A utility contractor reported that a John Deere 210G LC excavator was pulling hard to the left when traveling. The left track moved significantly slower than the right, and when parked on a slight grade, the left track would slowly creep backward, even with the travel levers in neutral.
Because the excavator had two distinct symptoms-loss of speed and creep-the technician first checked the travel motor hydraulic pressures. Gauges were plumbed into both the left and right travel motor supply lines. Under a full stall test, the right travel motor held 5,000 psi, while the left motor pressure peaked at only 3,500 psi and immediately bled down. This indicated a massive internal hydraulic leak in the left travel motor circuit.
The travel motor was removed from the track frame. The balancing valve (a counterbalance valve that prevents the machine from freewheeling down hills) was disassembled. The valve's internal poppet was heavily scored, and its sealing seat was cracked. This allowed pressurized oil to bypass the valve and return straight to the tank, robbing the motor of drive power and causing the downhill creep due to the loss of holding pressure.
However, the slow track speed was also caused by a mechanical drag. When the technician spun the travel motor input shaft by hand, it resisted turning. The travel reduction gear housing was drained, and the oil was filled with thick, metallic paste. The planetary reduction gears were disassembled, revealing that the primary needle bearings on the first-stage planet gears had completely disintegrated. The metal shavings from the bearings had chewed into the gear teeth, creating severe friction that was physically slowing the track down, forcing the hydraulic motor to work harder and eventually overpressuring the balancing valve.
The repair required installing a factory-remanufactured travel motor with a new balancing valve cartridge. The planetary reduction hub was completely rebuilt with new gear sets, needle bearings, and seals. The hub was refilled with the specified GL-5 gear oil. After reassembly, the excavator tracked perfectly straight, both motors stalled at exactly 5,000 psi, and the machine held its position securely on the grade without any creep.
