A recycling facility reported that a Komatsu WA380-8 wheel loader was losing drive power under heavy load. When the operator loaded the bucket from a stockpile and attempted to drive forward, the engine RPM would surge but the machine would barely move - the torque converter appeared to be slipping excessively rather than multiplying torque and delivering it to the transmission. The transmission oil temperature warning also illuminated after 20 minutes of heavy loading cycles, forcing the operator to shut down and let the machine cool.
The technician first verified the transmission oil level (correct) and inspected the transmission cooler's external fins - packed with dust, plastic film, and recycling-yard debris. He cleaned the cooler thoroughly, but the drive-power problem persisted. He then installed a pressure gauge on the torque converter's outlet pressure test port and ran the loader under varying load conditions. Under no-load acceleration, the torque converter outlet pressure read 8 bar (spec is roughly 8 to 12 bar depending on converter slip). Under heavy load, the pressure dropped to 3 bar - far below spec. This indicated the converter was not converting torque properly, and the excess slip was generating enormous heat.
He removed the torque converter from between the engine and the transmission and disassembled it on a bench. The torque converter is a fluid coupling comprising an impeller (driven by the engine), a turbine (connected to the transmission input), and a stator (an intermediate element that redirects fluid flow to multiply torque at low speeds and high slip). The stator is mounted on a "One-Way Clutch" that allows the stator to rotate freely in one direction (when the converter reaches its coupling phase) and lock in the other direction (when the converter is multiplying torque during high-slip operation). The one-way clutch's sprag elements were visibly worn - the sprags had lost their ability to lock, allowing the stator to spin in both directions. Without the locked stator, the converter could not multiply torque; the machine behaved as if it had a fluid coupling only, with maximum slip and minimal torque transfer under load.
The excess slip also explained the overheating: torque converters generate heat proportional to their slip rate. With the stator's one-way clutch failing to lock, the converter operated at maximum slip continuously, generating more heat than the (partially blocked) transmission cooler could dissipate.
The repair involved replacing the complete torque converter with a remanufactured unit (the stator's one-way clutch is not field-serviceable), replacing the transmission oil and filter, and back-flushing the transmission cooler to remove the accumulated debris. The technician also verified the transmission's oil pressure after reassembly - readings returned to the 8-to-12-bar specification across the operating envelope. After reassembly and a loaded test cycle, the WA380-8 delivered full tractive effort when loading from the stockpile, the converter outlet pressure held within specification under load, and the transmission oil temperature stabilized at normal operating range throughout a full shift.
