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 TRANSMISSION Transfer Case - MP 1222/1225/1226-NQG - Cab & Chassis Sierra, Cab & Chassis 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
NEUTRAL Mode Power Flow
Shifting to the NEUTRAL position, the high/low clutch is centered between the input shaft and
the high/low planetary carrier. The high/low clutch is not engaged with either the input shaft or
the high/low planetary carrier teeth. The 2/4 wheel drive synchronizer is in the 4HI mode
position.
SPECIAL TOOLS AND EQUIPMENT
SPECIAL TOOLS
Illustration
Tool Number/Description
DT-48021
Seal Installer
DT-48022
Output Bushing Installer
DT-48209
Bushing Remover
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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