TM 9-2320-361-20 1-21. COMPRESSED AIR AND BRAKE SYSTEM OPERATION (Contd) 1-62 b. Brake System Operation. HYDRAULIC BRAKE LINES - Directs brake fluid under hydraulic pressure to all six wheel cylinders. BRAKE PEDAL - Operator control for slowing or stopping vehicle. Applies force through brake linkage to master cylinder to actuate vehicle brakes. BRAKE LINKAGE - Transmits brake pedal force to master cylinder. HAND CONTROL VALVE (M275A2 only) - Controls semi-trailer brake system. Allows brakes to be applied and released manually. MASTER CYLINDER - Stores brake fluid and is the filling location for addition of brake fluid. Converts force from brake linkage into hydraulic pressure. AIR-HYDRAULIC UNIT - Combines hydraulic pressure from master cylinder and air pressure from compressed air system to supply increased hydraulic pressure to the vehicle brakes. WHEEL CYLINDER - Converts hydraulic pressure into mechanical force to press brakeshoes against surface of brakedrum. BRAKEDRUM - Encloses wheel cylinder and brakeshoes, and provides surface for brakeshoes to press against. BRAKESHOE - Applies friction to brakedrum to slow or stop rotation of wheels.