A mining site reported that a Liugong CLG856III wheel loader would occasionally lose steering assist when turning the wheels fully to the right. The steering wheel would become stiff for 3-4 seconds, then suddenly release and turn easily. The hydraulic oil temperature was also running higher than normal.
The technician first checked the steering pump pressure, which was stable. He then focused on the "Steering Priority Valve." In this machine, the steering pump supplies oil to both the steering cylinder and the lift cylinder. A priority valve ensures the steering gets oil first. He removed the priority valve cartridge and found the mounting bolts were loose, allowing air to be sucked into the valve body through the sealing surface. This air intake caused cavitation, leading to the intermittent stiffness.
However, the oil temperature issue remained. He inspected the steering cylinder rods. The chrome plating on the right-side cylinder rod was scored near the fully extended position. The scoring was caused by a burr on the piston rod wiper seal (dust seal). When the rod extended, the burr scratched the chrome, creating a leak path.
When the wheels were turned fully right, the high pressure (18 MPa) forced oil past the scratched rod and into the rod box. This internal leakage caused the pump to work harder to maintain pressure, generating the excess heat. The leakage also reduced the effective flow to the steering control valve, contributing to the stiffness.
The repair involved tightening the priority valve bolts to the specified torque and replacing the o-rings. The steering cylinder rod was polished with fine emery cloth to remove the scratch marks, and the rod seals (U-cups) were replaced. After bleeding the air from the steering lines, the machine steered smoothly in both directions, and the oil temperature stabilized.
