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NP231 doubler / crawlbox


mrblaine

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Why is that, Blaine?
Show me one install with the 3 side by side shifters that doesn't look like it was done by a spastic one armed monkey with a chainsaw.
Show me the weight of one and tell me why that is a good idea.
Show me one where the owner hasn't wanted to drive back to the company and burn it to the ground over staying in gear, pumping the oil out of the case and just overall bullshit.
Size is a problem, a big problem.
 

NashvilleTJ

I miss the snow...
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Show me one install with the 3 side by side shifters that doesn't look like it was done by a spastic one armed monkey with a chainsaw.
Show me the weight of one and tell me why that is a good idea.
Show me one where the owner hasn't wanted to drive back to the company and burn it to the ground over staying in gear, pumping the oil out of the case and just overall bullshit.
Size is a problem, a big problem.
Same opinion on the 4 speed Atlas?
 

mrblaine

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Wound’t engaging the rubicrawler slow the input shaft on the tcase?
It should, but we've had several locals who insisted on being mr. cool guy and depending on the little shifter to run around in lower range. After about a year of that, the t-case had to come out and get rebuilt. Something is taking about the case bearings.
 
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Mike_H

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It over-revs the t-case bearings and burns them out if you use the Rubi crawler first.
Thanks for clarifying.
No issues with the driveshafts, Mike. The rotating speeds of both vary directly with the speed of the vehicle, regardless of the gearing in the transfer case, the tranny, or any other overdrive or underdrive along the way. The speed issues with things like the teralow are how fast the gears themselves operate. In the case of the teralow it is the planetary which has the problem.
Yeah, DS speed is based on wheel speed, through the R&P. Thanks for the reminder. It would be an interesting exercise to do the math and calculate the various RPMS of components at different build levels and compare them to stock...
 

Mudflat

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Lumberton, Texas
Ok, so according to this chart, I'm less than ideal with 3.73 and 33s. To get back to stock (LJ came with 30s originally) I would need to be at 4.11 gears, but that's hardly worth doing for the cost and effort involved. "Best mix" would be 4.27 gears, but that also seems like only a small gain.

Someone suggested 4.88 gears "where I should be"... I would appreciate the 30% improvement in final gear ratio at low speed on the trail, but that would also increase my highway rpms into like 4cyl range (70mph in 6th gear on 4.88s would be 2924rpm)... would the 4.0 be ok with that? If so, then I'm all for it. I'll start with regearing and see how much lower I want to go on the trail after that.

View attachment 302041
This is the improvement I saw when changing from 3.07 to 4.56 (33” tires). I couldn’t tell if there was any improvement in fuel economy because the speedometer was so far off before the work was done.

BC779838-2220-4DA5-AEFB-1BDAE1720FD6.png
 
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mrblaine

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Thanks for clarifying.
I'm going to ponder this some more. I'm thinking they may have over torqued the case when they shouldn't have.
Yeah, DS speed is based on wheel speed, through the R&P. Thanks for the reminder. It would be an interesting exercise to do the math and calculate the various RPMS of components at different build levels and compare them to stock...
The whole thing is a mess. 2.72 is good for a lot of things behind the auto. 4-1 is better for a lot of things. A bit deeper isn't terrible for some things. The problem is 10.88 isn't as good as 7.4-1 and you can't get that without swapping to a 2.72 case which kicks out 4-1 as an option. I can't convince myself that giving up 4-1 is worth getting 7.4-1. And, I can't convince myself that using another planetary to get 4-1 and some other ratio is worth giving up 2.72-1 although I would be happier without that than not having 4-1. At least for what we do.
 

NashvilleTJ

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That isn't the same animal at all is it? Isn't the 4 speed just a 2 speed with essentially the Rubi crawler bolted onto the front of it?
Is the Rubicrawler a planetary? I don’t know. But the 4sp Atlas is just a two speed Atlas (pick your ratio) with a 2.72 planetary in the front. I do think a rubicrawer in front of an atlas 2.0 is an A position - much shorter driveline length than a stock 231, 241 or a 4 sp Atlas (assuming the Rubicrawler is strong enough. Again, I I don’t know).

I’ve always said that the 4 speed Atlas is one of the best mods I’ve ever done to my rig. Mine is 1:1, 2.0:1, 2.72:1, and 5.44:1. The reason I like it so much is that for my rig when I wheel I stick the case in 2.0:1 which is perfect for the trail. When I get into really technical stuff that I want to crawl, it’s literally a two finger pull of the planetary shifter to hit 5.44:1. It is crazy easy to shift - much easier than the case even in the best of circumstances. Unless I shift it for a front or rear dig, I never have to touch the tcase shifters.

I never run it in 2.72:1, so I’m only using three speeds - which was part of the reason for my original question.
 
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mrblaine

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Is the Rubicrawler a planetary? I don’t know. But the 4sp Atlas is just a two speed Atlas (pick your ratio) with a 2.72 planetary in the front. I do think a rubicrawer in front of an atlas is an A position - much shorter driveline length than a stock 231, 241 or a 4 sp Atlas (assuming the Rubicrawler is strong enough. Again, I I don’t know).

I’ve always said that the 4 speed Atlas is one of the best mods I’ve ever done to my rig. Mine is 1:1, 2.0:1, 2.72:1, and 5.44:1. The reason I like it so much is that for my rig when I wheel I stick the case in 2.0:1 which is perfect for the trail. When I get into really technical stuff that I want to crawl, it’s literally a two finger pull of the planetary shifter to hit 5.44:1. It is crazy easy to shift - much easier than the case even in the best of circumstances. Unless I shift it for a front or rear dig, I never have to touch the tcase shifters.

I never run it in 2.72:1, so I’m only using three speeds - which was part of the reason for my original question.
Yes, the Rubi is just a planetary stuck into the tail housing of the 42.

Your ratios while much better than what we can get otherwise, also benefit from a different motor up front.
 
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mrblaine

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Is the Rubicrawler a planetary? I don’t know. But the 4sp Atlas is just a two speed Atlas (pick your ratio) with a 2.72 planetary in the front. I do think a rubicrawer in front of an atlas is an A position - much shorter driveline length than a stock 231, 241 or a 4 sp Atlas (assuming the Rubicrawler is strong enough. Again, I I don’t know).

I’ve always said that the 4 speed Atlas is one of the best mods I’ve ever done to my rig. Mine is 1:1, 2.0:1, 2.72:1, and 5.44:1. The reason I like it so much is that for my rig when I wheel I stick the case in 2.0:1 which is perfect for the trail. When I get into really technical stuff that I want to crawl, it’s literally a two finger pull of the planetary shifter to hit 5.44:1. It is crazy easy to shift - much easier than the case even in the best of circumstances. Unless I shift it for a front or rear dig, I never have to touch the tcase shifters.

I never run it in 2.72:1, so I’m only using three speeds - which was part of the reason for my original question.
Guessing the t-case ratio is the 2-1?
 
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NashvilleTJ

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Yes, the Rubi is just a planetary stuck into the tail housing of the 42.

Your ratios while much better than what we can get otherwise, also benefit from a different motor up front.
Agreed, but I also ran that setup in front of the I6, and the benefit for me was exactly the same.
 

NashvilleTJ

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I'm going to ponder this some more. I'm thinking they may have over torqued the case when they shouldn't have.

That could very well be. Throwing the rubicrawler in there increases the input torque to the tcase by a factor of 2.72. So on the stock I6 it goes from 260 pound feet to 707 - and that’s just in 4th gear. First is much worse. That’s crazy when you think about it.

Edit - Throw it in first at 2.84:1 and all the sudden you are throwing 2,008 pound feet at the case.
 
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Gollywomper

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Corning CA
I'm going to ponder this some more. I'm thinking they may have over torqued the case when they shouldn't have.

The whole thing is a mess. 2.72 is good for a lot of things behind the auto. 4-1 is better for a lot of things. A bit deeper isn't terrible for some things. The problem is 10.88 isn't as good as 7.4-1 and you can't get that without swapping to a 2.72 case which kicks out 4-1 as an option. I can't convince myself that giving up 4-1 is worth getting 7.4-1. And, I can't convince myself that using another planetary to get 4-1 and some other ratio is worth giving up 2.72-1 although I would be happier without that than not having 4-1. At least for what we do.
That’s is pretty much what lead me to my decision. Is the 205 case wider to help get passed the trans?
 

Mike_H

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I'm going to ponder this some more. I'm thinking they may have over torqued the case when they shouldn't have.
That could be a possibility. The 2.72 gearing might be twisting the 231 case slightly and causing the non-thrust input bearings to operate as such. I wouldn't expect that to happen just cruising around, but with any kind of load...the Rubicrawler is essentially tripling input torque.