A contractor reported that a Kobelco SK210LC-8 excavator's upper structure would not swing. The engine ran fine, and the boom/arms worked normally. The operator could hear a slight "whirring" noise from the swing motor area, but the house didn't move.
The technician tested the swing parking brake. He loosened the brake case drain line. When the swing lever was moved, oil flowed out, indicating pilot pressure was reaching the brake release valve. He then checked the swing motor pressure. The pressure was zero when the lever was operated.
He removed the swing motor cover. The Kobelco SK210 uses a hydraulic coupling (a rubber spider) between the motor shaft and the reduction gear input shaft. Upon inspection, the rubber spider was completely shredded. The motor shaft was spinning freely inside the coupling hub, generating the "whirring" noise but transmitting zero torque to the gearbox.
He also checked the "Pilot Filter" located just before the swing motor. It was completely plugged with rubber debris. The blocked filter restricted the pilot flow to the "Brake Release Valve." This meant the brake was not fully disengaging. The combination of a destroyed coupling and a partially engaged brake (due to debris) prevented the machine from moving.
The repair involved replacing the rubber coupling spider. The pilot filter was replaced, and the pilot lines were back-flushed to clear the rubber particles. The swing gearbox oil was also checked for contamination. After reassembly, the swing torque was restored, and the machine rotated smoothly.
