low range or some other problem? I was never sure whether the warnings "dont drive over 35mph" for instance were because most people are stupid and dont realize that thats top speed in 5th now for instance. I don't want to break down by the side of the road after thinking i've been all clever. Afterall the 4x4 crowd leave these in "hi" on the road and "lo" is for lower speed crawling. My shaft speeds shouldnt be MUCH different with the tall axles but who knows.

The NP203 is like a 1.96:1 range - which is just about right to go between ultra steep highway gears for a V8 and nice low 10k trailering gears in low range. I have no plan to shift "on the go", i'd go into "lo" range when entering bad hills and probably not exceed 55mph in overdrive. Heck depending on the speed it might never come out of Lo when towing heavy stuff at all. Under light loads and normal use it'd use the high range.

Another discussion - NP203/205 Doubler Articles and Links

Note another possibility is I saw once someone made an adapter to hook the rear of a TH400 into the front of another TH400, making the rear trans like a 3 speed auxillary transmission itself, but one you actually could shift on the go, typically converted to a manual valve body. It's possible i'd consider that as well but I don't like how the slush trannies suck power so considered straight gears more efficient.

Originally Posted by oil pan 4

Toyota guys have been doing this since the 1980s.
Their transfe cases just happen to have the same bolt pattern on both ends and for some reason they are stackable.
They run 2 low ranges. Its the cheapest way to build a rock crawer that you can still drive on the highway just by changing tires.

Does an entire second transfer case bolt to the end (with some dead splitter hanging off the back) or is the box hacked up or is it a separate range box? What ratio does it use and what transmissions does it work with by chance?

[oil pan 4]

The transmissions found on 2.4 and 2.7L 4 cylinder engines.
I am not a toyota truck guy so I dont know them very well.

[slowmover]

Note another possibility is I saw once someone made an adapter to hook the rear of a TH400 into the front of another TH400, making the rear trans like a 3 speed auxillary transmission itself, but one you actually could shift on the go, typically converted to a manual valve body. It's possible i'd consider that as well but I don't like how the slush trannies suck power so considered straight gears more efficient.


Yeah, I had forgotten that one!! The second trans had no torque convertor (cut down like a marine case) and the operator had to have some skill in selection (road, load, traffic, etc).

[drmiller100]

you could probably do a 2 speed powerglide and do the same thing.

i had a race car with a 2 speed powerglide, no converter, full manual shift, and you cut hydrualic fluid to get "neutral" for stop and start.