The most common place for an excavator swing motor leak is just above the output pinion, where the shaft disappears up into the gearbox in larger excavators or the motor assembly in smaller machines.
There are a few common reasons why this happens:
- Excessive case drain from the motor. Over time the rotating group in the swing motor will wear out as it is one of the most frequently used and hard working components on the machine. Overheating and contaminated oil greatly accelerate the rate of wear. Tell tale signs of rotating group wear are that the motor is sluggish to operate, or the machine takes too long to stop when the cab control lever is released. When this happens, the motor is producing too much case drain. This case drain has to have an unrestricted flow back to the hydraulic tank via a return line filter. When the return line can’t cope with the volume being pumped down it, the pressure will back up into the motor case, breach the seal between the motor and gearbox before pressurising the gearbox and blowing the seal just above the output pinion. This results in the motor leaking. The remedy is to replace the rotating group and oil seals.
- Output bearing failure. A bearing will eventually fail through fatigue, abuse, or more commonly a lack of lubrication. There are three different ways that the output bearing can be lubricated:
- The bearing is filled with grease when assembled in the factory and they remain as a sealed unit throughout the lifespan of the motor.
- The bearing is lubricated via a grease nipple at service intervals
- Bearings that are not sealed off from the rest of the gearbox and are lubricated with gear oil.
When the bearing fails, the shaft becomes misaligned and lets either the gear oil or motor oil leak past the output seal. To avoid a total excavator swing motor breakdown, replace the output bearing and oil seal at the first signs of failure.
- Seal failure - In some cases, the output shaft seal will simply become brittle over time and let oil leak past. Overheating will accelerate this process.
To extend the service life of the repaired swing motor, it is important not to cut corners with servicing:
- Keep a close eye on the condition of the hydraulic oil
- Clean the oil cooler
- Regularly check the swing motor gearbox oil level
- Lubricate the output bearing (where applicable)