Home mechanic (basic tools) ยท Time: 15 to 30 min (editorial estimate) (estimate)
A dragging brake keeps rubbing after you let go of the lever or pedal. The bike feels slow, uses more fuel, and the disc or drum gets hot. Heat can boil the brake fluid or glaze the linings, and in the worst case lock the wheel. This check finds which part is holding the brake on.
Safety
- Do not touch a disc or drum to test heat after riding: hold the back of your hand near it. A dragging brake can burn you.
- If a wheel is very hard to turn or locks, do not ride.
- Brake fluid harms paint and eyes.
You need
- The bike on a stand so the wheel being tested is off the ground.
Steps
- Spin the wheel by hand with the brake released. It should turn several times on its own. A very light brush of pads is normal on a disc brake; a hiss that stops the wheel quickly is not.
- Rear wheel on a chain bike: remove tension first by checking chain slack. A chain that is too tight also makes the wheel hard to turn (K-Light 125 manual lists it as a cause). See Check and adjust chain slack.
- Feel for wheel bearing roughness while you spin it: Check wheel bearings.
- Pull the brake hard and release it, then spin again. If drag appears only after braking, a piston, cam or master cylinder is not returning.
- Disc brake: look at the lever or pedal. It must have a little free play before it moves the master cylinder piston. If the lever pivot is stiff or the rear pushrod is set too long, the piston stays partly on. Fix with Adjust the rear brake pedal or Service brake and clutch lever pivots.
- Disc brake test: put a rag round the bleed nipple and a tube into a bottle, open the nipple a quarter turn for a moment, then close it. If the wheel then spins freely, pressure was trapped by the master cylinder (go to Check the brake master cylinder). If it still drags, the caliper pistons or slides are sticking (Clean a brake caliper and free the pistons). Top up the reservoir afterwards and bleed if the lever is soft.
- Drum brake: loosen the adjuster several turns. If the drag stops, the brake was over-adjusted or the cam is sticking. If the cable does not return the arm, the cable is sticking: Lubricate control cables. Then service with Service a drum brake.
- CBS bike: also spin the front wheel after pressing only the rear pedal. Front drag after pedal use points at the CBS unit or rear pushrod: Check a combined braking system (CBS).
- Check for a bent disc that touches a pad at one point each turn: Check a brake disc.
Check your work
- After a short ride, both wheels spin freely and the discs or drums are only warm, not too hot to hold a hand near.
- The bike rolls freely when pushed in neutral.
If it did not fix the problem
- Go to Brake drags and the wheel does not spin freely and follow the steps.