A pipeline contractor reported that a Komatsu PC360LC-11 excavator gradually veered to the right when driving straight. The right track felt "spongy" and unresponsive, and after 30 minutes of travel, the right final drive was dangerously hot to the touch, with smoke coming from the track frame.
The technician first checked the track tension and found the right track was severely loose-almost dragging on the ground. He then tested the travel speeds with the tracks elevated. The right track rotated 25% slower than the left. He disconnected the travel motor case drain line and measured the flow; it was 8 liters per minute (spec is under 3 L/min), indicating severe internal leakage in the travel motor.
He removed the "Travel Motor Control Valve Block." The "Balance Valve" (a large spool valve that directs oil to the motor and controls the mechanical brake release) was seized in the "brake applied" position by a hard varnish buildup. Because the balance valve was stuck, the travel motor's mechanical multi-disc brake was never fully released. The operator was essentially driving the excavator with the parking brake partially engaged on the right side.
The severe friction from the dragging brake discs generated immense heat, which transferred through the travel motor housing into the final drive oil. The overheated final drive oil melted the track tensioner's grease cartridge, causing the grease to leak out and the track to lose tension. The "spongy" feel was the hydraulic oil boiling and cavitating inside the motor due to the extreme heat.
The repair involved replacing the travel motor balance valve cartridge and the entire set of brake friction discs (which were burnt and glazed). The final drive was drained, flushed with solvent, and refilled with fresh gear oil. The track tensioner was re-greased and adjusted to the proper sag. After reassembly, the excavator tracked straight, the right side operated smoothly, and the final drive maintained normal operating temperatures.
