To shift on the fly : Push the button on the dash "Axle Lock" , it will light up. Then you can shift from 2wdHigh to 4wd high on the fly. You do not have to stop. If the button is not pushed in, and you try to shift on the fly, it will grind. You should not ever shift into low range while moving and most likely can Not even do it, without grinding the hell out of the gears.