If I pull the FAD actuator and fork off the axle and then put tge jeep in 4wd and back to 2wd while parked, will the fork move back and forth or does it need to be rolling?
It'll move on its own, but if the splines aren't lined up, it'll require wheel movement to fully engage and lock the inner and outer shafts together. Conversely, if the splines are loaded and the FAD collar is bound, some wheel movement may be needed to fully disengage.
Same applies to the Rubicons front edisconnect sway bar coupler.