A beverage distributor noticed that the inside edges of the steer tires on a Hyster E50XN electric reach truck were wearing down to the cords in less than three months. The operators also complained that the truck felt "darty" and required constant steering corrections to keep the truck tracking straight in the narrow pallet racking aisles. If the operator took their hands off the wheel, the truck would immediately drift to the left.
The first step was to inspect the mechanical steering components. The steer axle kingpins, tie rod ends, and steering column U-joints were all checked for play, but everything was tight. The steer tires were replaced and the mechanical toe-in was adjusted to factory specifications. However, during the test drive, the truck immediately began pulling to the left again, indicating a hydraulic bias issue in the steering circuit.
The Hyster E50XN uses a dual-acting hydraulic steer cylinder to turn the rear wheels. The technician raised the rear of the truck and started the motor. With the wheels pointed straight, he disconnected the steering linkages and observed the cylinder rod. Even though the wheels were aligned, the cylinder rod was slowly creeping outward, turning the wheels to the left.
A pressure gauge was installed across the steer cylinder ports. In a neutral state, the pressure should have been equal on both sides of the piston. Instead, the rod-side pressure was 300 psi higher than the cap-side. The steer cylinder was removed and disassembled. The internal piston seal had suffered a localized failure-a section of the seal had extruded and hardened, allowing pressurized fluid to bypass the piston. This internal leak created a pressure imbalance that constantly forced the rod outward, inducing a permanent left-hand drift and keeping the tires in a slight state of misalignment during straight-line travel.
The root cause of the seal failure was discovered when the technician removed the steer axle pivot pin. The pin was slightly bent, a result of the truck being side-impacted by another forklift. The bent pin prevented the steer axle from articulating freely, transferring lateral shock loads directly into the steer cylinder during every bump, eventually fatiguing the piston seal.
The repair involved replacing the bent steer axle pivot pin and installing a complete seal kit in the hydraulic steer cylinder. The steering column rotary valve was also recalibrated to ensure centered flow. After the repair, the reach truck tracked perfectly straight with zero input, and the new steer tires showed completely even wear after a month of continuous service.
