A sand and gravel depot reported that a Lonking LG855B wheel loader lost power when climbing the ramp to the stockpile. The transmission temperature gauge read 130°C, and the oil had a burnt odor.
The technician first checked the "Transmission Oil Level." The level was high and the oil was frothy (aerated). He connected a pressure gauge to the main pressure test port. The pressure was low (0.8 MPa vs. spec 1.5 MPa) and fluctuated wildly.
He removed the transmission oil pan. He found a large amount of "Friction Material Dust" in the bottom. This indicated the clutches were slipping. However, the root cause was traced to the "Torque Converter." He removed the pump drive housing. The "Torque Converter Impeller Hub Seal" (the seal between the converter and the transmission input shaft) was severely worn.
The worn seal allowed high-pressure transmission oil to leak from the converter circuit into the transmission housing (overfilling it). This leakage starved the "Torque Converter" of oil, reducing the fluid coupling efficiency (causing the power loss). The lack of oil in the converter caused the turbine to spin freely against the friction of the remaining fluid, generating massive heat. The heat thinned the oil, causing the transmission clutches to slip.
The repair involved replacing the torque converter seal kit and the damaged clutch friction discs. The transmission filter was replaced, and the system was back-flushed to remove debris. After refilling with fresh YC-8 oil, the pressure stabilized at 1.5 MPa, and the temperature remained at a safe 85°C.
