Toyota Transfer Case Rebuild Upgrades - Toyota T-Case Beef

Gear Upgrades
Though the Toyota transfer case is a solid performer, there are still some modifications that will improve its gear capabilities. The biggest advantage of lower gearing is that obstacles can be traversed with much greater control. This, in turn, places less stress on driveline components.The first type of these low-range conversions is what is referred to as a dual-case setup. The Toyota transfer case has two major sections: the front reduction box that selects between high and low ranges, and the rear portion that selects between two-wheel-drive and four-wheel-drive.

In a dual-case setup, a machined aluminum adapter plate mates a second gear-reduction box to the front of the gear-reduction portion of the stock transfer case. This takes the stock 2.28:1 ratio and adds an additional 2.28:1 ratio gearset to provide a final ratio of 5.2:1. With such a setup you get a high- and low-range ratio for each of the two reduction boxes. With this you get 15 forward gears with transfer case ratios of 1:1, 2.28:1, and 5.2:1. You also have the advantage of running in two-wheel-drive low range by shifting only the forward transfer case into its low range.

Such a conversion does require some additional modifications to the truck, along with the transfer case modifications. Another hole must be cut in the cab floor to accommodate the additional transfer case shift lever. Also, the rear driveshaft must be shortened about 6 inches and the front driveshaft lengthened by an equal amount.

The second type of low-range conversion simply involves replacing several of the internal reduction-box gears. In this case, the high range still remains at 1:1, but the low range is reduced to 4:1, or with some kits, a whopping 4.7:1. This more than doubles your low-speed crawl torque and allows walking over difficult obstacles with much more smoothness and control.

Installing the replacement gears requires disassembly of the transfer case. However, only the transfer case modifications are needed and no further modifications to the truck are required. Since only the internals of the transfer case are modified, it is not necessary to modify the driveshafts or any other parts of the truck. For even lower ratios, consider combining a dual-case conversion with a set of lower-range gears.

Note that both dual-case conversions and low-gear conversions are available for use only with the gear-drive transfer cases. This is fine if you have a four-cylinder five-speed. But what about those with automatic transmissions, V-6 engines, or a new Tacoma truck? Marlin Crawler has come up with solutions to address most of these configurations.

In addition to its Ultimate kit, Marlin Crawler has dual transfer case kits and low-range gear kits available for all V-6 3.4L Tacomas with automatic or manual transmissions. For Tacomas with a swapped-in straight axle, both right-hand-drive and left-hand-drive conversion components are available. At the time of this writing, four-cylinder Tacoma parts were being designed as well.

A unique approach to overcoming the bulky stock crossmember is this crossmember/skidplate combo from Front Range Off Road Fabrication. It requires minor welding for installation but offers clearance gains of up to 3 inches, plus firmer mounting of the entire drivetrain to reduce the habitual tearing of stock motor mounts under extreme use.

A unique approach to overcoming the bulky stock crossmember is this crossmember/skidplate

Other Upgrades
Along with the many reduction-gear options available for Toyotas, there are some other interesting upgrades. One of these upgrades is the Twin-Stick Conversion Kit available from Front Range Off-Road Fabrication. The stock transfer case uses a single shift lever to move two shift rails inside the transfer case. One rail actuates high/low range and the other rail shifts from two-wheel drive to four-wheel drive. Possible combinations are 2-high, 4-high, and 4-low. However, there is no low-range option for two-wheel drive. Installation of a twin-stick kit provides you with one shifter to control each of the gearing and drive functions separately. With a lever shift this allows you to go from four-wheel drive to two-wheel drive in low range. This is especially useful for 'wheelers who run hard lockers in the front axle and find it hard to turn sharply when the front locker is engaged.

A unique approach to overcoming the bulky stock crossmember is this crossmember/skidplate combo from Front Range Off Road Fabrication. It requires minor welding for installation but offers clearance gains of up to 3 inches, plus firmer mounting of the entire drivetrain to reduce the habitual tearing of stock motor mounts under extreme use.

Adding lower gears and bigger tires is a natural progression to building a bigger and badder trail Toyota. However, getting a little extra ground clearance under your truck is always a good thing as well. We can even do it without adding more lift.

Toyota builds lots of its structural members from sheetmetal stampings that provide excellent strength with relatively light weight. Such is the case with the stamped and welded transfer case crossmember. Although strong, it is bulky and constitutes a low point under the frame. An easy way to gain ground clearance here is to use a replacement crossmember that provides sufficient beef without the thickness. A gain of nearly two inches in ground clearance can be had by building your own crossmember or purchasing one from one of the suppliers listed here. For belly clearance, it's almost like adding a four-inch-taller tire.

Whatever you're 'wheeling, you'll find Toyota transfer cases to be stout and reliable performers. With the wide availability of aftermarket beef-up parts and a number of stock interchange options, you can set up your truck or 4Runner to tackle any four-wheeling you may want to do.

For And Against
This table summarizes the pros and cons to using either of the two methods of gaining lower transfer case gearing.

Dual-Case Setup
Pros:
- Three transfer case ratios
- Improved front driveshaft angle
- Combines with 4.7:1 gears for the ultimate low-range
Cons:
- Requires driveshaft modifications
- Requires floorboard modifications
- Slight increase in driveline slop

Low-Gear Reduction
Pros:
- No other modifications required
- Preserves original drivetrain setup
Cons:
- Cannot pick "stock" low-range

Ratio Gains
The table below quickly summariezes the gain in the overall final-drive ration that can be gained through the use of reduction gearsets and/or dual-case conversions. Here the table assumes a common aftermarket 4.88:1 axle ratio and a 3.95:1 First gear (Toyota five-speed manual) ratio.