Transfer Case Shift Control Switch

Fig 1: Transfer Case Shift Control Switch

Courtesy of GENERAL MOTORS CORP.

The MP 3023/3024 ATC transfer case features a 4 mode shift control switch located on the instrument panel. When the ignition key is in the RUN position, the transfer case shift control module monitors the transfer case shift control switch to determine if the driver desires a new mode/range position. At a turn of the transfer case shift control switch, the lamp of the new desired position will begin flashing to inform the driver that the transfer case shift control module has received the request for a new mode/range position. The lamp continues to flash until all shifting criteria has been met and the new mode/range position has been reached, or has been engaged. Once the new mode/range position is fully active, the switch indicator lamp for the new position will remain ON constantly.

During normal driving situations, the transfer case can operate in the Auto 4WD mode. In the Auto 4WD mode, the transfer case shift control module monitors rear wheel slip speed, based on the inputs from the wheel speed sensors. When the vehicle experiences a rear wheel slip condition, the transfer case shift control module sends a pulse width modulated (PWM) signal to an electronic motor, which is the transfer case 2/4 wheel drive actuator assembly. This actuator rotates the transfer case control actuator shaft, applying a clutch. The clutch is designed to deliver a variable amount of torque, normally delivered to the rear wheels, and transfers it to the front wheels. Torque is ramped up to the front wheels until the front wheel speed sensors matches that of the rear speed sensors. Torque is ramped down to the front wheels. The process would repeat if rear wheel slip is detected again.

The MP 3023/3024 ATC transfer case has the added feature of also providing the driver with 4 manual mode/range positions:

• 4HI - 4 Wheel Drive high range
• 2HI - 2 Wheel Drive high range
• 4LO - 4 Wheel Drive low range, 2.68:1 gear ratio reduction
• Neutral

The driver may choose to select any of these mode/range positions while driving the vehicle. However, the transfer case will not allow a shift into or out of 4LO unless the following criteria has been met:

• The ignition switch is in RUN.
• The automatic transmission is in NEUTRAL.
• The vehicle speed is below 5 km/h (3 mph).

This transfer case also has a NEUTRAL position. A shift to the NEUTRAL position allows the vehicle to be towed without rotating the transmission output shaft. In the NEUTRAL position, the rear propeller shaft rotates the transfer case rear output shaft, in turn rotating the oil pump, thus providing constant lubrication during towing. NEUTRAL position may be obtained only if the following criteria has been met:

• The ignition switch is in RUN.
• The automatic transmission is in NEUTRAL.
• The vehicle speed is below 5 km/h (3 mph).
• The transfer case is in 2HI mode.

Once these conditions have been met, turn the rotary switch clockwise past 4 low and hold for 10 seconds. When the system completes the shift to NEUTRAL, the red NEUTRAL lamp will illuminate.

The NQH transfer case is available in 2 variations, depending on the engine and transmission configurations. The variations allow the transfer case to handle torque loads. When servicing the transfer case, it is important to understand which variation is being serviced because of the difference in parts.

Additional differences in these models are listed below:

MP 3023 ATC with 27T Input Spline

• The high/low clutch has bias pointing engagement teeth. The leading edges of the teeth are not symmetric.
• The rear output shaft rear bearing retaining rings are larger than the MP 3023 ATC with 32T Input Spline but smaller than the MP 3024. The inner diameter of the ring groove at the rear output shaft measures 37.5 mm (1.476 in).
• The rear output shaft bearing assembly inner diameter measures 40 mm (1.575 in) the width measures 18 mm (0.709 in).
• The rear output shaft bearing assembly surface on the rear output shaft measures 40 mm (1.575 in).

MP 3023 ATC with 32T Input Spline

• The high/low clutch has neutral pointing engagement teeth. The leading edges of the teeth are symmetric.
• The speed reluctor wheel profile thickness is thinner than the MP 3023 ATC with 27T input spline and the MP 3024, measuring 25.8 mm (1.016 in) thick.
• There is no snap ring between the speed reluctor wheel and the rear output shaft rear bearing assembly.
• There is no snap ring groove in the rear output shaft between the speed reluctor wheel and the rear output shaft rear bearing assembly.
• The rear output shaft rear bearing retaining ring is smaller than the MP 3023 ATC with 27T input spline and the MP 3024. The inner diameter of the ring groove at the rear output shaft measures 33 mm (1.299 in).
• The rear output shaft bearing assembly inner diameter measures 35 mm (1.378 in) the width measures 23 mm (0.906 in).
• The rear output shaft bearing assembly surface on the rear output shaft measures 35 mm (1.378 in).
• There is an additional harness bracket.

MP 3023 ATC, Common to LD

• The input shaft pilot bearing assembly is smaller than the MP 3024 ATC in order to accommodate the smaller rear output shaft. The outer diameter measures 38.1 mm (1.5 in).
• The rear output shaft is smaller than the MP 3024 ATC.
• The front output shaft drive sprocket is 27.2 mm (1.071 in) wide.
• The front output shaft driven sprocket is 29.4 mm (1.157 in) wide.
• The rear output shaft seal is smaller than the MP 3024 ATC. The inner lip diameter measures 46.1 mm (1.815 in).
• The rear output shaft bushing is smaller than the MP 3024 ATC. The inner diameter measures 48 mm (1.890 in).
• The rear case half has smaller bores than the MP 3024 ATC in order to accommodate the rear output shaft seal and the rear output shaft bushing.
• The control lever is thinner than the MP 3024 ATC, measuring 9.5 mm (0.374 in) between the bearing surfaces.
• The control actuator lever is thinner than the MP 3024 ATC, measuring 9.5 mm (0.374 in) between the bearing surfaces.
• The control actuator lever balls are larger than the MP 3024 ATC, measuring 13 mm (0.512 in) in diameter.
• The control actuator lever washer is thinner than the MP 3024 ATC, measuring 1 mm (0.039 in).

MP 3024 ATC

• The input shaft pilot bearing assembly is larger than the MP 3023 ATC in order to accommodate the larger rear output shaft. The outer diameter measures 41.275 mm (1.625 in).
• An input shaft pilot bearing retaining ring is used.
• The high/low clutch has neutral pointing engagement teeth. The leading edges of the teeth are symmetric.
• The rear output shaft is larger than the MP 3023 ATC.
• The front output shaft drive sprocket is 33.5 mm (1.319 in) wide.
• The front output shaft driven sprocket is 35.5 mm (1.398 in) wide.
• The rear output shaft rear bearing retaining rings are larger than the MP 3023 ATC. The inner diameter of the ring groove at the rear output shaft measures 38.5 mm (1.516 in).
• The rear output shaft rear bearing assembly inner diameter measures 41 mm (1.614 in). The width measures 18 mm (0.709 in).
• The rear output shaft bearing assembly surface on the rear output shaft measures 41 mm (1.614 in).
• The rear output shaft seal is larger than the MP 3023 ATC. The inner lip diameter measures 53.8 mm (2.118 in).
• The rear output shaft bushing is larger than the MP 3023 ATC. The inner diameter measures 56.08 mm (2.208 in).
• The rear case half has larger bores than the MP 3023 ATC in order to accommodate the rear output shaft seal and the rear output shaft bushing.
• The control lever is thicker than the MP 3023 ATC, measuring 10.5 mm (0.413 in) between the bearing surfaces.
• The control actuator lever is thicker than the MP 3023 ATC, measuring 10.5 mm (0.413 in) between the bearing surfaces.
• The control actuator lever balls are smaller than the MP 3023 ATC, measuring 10 mm (0.394 in) in diameter.
• The control actuator lever washer is thicker than the MP 3023 ATC, measuring 2.5 mm (0.098 in).