Mercedes-Benz ML450 Transfer Case Shift Motor Replacement Cost

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.

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.

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.

Since the transfer case is essential to drive, any failure resulting in inability to operate the vehicle normally will require immediate repair. In some cases, the transfer case shift motor can be disconnected to prevent erratic shifting, but if another drive mode is needed, it will be unavailable.

Transfer case shift motors in some makes and models are known for frequent failure, even in the first 50,000 miles. However, this is not typical, especially when shifting procedures from the manufacturer are followed. This is the best way to help the transfer case shift motor continue operation.

Transfer case issues on modern vehicles are obvious as a scanner will identify fault codes related to the issue. The vehicle may drive normally in most instances, so the issue may have to be replicated through driving to determine the cause of the fault. When a transfer case is obviously mechanically damaged, it must be removed, disassembled, checked against specifications, and diagnosed as repairable or not. Mechanical issues may cause failure of an otherwise functional transfer case shift motor.

Transfer case shift motor replacement involves removing the shift motor from the exterior of the transfer case housing, and moving the electrical connector from the old part to the new part. Then the new shift motor can be installed, ensuring the correct orientation. Finally, testing the shift motor according to the factory recommended shifting procedures will ensure the shift motor is functioning properly.

Even if a transfer case issue does not cause complete failure, the vehicle should be placed out of service. This is to protect the transfer case from further damage, and provide safety for the intended occupants. If the transfer case fails during operation, the vehicle may be left permanently in neutral or the transfer case may bind. If the transfer case is malfunctioning electronically it can cause erratic shifts from high to low gear and from two-wheel drive to four-wheel drive. Either situation can cause a dangerous situation while driving.

Many models of vehicle, even from the same model year, will use a different transfer case than another vehicle of the same type. This is due to differences in gear ratios, engine power, and intended use for the vehicle. Before replacing a transfer case shift motor, ensure that the proper part number is ordered to avoid incompatibility with the installed transfer case. If the vehicle has a variation which uses more or less advanced transfer case control, ensure the part numbers are correct for the intended model.

This is an easy diagnosis and an even easier repair. Most transfer case shift motors are external, so replacement is as easy as outlined. When diagnosing at home, it may be easiest to remove the shift motor and power it externally to determine if it functions under direct power. If a torque wrench is not available, purchase or borrow one to ensure protection of the transfer case housing.