A pipeline contractor reported that a Kobelco SK500LC-10 excavator would not shift into high-speed travel. The right track also pulled noticeably slower than the left track when traveling straight, causing the machine to veer right. After 30 minutes of travel, the right track motor housing was excessively hot to the touch, while the left was cool.
The technician first addressed the high-speed travel failure. The SK500LC uses a two-speed travel motor; a "Two-Speed Shift Solenoid" on the travel motor diverts pilot pressure to a secondary swashplate piston, tilting the motor to a lower-displacement (high-speed) configuration. He connected the diagnostic tool and found a "Travel Two-Speed Solenoid Short Circuit" code. He measured the resistance of the shift solenoid coil: 2 ohms (spec is 28 ohms). The coil's internal windings had shorted together, drawing excessive current and tripping the controller's protection circuit. The solenoid never energized, trapping the travel motor permanently in low-speed (high-torque) mode.
To diagnose the right-track pull and overheating, the technician performed a travel-motor case-drain flow test. With the machine traveling straight, the right travel motor's case drain flow was 18 liters per minute (spec is under 5 L/min), while the left was 3 L/min. The excessive case drain on the right side indicated massive internal leakage. He traced the travel circuit to the "Central Rotary Joint" (swivel joint) that routes hydraulic oil from the upper frame to the lower track motors. He removed the rotary joint and extracted the seal cartridges. The "Right Travel Pressure Seal" was deeply grooved and cross-leaking. High-pressure oil from the travel supply port was bleeding directly into the right travel motor's case drain port inside the swivel joint. The bled-off pressure reduced the right track motor's torque and speed (causing the right pull), and the constant high-pressure bypass generated the excessive heat in the right motor housing.
The repair involved replacing the shorted two-speed shift solenoid and installing a complete central rotary joint seal kit. The travel motor was inspected for damage from the overheated oil; the case drain filter was found packed with degraded seal material and was replaced. Fresh hydraulic oil was introduced. After reassembly, the excavator shifted cleanly into high-speed travel, both tracks ran at equal speed, and the right motor housing maintained a normal temperature under continuous travel.
