Mechanical Disk BrakesDisk brakes use two metal-backed pads held in place by magnets. There may also be a spring-loaded clip that keeps the pads in place. Pistons push the pads against a metal rotor. Activation can be via cable (mechanical) or a fluid-filled line (hydraulic). This section is for mechanical disc brakes, such as Avid. If you have a hydraulic system without pad adjustment knobs (such as Hayes), click here. For a hydraulic system with external adjusters (such as Coda), click here.
Proper function of the brake depends on (1) the rotor must be straight and smooth, (2) the caliper mechanism must be properly aligned with the rotor, (3) the pads must be positioned correctly, (4) there must be enough "pad" left, and (5) the lever mechanism must push the active pad tightly against the rotor, with "lever" to spare.
Spin the wheel. Check the rotor itself for warp and damage. Look for side-to-side wobble. See if the caliper opening is centered on the rotor.
Loosen the two bolts that hold the main body of the brake onto the mounting yoke or fork. These bolts aim forward along the axis of the rotor, with one above and below the calipers. The holes for these bolts allow for some side-to-side "play" that positions the caliper mechanism. (Don't take the bolts out; just back off the tension in the bolt enough to allow the rotor to "shift" a bit on its mounting.)
With the cable loose, push the activating arm upward a bit until it stops moving. (At this point, it has pushed the pads against the rotor.) Now back off about 1/2 to 3/4 inch of cable length.
To change the brake pads, remove the wheel. Grasp the handle of a brake pad. Move the handle towards the inside of the slot, and pull firmly. (On Avid and Hayes, there is a retaining clip that holds the pads. You need to overcome the tension on the clip.) The pad will slide out.
Insert each new pad. Pads are specific for inside versus outside (and top versus bottom). Push the pad back until you feel it click into place. Make sure the pads are seated correctly into the retaining clip, and positioned over the caliper piston. If a pad is inserted incorrectly, it won't work right.
Dial the adjuster pads inward, until each pad very nearly touches the rotor. Spin the wheel to be sure the pads don't rub the rotor.