ELBOW 0307980 - Caterpillar

TYPE="1" START="1">
Start the tractor engine and allow the pressure to reach the cut-out pressure. The cut-out pressure is 930 35 kPa (135 5 psi).
Place the control knob for the parking brake in the OFF position. Place the control knob for the secondary brake in the OFF position. The knobs are in the OFF position when the knob is depressed. Stop the engine.
Rapidly depress the brake pedal and release the brake pedal, until both of the control knobs automatically move to the ON position. Both of the knobs will automatically move to the ON position during proper operation. The knobs will move approximately at the same time.
Refer to the Testing and Adjusting, "Air Pressure Gauge - Test" for the installation of the gauge.
Read the pressure on the test gauge.
The correct pressure that will automatically engage the parking brake and the secondary brake is 275 35 kPa (40 5 psi). If the pressure on the gauge is not correct, the operation of either the parking brake control valve or the secondary brake control valve is not correct.
Disassemble the control valves. Check for worn parts or damaged parts.
If this does not correct the problem, install new brake control valves.