Check level with the machine on level ground, drain a sample and look at it. Milky oil means water ingress, metal means gear or bearing wear, and a burnt smell means overheating. Also check the swing brake function at the same time, because brake drag shows up first as oil temperature.
How to confirm it
- Park on level ground and stop the engine safely
The swing gearbox is at the center of the upper structure and its level plug is only meaningful with the machine level. Follow the lockout procedure for the machine before working around the swing area.
- Locate the level and drain plugs
Identify the level plug and drain plug from the service documentation. Some gearboxes have the level plug at the side and the fill point on top; some combine fill and level. Establish which design you have before opening anything.
- Clean around the plug and check level
Level at the plug with the machine level. A low level indicates a leak or a fill error; a high level indicates overfilling, which causes seal weeping and heat.
- Drain a sample and examine it
Look for color, smell and suspended material. Swing gearboxes typically hold a small volume of oil relative to their load, so contamination concentrates quickly and the oil degrades faster than in a final drive.
- Look for metal with a magnet
Fine gray fuzz is normal. Flakes or chips indicate gear tooth or bearing damage, which in a swing gearbox usually follows a period of contaminated or low oil.
- Check swing brake function at the same time
With the machine on level ground, swing and release the control. The upper structure should stop and hold. Drift, run-on or noise indicates brake or relief problems — and brake drag heats the oil and is a common cause of elevated gearbox temperature.
- Compare the swing gearbox oil appearance against your records
Trend matters more than any single sample. Oil that has changed noticeably since the last service is telling you something is developing, even if the current sample looks acceptable in isolation.
What to do about it
Contaminated oil: drain, flush and refill to specification, and find the water entry point. Swing gearboxes are usually more exposed than final drives because of their location, and a failed seal or a badly sealed fill point is the usual source.
Metal in the oil: the unit needs opening. Establish whether the gears are intact before deciding between bearings and seals, and a gear or shaft replacement, because the cost difference is substantial.
Oil hot or degraded: check swing brake release and swing relief pressure. A brake that is not releasing fully drags continuously and heats the oil, and the eventual result is catastrophic rather than gradual.
Low level with no visible leak: check the seals around the output shaft and the brake housing. Leaks in these locations drain into the carbody and are easy to overlook.
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Request a quoteFrequently asked
How is the swing gearbox different from a final drive?
It carries a smaller oil volume for a comparable load, and it houses the swing brake rather than a travel brake. That means contamination degrades the oil faster, and brake faults show up as oil temperature before they show up as swing performance.
Does swing gearbox oil need changing as often as final drive oil?
Follow the machine specification. In practice the smaller oil volume means contamination concentrates faster, so many operators change it at shorter intervals than the schedule requires when the machine works in wet or dusty conditions.
My swing gearbox oil is black. Is that a problem?
Dark oil alone is not conclusive, but a burnt smell or visible suspended material is. Take a sample and compare it against the previous service. A change in appearance between services is the signal that matters.