What is a Transfer Case Shift Motor?
Transfer cases are aptly named in that their function is to transfer power from the transmission output shaft, to the differentials. This function could be considered like a splitter for the transmission because the transfer case accepts the single shaft from the transmission and distributes power from that shaft to two individual driveshafts. There is much more, however, since the transfer case on modern vehicles can change the amount of power sent to the front and rear wheels, and many transfer cases are able to electronically shift from four-wheel drive to two-wheel drive. The electronic portion that allows these shifts to be possible is called the transfer case electronic shift motor, which is controlled by the transfer case control module.
How do Transfer Case Shift Motors work?
As the transmission output shaft spins, splines on that shaft are turning the input shaft for the transfer case. That provides rotational power to the transfer case, which is then distributed to the output shaft by one of two sets of gears. One set of gears will drive only the rear wheels, and the other set of gears will drive only the front wheels. The rear wheels will always be connected, so the switching will only lock in the front wheels. Transfer cases have a locking function as well, and this allows the front and rear wheels to turn at the same speed regardless of the load on each wheel. Again, there is more, since many transfer cases have two speeds - hi and lo. These are typically selected electronically through a transfer case shift motor the same as four-wheel or two-wheel drive is selected. Modern transfer cases have the added benefit of torque vectoring. This function allows a percentage of power from the transmission to be sent to the front or rear wheels on demand.
What are the symptoms of a bad Transfer Case Shift Motor?
Modern vehicles with electronically shifted transfer cases will show warning lights for the transfer case, traction control, and possibly anti lock brake systems, as well as any other manufacturer specific all wheel drive system warning light. Furthermore, the switch to change the transfer case between ranges and drive modes may blink or not light up at all. This is to signal that the electronic portion of the transfer case is inactive. Lastly, the transfer case may be stuck in one drive mode and/or drive range, or switch between these ranges without request from the driver.