Tech and upgrade options
By now, plenty of 'wheelers have discovered the versatility and durability of Toyota trucks and 4Runners. These sturdy four-wheel-drive vehicles have proven their prowess over a wide variety of terrain. However, for those wanting to push the limits of what they can do with their Toyotas, the aftermarket supply of parts for these rigs has exploded over the past few years, and parts now are available to turn a Toyota 4x4 into a hardcore 'wheeling machine.
As tire size grows, so does the strain on your rig's drivetrain. The well-known Achilles' heel of the straight-axle Toyota are the Birfield joints in the front axle. Upgrade kits are available, but some 'wheelers choose to forego such a modification and simply swap in beefy domestic solid axles to handle hardcore 'wheeling.
But as often as axles, engines, and trannies are swapped out of Toyotas for bigger and badder components, the stock transfer cases live on in many of these rigs. Why? Simply put, the transfer cases found in most Toyota trucks and 4Runners are stout and reliable.
From 1979 through '95, many Toyota trucks and 4Runners used a gear-drive transfer case: model RF1A. Beginning in 1984, a chain-drive transfer case of lighter design was also used in Toyotas with automatic transmissions, and from 1988 on, in V-6-powered vehicles. All V-6 models use the chain-drive case, while those trucks with four-cylinder engines come with either style, depending on type of transmission. While the gear-drive transfer case is more desirable from a standpoint of strength and reliability, both styles are quite robust and able to withstand considerable abuse.
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Subtle bearing and gear changes have been made in some of the units from year to year, but only three basic low-range ratios have been offered-2.28:1, 2.57:1, and 2.66:1. The high range on all Toyota transfer cases is 1:1.
The gear-drive, or counter-gear, transfer cases have a 2.28:1 low-range gear ratio and use a 21-spline input shaft. The transfer cases used in the manual-transmission turbocharged trucks also have a 2.28:1 ratio, but have a stronger 23-spline input shaft. Turbocharged 4Runners were built only with automatic transmissions. These and other automatic-transmission Toyotas use electronically controlled transfer cases with a 2.66:1 low-range ratio. These use a special viscous coupling system at the inputs to couple and release power to the drivetrain based on road conditions. Chain-drive cases used on V-6-equipped trucks have a low-range ratio of 2.57:1 and 23-spline input shafts. These VF1A cases are also called planetary gear cases.
In 1986, along with the introduction of independent front suspension, the automatic-transmission transfer case was changed so it could be shifted from 2-high to 4-high on the fly. Then in 1989, Toyota introduced the 4WDemand system on some models. This system allows the driver additional ability of shifting from 4-high to 4-low at slow speeds.
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Some of the later-model transfer cases also incorporate a small transfer case oil cooler that is plumbed into the rear of the case. On the Tacoma and newer 4Runners, the front driveshaft output is on the driver side, but is on the passenger side on older models.
Over the years, the Toyota gear-drive transfer cases have come with two different shifter styles. There was the top-shift style, with the shifters exiting the top of the transfer case reduction box, and there was the forward-shift style, with the shifters exiting from the top of the transmission tailhousing. Early models from 1979 to late '83 were top-shift, and used a slightly weaker, noisier gear design than later models. In the 1984 model year, Toyota upgraded the transfer case to a quieter gear design with the addition of a sub-gear and thrust washer on the counter-gear.
Carbureted models from about 1984 to '87 used forward-shift-style transfer cases, as did most all models starting about 1989 (trucks) and 1990 (4Runners) onward. Marlin Crawler sells a kit to convert forward-shift models to top-shift style, as needed for aftermarket dual-case or adapter kits.
The speedometer-drive gear (or electronic speedo sender for some years) for Toyota trucks lies in the transfer case. Unfortunately, unlike many domestic trucks, the speedometer gear cannot be changed to compensate for gearing and/or tire changes. Only an outboard speed converter can be used to recalibrate the speedometer on trucks with a cable.