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The Transfer Case - Tech

Split Case
Christian Lee | Writer
Posted July 1, 2009

Popular 4x4 Gear Boxes

Just as Dana 60 axles have found their way into small and mid-size 4x4s, heavier-duty transfer cases are also appearing in these vehicles in greater numbers. Heavy-duty, however, is a relative term. For example, some Suzuki Samurai owners upgrade to "heavy-duty" Toyota drivetrain, which is certainly a heavy-duty option when paired with the 1,300cc Suzuki engine. The NVG241OR used in late model Jeep Wranglers is finding its way in to earlier model Wranglers as a replacement for the NP231, and even the Toyota crowd is exploring use of later-model transfer cases found in Tacomas and FJs. Branching even further toward heavy-duty are the many aftermarket transfer case offerings, such as those available from Advance Adapters, JB Conversions, and STaK, to name a few. The new is merging with old and many 4x4s are reaping the benefits. Whether your 4x4 is a Jeep CJ-5, Toyota 4Runner, Suzuki Samurai, or whatever, you can build a competent transfer case to sustain your vehicle through countless trail adventures. Take a look at this overview of some of the more popular transfer cases -- both new and old -- that we see on the trail these days.

Aftermarket T-Case Guide

Tera Low231
The Tera Low231 transfer case is a complete replacement case half with the appropriate input shaft already in place. New mounting studs are also included. The Tera Low231 4:1 transfer case is equipped with a true 4:1 low ratio that operates through a heavy duty five-pinion planetary gear set. The Tera unit bolts directly to the factory front case half and adds a good degree of strength to the vehicle's 4WD system. The Tera case offers a higher input torque rating than stock and features thicker case walls to withstand cracking or fractures. Teraflex also offers its Tera 231 Extreme Short Shaft (ESS) kit and Tera 2Low231 kit to further increase strength and capability.

Advance Adapters Atlas
Advance Adapters offers its Atlas II and Atlas 4SP transfer cases for use in most 4x4s. The Atlas II transfer case is available with six different low range gear ratios, including 2.0:1, 3.0:1, 3.8:1, 4.3:1, 5.0:1, or 6.0:1. The high ratio is 1:1. This broad range of gearing allows the Atlas II to meet the needs of many applications, even in vehicles where excessive driveline length can create rear driveshaft issues. The Atlas II features a CNC-machined one-piece case crafted from 356-T6 heat-treated aluminum. The Atlas 4SP is a two-piece unit that includes a main case that it is similar to the standard Atlas case and a reduction housing that sits in front of that. The main case is actually the same raw casting as the Atlas II but features a variety of machining differences to adapt it to be 4-speed. The reduction housing uses a planetary assembly with a low gear ratio of 2.72:1 and 1:1 in high range. Available low range ratios include 2.0:1, 2.72:1, and 5.44:1, or 2.72:1, 3.8:1, and 10.34:1.

Advance Adapters Orion & Orion HD
The Orion and the Orion HD are designed to replace the factory transfer cases found in Toyota Land Cruisers and are offered with two different input spline choices to mate it to the 10-spline three-speed trans or the 16-spline four-speed unit. Though the Orion case is slightly larger in diameter than the stock TLC transfer case it is exactly the same length and the bolt pattern is the same. The Orion kit includes a new cast-iron case, four new gears with a 4.0:1 Low ratio, a new larger cluster pin, and a complete gasket, bearing, and seal kit. It also requires some parts from the factory transfer case to complete the installation. The Orion HD is a complete version of this transfer case that is fully assembled and ready to bolt-in. The HD unit features larger 1-3/8-inch diameter, 32-spline front and rear output shafts, a new shorter front output housing, an electronic speed sensor, and an adapter plate option that allows the HD unit to be installed in early Jeeps. A 3.0:1 low gear ratio offering is also available for the Orion and Orion HD transfer cases.

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