A rekeyable master keyable lock includes a plurality of key followers, a plurality of user racks and a plurality of master racks. One user rack and one master rack are associated with each key follower and are configured to be selectively disengaged from, and reengaged with, the key follower. When the user racks are disenggaged from the key follower, the valid user key can be replaced with a new user key. Reengaging the user racks with the key followers rekeys the lock cylinder to the new user key and invalidates the original user key. Similar functionality applies to rekeying the master key. Either the user key or the master key can be rekeyed without rekeying the other.

A rekeyable master lock includes a plurality of pin gears, with each pin gear engaged with a corresponding key follower. As each key follower rides up and down on the key bitting, it causes a corresponding pin gear to rotate. Each pin gear engages a user gear and a master gear so that, as the pin gear rotates, the user and master gears rotate. Each user and master gear, in turn, drives a corresponding user rack and a master rack. When a valid user key is inserted and rotated, the user racks or master racks are aligned along a common axis and held in alignment by a locking bar. Longitudinal movement of the user gear or master gear allows the rekeying function by decoupling and recoupling the user gear or master gear with the user racks or master racks.