A construction contractor reported that a Doosan DX225LC-5 excavator pulled to the left when traveling straight. The left track also felt "heavy" (dragging) when driving, and the machine traveled slower than usual.
The technician first swapped the "Travel Motor Hoses" at the main control valve. If the problem moved to the right track, it would be a valve issue. The problem stayed on the left track, indicating a motor or swivel joint issue.
He focused on the "Central Swivel Joint" (the rotating union that supplies oil to the tracks). He removed the joint assembly. The "O-ring" for the left travel circuit was cut. This cut allowed high-pressure oil for the left travel motor to leak into the "Return" channel. This caused the left track to receive less pressure (hence the drift/slow speed).
The "Dragging" sensation was caused by the "Travel Brake." The travel brake is spring-applied and hydraulically released. He found the "Brake Release Line" (a small pilot line inside the swivel joint) was blocked by a piece of Teflon tape (left over from a previous repair). The blockage prevented full pilot pressure from reaching the brake piston. The brake was partially engaged, creating the drag and heat.
The repair involved replacing all O-rings and seals in the central swivel joint. The blocked brake line passage was cleared with compressed air. The travel motor oil was drained and refilled. After reassembly, the machine traveled straight, and the dragging resistance disappeared.
