Final drive leaking: find the cause and act correctly
Zoltan Gal, Managing Director FinalDriveUpdated
If oil escapes between housing and sprocket, the floating seal is usually worn. If the travel motor is oily, it is the ports, plugs or cover. Act quickly: once the gearbox runs dry, bearing and gear damage develops within a short time.
A wet final drive is no reason to panic, but a reason to look closer. What matters is where the oil escapes and which oil it is. That tells you how urgent it is and what needs doing.
Where a drive starts leaking
| Location | Typical cause | Urgency |
|---|---|---|
| Gap between housing and hub (sprocket side) | Floating seal worn or damaged, often by wire or rope in the undercarriage | High, gearbox is losing oil |
| Hydraulic ports on the travel motor | O-rings, loose fittings, damaged hoses | Medium, hydraulic oil is lost |
| Plugs on the gearbox cover | Old washers, plug not tight | Low, fixed quickly |
| Cover or housing joint | Aged gasket, distorted housing | Medium |
| Gearbox overflowing, oil at the breather | Hydraulic oil passes the shaft seal into the gearbox, often due to pressure in the case drain line | High, damage to the travel motor likely |
Gear oil or hydraulic oil?
Gear oil is thicker, darker and smells distinctly of sulphur. Hydraulic oil is thin and usually lighter. If hydraulic oil escapes at the sprocket or the gearbox oil level rises, that points to an internal leak between travel motor and gearbox.
What to do
- Clean. Clean the drive thoroughly so you can locate the leak reliably.
- Drive briefly and watch. Where does a new oil film form first?
- Check the gearbox oil level. Too little oil: top up immediately and only move the machine gently. Too much oil: suspect hydraulic oil in the gearbox.
- Check the case drain line. It must be clear and lead to the tank without back pressure. A kinked hose or a capped line pushes the shaft seal out of the travel motor.
- Check the undercarriage. Remove wire, rope and stones from around the sprocket.
- Decide. Leaking ports and plugs can often be fixed on site. For a worn floating seal or an internal leak, read repair or replace a final drive.
Prevention
- Check the gearbox oil level monthly and change oil at the interval (oil change guide).
- Clean the undercarriage after working in mud, wire or rubble.
- Set track tension according to the operator's manual, an over-tensioned track loads bearings and seal.
- When fitting a drive, always connect the case drain line, never cap it.
Frequently asked questions
Why is my final drive leaking at the sprocket?
Usually the floating seal between housing and hub is worn or damaged by wire and rope in the undercarriage.
Can I keep working with a leaking final drive?
Only briefly and with the oil level under control. Once the gearbox runs dry, bearing and gear damage follows quickly.
Why is the gearbox oil level rising?
Hydraulic oil from the travel motor is entering the gearbox. A common cause is pressure in the case drain line, which damages the shaft seal.
How do I recognise gear oil?
Gear oil is thicker than hydraulic oil, darker and smells distinctly of sulphur.