Position the machine so the drain or level plug is at the correct orientation for that final drive design, then check level and drain a small sample. Milky oil means water has entered through a failed seal. Metal beyond fine fuzz means internal damage. Both demand action before the unit fails completely.
How to confirm it
- Position the machine per the specification
Most final drives require a specific plug position — commonly the plug at the horizontal centerline of the housing. Checking level with the machine in the wrong position gives a reading that is consistently wrong and consistently believed.
- Clean around the plug before opening it
Dirt around the plug migrates into the oil the moment the plug comes out. Clean the area thoroughly. On a dusty site this alone prevents a meaningful share of the contamination that would otherwise be introduced.
- Check the level
Oil should be at the level plug with the machine in the specified position. Low level means either a leak or a fill error. Overfilled units run hot and can blow seals, and overfilling after service is a common mistake.
- Drain a small sample into a clean container
Take enough to see clearly. Let it settle and examine color and consistency. Attach a magnet to the container wall or wipe the drain plug in the oil and look at what adheres.
- Interpret what you see
Amber and clear: healthy. Milky or gray: water ingress through a failed seal, which is the most common serious finding. Dark with a burnt smell: overheating, often from a tight track or low oil. Metal flakes or chips: internal damage, and the unit needs to come apart.
- Check for the source of any water
If the oil is contaminated, look for the entry point: the floating seal, the hub seals, or water entering through a breather or the fill. Repairing the gearbox without sealing the entry point repeats the job.
- Compare both sides
Check both final drives at every service. Comparing the two sides of the same machine tells you more than any absolute standard, because the two units have had the same working life.
What to do about it
Milky oil: drain, flush, reseal the unit and refill to specification. Recheck at a short interval, because residual moisture takes more than one change to remove. Caught at this stage, a final drive is a seal job.
Metal flakes or chips: plan on opening the unit. Bearing and gear inspection determines whether it is a repair or a replacement, and photographs of the drained oil help establish the likely level before it comes apart.
Low level with no visible external leak: check the hub seal and the area behind the sprocket. A seal that leaks behind the sprocket is easy to miss from outside.
Overfilled: correct the level and check for the reason. An overfilled final drive builds pressure and pushes oil past seals, and the resulting leak is often diagnosed as a seal failure rather than a fill error.
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Request a quoteFrequently asked
How often should I check final drive oil?
Level at every service, oil condition at intervals specified for the machine. On machines working in wet or dusty conditions, checking more often than the schedule is genuinely worthwhile given the cost of a final drive.
How much metal is normal?
A fine gray film on a magnetic plug is normal wear. Flakes, chips or a thick accumulation are not, and they indicate that something inside is breaking down. What matters most is the trend between services.
Can I use a different oil than specified?
Only if the specification matches. Final drives are heavily loaded gear sets and the specified oil carries the extreme-pressure additive package they need. Using a general-purpose hydraulic or engine oil in place of it shortens bearing and gear life.