A warehouse reported that a Heli CPCD20 forklift's forks would not stay tilted back. When the operator tilted the mast forward, it would slowly drift down. Additionally, the steering wheel shook violently when driving over bumps.
The technician first checked the "Tilt Cylinders." He extended the cylinders and checked the seals. There was a slight film of oil on the rod, but the drift was too fast to be just a seal leak. He then focused on the "Control Valve." He removed the "Tilt Spool." Underneath the spool, he found the "Load-Holding Check Valve" seat was scored. The scoring allowed oil to bypass the valve when the joystick was in neutral, causing the drift.
The "steering shake" was traced to the "Tilt Cylinder Mounting Bolts." The bolts securing the cylinders to the mast frame were loose. This allowed the cylinders to "hammer" against the frame when driving, transmitting the vibration to the steering column. The loose bolts were caused by a lack of routine torque checking.
The repair involved replacing the load-holding check valve cartridge. The cylinder mounting bolts were tightened to specification (and thread-locking compound was applied). The cylinder rod seals were also replaced to prevent future leaks. After reassembly, the forks held their position, and the steering vibration disappeared.
