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‘Tis the Season for 4-Wheel Drive

Transfers cases, axle actuators and other 4WD components need attention this time of year.

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As winter comes to the Northern states, our customers are getting ready for a long, cold and snowy season ahead. This is prime time for all of those neglected and put-off repairs to start coming out of the woodwork.

Batteries fail, people notice their heaters or wiper blades don’t work as well as they should, and folks begin thinking about mounting those snow tires piled up in the corner of their garage. Plow trucks are being resurrected from their corner of the fields, barns or backyards, and many people are shifting into four-wheel drive for the first time in months (or at least trying to … ).

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There are three methods of engaging the four-wheel drive: mechanical linkage, electric shift and vacuum actuation. All three methods have their weaknesses, especially for systems that are used seasonally. Mechanical linkages bind, rust and seize up. Their bushings deteriorate, or play in the linkages makes shifting in and out of 4WD a bit of a crapshoot. Electrical motors and actuators are susceptible to corrosion, electrical failure and – for stored vehicles especially – damage from mice and other obnoxious critters. Vacuum lines dry-rot, O-ring seals deteriorate and these rubber pieces also tend to attract unwanted attention from the rodent population.

Regardless of the actuation method, all axles and transfer cases require lubrication. Gear lube is the standard for axles, and even some transfer cases, but the increasing use of OEM proprietary fluids makes selecting the appropriate transfer-case fluid difficult without good reference materials. Most electronic catalogs offer some assistance, but can be a bit vague when it comes to specialized or proprietary fluids. When in doubt, an owner’s manual, service manual or an online search may yield specifications, including fluid types and fill quantities. While “married” transfer cases may share fluid specs with the transmission, ATF is inappropriate for some “divorced” cases and separate power-transfer units. “Universal” or “multi-vehicle” transmission and transfer-case fluids usually have a list of OEM approvals or equivalencies, but when in doubt, always err on the side of caution. If you just don’t know … SAY SO! It’s not a sign of weakness or stupidity, and if you point the customer in the direction of another expert source, you’re still the hero.

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Transfer-case motors (also known as “encoder motors”) are found on many push-button “shift-on-the-fly” 4WD systems. These motors control engagement of gears within the case, allowing the driver to shift into two-wheel drive or four-wheel drive, and high or low range. The encoder-motor-type units also communicate transfer-case position to the transfer-case control module, which monitors faults, initiates shift requests from the dash controls and can be responsible for lighting up the indicator or malfunction lamps.

Older 4WD systems used simple electrical or vacuum switches to control the indicator lights, as well as to engage the front-axle actuators. Axle actuators serve the same purpose as a transfer-case motor, “shifting” the axle in and out of “gear.” Axle disconnects allow the front axle shafts to spin independently of each other when disengaged, similar to manual locking hubs, although not as efficiently. When 4WD is requested, the actuator locks the shafts together, and connects them both to the differential. They are becoming more popular because these vacuum or electric actuators can be controlled from inside the cab, rather than getting out in the mud and locking hubs manually.

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The aftermarket has a healthy selection of vendors offering 4WD actuating components, switches, motors and seals. Specialty vendors also offer rebuild kits and other hard parts for many popular transfer cases. So, the next time a customer asks your advice on engagement, stick to transfer cases!

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