A steel mill reported that a Doosan ME958C wheel loader's boom shuddered violently when raised with a full bucket of scrap steel. The hydraulic tank made a loud "rushing" noise, and the oil temperature was exceeding 100°C.
The technician first checked the "Main Pump Pressure" with a gauge. The pressure was normal at 200 bar, but the needle vibrated wildly, indicating pulsating flow. He then inspected the "Boom Lift Pilot Hose" running from the joystick to the main control valve. The hose was routed too close to the exhaust manifold and had softened, creating a severe "kink" where it bent 90 degrees. The kink restricted the pilot oil flow, causing the main boom spool to open and close rapidly (chatter), resulting in the mechanical shudder.
The "Rushing Noise" and high heat were traced to the "Hydraulic Tank Breather Cap." The breather's air filter element was completely blocked by steel dust. As the large cylinders retracted, the oil returned to the tank, but the air inside couldn't escape. This created a pressurized vacuum in the tank, causing the main pump to cavitate (starve for oil). The cavitation generated massive heat and the rushing noise.
The repair involved rerouting and installing a new pilot hose, keeping it away from the exhaust manifold. The tank breather cap was replaced with a new element, and a magnetic pre-filter was installed. The hydraulic system was purged. Afterward, the boom lifted smoothly, and the tank pressure normalized, dropping the temperature to 75°C.
