Swing Motor Reducer Assembly for Komatsu PC1250-7 Excavator 706-77-01320 Common Faults & Troubleshooting Weak swing movement: Caused by worn piston and valve plate internal leakage, stuck cushion valve or faulty overload relief valve. Measure swing pressure and drain flow for diagnosis. Slow swing speed: Excessive motor internal leakage, insufficient pilot pressure or stuck control valve. Jerky swing and rebound stop: Stuck or worn anti-reverse cushion valve, contaminated