4LO Mode Power Flow

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Identifying 4LO Mode Power Flow

Courtesy of GENERAL MOTORS CORP.

Callout	Component Name
1	Input Shaft
2	Two/Four Shift Fork
3	Drive Chain
4	Rear Output Shaft
5	Front Output Shaft
6	Shift Detent Lever Assembly
7	High/Low Shift Fork

Fig 2: View Of 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).