A reach truck was struggling to lift a full pallet to the top tier. The operator reported that the truck would lift halfway, then struggle and bog down, sounding like the electric motor was stalling. The shop replaced the pump and the hydraulic motor, suspecting a weakening drive system.
We observed the truck in action. The motor wasn't stalling; it was actually drawing *less* current because the mechanical resistance was slowing the hydraulics down. We told the operator to stop lifting and looked closely at the carriage. The carriage rollers (side thrust rollers) were visibly wobbly.
On a tall reach truck, the mast rails are long, and even a 1/16th-inch offset at the bottom becomes a 2-inch bind at the top. The side rollers were worn flat, creating metal-on-metal contact. When the carriage lifted past the mid-point, the tension in the mast rails forced the carriage to bind against the rails. The hydraulic pressure was trying to fight this massive friction. The pump relief valve was bypassing because it couldn't generate enough pressure to lift the load *and* drag the carriage up a steel rail. We replaced the roller bearings and re-shimmed the carriage to the mast. The hydraulic system was fine; the mechanical friction was the thief stealing the lifting power.
