Abstract: Disclosed is a release mechanism suitable for releasing and disengaging a chain drive means associated with a drive mechanism for a movable extendable frame assembly. In the arrangement, the drive mechanism includes a drive, a wheel assembly and a drive chain associated with the drive to drive wheels associated with the frame assembly. The mechanism also includes a quick release for permitting the chain drive to be released and disengaged from driving the wheels. The quick release has a movable support mounting the drive, and in which the support is movable about a fixed point to raise and lower the drive from a lower chain tensioned position to an upper chain release position.