Chevrolet Silverado / GMC Sierra. Service manual — part 2903

Fig. 53: Magna Transfer Case Bar Code Label
Courtesy of GENERAL MOTORS CORP.

TRANSFER CASE DESCRIPTION AND OPERATION

Transfer Case Shift Control Switch

Callout

Component Name

1

Component Identifier

2

GM Broadcast Code

3

Supplier Code

4

Production Year

5

Julian Date of the Year

6

Assembly Line Number

7

Sequential Number

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Fig. 54: View Of Transfer Case Shift Control Switch
Courtesy of GENERAL MOTORS CORP.

The Magna Powertrain (MP) 1625/1626 RPO NQF transfer case features a 3 mode shift control
switch located on the instrument panel. When the ignition 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 single press 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 engaged.
Once the new mode/range position is fully active, the switch indicator for the new position will

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

remain ON constantly. In the event that the transfer case shift control module can not or will not
complete the shift, the indicator returns to the previously selected position; this is a Transfer Case
Shift Control Switch Indicator Flashes, then Returns to Previous Mode condition.

The MP 1625/1626 transfer case provides the driver with 4 manual mode/range positions:

2HI - 2 Wheel Drive high range

4HI - 4 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 PARK or 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. NEUTRAL position may be
obtained only if the following criteria has been met:

The ignition switch is in RUN.

The automatic transmission is in PARK or NEUTRAL.

The vehicle speed is below 5 km/h (3 mph).

The transfer case is in 2HI mode.

Once these conditions have been met, press and hold both the 2HI and 4LO buttons for 10
seconds. When the system completes the shift to NEUTRAL, the red NEUTRAL lamp will
illuminate.

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. This NEUTRAL position is a 4WD NEUTRAL, meaning the front and rear outputs of the
transfer case are engaged as though in 4HI. With a disengaged front axle, there is no power flow
to the front wheels, thus allowing towing with the front wheels off the ground or flat towing
without driveline binding.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

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

MP 1625/1626 Variations

All Canadian MP1625 Transfer Cases will be equipped with the 2300 series round pin chain.

Additional differences in these models are listed below:

MP1625: The input shaft seal is a single lip seal used only with dry cavity adapters

MP1626: The input shaft seal is a dual lip seal used specifically for the MW7 which has a
wet cavity adapter. These seals are also used for the MYD in order to retain a common part
number for this model.

2WD Mode Power Flow

Model

Transmission

Input
Shaft

Output

Shaft

Chain

Size

Chain

Series

Hi/Low

Planetary Application

MP 1625
Heavy
Duty
(HD)

MYD - 6L90

29T

Spline

31T

Spline

7/16 X

1.5 in

9600

Series

Rocker

Pin

Chain

5 Pinion

K2

MP 1626
Super
Heavy
Duty
(SHD)

MYD - 6L90

MW7 -
Allison

29T

Spline

31T

Spline

7/16 X

1.5 in

2300

Series

Round

Pin

Chain

5 Pinion

K2, K3

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado