An adjustable seat including a seat frame and a rack mounted to a substrate. First and second pinions are rotatably carried by the frame and meshingly engage the rack for relative movement of the rack. The second pinion is movable between an open position allowing rotation of the pinions, and an engaged position wherein the pinions are mutually engaged with each other and the rack, preventing relative movement of the rack and rotation of the pinions. A cam engages the second pinion for moving it between the open position and the engaged position.