2HI to 4HI

Shifting into the 4HI range causes the following to happen:
1. A switch in the shifter mechanism causes the 2HI indicator lamp to turn off and the 4HI indicator lamp to turn on. The front axle indicator lamp does not come on immediately.
2. Torque flows from the input gear to the mainshaft the same as in 2HI 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 triggers a vacuum switch. Engine vacuum is then applied to a vacuum actuator, (mounted on the right fender well), after a delay of about 3 seconds. The delay is provided by a restricted orifice. The delay allows the system to synchronize properly.
5. The vacuum actuator pulls a cable, which pulls the shift fork in the front axle. This connects the right axle output shaft to the front axle differential. Torque now is 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. For more information on the front axle shift mechanism and vacuum actuator.
7. If the shift lever is moved back to 2HI position, the operation in the preceding steps is reversed. In addition, when the transfer case switch turns the vacuum to the vacuum actuator off, it connects the vacuum actuator hose to atmosphere through a vent hose. The actuator can then return to the two-wheel drive position.