A vehicle assembly system automatically decks and automatically fastens body components to chassis components. The system uses an automatic decking and fastening unit that includes a base with an elevatable platform repositionable relative to the base by at least one actuator. A slidable unit carries a fastener driver, is supported on the elevatable platform, and is repositionable relative to the elevatable platform by at least one other actuator. The slidable unit also carries an arm that is repositionable relative to the slidable unit by yet another actuator. A pair of conveyors are positioned away from the base, are movable relative to the base and carry a pair of vehicle components. The conveyors are cycled so that the vehicle components are positioned relative to one another in a predetermined position, and the actuators are operated to reposition the fastener driver to a position determined by engagement of the slidable unit with one of the vehicle components.