Abstract: In an optical or magneto-optical disk drive system adapted to receive a shuttered disk cartridge, interference between the disk clamp and the shutter during cartridge insertion is obviated by securing the clamp onto a sliding mount plate which is normally biased to hold the clamp in a rearward position displaced from its normal operating position in alignment with the disk spindle-drive. A drive cam engaged by the leading edge of the cartridge during insertion is drivingly coupled to the mount plate by a double rack and pinion arrangement to drive the mount plate forward into normal operating position after the cartridge shutter is opened. To assure that the clamp is firmly positioned in alignment with the disk spindle-drive, the pinion is compliantly mounted to allow slight overtravel of the drive cam after the clamp mount is arrested by the precision stop thus exerting a forward bias force to the amount plate which holds the clamp mount firmly in place.