Home mechanic (basic tools) ยท Time: 30 to 45 min (estimate)
Some bikes use fluid, not a cable, to work the clutch. The lever pushes a small master cylinder; fluid moves to a slave cylinder at the engine, which releases the clutch. Air in the system squashes instead of pushing, so the clutch does not release fully: the bike creeps in gear and neutral is hard to find. Bleeding pushes the air out through a small valve (the bleed nipple) on the slave cylinder. Most small commuter bikes, including the K-Light 125, use a cable; this page is for bikes with a reservoir on the clutch lever.
Safety
- Check the reservoir cap. It tells you the fluid: brake fluid (often DOT 4) or mineral oil. Never mix them. The wrong fluid destroys the seals.
- Brake fluid hurts eyes and skin and strips paint almost at once. Wear glasses and gloves, cover paint with plastic sheet, and wash spills off with water.
- Never reuse old fluid. Use a sealed, fresh bottle.
You need
- Fresh fluid of the type on the cap.
- A ring spanner that fits the bleed nipple (an open spanner rounds it).
- About 60 cm of clear tube that fits tightly on the nipple, and a bottle to catch fluid.
Steps
- Turn the handlebar so the clutch reservoir is level. Cover the tank and paint.
- Clean the cap, remove it and the rubber diaphragm. Wipe the diaphragm clean; do not wash it in solvent.
- Top up the reservoir with fresh fluid. Do not fill above the upper mark.
- Fit the ring spanner on the bleed nipple at the slave cylinder, then push the clear tube onto the nipple and put the other end in the bottle with a little fluid in it.
- Squeeze the clutch lever and hold it in.
- Open the bleed nipple a little (about half a turn). Fluid and air come out and the lever goes towards the bar.
- Close the nipple while still holding the lever.
- Release the lever slowly.
- Repeat steps 5 to 8 until no bubbles come down the tube. Watch the reservoir every two or three strokes. If it runs low, air goes back in and you must start again.
- Close the nipple firmly but do not overtighten; use the torque in your manual. Remove the tube.
- Top up the reservoir to the level mark, refit the diaphragm and cap.
Check your work
- The lever feels firm, with a clear point where the clutch starts to release.
- Engine running, lever pulled: first gear goes in quietly and the bike does not creep.
- No fluid at the nipple, the hose joints or the slave cylinder after a few lever pulls.
If it did not fix the problem
- Air keeps returning or the fluid level drops: there is a leak, often at the slave cylinder seal or master cylinder. This needs a workshop. Do not ride with a clutch that will not release.
- Lever firm but the clutch still drags: Clutch drags.
- For more on handling fluid and bleeding, see Replace brake fluid and bleed the brakes; the method is the same.