A majority of bicycles use a rim style brake, such as a caliper or direct-pull cantilever, but some cyclists prefer disc brakes. Unlike rim-mounted brakes, disc brakes are placed on the side of the wheel hub, though they operate similarly with two brake pads squeezing the disc to slow the bicycle. This type of brake slips less in wet conditions and prevents the brakes from damaging the rim of the wheel.
Removing the Rim Brakes
The first step in converting your mountain bike to disc brakes is to remove all of the hardware and cables that were used for the rim-mounted brakes. The brake levers on your handlebars and the cables that ran to the brakes may be compatible with your new disc brakes, depending on the model you are using. Take all of the hardware off of the forks when you remove the brakes. It will also be useful to remove both wheels during this procedure.
Preparing for Installation
Before you begin mounting the hardware for the new disc brakes, ensure your bicycle has the necessary mounting fixtures. On the forks and the rear frame triangle, you need to have post mounts so the brake calipers can be attached to the frame. If your bike was manufactured before 2009, the mounts might not be present. The hubs of the wheels must have a six-bolt or center lock system that the brake rotors can be attached to.
Installing the Brakes
Install the brake rotors onto the wheels while you still have them off of the bike. The bolts that mount the rotors to the hubs should be tightened fully, but not overdone or they can strip. After the rotors are on, put the tires back on the bike and mount the brake pads to the front and rear frame brackets. Once the pads are mounted, thread the brake lines from the handlebars to the pads and test them to ensure they are working. Secure the brake lines to the bicycle frame with zip ties or existing cable mounts.
Adjusting the System
Your newly installed brakes must be adjusted to ensure that the calipers are aligned and the brake pads are properly positioned close to the rotor. First move the calipers vertically until the pads cover the entire rotor area. Sight down the brake rotor and rotate the wheel, noting how far the pads are from the rotor on each side. Tighten the calipers so the pads are approximately 1 mm from the rotor. Take the bike for a test ride and squeeze the lever for response. Adjust the brake lever with a hex wrench so it is between 1/2 and 1 inch from the handlebar when the brakes are fully engaged.