A steel pipe distributor reported that a Heli CPCD30 diesel forklift would shudder violently when the forks were raised above 4 meters. The shudder was most noticeable when the mast was tilting forward at height.
The technician first inspected the lift cylinder for internal leaks. The cylinders held pressure, ruling out piston seal failure. He then checked the "Flow Control Valve" (diverter valve) located on the main hydraulic block. This valve prioritizes flow to the lift cylinder. He found that the valve spool was slightly sticky due to varnish build-up from overheated oil. This stickiness caused a pulsating flow to the cylinders, contributing to the shudder.
However, the primary mechanical cause was found in the mast rails. He extended the mast to full height and checked the clearance between the inner and outer rails using a feeler gauge. The "wear shims" (plastic or bronze strips) on the inner rail were completely worn through. This allowed metal-to-metal contact. At full extension, the mast rails had excessive play (over 5mm), causing the rollers to chatter against the rail edge.
The repair involved replacing the mast wear shims. The technician used a high-strength nylon shim that is resistant to impact. The flow control valve was disassembled and cleaned with a solvent to remove the varnish. The hydraulic oil was also changed, and a magnetic filter was installed on the return line to catch any metal particles generated by the previous metal-to-metal contact. The mast now operated smoothly at all heights, and the shudder was eliminated.
