TM 10-3930-664-10 1-19. BRAKE SYSTEM SERVICE  BRAKES.    The  service  brakes  are  hydraulically  actuated  by  depressing  the  combination  service  brake  and inching pedal.  Four separate disc brake assemblies, one associated with each wheel, are mounted inside the front and rear axles. MASTER CYLINDERS.  Two separate circuits are used for the front and rear brakes.  Separate master cylinders contain the fluid used to operate the two circuits. PARKING  BRAKE.    Spring  actuated,  hydraulically   released   cylinder   sets   the   two   front   axle   disc   brake   assemblies preventing  the  front  axle  and  wheels  from  turning.    Parking  brake  is  automatically  engaged  when  the  engine  stops.    A toggle switch, located on the instrument panel, engages or disengages the parking brake when the engine is running.  In the ON position, the switch deactivates a solenoid valve allowing the spring to retract the cylinder rod and apply the parking brake.  In the OFF position, the switch activates the solenoid to hydraulically extend the cylinder  rod  and  disengage  the parking brake. 1-20. STEERING SYSTEM STEERING CYLINDERS.  A cylinder is integral to each axle.  Rod ends of the cylinder are attached to the wheel hubs and the cylinder is controlled by the steering wheel. STEERING CONTROL UNIT.  Connected directly to the steering wheel and located under the instrument panel.  Controls the steering function by directing the flow of hydraulic oil to the cylinders. STEERING   SELECTOR   VALVE.      Allows   the   selection   of   two   wheel,   four   wheel,   or   crab   steering   through   manual positioning of control lever.  Mounted to underside of floor. PRIORITY VALVE.  Provides a priority flow of hydraulic oil to the steering system.  Excess flow is directed to the hydraulic system.  Mounted beneath floor. STEERING  BYPASS  VALVE.    Disconnects  the  flow  of  oil  to  the  rear  steering  cylinders.    Used  only  when  towing  the 4KRTFL. 1-12