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.