Thread: 4wd Electronic Shifting, what are locking hubs for?
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Old Sun, July 31st, 2011, 03:17 PM
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The front driveshaft SHOULD NOT turn all of the time.

If the transfer case is shifting properly by going back to 2wd but the front axle shafts are still being driven by the front wheels, then the vacuum operated locking mechanisms in the hubs are not releasing. This is common for older trucks as the hub spline return is inhibited by sludge or gunk in the hubs....or the vacuum system check valve has failed and not allowing the vacuum to vent when 4wd is not selected. You would know in a hurry if the transfer case was still in 4wd mode...you couldn't drive on hard surfaces without the thing bucking like a saddle bronc in turns.

The reason for having a selectable locking hub is twofold. It allows high-speed on-the-fly switching to 4HI from 2wd and is a redundant system in case of vacuum actuation system failure.
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