Transfer Case: Description and Operation

Four-Wheel Drive (4WD) Systems

Mechanical Shift
The Borg-Warner 44-06 manual shift transfer case is a 3-piece aluminum design. The unit transfers engine power from the transmission to the front and rear axles. Under normal driving conditions the unit is in 2-Wheel Drive High (2H), but when desired, the operator may shift into 4-Wheel Drive High (4H) or 4-Wheel Drive Low (4L). The transfer case is shifted manually. The unit is lubricated by a positive displacement fluid pump that channels fluid flow through holes in the rear output shaft.


Principles of Operation
The Mechanical Shift On The Fly (MSOF) system is a manual shift 4WD system that allows the operator to chose between 2 different 4x4 modes as well as 2-wheel drive and neutral. The operator can switch between 2WD and 4H mode at speeds up to 88 Km/h (55 mph). To engage or disengage 4L range, the vehicle speed must be less than 5 Km/h (3 mph), the brake pedal pressed and the transmission must be in NEUTRAL (or the clutch pedal pressed in manual transmission vehicles).

The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to synchronize the front driveline. When the manual shift lever is moved, this activates the mode indicator switch, triggering the 4x4 module (PCM) to energize the electromagnetic clutch. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle Integrated Wheel Ends (IWEs) are engaged and the electromagnetic clutch is deactivated.

Feature Inputs:
^ Mode indicator switch.
^ Wheel speeds (via CAN communication).

Feature Outputs:
^ Transfer case synchronization clutch.
^ Integrated wheel end (IWE) vacuum solenoid.
^ 4WD mode (via CAN input to PCM).
^ Cluster Indicators (via CAN communication).


Electronic Shift
The Borg-Warner electronic shift transfer case is a 3-piece aluminum design. The unit transfers engine power from the transmission to the front and rear axles. Under normal driving conditions the unit is in 2-Wheel Drive High (2H), but when desired, the operator may shift into 4-Wheel Drive High (4H) or 4-Wheel Drive Low (4L). The transfer case is shifted electronically. The unit is lubricated by a positive displacement fluid pump that channels fluid flow through holes in the rear output shaft.


Principles of Operation
The Electronic Shift On The Fly (ESOF) system is an electronic shift system that allows the operator to choose between 2 different 4-wheel drive modes as well as 2-wheel drive. The operator can switch between 2WD and 4H mode at speeds up to 88 Km/h (55 mph). To engage or disengage 4L range, the vehicle speed must be less than 5 Km/h (3 mph), the brake pedal pressed and the transmission must be in NEUTRAL (or the clutch pedal pressed in manual transmission vehicles).

The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to synchronize the front driveline. When the Mode Select Switch (MSS) on the instrument panel is turned, the 4x4 module (PCM) activates the electromagnetic clutch and powers the transfer case shift motor. When the shift motor reaches the desired position, as determined by the contact plate position inputs to the 4x4 module (PCM), power to the shift motor will be removed. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle Integrated Wheel Ends (IWEs) are engaged and the electromagnetic clutch is deactivated.

Feature Inputs:
^ Mode Select Switch (MSS).
^ Wheel speeds (via CAN communication).
^ Contact plate position inputs A, B, C, D (grounded when closed, open circuit when open).
^ Transmission neutral.
^ Brake ON/OFF (BOO).

Feature Outputs:
^ Transfer case synchronization clutch.
^ Transfer case shift motor relays.
^ Integrated Wheel-End (IWE) vacuum solenoid.
^ Cluster indicators (via CAN communication).
^ AWD mode (via CAN communication to PCM).

Integrated Wheel End (IWE) System

The integrated wheel end (IWE) system contains the following:

^ Vacuum reservoir
^ IWE solenoid
^ IWEs (spring loaded vacuum hubs)
^ Vacuum hoses
^ Check valve

The IWE system uses vacuum hubs that engage the front wheel hubs to the front halfshafts or disengage the front wheel hubs from the front halfshafts.

The IWE solenoid receives engine vacuum from the vacuum reservoir.

When the 4-wheel drive system is in 2WD mode, the 4X4 module (PCM) supplies a ground path to the IWE solenoid to apply vacuum to the integrated wheel ends (disengaging the front hubs from the front halfshafts). In 4WD mode, the 4X4 module (PCM) does not supply the ground path to the IWE solenoid, vacuum is not applied to the integrated wheel ends and an internal spring keeps the front hubs engaged to the front halfshafts.