Principles of Operation

WARNING: This page is about a different car, the 2004 Mercury Mountaineer and 2004 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.

The constantly activated, automatic, all-wheel drive transfer case has no external controls. A two-piece aluminum case houses the assembly. The unit is chain-driven. A non-repairable viscous coupling provides torque distribution to the front and rear transfer case outputs. The viscous coupling contains slotted alternating plates through which a high viscosity transmission fluid flows. The resistance of the fluid shear causes the plates to transmit at the approximate ratio of 35 percent to the front output and 65 percent to the rear output.

Torque flows through the input shaft to the front planetary gear assembly outward to the ring gear and to the upper output shaft. Torque also flows through the front planetary gear assembly to the overdrive sun gear and outward to the upper drive sprocket. The torque flow continues from the upper drive sprocket through the drive chain to the lower drive sprocket and to the front output shaft. The viscous coupling provides the connection between the ring gear and the overdrive sun gear.