Chevrolet Silverado / GMC Sierra. Manual — part 2955
Fig. 62: 4HI Mode Power Flow
Courtesy of GENERAL MOTORS CORP.
In the 4HI mode, the power flow to the rear propshaft (9) is the same as it is in the 2WD mode.
To deliver power flow to the front propshaft (15) during the 4HI position, the transfer case
control module commands the 2/4 wheel drive actuator assembly (13) to apply the clutch to a
calibrated torque. The 2/4 wheel drive actuator assembly (13) turns the control actuator shaft. A
brake in the 2/4 wheel drive actuator assembly (13) holds the control actuator shaft in the full
clutch position. The control actuator shaft is cam designed and the cam action moves the control
actuator lever (12). The control actuator lever (12) pivots against the control lever (17) and
moves toward the clutch pressure plate (4), to engage the clutch (5). As more pressure is applied
to the clutch pressure plate (4), the clutch discs (5) are compressed. Using inner clutch discs,
which are engaged with the clutch hub, and the outer clutch discs, which are engaged with the
clutch housing (6), the power flow is delivered to the clutch housing (6). The clutch hub is
splined to the rear output shaft (8), and the clutch housing (6) rotates on a needle bearing on the
rear output shaft (8). The chain drive sprocket (7) is splined to the clutch housing (6). The power
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
flows from the drive sprocket (7), through the chain (10), to the chain driven sprocket. The
driven sprocket is splined to the front output shaft (14). The power flow is delivered to the front
propshaft (15) through the front output shaft (14).
During the Auto 4WD mode, the power flow is the same as it is in the 4HI mode. Except, during
the Auto 4WD mode, the 2/4 wheel drive actuator assembly (13) rotates the control actuator shaft
to the correct torque level positions. Rotating the control actuator shaft to the various positions
changes the clutch torque level. When a difference of front wheel speed to rear wheel speed is
recognized, the transfer case control modules command for more, or less clutch torque.
4LO Mode Power Flow
Fig. 63: 4LO Mode Power Flow
Courtesy of GENERAL MOTORS CORP.
When shifting the transfer case to the 4LO mode, it commands the 2/4 wheel drive actuator
assembly to turn the control actuator shaft, to move the high/low shift fork (9). The shift fork (9)
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
moves the high/low clutch (5), which is slip splined on the rear output shaft (6) toward the rear of
the transfer case. The high/low clutch (5) outer teeth disengage from the input shaft (2) inner
teeth. The high/low clutch (5) outer teeth then engage in the planetary carrier teeth. The power
flow is now from the input shaft (2) planetary teeth to the planetary gears (3) in the carrier.
Rotating the planetary gears (3), which are engaged in the high/low internal gear (4), the
planetary carrier rotates. The planetary carrier engaged to the high/low clutch (5), drives the rear
output shaft (6), providing a 2.68:1 reduction to the speed of the rear output shaft (6). The power
flow to the front propshaft (8) is the same as it is in the 4HI.
NEUTRAL Mode Power Flow
Shifting to the NEUTRAL position, the high/low clutch is centered between the input shaft and
the high/low planetary carrier. The high/low clutch is not engaged with either the input shaft or
the high/low planetary carrier teeth.
Service 4WD Indicator
The Service 4WD indicator is an integral part of the cluster and cannot be serviced separately.
This lamp is used to inform the driver of the vehicle that a transfer case system malfunctioned.
The Service 4WD indicator is controlled by the transfer case shift control module via Class 2.
Transfer Case Two/Four Wheel Drive Incremental Sensor
The incremental sensor is mounted to the transfer case actuator assembly and is replaced as an
assembly. The incremental sensor converts the shift detent lever shaft position, representing a
mode or range, into an electrical signal input to the transfer case shift control module. The
module detects what position the transfer case is in by monitoring the voltage returned on the
incremental encoder impulse signal circuit. This voltage translates into AUTO 4WD, 2HI, 4HI,
NEUTRAL, and 4LO or in transition between gears.
Transfer Case Two/Four Wheel Drive Actuator Assembly
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
Fig. 64: Transfer Case Two/Four Wheel Drive Actuator Assembly
Courtesy of GENERAL MOTORS CORP.
The transfer case two/four wheel drive actuator assembly consists of a permanent magnet DC
motor and gear reduction assembly. It is located on the left hand side, driver's side, of the transfer
case. When activated, it turns the shift detent lever shaft of the transfer case, clockwise or
counterclockwise, to shift the transfer case. The motor/encoder is controlled with a PWM signal
by the transfer case shift control module. This circuit consists of a driver on both the Motor A and
Motor B circuits. The encoder motor is bi-directional in order to allow the motor to shift the
transfer case from 2HI or 4HI to NEUTRAL and 4LO positions.
Transfer Case Actuator Shaft Position Sensor Assembly
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
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