On part-time four-wheel-drives, the front wheels and axle drive shafts are splined together through the differential side gears.
When the vehicle is using a two-wheel drive range, the front axle drive shafts, final drive assembly and front propeller shaft all turn with the road wheels, but do not transmit any drive.
Free-wheeling hubs can be installed on the front hubs, to disconnect the hubs from the axle shafts, and prevent rotation of the front axle components.
This reduces wear and noise and improves performance and fuel economy, in a two wheel drive range.
When "lock" is selected on this manually-engaged type, it acts on this sleeve. It has external splines into the free-wheel hub body, and internal splines to engage a hub on the axle shaft. The sleeve locks the two components together.
In a four-wheel drive range, the drive is transmitted from the axle shaft, through the clutch, to the hub and road wheel.
When "free" mode is selected, the compressed spring pushes the clutch sleeve out of engagement, leaving the wheel free to rotate without turning the axle shaft.
