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Toyota Transfer Case Upgrade - Building A Better 'Yota 'Case

Posted in How To on October 31, 2006 Comment (0)
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Geardriven Toyota R1FA transfer cases benefit from huge aftermarket support. These transfer cases were used in four-cylinder pickups and 4Runners from 1979 through 1995. Thanks to the aluminum cast construction, these cases are lightweight (70 pounds), and with all gear internals, they are plenty strong. Even with motor swaps and 1-ton axles becoming more common under Toyotas, rarely does anyone feel the need to swap out the stock transfer case.

Now that you've decided to keep your Toyota transfer case though, how do you decide what products you need in order to conquer the toughest terrain? Worry not, Off-Road has rounded up information on some of the many aftermarket components available for the R1FA transfer case.

The R1FA transfer case is a split unit, with the front half providing gear reduction and the rear half controlling the engagement of four-wheel drive. Dual transfer case adapters mate the gear reduction half of the case to a complete transfer case, allowing twice the gear reduction when both cases are in Low range. With all of these adapters, expect to cut a hole in the floorboard for the additional shifter and make modifications to the driveshafts and speedometer cable.

Advance Adapters makes cast-aluminum transfer case adapters that are available from a variety of vendors. These adapters have been in production longer than any of the competition's and are also the most widely used at this time. The adapters are available for both 21- and 23-spline transfer cases and use bearings that are standard across the Advance Adapter product line for easy replacement, should that become necessary.

Inchworm machines an adapter plate from solid billet 6061-T6 aluminum, while the coupler shaft is machined from a factory output shaft. The Inchworm adapter is machined to close tolerances - parts fit right, run true, and last a long time. Together, the adapter plate and extra Toyota reduction box are about 6-3/8 inches long. This adapter uses factory Toyota bearings for easy replacement if necessary.

Marlin Crawler offers a cast-aluminum dual transfer case adapter featuring double roller bearings and an oversized billet mainshaft. The double roller bearing is 5/8 inch wider than the competition's and has two sets of rollers, amounting to 32 total bearings, compared to the standard nine. Marlin also preassembles its adapter plate by pressing in the double roller bearing, installing the three bolts on the mainshaft, pressing in the supplied cage roller bearing and lubing it, and installing the necessary dowel pins. The company even supplies a shift light plug with gasket and a new genuine Toyota transmission output seal.

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Replacement Low range gears offer a much lower Low-range ratio than the stock 2.28; however, the High range of 1:1 is not affected. This makes the gears well suited to a vehicle that sees a lot of highway miles, since there will be no noticable change when the vehicle is not in Low range. Note that all of these gears are physically larger than the stock gears and thus require grinding or machining of the shift rails in order to fit the larger gears.

Advance Adapters makes gears in 4.0, 4.7, and 5.0:1 Low range ratios. The gears are shipped complete with everything needed for the installation, including quality bearings and seals, gaskets, and detailed instructions. Advance Adapters also offers full transfer case rebuild kits with additional bearings and snap rings. These gears are available from a variety of vendors.

Marlin Crawler sells 4.7:1 transfer case gears that are made in Japan by the same gear cutter that manufactures the stock transfer case gears for Toyota. Marlin's gears feature larger gear teeth than the competition, as well as "total spline" input gears that are thicker than stock and feature longer splines designed to eliminate problems of stripped-out couplers and broken input gears.

The vast majority of RF1A transfer cases came equipped with 21-spline input shafts. These shafts are strong enough to withstand the increased input torque of dual case applications and larger motors in most instances. A stronger 23-spline input gear was available in turbocharged Toyota pickups with manual R151F transmissions. These stronger input shafts are still available from Marlin Crawler and Inchworm Rock Walkin' Gear and can be retrofitted into any RF1A transfer case. The higher spline count is only compatible with the R-series transmissions, however, or when used in conjunction with a 23-spline dual case adapter. In this scenario, a front transfer case with a 21-spline input could be mated to an L-, G-, or W-series transmission and then connected with a 23-spline rear case.

The stock output shaft in the R1FA transfer case has a machined depression behind the teeth, near the center of the shaft, right next to the clutch dog. This depression can become a point of failure when the drivetrain is bound up, particularly when other components in the driveline have been upgraded. Twenty-three-spline input shafts, large axles, and beefy driveshaft U-joints will transfer the weak link to the transfer case output shaft. All-Pro's heavy-duty output shaft removes the groove next to the clutch dog that is prone to failure and replaces the 30-spline clutch hub with a stronger 31-spline unit. The result is a shaft that is 0.215 inch larger than the shaft it replaces. The shaft and clutch hub are made from high-quality, 8620 gear steel.

Twin stick shifters offer the ability to switch between High range and Low range independent from the selection of 2WD or 4WD. This can be particularly useful on high-traction surfaces when the rig has an automatic front locker. A twin stick makes tight turns much easier, allowing rear-wheel drive with the slow speed control of Low range. By having 2-Lo, the front axle is relieved from undue stress, and four-wheel drive can be re-engaged, even while moving, by just throwing one lever. In order to use the twin stick, the transfer case must be partially disassembled and the interlock pin removed from between the shift rails.

FROR was the first company to manufacture a twin stick for Toyota transfer cases. The shifter is 100-percent bolt-in and available in custom lengths to accommodate body lifts. The FROR unit is a completely sealed assembly that is rebuildable and made of all-new parts.

The Marlin Crawler twin stick features a low-profile billet base. Its compact design is great for low-clearance applications, and the vent breather is tucked below the billet casing on the top of the baseplate. This simple design has no attached bolts or brackets that might become loose over time.

Once you have invested a large amount of time and money into your transfer case, it would be wise to protect your investment. Luckily, there is a variety of crossmembers that provide increased protection (and ground clearance) for your new transfer case(s).

All-Pro manufactures crossmembers for single case or dual case applications that feature integrated skidplates. These crossmembers are made of mild steel square tubing and fully welded. The All-Pro crossmember offers 1-3/4 inches more ground clearance than the stock crossmember and bolts to the stock frame mounts. All-Pro's crossmember comes in bare metal ready to paint.

BudBuilt offers crossmembers for single or dual case applications and are available to accommodate any amount of drivetrain lift (specify when ordering). The BudBuilt piece bolts in place of the stock crossmember but provides almost 2-1/2 inches more clearance, as well as better protection than stock. Constructed out of a single piece of laser-cut, hot-rolled, pickled-and-oiled 3/8-inch steel, the BudBuilt crossmember is smooth enough to allow the vehicle to slide over obstacles. Bud's dual transfer case crossmember allows for the use of two stock rubber mounting brackets to limit movement in the drivetrain.

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FROR builds a crossmember that connects to the back of the transfer case and sits between the framerails. By mounting from the back side of the transfer case, driveshaft interference with the front driveshaft on dual-case-equipped trucks is eliminated. The crossmember will fit with single or dual transfer cases, however some welding is required, and it will not fit IFS trucks due to interference with the torsion bar mounts. The mounting allows the user to raise the transfer cases as high as desired and leaves very little protruding below the frame. The 3/8-inch-plate FROR unit also provides increased rigidity compared to the stock crossmember, resulting in fewer broken motor mounts.

When swapping from rear drum brakes to disc brakes, sometimes the stock parking brake is not retained. This can pose a safety hazard and also disqualify your vehicle from some organized four-wheel-drive events. Moving the parking brake to the back of the transfer case remedies this problem and also offers greater holding thanks to the gear multiplication from the ring-and-pinion. All-Pro Off-Road produces a parking brake kit that comes assembled with the mounting bracket, actuating arm, caliper, rotor, and all necessary hardware. All steel parts associated with the mounting bracketry are powdercoated black. Note that the transfer-case-mounted parking brake is not compatible with all crossmembers, so All-Pro has come up with an innovative solution. The company recently introduced a crossmember called the Triple X. The Triple X integrates the crossmember, skidplate, and parking brake into one unit.


All-Pro Off-Road
Hemet, CA 92543
Inchworm Rock Walkin' Gear
Shingle Springs, CA 95682
Marlin Crawler
Fresno, CA 93703
Advance Adapters Inc.
BudBuilt Frames & Accessories


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