Vacuum Disconnect -
Various Jeeps are equipped with a vacuum operated disconnect on the front axle. With this setup the passenger side axle is actually two pieces, an inner shaft and an out shaft. When disconnected the shafts spin independently, meaning the passenger side tire is not connected to the differential. Here is an example of it unlocked. Here is an example of it locked. When unlocked the driveshaft will always sit still even when driving down the highway. This system usually gets a bad wrap, however, there's nothing wrong with it. If yours is working, I'd say leave it alone.
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