How to Repair Disc Brakes on a Bicycle

For mountain bikes, disc brakes are ideal, no matter the conditions.

For mountain bikes, disc brakes are swiftly becoming the industry standard for braking. Disc brakes are renowned for their ease of use and lack of maintenance, as well as their superior modulation and stopping power. They are also becoming more common as manufacturers figure out ways to make them less expensive. But as with any component on a bicycle, things can go awry. Fortunately, disc brakes are fairly simple devices that can be adjusted with minimal tools and hassle.

Things You'll Need

• 5 mm allen wrench
• Flathead screwdriver
• 15 mm socket wrench
• Bicycle repair stand
• Rag
• Acetone in a spray bottle or can

Instructions

Rubbing disc brakes

1. Put your bicycle into a bicycle repair stand so its wheels are elevated off the floor. Spin the affected wheel and watch as the disc rotor passes through the caliper. The rotor is the circular piece of metal attached to the wheel, and the caliper is the rectangular piece the rotor passes through. If the rotor is not straight, you need to replace the rotor or have it trued by a professional bicycle mechanic.

2. Loosen the bolts attaching the disc brake caliper to the frame or the mounting bracket using a 5 mm allen wrench. Use your hand to spin the wheel in the frame with the caliper loose.

3. Depress the brake lever to halt the spinning wheel. While holding the brake lever, firmly tighten down the caliper bolts using a 5 mm allen wrench.

4. Spin the wheel again to ensure that the rubbing is gone. If it continues, loosen the caliper bolts from the bracket or frame and move the caliper back and forth over the rotor until the brake pads in the caliper do not make contact with the rotor. Do not depress the brake lever while centering the caliper.

5. Tighten the caliper bolts using the 5 mm allen wrench. Spin the wheel to ensure there is no rubbing. If it continues to rub, repeat the steps above until the rubbing ceases.

Bad stopping power

1. Put the bicycle in the repair stand. Look into the affected caliper and look at the brake pads. If there is less than a millimeter of pad remaining, it is time to replace the pads. If the pads look okay, move onto the next step.

2. Remove the wheel from the bicycle. If you have quick releases, flip open the lever and remove the wheel from the bicycle. If you have bolt-on wheels, loosen the bolts with a 15 mm allen wrench to remove the wheel.

3. Spray acetone on a clean rag and wipe it along the disc brake rotor. This will help ensure there is no grease on the rotor. Also, spray acetone into the caliper to remove any grease. Wipe off excess acetone with a rag.

4. Replace the wheel into the bicycle. Tighten down the quick release with your hands or use a 15 mm socket wrench to evenly tighten the axle bolts.

5. Remove the bike from the stand and go for a low-speed test ride. If the bike continues to have poor braking power, the brake pads will need to be replaced. If the brake levers move all the way to the bar when used, the brakes will need to be bled by a professional bicycle mechanic.

Tips & Warnings

• Keep an eye on your brake pads. Riding worn out brake pads can cause the rotor to warp and damage the caliper.

• A little rubbing is typical during a ride. Brakes heat up during riding, which can often cause the rotors and brake pads to rub, particularly after long descents.

• Never ride your bicycle if you do not feel that its braking is sufficient to stop in an emergency.

• Avoid getting any sort of grease on the brake's rotors or pads, as this could contaminate the brake pads and severely affect stopping power.

References

• Park Tool: Shimano Disc Brake Adjustment
• Bicycling Magazine: How to Maintain Disc Brakes