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Ive got them.... the unconventional way. I am running the NV4500 off my 4b. Then there is a dana 300 mated to the trans. I ad it twin sticked for the high low operation only (it is a passenger drop and I have a ford d60 front).

Then I had a stub shaft made to run to my divorced NP205 (ford).

I love the set up, as it is cheaper than having the adapters to mate two cases (about 600 dollars). I have 90 in te twin stick, 250 in the 32 spline output (a must in my book) and 80 fo rthe stub shaft.

I ave some property that I have to jump a drainage ditch to get on the property until I get a culvert put in. I can shoft the d300 into low (2.6 to 1) for 2wd low and crawl up the ditch. Then when I need to pull up roots, trees etc. Then I can shift the 205 in 4h and use the d300 as a gear splitter for a lower crawl than the 205, when i need more speed, shift the d300 back in high. THEN IF ITS REAL NASTY, both cases in low and first in the nv4500 and I have 119 to 1.

If any of the cases need service, I can pull them independantly which is nice. Also, if you plan a setup like this correctly, you can position the divorced case in the moddle of you rig and run same length driveshafts and carry one. Also a nice thought.

I dont know anyone running a married double so I wont comment as I have nothing to offer there..... all theoretical knowledge.
 

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I know a guy with a Marlin doubler in his FJ60. I'll see if I can gete him to post up here.. I'm sure it can help in a place where you need it but at 63:1 I was feeling pretty good last time with 35's. I think 100:1 would be all you would need and then some.. At 63:1 I would idle whenever I need to get up something, or even use my brakes against the idle to slow down to 300 to 400 rpms, and lower than most trucks at 100:1 :)
 

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I have no real use for 119 to one. A gear splitter for 2L was first priority. Also the 1.96 (or whatever it is) to one NP205 leaves a little to be desired sometimes if there is too much wheel spin. Then I can use the 2.6 in the d300 and 4h.

Essentially I have a cheap three speed transfer case.

the 119 to 1 is cool factor that I didnt have to pay for
 

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Without getting too math intensive let me see if I have this figured out for educational purposes since I'm not an off roader.

Final gear ratios act as torque multipliers at the expense of the tires RPM's, right?

So if you have a near stock 4BT with a rated torque at an even 300 (to make it simple) spinning at 1800 RPM run through a doubler and rear axle giving a crawl ratio of 100:1 your tires would be turning 18 RPM with 30,000 ft/lbs of torque trying to keep in contact with the ground, correct?
300 x 100 = 30,000
1800/100 = 18
 

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I am not sure if the torque divides out evenly like that or if there is a formula to guesstimate the torque. Either way, its gobs of power. For reference, a 5 HP winch motor will be in a winch rated for 12-15000 pounds with a gearing of 265-315 to 1.

With super low gearing, you are putting TREMENDOUS torque and break things readily if not careful. There are instances where its not the torque but the superslow speed that is sought after (slickrock, loose ground with obstacles, any obstacle where vehicle momentum and wheel speed hurt), downhill obstacle navigation ( using the gearing and engine as a brake to prevent wheel lockup). Applications are specific and short lived in the 100 crowd.

Another reason some run dual cases is to run thicker higher geared ring and pinions. Then with the larger tires with higher gears, reduction may be better met in the transfer case and not the differential.

I was after the choice between 1.96 4l and 2.6 4l with the ability to use 2l. I am also clearing land I have bought so 119 to 1 can let me pull stuff, me get out of the truck and do what i need to do as it is traveling neck and neck with the snails.
 

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be careful with an auto and high crawl ratios. I believe over 60:1 with an auto is considered "too" much. You won't be able to stop. You may have better luck with hydroboost brakes but it's hard to say. WIth a manual it isn't an issue.

i believe the torque multiplies exactly so 116:1 is 116x the torque. most quoted torque values of the 4bt are at 1500 rpms i'm pretty sure. I know it is with the sheets that i have showing power curves.

the crawl ratios hould also reduce the rpms in the same ratio.

be VERY careful with high crawl ratios and components. you will find yourself replacing many many components with too much torque and traction. it sounds like asking for trouble to me. If you can do it with the drivetrain you have, by all means go for it though :D
 

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Yes, thats why I emphasize the power and potential or breaking stuff. You must be purposeful and desciplined.

The only question I have with the gear multiplying and power is the truck has diferential gears which in my case are 4.10. If I were to dyno at the wheels, Id get 300 tq for the sake of ease.

Only the transfercases would be multiplying at that point (high being 1 to 1). In my case of duals 1.96x 2.6. Although on a dyno you pull in the gear that is one to one (4th NV4500) so does that mean you mulitply torque times transfer case gears or torque times final gear ration diffs included.

Lee to answer your other question, I have not used 119 for anything other than stumps. It is a selling point. If I am forced to sell my rig, it is a cool factor some kid will pay extra for;). To answer your other question, stock 4x4s come with final crawls of 35-45 to 1 (in general). Most that add bigger tires regear to get them in the 60-75 to 1 range. This is most I read about in Petersons, 4 Wheel and Ofroad, friends, rigs I read about. That seems to be more than suffecient or most.
 

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ok charles, i like the explanation!

that kind of explains why i have told people some of my early build issues were brought on/intensified by the large amount of useable tq off-idle with the 4bt.


thats kind of why i have always been leery of the 700r4. too much tq at too low rpm. i have no proof, just my gut.

i cannot for the life of me remember the guy that swapped the 4bt tht could almost pop ujoints at will. they werent 1410 or 1450 mind you. but it was still a thought.

i once pinned myself against the gargae door with a running 4bt rig. luckily it was in pieces and i could get to enough stuff to kill it.
 

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maybe not gear reduction, but I once read that someone had mounted the 203 gear reduction box backwards on a 203/205 doubler to use as an overdrive unit...it would be alot cheaper than an aftermarket overdrive box (2k new) has any one heard of this being done??
 

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Power = Force x Velocity.
Power also = Torque x Rotating Speed.

The torque does multiply through by your gear ratio, but you also need to take friction into account.
The torque needed to mesh gears and turn bearings reduces the torque available at the load end of the shaft.

But as has been pointed out. The primary reason for silly low ratios is vehicle control. My truck can slip all the wheels offroad at idle in first gear low ratio at idle.
 

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The 203 that was run backwards is in a rig in Canada. He was running rockwells or maog portal axles and needed to get the gear ratio higher.

Some issues with running the 203 backwards. Oiling is first, it was designed to lubricate itself running as underdrive. I believe said person overfilled. Two was overheating. I know it sounds funny, just what he said.

Also, I would not want to rely on a chain driven anything for overdrive. IMHO that is a need best suited by gears, not sprockets.

For a trail only limited application...... maybe not so bad.
 

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Also, I would not want to rely on a chain driven anything for overdrive. IMHO that is a need best suited by gears, not sprockets.

For a trail only limited application...... maybe not so bad.
Why? It appears to me that a chain 2" wide can carry a much higher load than the few teeth that mesh between two gears. The killer is wear/stretch, though.
Mikel
 

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ive driven toyotas with doublers and have ridden in full size chevys with the 203/205 doubler.both worked very well for what they were built for(rocks,boulders). the toy setup worked better for several different types of terrain because one of the cases had the stock 2.3?:1 and his second case had a 4.?:1. that seems to make more sense than running two similar ratios.in my last rig i had a 6.4:1 in the t-case and 5.13:1 in the diffs with 37"bfg krawlers. i loved this setup for the price and simplicity but there was definitly some gearing missing between high and low range.i agree totally with charles pertaining the idea of gearing as far downstream as possible.that why the 404unimog axle rock!if i remember correctly the mog axleshafts were not to much different in size to the ford 9" but you can run 44" tires on them no problem.also the ring gear doesnt nned near as much beef either equaling more clearance.i always thought it would be cool to build a bolt on portal type hub to bolt onto say a d44.this would give you clearance for tires,more streangth upstream,and gearing for your big tires all in one.anyway back to topic.i dont think anything more than 100:1 is nessisary with the 4bt.but..its like having too much power.you dont have to use it but its there if you want it.and doublers are cool!
 
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