Transfer Case Power Flow

Input torque from the transmission is transferred to the input shaft of the transfer case and then onto the differential coupling. The coupling is connected to the differential housing. The planetary gears are held in place by the differential housing, which are connected to the differential internal gear, and the sun gear. The torque is then distributed to both the differential internal gear, and the sun gear, which are connected to the outputs of the transfer case. The internal gear is connected directly to the rear output flange, the sun gear is connected directly to the drive chain sprocket and therefore to the chain drive, which provides front output flange rotation.

Front Casing Assembly 

The front casing assembly provides the location for the input shaft bearing and the front output flange bearing. It is also equipped with threaded holes to mount the chassis mounting bush, 2 lifting eyes and a breather cartridge for the transfer case breather pipe. The breather pipe allows equalization between atmospheric and internal transfer case pressure.

The front casing has an additional boss cast on the inside. The boss is used to mount two snubbers - one on drive side of the chain and one on the coast side - which are secured with 2 screws. The snubbers are suppressing chain vibrations which can occur under medium acceleration conditions, therefore improving NVH (Noise, Vibration and Harshness) issues. During normal operation the chain does not contact the snubbers.

Rear Casing Assembly 

The rear casing assembly provides the location for the rear output flange bearing, the oil fill and drain plug. Fins are cast into the rear casing assembly to improve heat dissipation. The part number & serial number are printed on a bar code label.

Chain Drive 

The chain-drive transfers drive from the center differential to the front output flange. A 3/8" pitch chain connects the sprocket on the transfer case input shaft with the sprocket on the front output flange. As both sprockets have the same number of teeth, the rotational speed of both sprockets is identical. During the vehicle operation the chain delivers the oil upwards and provides the lubrication for the input shaft, the output flange bearings, and the center differential assembly.

Center differential 

The center differential assembly is the primary feature of the transfer case. Torque is transmitted through the center differential coupling and housing, and distributed by the planetary gear set to the differential gears and the front and rear output flanges.

The assembly comprises 6 planetary gears, which are equally spaced within the center differential housing. The planetary gears are supported in both directions by the differential casing and the differential cap.

The different basic torque distribution results from the different circle diameters of the internal gear and the sun gear. If an axle loses traction, the bias between the casing, the planetary gears and the cap generates internal friction inside the differential, and the torque directed to the other axle.