A sand and gravel site reported that a Liugong CLG856III wheel loader would not move in forward or reverse. The engine ran normally, and the bucket hydraulics worked. The transmission temperature was normal. The operator checked the fuses and found them intact.
The technician first checked the "Gear Selector Solenoids" on the transmission valve block. He applied 24V power to each solenoid manually. He could hear the solenoids clicking, indicating they were functional. He then removed the transmission oil dipstick. The oil was a dark grey color with a metallic sheen, indicating severe mechanical wear.
He removed the transmission oil pan. He found a large piece of broken metal lying in the bottom. It was a fragment of the "Parking Brake Cam Shaft." The CLG856III uses a spring-applied, hydraulically-released parking brake inside the transmission. The cam shaft is used to mechanically release the brake for towing. The shaft had sheared off, and the fragment had fallen into the control valve area, blocking the "Direction Control Spool" from moving.
Furthermore, upon disassembling the torque converter, the technician found the "Pump Drive Hub Bearing" had collapsed. The bearing debris had entered the transmission oil, circulating through the pump and eventually jamming the cam shaft mechanism.
The repair involved replacing the torque converter (due to hub damage), the parking brake cam shaft, and the main control valve spool (which was scored). The transmission was flushed thoroughly with diesel. A magnetic filter was installed on the suction line to catch any remaining debris. After reassembly, the machine selected gears and drove normally.
