Excavator Hydraulic Pump 708-1L-00640 708-1L-00641 Komatsu PW95R-2 Main Piston Pump Pressure Pump Common Faults & Symptoms Slow machine movement, weak digging power, worse performance when hot: Wear of internal plungers, slippers and valve plate causes increased internal leakage and excessive case drain flow. Engine lugging and speed drop under load: Stuck power control spool and faulty servo piston prevent the displacement mechanism from reducing displacement normally.