Part 6: Atlas four-speed t-case install
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.
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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.
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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