A system in which an easily replaceable cartridge containing conveyor mechanisms such as wheels and belts, and a base for mounting the cartridge transports documents. The cartridge includes a carcass having a plurality of recesses in which respective wheels are disposed. When the cartridge is not mounted on the base, the wheels are retained within the recesses in contact with the carcass by belts which encircle the carcass. The base includes a plurality of bearing members of like member to the wheels. When the cartridge is mounted on the base, the wheels are engaged by the bearing members. The base is provided with a tensioning device which, when operated, tensions the belt and spaces the wheels away from the carcass, permitting them to rotate freely about their associated bearing members. At least one of the wheels is retained upon a hub assembly by a click-on, click-off mechanism requiring only single handed operation.