Most scooters have a small sealed gear case behind the rear pulley that reduces speed from the clutch to the rear wheel. It has its own oil, separate from the engine oil, with a filler bolt and a drain bolt. Shaft-drive motorcycles also use gear oil in the rear drive.
What it does
The oil coats the gears and bearings so metal does not touch metal. Gear oil is thicker than engine oil and made for high tooth pressure. It is a small amount, so it gets dirty quickly if it is never changed. If the case seal leaks, the level drops and oil can reach the rear brake or tyre.
Signs it is worn or failing
- Oil on the rear wheel, case or brake: Oil leaking from the scooter rear gear case. Oil on the brake or tyre is dangerous: clean it off and fix the leak before riding.
- Whine or rumble from the rear hub area: Noise from the drive case.
- Drained oil is black, milky (water) or has metal chunks. Fine grey paste on a magnet is normal; chunks mean gear damage.
When to replace it
Change at the interval in your scooter's manual, and whenever the case seal or gears are serviced.
What to match when buying
- Viscosity and type written in the manual or on the case, for example a gear oil grade or, on some scooters, engine oil. Do not guess.
- Quantity is small and exact; buy the amount the manual gives and measure it.
- Buy sealed bottles from a known brand. Refilled or unlabelled bottles may be old engine oil.
- New sealing washers for the drain and filler bolts.
Fitting notes
- Remove the filler bolt first, then the drain bolt, so you know you can refill.
- Shield the rear tyre with cardboard while draining.
- See Change scooter final drive oil.