Lower Gearing for a 2006 Jeep TJ Wrangler Rubicon 4x4

[ElkinJeep]

My 2006 Jeep TJ Rubicon 2006 automatic has 5.38:1 ratio Dana 44 axles doors, lockers front and rear with the NV241-J transfer case (4.0:1 gear ratio Rock-Trac) and a 42RLE automatic transmission.  Considering these variables, could you please recommend a transfer case and total kit that could fit in my Jeep?

[Moses Ludel]

Hi, Elkin…Are you seeking a transfer case?  Are you asking about a replacement Atlas transfer case from Advance Adapters?  Advance Adapters is a valued sponsor of the magazine and forums.  The magazine does not sell products.  If you are interested in an Atlas transfer case, you can get answers to technical questions or purchase an Atlas transfer case directly from Advance Adapters.  The Advance Adapters website is:  https://www.advanceadapters.com.  The Advance Adapters phone number for technical support and sales is:  1-800-350-2223. 

One option that you have with your NV241-J transfer case is to keep the NV241-J and add the Advance Adapters “Rubicrawler”.  The Rubicrawler is designed as a bolt-in fit for TJs equipped with the 42RLE.  At the magazine, I cover this product and its installation:  https://www.4wdmechanix.com/Advance-Adapters-RubiCrawler-for-TJ-and+JK-Wrangler 

If you have further questions about your TJ Rubicon and modifications, I would be pleased to answer your questions.

Moses

[ElkinJeep]

Moses, I am beginners  in the off-road world, I bought my Jeep 2 years ago, I am in Bogota Colombia South America.

I have 2 options:

1. Atlas 4.3 to 1. It’s going to be pretty close to what I have now with a slightly better crawl ratio.

2. Rubi-Crawler is 2.72:1 ratio, my transfer case is 4.0:1 ratio

Really I do not know which to do.  What do you think about each option?

Elkin

[Moses Ludel]

Hi, Elkin…You have the option of the 4.3:1 Atlas, which is a slight ratio gain over your 4:1 Rock-Trac.  The Rubicrawler has a planetary reduction, and the unit fits neatly between your 42RLE and the NV241-J Rock-Trac.  I like the Rubicrawler because you do not need to resize the drivelines or make major modifications.  The Rubicrawler fits between the transmission’s main case and the transfer case.  You fit the Rubicrawler’s cable shift linkage, and that’s about it.  Labor time for installation is shorter, and there is no need for major chassis or fit-up changes. 

The Rubicrawler would provide an additional reduction of 2.72.  Your lowest (crawl) ratio in first gear, low range, using low reduction in the Rubicrawler, would look like this: 

2.84:1 (42RLE first gear ratio)  X  4:1 (Rock-Trac Low Range)  X  2.72:1 (Rubicrawler in reduction gear)  X 5.38:1 (axle ratios)  =   166.23:1 

This is all the reduction you will ever need or want.  At the same time, you would not modify your current crawl ratio of 61.12:1 when the Rubicrawler is in 1:1 (direct) ratio.  You would have extreme reduction if you ever need it plus your current ratios when the Rubicrawler is not in Low/Reduction mode. 

Unless your transfer case is damaged, the NV241-J is a strong unit (used in many full-size 4x4 trucks) that should hold up well with the 4.0L inline six engine.  If you installed a bigger V-8 engine conversion, the added strength of the gear-drive Atlas would be a consideration.  With the 4.0L, You did not describe your tire size, but I would guess you have 37” or larger diameter tires?  The 5.38:1 axle gearing is usually for 37”-42” tires.  What size tires do you have on the TJ Wrangler? 

The Rubicrawler would be the quickest and simplest installation.  You could add an Atlas transfer case to the package, however, the gain would only be a 0.3:1 additional reduction.  I would start with the Rubicrawler.  That should meet all your needs. 

Moses

[ElkinJeep]

Moses, thank you for your time, my jeep has tires 35” 

[Moses Ludel]

Very nice Jeep, Elkin, thanks for posting photos!  I like the "half-cab" look and accessories.  So, with 35" diameter tires and 5.38 axle gearing, plus the 4:1 low range ratio, do you need more gear reduction?  The 42RLE has a torque converter, equivalent to even more gear reduction...Where would you find a need for an even lower crawl ratio like the Atlas or Rubicrawler?

Moses

[ElkinJeep]

When I am off-road rock crawling in 2L the jeep runs very rudely, i would like to run slowly, also i want to choose rear gear in 2L and front gear in 4H or neutral.

[Moses Ludel]

Elkin...I understand your need to stabilize the idle/crawl in low range.  The "2L" and "4H/front-only" functions are only available with an Atlas transfer case.  (A Dana 300 from the Jeep CJ era can accomplish this with a "twin-stick" conversion.  However, a Dana 300 will not work with your TJ drivelines and front axle's center section location.)

If you need the 2L or 4H/front-only functions, you would need to change the transfer case.  The NV241-J is incapable of performing these modes.  An Atlas 4-speed transfer case would accomplish what you want to do.  Note the available ratios at the Advance Adapters link below.  I added a video interview with Steve Roberts at Advance Adapters that will be helpful:

https://www.advanceadapters.com/products/atlas-4-speed-transfer-case-builder/

https://www.4wdmechanix.com/HD-Video-Advance-Adapters-Atlas-Transfer-Case-Design-and-Shifting?r=1

Moses

 

 

 

[ElkinJeep]

Thank you Moses I will let you know my next step. 

[Moses Ludel]

Elkin, you have two distinct options here.  You can choose one or the other:

1)  Install a Rubicrawler for additional 2.72:1 reduction using the original NV241-J transfer case.  This is a "bolt-in" addition.

2)  Install a 4-speed Atlas, choosing the ratio combination that you prefer.  Here, you would not use a Rubicrawler.  You would likely need to change the lengths of your driveshafts.

Moses