Changing final drive oil: guide for excavators and mini excavators
Zoltan Gal, Managing Director FinalDriveUpdated
Change the gear oil in the final drive every 250 to 500 operating hours, at least once a year. Unless the machine manufacturer specifies otherwise, 80W90 gear oil is suitable. Drain it warm and fill up to the level port.
A final drive has two separate oil circuits: the travel motor runs on hydraulic oil from the machine's tank, the planetary gearbox has its own gear oil fill. Only the gear oil is changed. The job takes just under an hour and is one of the most important services on an excavator.
Interval, oil type and quantity
| Item | Recommendation |
|---|---|
| Check oil level | Once a month, more often under heavy use |
| Oil change | Every 250 to 500 operating hours, at least once a year |
| Oil type | Gear oil 80W90, unless the machine manufacturer specifies otherwise |
| Quantity | Until oil runs out of the level port. The exact quantity is in the operator's manual. |
| Sealing washers | New at every change |
Do not mix different oil types. For a new final drive, follow the drive or machine manufacturer's recommendation for the first change.
Tools and materials
- Drain pan with enough volume, funnel or oil pump
- Suitable hex or ring spanner for the plugs
- New sealing or copper washers for the plugs
- 80W90 gear oil or the oil specified by the manufacturer
- Clean rags, gloves, optionally a magnet to check for chips
Step by step
- Warm up the drive. Warm oil drains better and carries dirt out.
- Position the machine. On level ground, move the excavator until one plug is at the very bottom (drain) and the second roughly half way up (level and fill port). On drives with three plugs, the third is at the top.
- Clean the area. Clean around the plugs so no dirt falls into the gearbox.
- Drain the oil. Open the upper plug first, then the lower one. Let the oil drain completely into the pan.
- Inspect the old oil. Look closely at the oil (see table below). Chips or milky oil are a warning sign.
- Close the drain plug. With a new washer and appropriate torque.
- Fill new oil. Fill through the middle port until oil runs out of the level port. On many drives the gearbox is then about half full.
- Close and test drive. Close the plugs with new washers, drive briefly and check for leaks.
What the old oil tells you
| Finding | Meaning |
|---|---|
| Clear, dark, no residue | Normal condition |
| Fine debris on the magnet | Normal wear, compare at the next change |
| Coarse chips, fragments | Bearing or gear damage, have the drive checked |
| Milky, light | Water in the gearbox, usually via the floating seal |
| More oil than expected, thin | Hydraulic oil is entering the gearbox from the travel motor |
| Hardly any oil in the gearbox | External leak, see final drive leaking |
If the oil points to damage
With chips or water in the gearbox, take a close look before bigger damage develops. Whether a repair or a new drive makes more sense is covered in repair or replace a final drive. More service points are in final drive maintenance.
Frequently asked questions
What oil goes into a final drive?
The planetary gearbox takes gear oil, usually 80W90, unless the machine manufacturer specifies otherwise. The travel motor itself runs on the machine's hydraulic oil.
How often should final drive oil be changed?
Every 250 to 500 operating hours, at least once a year. Check the oil level monthly.
How much oil goes into a final drive?
Fill until oil runs out of the level port when it sits half way up. The exact quantity is in the machine's operator's manual.
Why is the oil in my final drive milky?
Milky oil contains water. It usually enters the gearbox via a worn floating seal, for example after working in water or mud.