4WD Actuators

In the days when Four-Wheel Drive (4WD) trucks were almost exclusively used by the military, farmers, and rugged outdoorsmen, engaging 4WD was simple – just throw a lever to mechanically engage the transfer case and turn the dials to lock the manual hubs. But these days 4WD, and All-Wheel Drive (AWD), have become mainstream, standard or optional equipment on a plethora of trucks and SUVs. On vehicles with part-time 4WD, the driver must manually activate 4WD and vehicle makers realized that engaging manual hubs in the middle of a snowstorm wasn’t going to cut it. With the touch of a button or the turn of a knob, the part-time transfer cases on modern trucks and SUVs electronically engage and 4WD actuators connect the front differential to the wheels. However, with convenience comes complexity and greater possibility for problems, and unlike the anvil-like simplicity and reliability of manual locking hubs, 4WD actuators are subject to vacuum leaks, and mechanical and electrical failure. No matter what type of 4WD actuating difficulty you’re having, we have the actuators and related components to restore consistent 4WD engagement.

Unlike AWD and full-time 4WD drivetrains, part-time 4WD systems, which are found on trucks and truck-based SUVs, are designed to operate in two-wheel drive and power just the rear wheels whenever the vehicle is on dry pavement. Vehicles with part time transfer cases cannot be driven on dry roads when in 4WD because, while the front and rear driveshafts turn at the same speed, the front and rear wheels need to turn at different speeds when turning a corner. Using 4WD on dry pavement with a part time transfer case can result in “transmission wind-up”, which can cause understeer and tire skid, and in extreme cases, driveline damage. Loose surfaces like snow and dirt allow the tire slippage needed when a part-time transfer case is engaged. AWD and full-time 4WD vehicles, with their center differentials, can send power to all 4 wheels on any driving surface without needing any input from the driver. Nevertheless, part-time 4WD is the drivetrain of choice for driving in deep snow and serious four-wheeling because of its ruggedness and 2-speed transfer case, which provides a low range that multiplies torque for tackling the toughest off-road conditions.

Automatic locking hubs were an early original equipment alternative to manual locking hubs. But while the driver doesn’t have to get out of the vehicle, they often require that the vehicle move a short distance for them to engage, which may not be possible if the vehicle is stuck. Today most vehicles employ a 4WD actuator, sometimes called a front axle actuator, shift actuator, or differential actuator, which is mounted on the differential housing or axle tube. This is positioned over a 2-piece axle, with one piece connected to the wheel and one piece to the differential. When 4WD is selected by the driver, the transfer case is engaged and begins to turn the front driveshaft. A fork in the actuator moves a collar that locks two gears and the axle shafts together, sending power to the front wheels. The fork is driven by a vacuum, electric, or thermal motor. On most systems the motor is part of the actuator assembly, but on some systems the vacuum motor is remotely mounted and connected to the axle and fork with a cable. The exception to the above are vacuum actuators that mount at the steering knuckles and connect the hubs to the axles when 4WD is selected.

4WD actuators operate in a harsh environment, exposed to dirt, debris, heat, road salt, oil and other fluids, and weather conditions including rain, snow, ice and ambient temperature extremes. These factors, along with use and age, can cause a myriad of symptoms and defects that manifest themselves in different ways according to system. Vacuum hoses can swell when exposed to chemicals or dry out and crack from heat and age, resulting in vacuum leaks. The diaphragms in vacuum actuators can fail in a similar manner. On some vacuum hubs the vacuum holds off the actuator, so if it fails the axle stays engaged. Electric motors can fail, and environmental conditions can corrode electrical connectors. This can also affect vacuum systems where vacuum is directed by an electric solenoid. Thermal actuators may fail to engage in cold weather and if the axle is submerged, the cold water may cause the axle to disengage. Mechanical components of the system like the shift fork and shift cable can also wear and fail. These defects can result in an axle that fails to engage and provide four wheel drive, or the axle may stay engaged when four wheel drive is not wanted.

On vacuum systems component integrity can be checked with a vacuum pump. Electrical components can be checked with a digital multi-meter and a scan tool. Depending on year, make and model a 4WD problem may set a diagnostic trouble code and illuminate a malfunction light on the dash. A scan tool can be used to read trouble codes and observe the operation of components in the system. If testing and diagnosis reveals that replacement parts are needed, we have the 4WD actuators to restore reliable 4WD engagement and vehicle performance. All our 4WD actuators and related components are made to original equipment specifications, so when repairs are completed you can count on the performance and durability your vehicle was designed to deliver. In some cases, our replacement parts have been improved and made stronger based on analysis of common component failures. In addition to all types of 4WD actuators, we also have 4wd switches, indicator light switches, wiring harnesses, hub locking solenoids, shift forks, cables, relays, connectors, and actuator housings, as well as complete kits for select applications that come with everything needed for a thorough repair including shift actuator, fork, collar, gears, seals, gaskets and more.