651E and 657E Wheel Tractor-Scrapers Air System and Brakes Caterpillar

Performance Checks

Note: If the performance checks indicate that air pressure is not available at the supply passage(s) of the control valves, loosen the connection at the supply passage and use soapy water in order to check for air pressure.

If the performance checks give an indication of leakage through a control valve, disconnect the delivery hose at the end opposite the delivery passage. Put the end of the hose in a pan of water to check for leakage.

Problem

The service brakes do not engage correctly.

Probable Cause

• There is no air pressure at the inlet passage of the brake control valve.

• Wear or damage to the brake control valve permits little air pressure or no air pressure at the outlet passages.

• Wear or damage to the components between the brake control valve and the tractor brake actuators is preventing the flow of air.

• Wear or damage to the scraper relay valve permits little air pressure or no air pressure at the delivery passages to the brake actuators.

• The brake actuators have wear or damage.

• The rod travel of the brake actuators is out of adjustment.

• The brakes have wear or damage.

Problem

The service brakes do not release correctly.

Probable Cause

• Mud or dirt under the pedal does not allow the brake control valve to release fully.

• Wear or damage to the brake control valve restricts the release of air pressure to the tractor relay valve on the brake actuators and/or the scraper relay valve.

• Wear or damage to the scraper relay valve restricts the release of air pressure from the scraper brake actuator.

• The components between the brake control valve and the tractor brake actuators have wear or damage.

• The brake actuators have wear or damage.

• Wear or damage to the parking and secondary brake control valve releases the air pressure to the parking and secondary brake chambers in the brake actuators.

• The quick release and holding valves and/or the double check valve have wear or damage.

Problem

The parking and secondary brakes do not engage correctly.

Probable Cause

• Wear or damage to the parking and secondary brake control valve restricts the release of air pressure.

• The quick release and holding valves and/or the double check valve have wear or damage.

• The rod travel of the brake actuators is out of adjustment.

• The brakes have wear or damage.

• The brake actuators have wear or damage.

Problem

The parking and secondary brakes do not release correctly.

Probable Cause

• Wear or damage to the parking and secondary brake control valve releases the air pressure to the parking and secondary brake chambers in the brake actuators.

• The quick release and holding valves have wear or damage.

• The brake actuators have wear or damage.

Problem

The tractor retarder does not engage correctly or the scraper retarder does not engage correctly.

Probable Cause

• There is no air pressure at the supply passage of the control valve.

• Wear, damage or incorrect adjustment to the control valve permits little air pressure or no air pressure at the delivery passage.

• The regulator valve has wear, damage or incorrect adjustment.

• The hydraulic valve for the retarder has wear, damage or incorrect adjustment.

• The retarder has wear, damage or incorrect adjustment.

Problem

The tractor retarder does not release correctly or the scraper retarder does not release correctly.

Probable Cause

• Wear, damage or incorrect adjustment to the control valve restricts the release of air pressure from the line to the regulator valve.

• The regulator valve has wear, damage or incorrect adjustment.

• The hydraulic control valve for the retarder has wear, damage or incorrect adjustment.

Problem

The differential lock does not engage correctly.

Probable Cause

• There is no air pressure at the supply passage of the differential lock.

• Wear or damage to the differential lock valve permits little air pressure or no air pressure at the differential lock.

• The differential lock has wear or damage.

Problem

The differential lock does not release correctly.

Probable Cause

• Wear or damage to the differential lock restricts the release of air pressure from the line to the differential lock.

• The differential lock has wear or damage.

Problem

The apron will not lower when the switch on the bowl control lever is pushed.

Probable Cause

• There is no pressure air at the supply passage of the apron control valve.

• Wear or damage to the apron solenoid valve permits little pressure air to the air control valve on the implement control valve.

• Wear or damage to the air control valve

• Wear or damage to the trigger switch

• There is no power to the switch or to the solenoid valve.

Problem

The apron does not stop when the trigger (switch) on the bowl control lever is released.

Probable Cause

• Wear or damage to the apron solenoid valve permits little pressure air from the line to the air control valve on the implement control valve.

• Wear or damage to the air control valve

• Wear or damage to the trigger switch

• There is no power to the switch or to the solenoid valve.