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Old 11-27-2017, 11:19 PM   #11
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Originally Posted by arctictraveller View Post
I could be wrong, but Gearvendors calls thier units underdrive/overdrive. Perhaps the term is misleading when they talk about gear splitting plan though. First OD would be lower than second non OD, but thats no help when crawling. Gear Vendors Under/Overdrive Ford Truck-Car-Van 2-Wheel Drive 4-Speed and 5-Speed Automatics.

As for your concerns about using a transfer case with a semi-float, is that because its a diesel? Plenty of conversions are done with semi's, perhaps the vast majority are.
Their combo name is just marketing. It's an overdrive with a ratio that works well for spitting, but it's either in direct, or overdrive when switched on.

I wouldn't recommend 2-low with a semi-float just because you can easily overload it with input torque. At least with 4x4 some of the torque is going to the front axle.

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Old 11-28-2017, 07:51 AM   #12
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Originally Posted by carringb View Post
Their combo name is just marketing. It's an overdrive with a ratio that works well for spitting, but it's either in direct, or overdrive when switched on.

I wouldn't recommend 2-low with a semi-float just because you can easily overload it with input torque. At least with 4x4 some of the torque is going to the front axle.

OK, that's what had me scratching my head.


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Old 11-28-2017, 07:58 AM   #13
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I'd go the easy route since no route here is cheap. Convert to 4x4. Ujoint is the most affordable if you can do some of the work. It's not that hard. I did an MG coil conversion and learned a lot. Nothing was particularly difficult. I had to buy maybe two tools.

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Old 11-28-2017, 08:58 AM   #14
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Just a thought , correct me if I'm wrong.
I've read about shiftable, underdrive gearboxes. typically mounted between the transmission and transfer case . (planetary doubler )

The planetary doubler has a compact case which accepts the planetary gear set from a transfer case , and when used as intended ( mounted between the transmission and transfer case) is like stacking two transfer cases.

What if you installed just the doubler to the tail shaft of the trans and forego the transfer case. The output shaft of the doubler to the drive shaft to the rear.

In essence half a transfer case.

IMO this would be a compact shiftable, underdrive gearbox.
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Old 11-28-2017, 09:29 AM   #15
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JackTuppVan, that looks pretty sweet --- !
--- so that "planetary doubler" is indeed a **shiftable** unit on its own? Acts as a two-speed unit, and not just as a singular-fixed-gear-reduction ratio? Curious who makes that.

It would need to have two selectable [input : output] rpm ratio modes....1:1 for standard cruising, and then perhaps something like 2:1 for crawling/climbing.

If that's indeed a commercially-available "thing"....then for sure color me as interested as B350 is....


EDIT:
Is it this one? Sure looks like it....very cool....
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Old 11-28-2017, 09:59 AM   #16
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My understanding ... it's Half of a transfer case in a compact custom housing that can be clocked 360 degrees .

Shiftable while at a standstill , not on the fly

My guess is a custom coupling to mate the output to the driveshaft would be needed, and then again there may be some combination of off the shelf pieces may be used.

I have no experience with these particular units , and my knowledge of these units is limited to what I have read.

more info here

BlackBox GearBox - The Latest In Underdrive Technology

Universal Strong Box Underdrive
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Old 11-28-2017, 10:35 AM   #17
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Ya know... I've installed a few doublers in GM's using just the "range box" off of an NP203 sandwiched between a TH400 and NP205. The problem is that thoes still had to be mated to a 4x4 transmission and had a custom adapter behind them to mate to the second case. I've also seen aluminum cases that had the range box section of the case cut off and plated over to accomplish the same thing.

Just because my wheels are now turning, how about a divorced transfer case? You'd have a short driveshaft between your current transmission that connects to your stand alone transfer case that would be mounted to its own separate crossmember. I know Ford ran their stock 4x4's like that in the early '70's, maybe you could junkyard fab your own similar setup? Having a machinist friend may get you far. I'd be willing to bet that someone on Pirate4x4 has divorce mounted a 203 range box before, get to googling!
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Old 11-28-2017, 10:48 PM   #18
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Great info guys! I think we’re on the right track with the “doublers.”

I sent inquiries to three of the suggested underdrive/doubler fabricators. Responses so far:

NorthWest Fabworks- BlackBox GearBox can only be used in conjunction with a transfer case.

ORD- Waiting on response regarding their Doubler.

Behemoth Drivetrain- Universal Strong Box Underdrive is an option. This is the email received-
We have divorced input and output options available. This will give you a separate unit that you will run a short driveshaft from transmission to strong box, and another driveshaft from output of Strong Box to rear axle.
The complete Strong Box with divorced input and output is $1650.00 + $85 USA Shipping.
Cable shifter kit is $130. Mount kit is $85 each. We recommend 2 mount kits to support both front and rear of Divorced Strong Box.

So, the option is there albeit not super simple or much cheaper than installing a transfer case.
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Old 11-29-2017, 09:44 AM   #19
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Third response came this morning.

ORD- Doubler is meant to be used with a transfer case. Here’s their response-
Unfortunately the output of our doubler is setup to mate to a transfer case, we don't have an option for an output for a driveshaft.

If only a transfer case could be dissected, case cut and reduced to use only the rear output...
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Old 11-29-2017, 03:53 PM   #20
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Other than re-gearing the rear ring and pinion, and living with lower highway speeds and fuel mileage, I don't see a low-buck solution.

Oh wait, here's some out of the box idea; I read somewhere, Pirate 4x4 maybe, where a guy proposed swapping out his rear driveshaft for a modified forklift driveshaft, after getting to the trailhead. Some folklift driveshafts (he explained) have an integral shaft mounted speed reducer, a compact planetary gear set, that's 2:1 ratio reduction. I never worked on a forklift, but it's possible in theory I guess. Nevermind, no one wants to crawl under anything in the snow... :-)

The Gearvendor under/over unit is $3100 plus driveshaft work, plus install (I think they will make either, over or underdrive). Just remember it's one more aftermarket system to possible break.

Installing a used 271 transfer gearcase ($400) onto your existing E4OD ($500), linkage ($300), crossmember, shifter thru the floor, shortening the drive shaft ($200), and shortening the mid-mount fuel tank ($70 kit, $250 labor)) might wind up being half the price in parts, but after considering labor hours, around the same money. At least with the t-case option you'd be that much closer to 4x4 if you ever wanted to go 'full monty' and add a dana 60 front axle and springs.
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