DESCRIPTION AND OPERATION
TRANSFER CASE DESCRIPTION AND OPERATION
The Borg Warner (BW) model 4493/4494 NR4 transfer case is a 2-speed, full-time 4WD,
transfer case. The transfer case has an external planetary type differential, which has 2 different
sets of pinion gears. The planetary differential provides a 40/60 torque split front/rear full-time.
This means the front and rear propeller shafts are constantly being driven for maximum traction in
all conditions. A high/low planetary carrier assembly provides the high and low ranges, which is a
6-pinion gear, sun gear and annulus gear arrangement, giving a 2.64 low range reduction ratio in
the BW 4493 and a 4:1 ratio in the BW 4494.
The BW 4493/4494 case halves are high-pressure die-cast magnesium. Ball bearings support the
input shaft, the mainshaft, the front output shaft and the rear output shaft. A needle roller bearing
is located inside of the input shaft gear to support the front of the mainshaft. The rear of the
mainshaft is supported by a bronze bearing inside the rear output shaft. The transfer case requires
DEXRON III ATF Fluid GM P/N 12378470 (Canadian P/N 10952622), which is red in color.
An oil pump pumps the fluid through the mainshaft oil gallery to the gears and bearings.
Transfer Case Shift Control Switch
Fig. 147: Transfer Case Shift Control Switch Replacement
2007 Hummer H3
2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3