The 4SP includes as standard equipment the stronger 32-spline front output shaft, a redesigned shaft and bearing arrangement on the rear output, and slightly different machining on the aluminum case to accommodate the new configuration. Other than these changes, the transfer case portion of the 4SP is the same tried, used, abused, and proven Atlas on which we all depend. The new Atlas 4SP retains availability of both lefthand- and righthand-drop models, the multiple clocking options with four sets of mounting holes, numerous yoke choices, and most of the various input shaft spline counts that are offered on the original Atlas II.
I have an Atlas II in two of my trail Jeeps and absolutely love the deep Low range and abuse-proof attributes they offer. The only drawback I could find was the 4.3:1 reduction that I preferred for rockcrawling was too low and slow for moderate trail work. While great for tackling challenging boulder fields, the 4.3:1 was not so well suited for a simple dirt two-track into the mountains to find those boulder fields.
The Atlas 4SP solves that problem. With the 2.7 reduction ratio in the planetary set engaged and the transfer case in High range, the new 4SP offers a "stock" transfer case-like reduction for those long sojourns in the mountains or desert. If we run across a trail section that requires a little more control for elegant rock dancing, popping the planetary back to 1:1 and dropping the Atlas into its 3.8:1 position creates the deep gear reduction required to carefully crawl through the biggest rocks. Engaging the deeper gearing on both the transfer case and planetary? It yields a "snap-a-chalk-line-to-verify-if-it-is-moving" 10.34:1 reduction. In the Scrambler with its Chevy NV4500 and 4.88 gears, the total crawl ratio is now 324:1! That is a might too low to be of much practical use in my particular application, but an automatic transmission and higher axle ratio would utilize this "doubled-down" configuration quite nicely.
We hope you enjoyed stepping into the shop as we dropped the "old" Atlas II in our trail-worn '82 CJ-8 and replaced it with a new Atlas 4SP. We also used this opportunity to try out a slick new possibility from Off Again Auto that eliminates the common but bulky output flange to accommodate a 1350 CV driveshaft.
A quick test fit of the new 4SP proved that the existing body clearances would still be adequate in spite of the longer length and the need for a planetary assembly shifter bracket on top of the new 'case. The custom crossmember/skidplate felt the heat of the trusty plasma torch in order to gain the required clearance. | 
Not only was the shifter mechanism easy to assemble, the rest of the Atlas installation just keeps getting better and better as more history is compiled. The latest Atlas manual is chock-full of useful information, guides, photographs, and so on. It even details an input shaft swap in case you change your transmission at a later date. | 
This small collection of quality pieces coagulates into the shifter assembly for the new planetary unit. Brief but concise instructions from Advance Adapters make it all fit together in a few minutes. |