Chevrolet Silverado / GMC Sierra. Manual — part 2861
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
The input shaft pilot bearing assembly is larger 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 edge of the teeth are
symmetric.
The rear output shaft is larger.
The front output shaft drive sprocket is 38.1 mm (1.5 in) wide.
The front output shaft driven sprocket is 38.1 mm (1.5 in) wide.
The rear output shaft rear bearing retaining rings are larger, the outer diameter of the ring
groove at the rear output shaft measures 38.5 mm (1.516 in).
The rear output shaft rear bearing assembly is larger, the inner diameter measures 41 mm
(1.614 in).
The rear output shaft seal is larger, the inner lip diameter measures 54.2 mm (2.134 in).
The rear output shaft bushing is larger, the inner diameter measures 56.08 mm (2.208 in).
The rear case half has larger bores to accommodate the rear output shaft seal and the rear
output shaft bushing.
2WD Mode Power Flow
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis Silverado,
Sierra & Silverado
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