INTRODUCTION TO THE HMMWV - OD1615 - LESSON 3/VASE 1
a. Service Brakes.
The service brake system consists of the brake
pedal, pushrod, hydro-boost, master cylinder, combination valve, calipers,
rotors, and lines; hoses; and fittings.
When the driver steps on the brake pedal, the pedal force is transferred
through the bellcrank assembly, directed into the hydro-boost unit, where it
is hydraulically boosted and passed on to the master cylinder.
From the
master cylinder, fluid pressure in the brake lines passes through the
combination valve and on to the disc brake calipers. The calipers close on
the rotor, providing a stopping force.
The braking system is split front
and rear so that if a hydraulic failure occurs to either the front or the
rear brakes, the vehicle may still be stopped with the other two brakes.
b. Parking Brakes.
The parking brake is a lever operated brake that
functions through a cable linkage.
Its primary purpose is to hold the
vehicle stationary. A secondary purpose of the parking brake system is to
stop the vehicle in the event that there is a complete service brake
failure.
The parking brake consists
of a parking brake lever, cable linkage,
mechanically operated brake
shoes and a rotor, mounted to the rear
differential between the drive
shafts. When the driver pulls on the parking
brake lever, the cable linkage
squeezes the brake shoes on the parking brake
rotor.
c. Components of the Service Brake System.
In the paragraphs that
follow, the components that comprise the service brake system will be
discussed.
(1) Master Cylinder.
The HMMWV is equipped with a dual reservoir
master cylinder. The master cylinder has two fluid outlet ports, a piston
bore, and two hydraulical piston assemblies.
The piston assemblies are
located in the piston bore and are operated in tandem by a pushrod.
The
master cylinder on the HMMWV holds .69 pints of brake fluid silicone (BFS).
The dual master cylinder contains two brake circuits that are separated
hydraulically. The individual brake systems may be designed to divide the
system front to rear, diagonally, or in various
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