WHEEL & TIRE AR 3657288 - Caterpillar

Illustration 1 g00533964
Location of the front brake air ratio valve
(1) Output port
(2) Supply port The front brake air ratio valve is located at the rear of the cab behind a cover. The front brake air ratio valve controls the air pressure to the front brake air relay valve when the front brake control is in the ON position.
Illustration 2 g00533974
(1) Output port
(2) Supply port When the service brake pedal is partially depressed, and the air pressure at supply port (2) is below 448 kPa (65 psi), the front brake air ratio valve will only allow 50 percent of the air pressure to flow from outlet port (1) to the front brake air relay valve. The hydraulic caliper service brakes for the front wheels are partially applied. When the service brake pedal is fully depressed and the air pressure at supply port (2) is at least 448 kPa (65 psi), the front brake air ratio valve will allow full air pressure to flow from outlet port (1) to the front brake air relay valve. Now, the hydraulic caliper service brakes for the front wheels are fully applied. When the service brake pedal is released the air pressure to the front brake air relay valve will flow out of the exhaust port that is located on the top of the front brake air ratio valve.When the service brake pedal is partially pressed, only partial engagement of the front brakes is allowed. The rear service brakes will engage first and the operator will have more control of the machine. When the service brake pedal is fully applied, the operator will receive the maximum braking capacity.