A reach truck was lifting a heavy double-stacked pallet to the top tier of a rack. As the operator tilted the mast back, there was a violent "BANG." The carriage dropped six inches, the load shifted dangerously, and the operator panicked. The shop assumed a lift cylinder had blown a seal, but the cylinders were dry.
We looked at the mast chain anchors. Lift chains attach to the carriage and anchor to the mast crossbar using heavy steel pins that pass through the chain links and secure with a cotter key. Over years of use, the chain links microscopically rub against the hardened steel anchor pin.
Because the anchor pin cannot rotate in its fixed mount, the chain eventually wears a deep groove into the pin. Furthermore, the inner chain links seize up with rust and lack of lubrication, preventing them from articulating smoothly over the pin. When the operator tilted back a heavy load, the shock load hit the seized chains. The chain couldn't flex, acting as a solid steel bar, and the groove on the anchor pin acted as a stress fracture point. The pin sheared completely in half. The chain slipped off the crossbar, dropping the carriage. Never just lubricate the outside of forklift chains; the penetrating oil must reach the inner links to prevent them from binding and shearing the anchor hardware.
