The drain or level plug must be at the position specified for that final drive design, typically the horizontal centerline. Draining and filling from the wrong position means the unit is never correctly filled, and the resulting fault gets diagnosed as wear.
Procedure at a glance
| Step | Note |
|---|---|
| Position the machine | The plug must be rotated to the specified position. Follow the machine documentation — this varies between final drive designs. |
| Clean around the plug | Grit around the plug enters the gearbox. Clean thoroughly before opening. |
| Drain fully into a clean container | Examine what comes out. Color and metal content determine the next step. |
| Check the magnetic plug | Fine gray fuzz is normal. Flakes, chips or heavy buildup indicate internal damage. |
| Inspect accessible seals | With the oil drained, look at the seals you can reach. This is the best opportunity to spot a leak that will otherwise contaminate the new oil. |
| Refill to the correct level with the specified oil | Final drive oil carries extreme-pressure additives. Substituting a general-purpose oil shortens gear and bearing life. |
| Re-check level after the machine has moved | Run the machine briefly, then re-check. Residual oil that drains back can leave the level above specification. |
How to confirm it
- Confirm the correct plug position for this final drive
The machine documentation specifies which plug is drain, which is level and which position the unit must be in. There is no single universal rule: final drive designs differ, and assuming produces a wrong fill.
- Clean the area around the plug thoroughly
On a dusty site this is the single most important step for protecting the unit. Everything you leave around the plug goes inside.
- Drain into a clean container and examine the oil
Let the oil settle and look at it in good light. Milky oil means water ingress. Dark or burnt oil means overheating. Metal content tells you whether the unit is healthy, and this examination is the reason for draining it in the first place.
- Check the magnetic plug and strainer where fitted
Fine gray coating is normal wear. Anything coarser indicates a component is breaking down, and the decision about the final drive has just changed.
- Look at the seals you can reach
With the oil out, inspect the accessible seal areas. Catching a weeping seal now prevents the same contamination from recurring in the new oil, which is often the difference between one repair and two.
- Refill with the correct oil to the correct level
Use the specified oil, not a general-purpose substitute, and fill to the level plug with the machine in the specified position. Check the level again after moving the machine.
- Record the oil condition and the hours
Write down what the drained oil looked like. On the next change, the comparison tells you whether the unit is stable or deteriorating, and that is more useful than any single inspection.
What to do about it
Milky oil: reseal the unit. Water enters through a floating seal or a hub seal, and resealing is what prevents the eventual bearing failure. Refill, then recheck at a short interval to confirm the contamination has gone.
Metal flakes: the unit needs opening. Establish whether the gears are intact, which determines whether it is a bearing and seal repair or something larger, and quote the correct level of repair rather than assuming the worst.
Recurring contamination after a reseal: the water entry point was not addressed, or the fill and vent points are letting water in. These need identifying rather than resealing again.
Overfilled after refill: correct it. An overfilled final drive builds pressure and pushes oil past seals, and the leak that results is often mistaken for a seal failure rather than a filling error.
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Request a quoteFrequently asked
Does the machine need to be in a special position?
Yes. The specified plug position is part of the procedure for that final drive design, and filling with the plug in the wrong position is the most common cause of an incorrectly filled unit.
Can I use a different oil if the specified one is unavailable?
Only if the specification matches. Final drives are heavily loaded gear sets requiring an extreme-pressure additive package. Using a general-purpose hydraulic or engine oil reduces gear and bearing life, and the saving does not survive one repair.
How do I know if my final drive needs more than an oil change?
By what comes out of it. Fine gray fuzz and clear oil mean the unit is healthy. Milky oil means a seal repair. Metal flakes or chips mean the unit must be inspected internally. Drain and look before deciding anything else.