A logistics warehouse reported that a Clark C25 forklift steering wheel would vibrate violently (buzz) when turning, and the steering response felt jerky, as if the rear wheels were skipping. The vibration was worse when the machine was stationary and the operator turned the wheel.
The technician first checked the hydraulic steering cylinder for leaks, which was dry. He then checked the steering orbitrol (control valve). The orbitrol is a "hydrostatic" steering unit where the steering wheel is mechanically linked to a metering valve. He noticed that the steering column itself had a slight "wobble."
Upon removing the steering column cover, he found that the U-joint (universal joint) connecting the steering wheel shaft to the orbitrol was worn, with play in the needle bearings. This play caused the steering input to oscillate, contributing to the vibration. However, the "buzzing" sensation was hydraulic.
He knew that air in the system can cause "aeration" and vibration. He jacked up the rear of the forklift and turned the steering wheel fully left and right 10 times with the engine at idle. He heard a gurgling sound in the hydraulic tank. He found that the "return line" fitting on the steering cylinder was slightly loose, allowing air to be sucked in during low-pressure cycles.
The repair involved tightening the return line fitting and bleeding the steering system by cycling the cylinder. The worn U-joint was replaced with a new greasable unit. After the air was purged and the mechanical linkage was tight, the steering became smooth and quiet.
