A port logistics company reported that a LiuGong CLG855N wheel loader developed a violent, uncontrollable shaking of the steering wheel and front axle (commonly known as "death wobble") when driving at speeds above 25 km/h. At low speeds, the steering felt normal, but occasionally the steering wheel would refuse to return to center automatically.
The technician first inspected the mechanical steering components. The tie rod ends and kingpin bearings showed no play. He then focused on the "Full Hydraulic Steering Gear" (Orbitrol). The Orbitrol relies on a precise rotor/stator metering mechanism to route oil to the steering cylinders. He bypassed the Orbitrol and drove the machine; the wobble stopped, confirming the hydraulic circuit was causing a resonance feedback loop.
He disassembled the "Steering Cylinder Cushion Valves" (relief valves located in the cylinder end caps designed to absorb shock when the wheels hit a pothole). The internal springs were broken and the poppets were scored. The broken cushion valves failed to absorb road shock, transmitting hydraulic pulses back to the Orbitrol. Furthermore, when he drained the hydraulic tank, he found the oil was severely emulsified (milky white) from water ingress. The water had corroded the internal metering edges of the Orbitrol rotor, causing it to bind intermittently. When the machine hit 25 km/h, the hydraulic pulses from the bad cushion valves hit the sticky rotor, creating a high-frequency hydraulic resonance that shook the entire front end.
The repair involved replacing both steering cylinder cushion valve assemblies and installing a remanufactured Orbitrol steering gear. The hydraulic tank was steam-cleaned to remove the emulsified oil sludge, and fresh ISO 68 oil was installed. The source of the water was traced to a cracked filler cap, which was replaced. After the repair, the loader tracked straight at 35 km/h with no vibration.
