Last month we showed you how DC Customs of Ukiah, California, added hydraulic bumpstops to the rear of our Brute pickup via JKS's innovative new ACOS PRO kit. Along with a pair of Walker Evans Racing Shocks, these upgrades allowed us an additional 21/4 inches of lift without the use of longer coil springs. We're happy because it was enough clearance to install a set of smooth-running 40-inch Goodyear MT/Rs on Poison Spyder bead locks. Plus the rear of Teal Brute feels more controlled over the rough stuff. We love the look and feel of larger tires as well, we think they complement the Brute's larger proportions. Piloting Teal with such massive meats turns almost any rock garden into child's play, practically dissolving boulders the size of wheelbarrows.
Serious crawling requires...
Serious crawling requires low gearing. Thanks to our new Atlas four-speed we have a final crawl ratio of 87.16:1. Here the author shows off Teal's newfound tugging abilities.
This is the four-speed with...
This is the four-speed with all the little extra parts and pieces installed. Notice the thin spacer ring (arrow) added in front of the reduction housing. This enables the unit to bolt up to our 545RFE automatic transmission.
This is how our new four-speed...
This is how our new four-speed Atlas arrived to us. Packed cleanly in a special foam-filled box, we were impressed literally right out of the box. We've seen how easy it is for heavy items to suffer damage during shipping, but this pack job left very little opportunity for issues.
The jump from 4.10:1 to 5.38:1 differential gearing also helped Teal cope with the added circumference. However we found our transmission temperature increased slightly with the increased tire diameter as further torque-converter slippage was necessary to get the 40s up and over obstacles in low range. For this reason we decided to look into lower gearing options for our Atlas II transfer case. We contacted the friendly folks at Advance Adapters about installing a 5:1 low gear ratio (we had a 4.3:1). After a brief conversation about our intended usage we were convinced that we should lose the two-speed Atlas altogether in favor of the trick new four-speed version. Our reasoning was simple: We would end up with a lower low-range ratio, plus thanks to the Brute conversion, we already had a much longer rear driveshaft with which to work (the four-speed has a 3-inch longer case). And the idea of having four separate ratios to work with meant that we'd probably have the right gear for any situation. The Atlas 4SP Trans-Four case comes in two different configurations: Lowest low-range ratio of 5.44:1 or 10.34:1. We opted for the 5.44:1 version because we didn't think the 10.34:1 was necessary with our 545RFE automatic transmission. We set the project in motion and once we had all the parts in stock, we headed up north to Ukiah, California, to have our friends at DC Customs perform the installation.
Our first order of operation...
Our first order of operation was removal of the old Atlas II (seen on the floor). As you can see from this shot we performed a few other modifications while we were at it. The running joke at DC Customs is that this corner of the shop is actually Teal's second home. She's been parked here for at least a week or two each month since May 2007. Lucky for us, DC Custom's owner Dustin Chernoh welcomes Teal with open arms.
While the regular Atlas II...
While the regular Atlas II and the new four-speed do share some similarities, like the main case is the same raw casting, machining variations make a four-speed quite different in the end. The main case still functions the same but the four-speed's reduction housing is operated independently via a cable shifter.
We found a handy spot just...
We found a handy spot just left of the transmission shifter to install the new cable shifter. Here you can see Dustin drilling the first of two holes in the Tuffy center console to mount the shifter bracket. Dustin fabricated a simple "L" bracket to accept the shifter flange. We routed the shifter cable through a 2-inch hole in the tranny tunnel. We wrapped the shifter cable in 11/2-inch hose to prevent chaffing.
Advance Adapters provides...
Advance Adapters provides a special lubricant that works best in the Atlas line of transfer cases. It is very important to fill the planetary reduction housing prior to installation. Once installed the reduction unit cannot be filled. This housing holds a six-gear planetary assembly that has a low range of 2.72:1 and a 1:1 in high range. This planetary assembly has been rated to withstand 5,555 lb-ft of torque and up to 11,000 pounds gross vehicle weight.
Just as we expected, the new...
Just as we expected, the new four-speed fit like a glove. Next we took measurements for extended and collapsed driveline lengths. Then we placed an order with David Rodrigue Drive Line in Ukiah, California. The front driveline required a longer tube while the rear simply needed to be shortened a bit.
In the end, the shifter setup...
In the end, the shifter setup tucked cleanly between the driver seat and the console, right within reach of the driver. The trick billet-aluminum knob matched our B&M billet transmission shifter and the whole arrangement now allows us to choose between the following combination of gear ratios: 1:1, 2.0:1, 2.7:1, and 5.4:1, or had we gone with the 10.34 version we would have had: 1.1, 2.7:1, 3.8:1, and 10.3:1. Now our transmission temperature remains consistent, and our final crawl ratio of 87.16:1 is just right for even the toughest of trails.
Formula: First (or lowest) gear ratio of transmission x transfer-case low-range ratio x differential ratio = crawl ratio.
Example: 3.00 x 5.4 x 5.38 = 87.16:1