First, conduct a basic visual and operational inspection. Check the motor housing, shaft seals, flange joints and drain ports for persistent external oil leakage, cracks, deformation or loose Bolts. Inspect the hydraulic oil for metal debris, discoloration or water emulsification, which signals internal wear. Observe the slewing performance: the machine should rotate smoothly at a consistent speed without stuttering, abnormal vibration or sharp metallic noise. After stopping operation, the upper carriage must stay locked firmly without slow drifting or creeping, a key indicator of a faulty built-in brake or excessive internal leakage. Excessive heat and abnormal noise are obvious warning signs, after ruling out issues with reduction gears, bearings, pilot valves and fuel contamination.

Second, perform pressure and internal leakage testing, the most reliable method. Install a hydraulic pressure gauge to conduct a stall pressure test, and compare the reading with the factory rated pressure. If the stall pressure cannot reach the standard value (with normal main pump and relief valve performance), the motor suffers from internal wear of pistons, valve plates or cylinder blocks. Measure case drain flow: abnormally high drain flow means severe internal leakage and greatly reduced volumetric efficiency, resulting in insufficient torque.

Finally, carry out disassembly inspection for confirmation. Check pistons, valve plates, bearings and spline shafts for scoring, burn marks and excessive clearances, and verify brake friction plate wear.

A healthy slewing motor features steady speed, correct stall pressure, minimal case drain flow, no leaks or abnormal heat, and reliable brake holding.

Systematic checks prevent misdiagnosis and extend the service life of hydraulic components, improving overall machine uptime on job sites.