A large capacity electric counterbalance forklift was towed into the shop because the steering wheel was completely locked solid. The operator said he was making a sharp turn when there was a loud "clunk," and the wheel wouldn't budge. The maintenance team assumed the electric power steering (EPS) motor had seized up and ordered a replacement, but when they went to unbolt the motor, they found it spun freely by hand.
This is a classic failure mode on modern electric forklifts that utilizes a column-assist EPS system, where the electric motor sits under the floorboard and connects to the steering column via a splined shaft. The motor wasn't locked; the steering column itself was mechanically jammed.
When we dropped the EPS motor down, we found the issue immediately. The coupling that joined the EPS motor shaft to the steering column shaft was completely destroyed. The internal metal splines had been sheared off perfectly clean, leaving a smooth, round hole. Electric power steering motors produce an immense amount of low-end torque. If there is any misalignment between the motor and the steering column during assembly-often caused by a missing alignment dowel pin or a bolt that was tightened unevenly-the spline coupling absorbs a massive amount of twisting stress. Over months of operation, the metal fatigues until the splines finally strip out.
When the operator turned the wheel, the steering column turned freely inside the hollow EPS motor shaft, but because the jagged edges of the sheared metal were now binding against each other inside the coupling, it felt exactly like a mechanical lock to the operator. Replacing the EPS motor alone wouldn't have fixed this; the coupling had to be replaced, and the mounting brackets had to be meticulously realigned with a dial indicator before torquing the bolts to ensure the shafts were perfectly concentric. It's a reminder that high-torque electric systems will destroy alignment faults in a hurry.
