Sierra Classic 2500 4WD V8-6.0L (2007)
4LO Mode Power Flow
During a range shift request to 4LO, a separate cam profile, on the same shift detent lever (12), moves the high/low shift fork (13). The high/low shift
fork (13) moves the high/low range sleeve (6) rearward. The high/low range sleeve (6) outer teeth disengage from the input shaft (2) high-speed teeth.
The high/low range sleeve (6) outer teeth then engage in the high/low planetary carrier teeth (5). The power flow is now from the transmission (1) to
the planetary teeth on the input shaft (2) to the planetary gears (3) in the carrier. Rotating the planetary gears (3), which are engaged in the annulus
gear (4), rotates the planetary carrier. The planetary carrier delivers the power to the high/low range sleeve (6). The high/low range sleeve (6) then
drives the rear output shaft (7), providing a 2.72:1 gear ratio reduction to the rear output shaft (7). The 2/4 wheel drive synchronizer (8) is still
engaged to drive the drive sprocket (9), as in the 4HI position, providing the engine power to the rear propeller shaft (10) and to the front propeller
shaft (11).
NEUTRAL Mode Power Flow
Shifting to the NEUTRAL position, the high/low range sleeve is centered between the input shaft and the high/low planetary carrier. The high/low
range sleeve is not engaged with either the input shaft or the high/low planetary carrier teeth. The 2/4 wheel drive synchronizer is in the 4HI mode
position.
Electrical Components
Below is a list of major components that make up the automatic transfer case (ATC) system.
Front Axle Actuator
The front axle actuator engages and disengages the front axle. The front axle actuator consists of a permanent magnetic (PM) motor, a worm gear
controlled plunger, a front axle switch and an electronic control circuit. When a range shift to 4HI, or 4LO is requested, the transfer case shift control
module requests engagement of the front axle by grounding the axle actuator control circuit through a current limiting driver. The front axle actuator
also sends a return signal to the TCCM indicating when the 4WD is engaged.
