Chevrolet Silverado / GMC Sierra. Service manual — part 2861

Fig. 51: Transfer Case I.D. Label
Courtesy of GENERAL MOTORS CORP.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Fig. 52: Magna Transfer Case Bar Code Label
Courtesy of GENERAL MOTORS CORP.

TRANSFER CASE DESCRIPTION AND OPERATION

The Magna Powertrain (MP) 1222/1225/1226, RPO NQG transfer case is a 2-speed, part-time
with mode shift-on-the-fly capability. It has a chain driven front output shaft and an epicyclical
low range planetary arrangement. The MP 1222/1225/1226 transfer case features a 4 position
shift lever control located in the vehicle floor plan. As required, the operator can select 4HI
position from 2HI on-the-fly, as described in the owners manual. A dash mounted 4WD lamp
continues flashing during shifting, until all criteria have been met and the new mode/range
position has been reached. Once the new mode/range position is fully engaged and the front axle
disconnect locks in, the dash light 4WD indicator lamp remains ON constantly. Range shifting
functions similarly, although it should be limited to speeds 5 km/h (3 mph) or less.

The 4 manual mode, or range gear positions, of the MP 1222/1225/1226 transfer case are:

2HI - 2 wheel drive high range

4HI - 4 wheel drive high range, part-time

4LO - 4 wheel drive low range, 2.68:1 gear ratio reduction

N - NEUTRAL, 4 wheel

When the ignition switch is placed in the run position and the 4WD shift lever is in the 4WD
position, the transfer case switch closes, supplying a ground to the axle actuator control circuit.
With the ground applied, the logic of the front axle actuator actuates a DC motor to engage the
front axle and supply voltage to the axle switch signal circuit. The axle switch signal circuit
notifies the engine control module (ECM) and the Anti-Lock Brake System that the vehicle is in
the 4WD mode. The 4WD indicator is commanded on via a GM LAN serial data signal from the
ECM. When the 4WD shift lever is in the 4WD low range position, the transfer case switch closes
and supplies a ground on the 4WD low signal circuit. This informs the ECM that the vehicle

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 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

transfer case is in low range. When the vehicle is in low range, the transmission control module
(TCM) changes the shift pattern of the automatic transmission.

During normal driving situations, the transfer case can operate in the 2WD mode. The driver may
choose to select any of the mode/range gear positions while driving the vehicle. However, the
transfer case should not be shifted into or out of 4LO unless the following criteria have been met:

The transmission is in NEUTRAL.

The vehicle speed is less than 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,
providing constant lubrication during towing. Note, 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 disconnecting front axle, there is no power flow to the front wheels, allowing towing with
the front wheels off the ground or flat towing without driveline binding. Again, the transfer case
should not be shifted into or out of NEUTRAL unless the following criteria have been met:

The transmission is in NEUTRAL.

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

The NQG transfer case is available in 3 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 1222/1225/1226 Variations

Model

Transmission

Input
Shaft

Output

Shaft

Chain

Size

Chain

Series

Hi/Low

Planetary Application

MP 1222
Light Duty
(LD)

M30 - 4L60-E

27T

Spline

32T

Spline

7/16 X
1.25 in

9600

Series

Rocker

Pin Chain

3 Pinion

K1

MP 1225
Heavy
Duty (HD)

MYD - 6L90

29T

Spline

31T

Spline

7/16 X

1.5 in

9600

Series

Rocker

Pin Chain

5 Pinion

K2

MP 1226
Super

MYD - 6L90

2300

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

All Canadian MP1225 Transfer Cases will be equipped with the 2300 series round pin chain.

Additional differences in these models are listed below:

MP1222

The input shaft seal is a dual lip seal used with wet cavity adapters.

The input shaft pilot bearing assembly is smaller to accommodate the smaller rear output
shaft, the outer diameter measures 38.1 mm (1.5 in).

The high/low clutch has bias pointing engagement teeth, the leading edge of the teeth are not
symmetric.

The rear output shaft is smaller.

The front output shaft drive sprocket is 31.75 mm (1.25 in) wide.

The front output shaft driven sprocket is 31.75 mm (1.25 in) wide.

The rear output shaft rear bearing retaining rings are smaller, the outer diameter of the ring
groove at the rear output shaft measures 37.5 mm (1.476 in)

The rear output shaft rear bearing assembly is smaller, the inner diameter measures 40 mm
(1.575 in).

The rear output shaft seal is smaller, the inner lip diameter measures 46.2 mm (1.819 in).

The rear output shaft bushing is smaller, the inner diameter measures 48 mm (1.890 in).

The rear case half has smaller bores to accommodate the rear output shaft seal and the rear
output shaft bushing.

MP 1225

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

MP 1226

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.

MP 1225/1226

Heavy
Duty
(SHD)

MW7 -
Allison

29T

Spline

31T

Spline

7/16 X

1.5 in

Series

Round

Pin Chain

5 Pinion

K2, K3

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado