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NP231 doubler / crawlbox

Wildman

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How long is the D300 case vs an NP231?

D300 11.5" & NP231 21"

 

SkylinesSuck

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Wahh??? 10" shorter?!?! That would help out biggly with drive line angles. I mean, my JB SS SYE arrives today and I have every intention of installing it, but as a long term project, it's worth looking into for me. A longer shaft would allow for more lift down the road and the 4:1 ratio would be yuge for me.
 
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Irun

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Yes never said they were CHEAP....

But the box with 4:1 LoMax gears and 32 spline front output shaft is $3500 which makes it about $250 more than and Atlas. I wonder which is stronger?
I'm now curious about strength, size, and weight. At 72.6 pounds ("Complete case with 4:1 gears, 32 spline shafts") this looks like a compact, lightweight, and strong solution to an existing problem. Personally, given the price of a used Rubicon case, I'd have zero problems paying $3500. :unsure:
 
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LincolnJr

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So one option would be to use the Rock Box DIY kit and the LoMax 4:1 gears, which puts you at $2100 (as opposed to finding a used NP241, which are selling for nearly the same price). You'd also have to get at least a new rear driveshaft because of the length difference - I'm not sure if the front would change. I'm also not sure what else you'd need to buy to put this all together - it says the Rock Box DIY comes with complete shifting assembly... Great option for standard wheelbase TJs, brand new 4:1 t-case, fairly straightforward setup.

Another option would be to source a second 231 ($150-200), get the Froehlich adapter ($475), 6-pinion planet gear ($150), short SYE kit ($450), (optional 231 rebuild kit - $250), and a pair of cable shifters ($340 for 2). Beef up your current 231 with the 6-pinion, rebuild kit, and SYE; weld up (not sure how much someone would charge for this for those of us without welding capabilities). You might be able to get better prices on some of these things - I just did some quick google searches - but all of this adds up to about $1800. Or, applying the principle of Jeep Parts Cost Justification, if you already own (or were already planning to buy) an SYE, one of the cable shifters, etc., this build could be more like $1200. You would definitely need both new driveshafts as the entire t-case is moving back - front will need to be longer and rear will need to be shorter. What else am I missing?
 
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Wildman

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Wahh??? 10" shorter?!?! That would help out biggly with drive line angles. I mean, my JB SS SYE arrives today and I have every intention of installing it, but as a long term project, it's worth looking into for me. A longer shaft would allow for more lift down the road and the 4:1 ratio would be yuge for me.

Novak has a shorter rear shaft kit for it also. Just something else to look at.

I'm now curious about strength, size, and weight. At 72.6 pounds ("Complete case with 4:1 gears, 32 spline shafts") this looks like a compact, lightweight, and strong solution to an existing problem. Personally, given the price of a used Rubicon case, I'd have zero problems paying $3500. :unsure:

Yes it is another option to be looked at. And with the aluminum case it cuts down on the weight.
And then with your Rubi-Crawler you have dual cases too.
 

Irun

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Novak has a shorter rear shaft kit for it also. Just something else to look at.



Yes it is another option to be looked at. And with the aluminum case it cuts down on the weight.
And then with your Rubi-Crawler you have dual cases too.
Exactly what I was thinking. With the 4:1 ratio and the RubiCrawler you then end up with 4 speeds in 4wd, i.e. 1:1, 2.72:1, 4:1, and 10.88:1. The 10.88:1 was basically useless, but the ability to easily switch back and fourth between 2.72:1 and 4:1 is the single biggest reason I like running a multi-speed box configuration. :)
 

Gollywomper

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I would lean towards the Midnight Metalworks box. It is a small USA company. Not a corporate investment deal. No doubt if I ever crack my case I would go with the Midnight box
 
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Wildman

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Exactly what I was thinking. With the 4:1 ratio and the RubiCrawler you then end up with 4 speeds in 4wd, i.e. 1:1, 2.72:1, 4:1, and 10.88:1. The 10.88:1 was basically useless, but the ability to easily switch back and fourth between 2.72:1 and 4:1 is the single biggest reason I like running a multi-speed box configuration. :)

I would disagree with you on this. But I had 7:1 in my Suzuki and I loved it for SOME things.

With the STaK's I have 3.05 & 5.44 low ranges and there are times I do wish I had a lower ratio. Granted you wouldn't use it much but I do think there are times where it would be used. I honestly thought about adding something like the NWF Black Box in front of the STaK's.

There are some trails up here where I use the 5.44 low to go down them due to how steep they are and being in the low low range I can just crawl down them and not use the brakes much. I'd done the same trail in a CJ5 with a stock D300 and it was a major PITA trying to go down. I really disliked it.

If my STaK's blows up I'd seriously consider the Metalworks box and a NWF Black Box to replace it with.
 
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freedom_in_4low

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otherwise one is skidding slow and the other fast.

this is where it breaks down for me. Why would both be skidding? If they're faced with a conflict between the tire rolling speed and the driveshaft speed, the two sides will fight each other until one loses. The winner keeps the traction, the loser does whatever the spider gears tell it to do, which will depend on the terrain and the steering input's influence on the front driveshaft speed.
 

freedom_in_4low

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The front tires always win, that's the trick. The rear tires don't win or get traction, they just tag along for the ride. Having them spin the correct speed is what helps.

sure, the front has all the weight transfer so it's going to determine the driveshaft speed but that's where it's influence ends. Once one rear tire breaks loose, the only torque being applied to the tire that still has grip is what's produced by the dynamic friction of the tire that's skidding. This is in contrast to a locked diff, where any difference in what the driveshafts need to spin due to terrain or steering input would cause both rear tires to break loose.

This is pretty well demonstrated by the single tire stripe that an open diff vehicle leaves in a burnout.

It still leaves it open which method is best for a steep descent, but at that point it's just personal preference. Do you want the rear to contribute more to controlling the descent, but any loss in traction loses both sides, or do you want the rear to keep at least one tire with grip but not really contribute anything? As I stated, I'm in the second camp. If I could go down in FWD and let the rear just roll, then yeah, that would probably be the best.
 
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freedom_in_4low

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But why FWD? The rears can’t do anything much different than the front when in 4wd.

the front axle has all the weight, and all the grip, so it's the most capable of controlling your descent. It doesn't need help from the rear axle to slow the rig. The rear just needs to not slide around and get the rig sideways.