Drain and inspect the oil first. Milky oil means a failed seal and water ingress — a seal and bearing job. Oil with metal means gear or bearing damage — a bigger repair. Noises that change with load point to bearings or gears; noises that follow speed only often trace to the chain or sprocket instead.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Whining or rumbling that rises with travel speed | Gear or bearing wear inside the final drive. Can also come from a worn sprocket or a dry chain. |
| Metallic knocking or clunking under load | More serious — gear damage or a badly worn bearing. |
| Final drive housing hot to touch after travel | Bearing wear, low oil, or excessive load from an over-tight track. |
| Milky or gray oil on draining | Water ingress through a failed seal. The most common serious finding. |
| Metal particles on the drain plug magnet | Normal fine fuzz is expected; flakes, chips or a heavy buildup indicate damage. |
| Oil level low with no visible external leak | Seal failure allowing the oil out through the hub, or a leak hidden behind the sprocket. |
| One side noisy, other quiet | Confirm the machine is on level ground and the noise is genuinely one-sided. Then inspect that unit. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Floating seal failure | Water and abrasive material enter the gearbox. Progresses from contaminated oil to failed bearings if not corrected. |
| Bearing wear | Noise that increases with load and speed, with metal in the oil. |
| Gear tooth damage | Knocking or clunking under load. Usually follows a period of contaminated oil. |
| Low oil level | Overheating and rapid wear. Sometimes the oil left through a failed seal; sometimes it was never filled correctly. |
| Over-tight track | Continuously loads the final drive and accelerates everything inside it. |
| Worn sprocket | Noise that sounds like the final drive but originates outside it. |
| Loss of the travel brake or its seal | Drag, heat and abnormal noise after travel stops. |
How to confirm it
- Drain and inspect the oil before anything else
Drain a sample into a clean container and let it settle. Milky means water. Metal content tells you what has failed. Oil condition decides the scale of the repair, and it costs nothing to check.
- Confirm the noise location
Run the machine on a hard level surface and listen at each side. Noise from the sprocket area with clean oil usually means the sprocket and chain rather than the gearbox itself. This distinction decides whether you are buying gears or a sprocket.
- Check the oil level
Confirm the level is correct and has not been overfilled. Both extremes cause heat and noise, and overfilling is common after service.
- Check track tension
An over-tight track loads the final drive continuously. Correcting tension is free and sometimes resolves a heat complaint on its own.
- Test for damaged bearings
With the machine safely raised, rotate the sprocket and feel for roughness, backlash and end play. Rough rotation with clean oil supports a bearing problem rather than a gear problem.
What to do about it
Milky oil with no metal: reseal the unit, replace the affected bearings if inspection shows roughness, refill with the specified oil and recheck at a short interval. This is a seal job and repairing it early is the whole point of checking the oil.
Metal in the oil with rough rotation: the unit needs opening and probably new bearings, possibly gears. Photographs of the drained oil and of the internals let us quote the honest level of repair rather than the most expensive one.
Noise that follows speed but disappears when the machine is raised: the fault is likely in the sprocket, chain or idler rather than the final drive. Test before spending.
If the housing is cracked or a shaft is damaged, a complete unit or a remanufactured exchange is usually the practical answer. Confirm the exact variant by machine serial number — final drive part numbers change across serial breaks and interchange between similar machines is not safe to assume.
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 final drive oil be changed?
Follow the machine specification, and check the oil level more frequently than you change it. Oil color is the cheapest early warning system on the machine, and it takes a minute.
Some fine metal on the magnetic plug — is that a problem?
Fine gray fuzz is normal wear. Flakes, chips or a thick coating are not. Compare against what you find at the next service — the trend is more informative than a single sample.
Can I repair a final drive or do I need a new one?
Frequently repairable, particularly when caught at the seal stage. The economics depend on gear and housing condition. Send us the machine serial number, photographs and the drained oil appearance and we can indicate the likely level of repair before it comes apart.