An aggregate quarry reported a critical issue with a Komatsu WA380-8 wheel loader: the machine would abruptly lose forward drive power under heavy load while climbing a steep stockpile ramp. The engine rpm would flare up, but the machine would stop moving, as if the transmission had shifted into neutral. After letting the machine sit for ten minutes, drive would temporarily return. Because the failure occurred without triggering any electronic transmission codes, the diagnostic process required a deep dive into the hydraulic and mechanical subsystems.
The first step was verifying main transmission pressure. A gauge was connected to the forward clutch test port. Under normal load on flat ground, the pressure held at a steady 280 psi. However, when the loader was driven up the stockpile ramp, the pressure plummeted to 50 psi right as the machine began to slip. This indicated either a massive internal leak in the forward clutch pack or the pump was starving for fluid.
The technician dropped the transmission oil pan and found a significant amount of fine metallic shavings stuck to the magnetic drain plug. The next logical step was to inspect the transmission suction strainer inside the pan. The strainer was almost completely occluded by a thick, gelatinous sludge-friction material from the clutches mixed with degraded hydraulic oil. When the loader was under heavy load, the pump would cavitate trying to pull fluid through the blocked strainer, causing the pressure drop and the subsequent clutch slippage.
However, the plugged strainer was a symptom of a larger mechanical failure. The suction strainer was cleaned, the oil was refilled, and the machine was tested again. While the slipping improved under moderate loads, it still occurred under maximum torque. The decision was made to remove and inspect the torque converter. Upon splitting the torque converter housing, the root cause was discovered: the weld holding the impeller hub to the pump drive had completely fractured.
Under heavy load, the fractured hub was twisting slightly on the pump drive, causing the torque converter impeller to lag behind the engine speed. This rotational mismatch prevented the converter from generating sufficient fluid coupling force, starving the transmission clutches of pressure. The friction generated by the slipping hub had contaminated the oil, which in turn plugged the suction strainer. The repair involved installing a factory-remanufactored torque converter, flushing the entire transmission cooler circuit, and replacing the suction strainer. Post-repair, the loader climbed the stockpile ramp at full capacity with zero slippage.
