A gravel quarry reported that a LiuGong CLG856III wheel loader was becoming increasingly difficult to steer, especially when the engine was at idle. The steering wheel felt stiff, and a loud "whining" noise was heard from the rear of the machine whenever the steering wheel was turned. The implement (bucket) hydraulics worked fine.
The technician began by checking the hydraulic oil level, which was correct. He then tested the steering system pressure. The main steering relief valve was set to 17 MPa, but the gauge fluctuated wildly between 10 and 17 MPa when turning. The noise and fluctuating pressure suggested "cavitation"-air entering the suction line or the pump starving for oil.
The steering system on the CLG856III uses a priority flow control valve that ensures the steering gets oil before the implement circuit. The technician inspected the suction hose from the tank to the pump. The outer casing looked intact, but when the hose was bent, it felt mushy. He cut the hose open and found the inner wire reinforcement had corroded and collapsed internally. This internal restriction was starving the pump, causing the cavitation noise and the stiff steering (due to lack of flow).
However, there was a secondary issue. The priority valve spool was also found to be stuck. The spool has small orifices that sense pilot pressure. Debris from the deteriorating hose had lodged in the spool bore, preventing the valve from fully opening to the steering cylinder. This compounded the pressure drop.
The repair involved replacing the entire suction hose assembly with a new, high-pressure wire-braided hose. The priority valve was disassembled, the spool was honed, and new seals were installed. The hydraulic tank was drained and flushed to remove any remaining hose debris. After refilling with fresh ISO 46 hydraulic oil, the steering became light and responsive, and the whining noise disappeared completely.
