Four-Wheel Drive High Range Operation

Shifting into the "4 Hi" range causes the following to happen:

1. The front axle indicator lamp does not come on until the front axle engages.
2. Torque flows from the input gear to the mainshaft the same as in the "2 WHEEL" position. The shift linkage moves the mode synchronizer sleeve into engagement with the clutch teeth of the drive sprocket. This locks the drive sprocket to the mainshaft through the synchronizer sleeve.
3. Torque is transmitted through the drive sprocket and drive chain to the driven sprocket and output shaft. Torque then flows through the front propeller shaft to the front axle.
4. The shift mechanism in the transfer case closes the transfer case switch. Current is then applied to the front axle thermal actuator and front axle switch. In the K30 vehicles, power is also supplied by the transfer case relay to the transfer case synchronizer.
5. The thermal actuator contains a heating element, a gas charge, and a piston. When current is applied the heating element heats the gas. The gas expands, pushing the piston out after a delay of a few seconds. The piston actuates the shift fork in the front axle. This connects the right axle output shaft to the front axle differential. Torque is then available at the front wheels.
6. The front axle shift mechanism, when fully engaged, closes a switch, causing the front axle indicator lamp to come on.
7. If the shift lever is moved back to the "2 WHEEL" position, the operations in the preceding Steps are reversed. The current to the thermal actuator is turned off. The gas cools, and the piston retracts allowing the shift fork in the front axle to return to the two-wheel drive position.