Disc brakes are featured on many of today's mountain bikes. Modern disc brakes are relatively light, easy to maintain and perform well in all weather conditions. Each brake--front and rear--is outfitted with a pair of pads, which grip the sides of the wheel during braking. Because of friction, the surface of the pad becomes increasingly worn, and in time will need to be replaced.
1. Remove the appropriate carbon wheel from the bicycle. This will be the wheel that corresponds to whichever brake you're servicing. If removing the rear wheel, first shift to the smallest rear cog and largest front chain ring. This position eases the removal of the wheel from the drive chain.
2. Use a pair of pliers, and remove the brake pad fix bolt clip. The fixing bolt passes through the brake pad, helping hold the pad in place. The clip at the end ensures that the fixing bolt doesn't somehow work itself free.
3. Unscrew the fixing bolt by turning it counterclockwise with a proper size Allen wrench (usually 2.5 to 3 mm). Remove the fixing bolt and set it aside.
4. Slide the brake pads and return spring (this will be found in the middle of the pads) from the brake caliper.
5. Pry the pistons inside the caliper apart, using a flat-blade screwdriver or plastic tire lever. The pistons will be visible now that the old brake pad has been removed.
6. Place the new pads (with the return spring in the middle of the pads) into the caliper. Make sure the eye holes in the pads and return spring are oriented so that the fixing bolt can pass through each part. The pistons will now hold the pads in place.
7. Reinstall the fixing bolt, and tighten it in place. The bolt should pass through the caliper, brake pads and return spring.
8. Reinstall the retaining clip through the eyelet at the end of the fixing bolt.
9. Install the wheel back onto the bicycle. To "scuff" (or break in) the pads, take the bike outside and perform a few hard stops with the brakes.