A excavation contractor reported that a Caterpillar 323 excavator's right track suddenly emitted a loud, metallic grinding noise, and the right track completely lost drive torque. The left track functioned normally, and the machine could only pivot in circles using the left track. Before the failure, the operator had noticed a slow oil seep from the right final drive housing for several weeks.
The technician first removed the right final drive's oil fill/drain plug. Instead of gear oil, thick black sludge containing metallic flakes drained out-the gear oil had been completely depleted, and the steel flakes were evidence of severe internal gear damage. He then attempted to rotate the sprocket by hand using a pry bar; it was locked solid, indicating the planetary gear set had seized.
He unbolted the final drive from the travel motor. The "Travel Motor" output shaft splines were stripped, and the planetary gear carrier was completely destroyed-the sun gear and planetary pinions were missing teeth, and the internal ring gear had been scored deeply. The root cause was traced to a degraded final drive oil seal on the sprocket side. The seal had failed from exposure to abrasive dirt and high-pressure washing, allowing the gear oil to slowly leak out over several hundred operating hours. As the oil level dropped, the planetary bearings ran dry, overheated, and disintegrated. The bearing debris then circulated through the gear set, destroying the planetary carrier and stripping the motor's output splines.
The repair involved replacing the complete right final drive assembly (the planetary carrier, ring gear, and sun gear were unsalvageable) and rebuilding the travel motor with a new output shaft and internal rotating group. The travel motor's case-drain filter was found packed with metallic debris and replaced. The left final drive was inspected and its oil level was correct, but the technician proactively replaced its output seal as a preventive measure, since both seals were the same age. Fresh gear oil was installed in both final drives, and the machine was operated at low speed for a test cycle. Post-repair, the right track delivered full drive torque, the grinding noise disappeared, and the final drive housing maintained a normal operating temperature.
