Check the cush drive rubbers

Home mechanic (basic tools) · Time: 30 to 60 min (estimate)

The cush drive is a set of rubber blocks between the rear sprocket carrier and the wheel hub. They soften the jolt when you open or close the throttle and protect the chain and gearbox. When the rubbers go hard, crack or shrink, you feel a clunk or snatch from the rear every time the drive changes from pulling to slowing. On the K-Light 125 the sprocket sits on studs in a carrier with rubber dampers in the left side of the hub, held by a large circlip.

Safety

• Bike on the centre stand, engine off, key out.
• Support the bike well when the rear wheel is out. A bike falling off a stand can crush a foot or hand.
• The rear axle nut must go back to the correct torque.

You need

• Tools to remove the rear wheel (Remove and refit the rear wheel).
• Circlip pliers if the carrier is held by a circlip.
• A new set of rubbers if needed. Always replace the whole set.

Steps

1. With the bike on the stand and in neutral, hold the rear sprocket with a gloved hand and rock the wheel backwards and forwards. A short, springy movement is normal. A clear free gap before the rubbers push back means they are worn.
2. Check the chain slack first, because a slack chain also clunks: Check and adjust chain slack.
3. Remove the rear wheel.
4. Lift the sprocket carrier out of the hub. On some wheels it pulls straight out; on the K-Light the circlip, washer and sprocket come off, then the sprocket studs and the damper.
5. Take out the rubber blocks. Look for cracks, crumbling, flattened faces, hard shiny surfaces or oil soaking. K-Light 125: replace the rear wheel damper if it is damaged or cracked.
6. Check the vanes on the carrier and in the hub for wear or cracks.
7. Check the carrier bearing (if fitted) and the wheel bearings while the wheel is out (Check wheel bearings).
8. Fit the new rubbers. If they are tight, a little soapy water helps them slide in. Do not use oil or grease on rubber.
9. Refit the carrier, sprocket and wheel. K-Light 125 rear sprocket nuts: 45 to 50 N·m in two or three passes, criss-cross, if you removed them.
10. Set the chain slack and tighten the axle nut to the correct torque.

Check your work

• The springy movement at the sprocket is short and firm.
• On a test ride, opening and closing the throttle no longer gives a clunk from the rear.

If it did not fix the problem

• Clunk remains: Clunk or snatch from the rear wheel; check the swingarm and shock mounts (Check the swingarm pivot) and the engine mounts (Check engine mounting bolts).

Reference values (K-Light 125)