The swing gearbox multiplies torque between the swing motor and the swing pinion that drives the ring gear, and it does it in a small oil bath that nobody samples. Checking it is a three-part job: level at the port, condition at the sight or sample point, and metal at the drain plug magnet. The level is a stick or port check at the machine's specified attitude, the condition is read through a small sample drawn from the drain, and the metal reading — pastes, flakes or glitter on the plug magnet — is the earliest warning the reduction can give before noise, before play, and before the six-figure conversation. Done at the interval the manual specifies, it is the cheapest health check on the machine.
Reading the sample and the magnet
| What you find | What it means |
|---|---|
| Level low, oil clean | A leak at a rotating seal. Trace and reseal; top up with the specified grade and recheck at a shortened interval. |
| Oil milky or cloudy | Water entry through a breather or seal. Find the entry, replace the oil, and check the reduction for corrosion pitting at the next sample. |
| Fine dark paste on the magnet | Normal collection. Clean the plug, refill, and keep the interval. |
| Flakes or a thick furry metal build | Gears or bearings shedding. Monitor closely for noise and play, and plan the reduction rebuild before it seizes in the ring gear. |
| Level rising over time | Hydraulic oil entering through the motor flange. The swing motor seal is the suspect, and the gearbox oil must come out before it loses its lubrication. |
How to confirm it
- Position the machine as the manual specifies and stop the swing fully
Some checks are done with the upperstructure at a marked position; the oil must be still and the gearbox level as the book intends. A swing brake left applied while the oil settles gives a consistent reading.
- Find the level port and read the level
The plug or dipstick is usually on the reduction housing, sometimes behind the swing platform's covers. Oil below the mark after a known interval means a leak — gearbox oil does not burn, it only leaves — and oil above it means a hydraulic leak into the gearbox, which is worse.
- Draw a small sample from the lowest point
Crack the drain plug just enough to catch a few milliliters into a clean glass jar. Read it warm and settled: dark oil is service life, milky oil is water, glitter in the light is bearing or gear metal, and a gray paste on the magnet is wear in progress.
- Read the drain plug magnet before you close it
A fine dark paste is normal wear collected by design. Metal flakes or a thick furry build mean gears or bearings are shedding, and the reduction is a monitoring case until the next check, or a repair case if the paste is accompanied by noise or swing play.
- Refill with the specified oil to the level mark
Swing reductions specify gear oil by viscosity grade, and some use the same oil as the final drives and some do not. Fill to the mark, not by feel, and record the volume and the date in the machine file so the next check has a consumption history.
What to do about it
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Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| Gearbox oils | OEM-specification gear oil at the manual's viscosity grade. The swing reduction is not a place to experiment with multi-purpose oil. |
| Pinion and motor flange seal kits | Genuine or OEM-quality to the reduction model; a seal that holds oil in is also keeping grit out of the gear mesh. |
| Swing reduction bearings and gear sets | Genuine or OEM-quality matched to the model and ratio. Gear mesh is the calibration of a reduction, and mismatched sets whine their whole life. |
Need the parts this covers?
Send the machine model, serial number and the part numbers you need. We confirm fitment before payment and state the grade of every line — genuine, OEM-quality or aftermarket.
Request a quoteFrequently asked
How often should swing gearbox oil be checked?
At the manual's interval — commonly hundreds of hours, far longer than engine oil — and immediately after any deep-water swing work or a washdown that submerged the reduction. The thirty-minute check described here fits inside that interval without tools beyond a jar and a socket.
Can I use the same oil as the travel reductions?
Only if the manual says so. Some machines standardize one gear oil across all reductions, and some specify different grades for the swing and travel drives. The plate on the reduction or the book is the authority, and mixing grades dilutes the only specification the mesh was designed around.
What does swing play have to do with the gearbox oil?
Two different checks for two different faults: play between the upperstructure and the house is the swing bearing, and play or roughness in the rotation itself is the reduction. A reduction shedding metal eventually shows as rough swing, and the oil check catches it months earlier. Both checks belong in one visit.