A construction site reported that a Hyundai R210LC-7 excavator's swing would not stop immediately (long coasting), and hydraulic oil was leaking from the "Swing Motor Breather Cap."
The technician disassembled the swing motor. He found the "Housing Seals" (between the valve plate and the housing) were blown out. This allowed high-pressure oil from the working port to leak into the "Case Drain" chamber. The case drain chamber is designed to return internal leakage oil to the tank.
He then checked the "Case Drain Hose" that runs from the motor to the hydraulic tank. The hose was crushed by a fallen rock. The crushed hose blocked the flow of return oil. Because the case drain was blocked, the pressure inside the swing motor housing built up rapidly. The pressure blew out the housing seals.
The blown seals allowed the "Swing Brake Piston" to lose pressure. The brake is spring-applied and hydraulically released. The leakage meant the brake piston could not fully disengage (causing drag) nor fully engage (causing the coasting). The oil leaking from the breather cap was the overflow from the pressurized housing.
The repair involved replacing the crushed case drain hose with a new "Wire-Braided Hose" and rerouting it for better protection. The swing motor seals were replaced. The breather cap was cleaned. The system was filled, and the swing brake was tested. It held the machine firmly on a 30-degree slope.
