Chevrolet Silverado / GMC Sierra. Service manual — part 2862

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

Fig. 53: 2WD Mode Power Flow
Courtesy of GENERAL MOTORS CORP.

The transfer case is shifted by a remote mounted shift lever, which is connected by linkage to the
shift lever (9) on the shift detent lever shaft. The shift detent lever shaft rotates the cam shaped
shift detent lever assembly (10) and moves the high/low range shift fork (11) or the 2/4 wheel
drive mode shift fork (8). Depending on the selected mode or range, the shift forks move either
the high/low clutch (4) for the high/low range planetary assembly (3) or the synchronizer sleeve
(6) for the 2/4 wheel drive mode. In the 2WD mode, the engine power from the transmission (1)
is delivered to the input shaft (2). The engagement teeth on the inside of the input shaft (2) are
engaged to the outer teeth on the high/low clutch (4). The high/low clutch (4) is slipped splined
to the rear output shaft (5). The engine power flows from the high/low clutch (4) to the rear
output shaft (5) and is delivered to the rear propeller shaft (7).

4HI Mode Power Flow

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

Fig. 54: 4HI Mode Power Flow
Courtesy of GENERAL MOTORS CORP.

In the 4HI mode, the engine power from the transmission (1) is delivered to the input shaft (2).
The engagement teeth on the inside of the input shaft (2) are engaged to the outer teeth on the
high/low clutch (3). The high/low clutch (3) is slipped splined to the rear output shaft (4). During
a shift mode from 2HI to 4HI the cam profile on the shift detent lever assembly (14) pushes the
2/4 wheel drive mode shift fork (9) and the synchronizer sleeve. The sleeve, engaging the
synchronizer (8) equalizes the front propeller shaft (12) and rear propeller shaft (7) speeds. Then
the sleeve engages to the drive sprocket (6). The engine power flow for driving the front
propeller shaft (12), now travels from the rear output shaft (4) to the synchronizer hub (5), which
is splined to the rear output shaft (4). The power flows from the synchronizer hub (5) to the
sleeve and then to the drive sprocket (6). The power flow is transmitted by a chain (10) to the
driven sprocket on the front output shaft (11) and to the front propeller shaft (12). The front and
rear propeller shafts are being driven at equal RPM, therefore giving a four wheel drive mode.
This mode should only be used for extra traction. Using this mode on dry pavement causes tire
scuffing when turning.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

4LO Mode Power Flow

Fig. 55: 4LO Mode Power Flow
Courtesy of GENERAL MOTORS CORP.

During range shift request to 4LO, a separate cam profile on the same shift detent lever assembly
(12) moves the high/low shift fork (13). The high/low shift fork (13) moves the high/low clutch
(6) rearward. The high/low clutch (6) outer teeth disengage from the input shaft (2) high-speed
teeth. The high/low clutch (6) outer teeth then engage in the high/low planetary carrier teeth (5).
The power flow is now from the transmission (1), to the planetary teeth on the input shaft (2), to
the planetary gears (3) in the high/low planetary carrier assembly (5). Rotating the planetary
gears (3), which are engaged in the high/low internal gear (4), rotates the high/low planetary
carrier assembly (5). The high/low planetary carrier assembly (5) delivers the power to the
high/low clutch (6). The high/low clutch (6) then drives the rear output shaft (7), providing a
2.68:1 gear ratio reduction to the rear output shaft (7). The sleeve is still engaged to drive the
drive sprocket (9), as in the 4HI position, providing the engine power to the rear propeller shaft
(10) and to the front propeller shaft (11).

2008 Chevrolet Silverado 1500

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

Sierra & Silverado