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Advance Adapters Atlas II
Advance Adapters Atlas II, Part I

By Chris Shontz

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Production Shots

Advance Adapters Atlas II
Empty Cases
Advance Adapters Atlas II
Tail Housings
Advance Adapters Atlas II
Front Outputs
Advance Adapters Atlas II
32 and 26 Front Outputs
Advance Adapters Atlas II
Atlas II In Progress
Advance Adapters Atlas II
First Step
Advance Adapters Atlas II
Case Assembly
Advance Adapters Atlas II
Atlas II Department
Advance Adapters Atlas II
Inside Atlas II
Advance Adapters Atlas II
Completed Atlas II

Shift Levers
A notable difference between the operation of the Atlas II and the NP231 is that the Atlas II is a twin-stick design that allows for a much greater variety of drive configurations.

As you can see pictured on the right, the operation of the stock transfer case is straight forward. One swift pull of the ergonomic lever from high range 2WD will give you your choice of high range 4WD, Neutral, or low range 4WD.

Advance Adapters Atlas IIThe Atlas II twin-stick setup allows six different drive configurations, which are as follows: Neutral, 2WD High (rear), 4WD High, 2WD Low (rear), 4WD Low, and 2WD Low (front).

The low range 2WD settings come in handy to reduce drivetrain binding when one encounters tight turns on the trail. This is particularly useful for those equipped with locked differentials and in situations when vehicle control is needed, but 4WD certainly isn't. 2WD low can be disengaged at any time while driving by shifting the respective handle into neutral. Low range can be engaged while slowly rolling forward at a speed no faster than 5 mph.

Advance Adapters Atlas II

Advance Adapters Atlas II

Advance Adapters Atlas II

Advance Adapters Atlas II

Slow Drag Race
To get an idea of how the crawl ratio of the Jeep is going to improve with the Atlas II, we tested the NP231 over a span of 45 feet. We recorded the time it took for the Jeep to idle at 900 RPM in 1st gear, low range, from point A to point B, and repeated this test 10 times to find our average time. This test only indicated speed and not torque, which really comes into play when crawling up and over boulders on the trail.

It took an average of 15.58 seconds for the vehicle to go 45 feet equipped with the NP231 transfer case in low range.

Replacing the NP231 with the Atlas II transfer case should nearly double the amount of time it takes to travel 45 feet. We will look at these statistics again in the Atlas II follow-up.

NP231 (2.72:1) Atlas II (4.33:1)
1st 38.86:1 61.86:1
2nd 23.64:1 37.63:1
3rd 14.61:1 23.26:1
4th 10.15:1 16.15:1
5th 8.02:1 12.76:1


The transfer case is the heart and soul of any 4WD system. We are confident that the Atlas II provides top-notch performance and beef for the serious four-wheeling enthusiast, regardless of vehicle configuration. While the price tag is not for the faint of heart, the Advance Adapters Atlas II is living proof that you get what you pay for and we are confident that it will live up to its reputation throughout our review and the life of our Jeep.

Next, we will be having our Atlas II professionally installed at OK Auto, 4WD& Tire with a Tom Wood rear driveshaft. You'll be able to read about it here in another article soon!

Advance Adapters Atlas II


AX-15 gear ratios:
    1st - 3.83
    2nd - 2.33
    3rd - 1.44
    4th - 1.00
    5th - 0.79
    Rev - 4.22

Crawl Ratio Calculations:
Transmission 1st Gear    x    Transfer Case Low Range Ratio    x     Axle Gear Ratio   =   Crawl Ratio
Example:    AX-15 (3.83)   x    NP231 (2.72)   x    3.73   =   38.86




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