Abstract: A fluid actuated brake assembly for use with a parallelogram linkage on a dental tray support arm is described. Floating brake shoes positioned on opposite sides of one member of the parallelogram linkage with one of the brake shoes pivotably and slideably attached to the other member of the parallelogram linkage provides a braking and locking effect between the two members of the parallelogram linkage to provide an efficient brake for a dental tray support arm. Upon fluid actuation of the brake assembly, the brake shoes grip one member of the parallelogram and form a rigid connection with the other member of the parallelogram to prevent relative movement of the parallelogram linkage members. The frictional brake assembly also provides an override feature above a predetermined force level to prevent accidental jamming of the dental tray support arm against an object.