1. Engaging 4WD (4 High or 4 Low): When you shift the transfer case into 4WD, a vacuum signal is sent to the hubs.
2. Vacuum Actuator: Each front wheel has a vacuum actuator (sometimes called a vacuum hub) attached to the hub assembly. This actuator is a small diaphragm-like device.
3. Vacuum Application: The vacuum signal causes the diaphragm in the actuator to expand, pushing a mechanism that locks the front axle's stub shaft to the wheel's rotating hub. This connects the front wheels to the driveshaft.
4. Disengaging 4WD (2WD): When you shift back to 2WD, the vacuum is released from the actuators. A spring within the actuator then retracts the locking mechanism, disconnecting the front wheels from the driveshaft. The front wheels are now free to spin independently of the driveshaft, allowing for 2WD operation.
Important Considerations:
* Vacuum Leak: If there's a leak in the vacuum system (hoses, actuator seals), the hubs may not engage or disengage properly. You could have one hub locked and the other not. This is a common problem with these systems as they age.
* Manual Override (sometimes): Some, but not all, 1996 Dodge Ram 1500 models might have a manual override. Check your owner's manual, but this typically involves pushing/pulling a button or lever on the hub itself. This is usually only for emergency situations to free the hub if it is stuck.
* Indicator Lights: Your truck should have indicator lights (often on the dash) that show whether the 4WD is engaged and typically whether the hubs are engaged. If the lights don't match the shift position, you have a problem in the system.
In short, it's a simple system but reliant on proper vacuum operation. If your 4WD isn't working correctly, check the vacuum lines for leaks and the vacuum actuator for proper operation before diving into more complex transfer case or axle issues. A vacuum gauge can be helpful for troubleshooting.
