TM 10-3930-653-14&P BRAKE SYSTEM Type: Front two-wheel braking, internal expansion, hydraulic type Pedal Ratio: 5.5 Master Cylinder: Type: Conventional type Cylinder Bore: 19.05 mm (0.75 in) Wheel Brake: Type: Duo-servo type with parking brake Wheel Cylinder Bore: 28.58 mm (1.125 in) Lining Size: 76 mm x 8 mm x 348 mm Width x Thickness x Length: (2.99 in x 0.32 in x 13.70 in) x 4 pcs. Surface Area: 264 _cm2 x 4 (40.92 _in2 x 4) Inner Dia. of Brake Drum: 314 mm (12.36 in) Parking Brake: Front two-wheel braking, internal expansion, mechanical type GENERAL DESCRIPTION The brake system is the front two -wheel braking type consisting of a master cylinder, wheel brakes and a brake pedal. MASTER CYLINDER The cylinder contains a valve seat, check valve, return spring, primary cup, separator, piston, and secondary cup, which are all held in place with a stop washer and a stop wire. The exterior of the cylinder is protected from dust by means of a rubber dust cover. The  piston  is  actuated  through  the  push  rod  by  operation  of  the  brake  pedal  as  follows:    as  the  brake  pedal  is pressed, the push rod pushes the piston forwards. The brake fluid in the cylinder flows back to the reserve tank through the return port until the primary cup blocks up the return port. After the primary cup passes the return port, the brake fluid in the cylinder is pressurized and opens the check valve, flowing through the brake lines to the wheel cylinders. Thus, each wheel cylinder piston is forced outwards. This brings the brake shoes into contact with the brake drum and slows or stops the truck. Meanwhile, the cavity caused behind the piston is filled with brake fluid led through the return port and inlet port to lubricate the piston. When the brake pedal is released, the piston is forced back by the return spring. At the same time, the brake fluid in each wheel cylinder is pressurized by the force of the brake shoe return spring, thus returning into the master cylinder through the check valve. When the piston returns to its original position, the fluid in the master cylinder flows into the reserve tank through the return port. The brake fluid in the brake lines and wheel cylinders has a residual pressure proportioned to the set pressure of the check  valve,  which  makes  each  wheel  cylinder  piston  cup  securely  seated  to  prevent  oil  leakage  and  eliminates  a possibility of vapor lock when the truck is sharply braked. 4-223