A closure assembly for a motor vehicle includes a closure member, a guide track and a carrier operably secured to the guide track for movement along the guide track and carrying the closure member therewith. A rack has a plurality of teeth and extends along the guide track. A pinion gear is carried by the carrier and has teeth engaging the rack. A motor is operably connected to the pinion gear to selectively move the closure member from one position to another. The carrier includes at least one engagement member biased into engagement with the guide track to prevent binding of the carrier with the guide track and to maintain contact between the pinion gear and the rack.