Sierra Classic 2500 4WD V8-6.0L (2007)
4HI Mode Power Flow
In 4HI mode, the engine power from the transmission (1) is delivered to the input shaft (2). The engagement teeth on the inside of the input shaft (2)
are engaged to the outer teeth on the high/low range sleeve (3). The high/low range sleeve (3) is slip splined to the rear output shaft (4). During a shift
mode from 2HI to 4HI, the cam profile on the shift detent lever (14) pushes the 2/4 wheel drive mode shift fork (9) and the synchronizer sleeve. The
sleeve, engaging the synchronizer (5), equalizes the front propeller shaft (12) and rear propeller shaft (7) speeds. The sleeve then engages to the 2/4
wheel drive synchronizer gear (8), which is splined to the drive sprocket (6). The engine power flow for driving the front propeller shaft (12), now
travels from the rear output shaft (4) to the synchronizer hub, which is splined to the rear output shaft (4). The power flows from the synchronizer hub
to the sleeve and then to 2/4 wheel drive synchronizer gear (8). The power flow is transmitted by a chain (10) to the driven sprocket on the front
output shaft (11) and to the front propeller shaft (12). The front and rear propeller shafts are being driven at equal RPM, therefore giving a four wheel
drive mode. This mode should only be used for extra traction. Using this mode on dry pavement causes tire scuffing when turning.
