Ready? This is from a real live 91 Sidekick manual.
When the car is equipped with these automatic free wheeling hubs is startedd out with the gear shifft lever shifted from 2H to 4H or 4L, the drive power as shown in the diagream below is transmitted to the hub, slide gear and cam. the cam lobe then disengages from the retainer slot and rides on the retainer lobe. As a result, the cam shifts the slide gear to the right as shown in the figure. This shift causes the slide gear to mesh with the gear at the inner side of free wheeling hub body installed on the drive axle housing resulting in automatically creating 4WD with axle shaft drive power being transmitted to wheel hub (wheel).
When the transfer case shift lever is shifted from 4H or 4L to 2H and slowly started to advance in the opposite direction (that is, reverse if advancing forward or advance ahead if reversing), at the same time, the car movement causes the front wheel and front free wheeling hub body to revolve in the direction reverse to previous revolution. As a result, the gear at inner side of free wheeling hub body and its meshed slide gear together with the cam fixed to the slide gear all start to rotate in reverse direction. When the cam lobe is rotated to the retainer slot position, the return spring causes the cam lobe to to return to slot position from its former lobe position on the retainer. The slide gear fixed on the cam shifts to the left as shown in the figure. The gear maintained at inner side of freewheeling hub body then becomes disengaged so that the front wheeling hub becomes free. This operation (4WD -> 2WD) is completed within 2 meters of vehicle advance distance.
there. got that?