Propel Pump Servo Control Test Procedure Caterpillar

Problem:

The following test procedure is intended to isolate a specific propel pump control performance problem. The test will rule out or identify if a servo piston binding condition is present.

Solution:

1. Install two "FLUKE" or equivalent multimeters to monitor the left and right forward EDC coils current. This can be accomplished by disconnecting the wire at pin #10, located in the 40 pin connector of the propel MPC-10 controller, and installing a test lead in pin # 10. The test wire is then connected to one side of the multimeter, the other side is connected to the original wire removed from pin #10 thus putting the meter in series with the left forward EDC coil to monitor drive current. (0-100 mA) The right forward EDC drive current is to be monitored at the same time using pin #33 at the propel MPC-10 connector by installing the second meter in series with the right forward EDC coil similar to the procedure described for the left.

2. Warm up the hydraulic system to 100-120 (F, restrict airflow and run the feeder system at full speed with conveyor ratio dials set at 25% while driving the machine as fast as possible in the pave range.

3. The machine can be tested on stands in the shop or on the ground if space to drive the machine is available. Turn the propel speed dial full counterclockwise, select pave range, and move the propel lever forward. Slowly turn the speed dial up while monitoring the forward EDC current, increase until 30 mA is observed. Do not steer the machine, allow the machine to propel for 30-45 seconds monitoring both forward EDC currents. The currents should remain steady with only slight variations of approximately 1-2 mA. Servo piston binding will cause fluctuations to occur such as constant hunting up and down of the EDC current, 15-30 mA, while the machine maintains constant track speed. If the currents are steady at 30 mA the same test will be required at 40 mA, 50 mA, 60 mA, 70 mA & 80 mA. The speed dial should be increased slowly and both meters observed for 30-45 seconds at each of the EDC current levels. If the forward EDC current fluctuations are observed the servo piston is binding. The reverse servos are tested in the same manner using pins #11 & #34. If servo piston binding is observed, pump disassembly and inspection will be required.

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