Transfer Case Description and Operation

WARNING: This page is about a different car, the 2003 GMC Yukon, 2003 Cadillac Escalade EXT, 2003 Cadillac Escalade ESV, and 2003 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.

The Borg Warner (BW) model 4481, RPO NR3 transfer case is a one-speed, full time, all wheel drive (AWD), transfer case. The transfer case provides power to both axles, through an external planetary type differential, which has two different sets of pinion gears. The planetary differential provides a 40/60 torque split, front/rear, full time. This means both axles are constantly being driven for maximum traction in all conditions.

The transfer case external type planetary differential functions the same as a typical rear axle differential. The transfer case differential pinion gears function as the spider gears, and the sun gears function as the side gears.

The following actions occur because of the planetary differential:

If the vehicle is on a hoist, the front propeller shaft can be rotated by hand.
The vehicle cannot be driven if one propeller shaft is removed.
Operating the vehicle on the hoist can damage the differential pinion gears, by over-spinning.
Operating the vehicle with one propeller shaft removed causes over-spinning of the differential pinion gears.

The BW 4481 design of the planetary differential allows the use with the Vehicle Stability Enhancement System (VSES) vehicles. The VSES takes use of the planetary differential, by applying braking to a tire that has less traction and dividing the engine torque to the other axle.

The BW 4481 case halves are high-pressure, die-cast magnesium. Ball bearings support the input shaft, the front output shaft, and the rear output shaft. The transfer case requires DEXRON®(R) III ATF GM P/N 12346143 (Canadian P/N 10952622), which is red in color.

Fig 1: Transfer Case Power Flow Diagram

Courtesy of GENERAL MOTORS CORP.

When the BW 4481 is operating in the AWD mode, the power flows from the transmission to the transfer case input shaft (1). The input shaft (1) delivers the power to the planetary differential (4). The case of the planetary differential (4) is splined to the input shaft (1). The planetary differential (4) splits the torque 40 percent through the front differential pinion gears (3) to the front sun gear (8). The front sun gear (8) is engaged with the drive sprocket (2), which drives the chain (9) to the front output shaft (10), and power is delivered to the front propeller shaft. 60 percent of the torque to the rear output shaft (6) goes through the rear differential pinion gears (7) and rear sun gear (5), which is connected to the rear output shaft (6) and to the rear propeller shaft.