A limestone quarry reported that a Lonking LG855B wheel loader's engine would stall (die) whenever the machine tried to drive into a rock pile. The machine worked fine on flat ground, but under high torque load, the engine RPM dropped to zero.
The technician checked the "Air Filter" and "Fuel Filters," which were clean. He then focused on the "Transmission." He noticed that the transmission temperature was rising rapidly. He removed the "Torque Converter Inspection Cover." He found metal shavings in the housing.
He removed the transmission and disassembled the "Torque Converter." The "Lock-Up Clutch" (which connects the engine directly to the transmission for high speed) was seized in the "Engaged" position. The friction plates had welded to the housing due to overheating.
The "Lock-Up Solenoid Valve" on the valve body was also stuck open by dirt. This valve controls the oil pressure that engages the lock-up. The stuck valve applied pressure to the lock-up clutch all the time. When the loader entered a pile, the resistance was high. Because the lock-up was engaged, the engine was mechanically connected to the wheels with no "slip" protection. The sudden load stalled the engine (like trying to start a car in 4th gear).
The repair involved replacing the torque converter lock-up clutch plates and the failed solenoid valve. The transmission oil cooler was flushed to remove the metal debris. After reassembly, the torque converter allowed "slip" during loading, and the engine maintained power.
