Spin the wheel while sighting along the brake pads. See how much pad you have left. See if the caliper mechanism is straight, and aligned along the rotor.

Check the rotor itself for warp and damage. If the rotor wobbles, has "dings," or is severely worn, click here.

If your specific brake doesn't let you actually see the pads from outside the brake mechanism, you'll need to pull the pads out to check the wear.

Some brake systems require you to manually adjust the brake pad's starting position as the pad wears down. Most mechanical (cable-operated) disk brakes are this way.

To adjust the brake pads to compensate for wear (for example, when the brake lever is starting to come close to the handlebar), find the pad position adjuster. On the Coda brake pictured, the outer-side pad is moved inward by rotating the disk containing the oil valve with a hex wrench. On Avid brakes, there's a knob that you turn with your fingers.

There's a similar disk on the opposite side -- a bit harder to get to because of the spokes. Adjust both pads inward, with the WHEEL side a bit closer to the rotor. Spin the wheel to be sure the pads don't rub, and grasp the brake lever a few times. If the rotor moves sideways (towards the spokes) at all, you need to move the wheel-side pad inward (towards the rotor).

If it's time to replace the brake pads and clean the mechanism, remove the wheel from the dropouts. This should allow you to access the pads.

If you have a Lefty shock, you can't remove the wheel easily. Instead, carefully remove the hydraulic cylinder from the frame. Be sure you're working in an area where you won't drop the tiny spacing shims into the grass.

The thin washers between the frame and the cylinder are spacing shims. Don't lose them, and be sure you get the correct number back on the bike. Lift the cylinder assembly clear of the disk.

Now remove the old brake pads. On the Coda brake, this is done by grasping the handle of the brake pad. Push inward towards the slot, then slide the pad back, out toward your hand.

Clean the interior of the brake mechanism with a Q-tip, removing all dirt, sand, and oil.

Now slide the new pads into the slot, metal side out, pad side in (so the pads will be touching the rotor, and the metal part will be pushed by the brake mechanism).

If you have manually adjusted pad position, dial the brake pad position adjusters (both inside and outside) to bring the brake pads apart. Now slide the brake mechanism over the rotor and bolt it into position, being careful to replace all the shims.

Now again adjust the brake pad position until you see both pads begin to approach the rotor, when sighting along the rotor into the brake mechanism.

Adjust the brake lever so you have about 1-1/2 inches of space between the lever and the handlebar when the brake is pulled. (You adjust this at the brake mechanism itself, by turning the pad position adjustment disk on the side of the brake as above.)

Test the brake lever for the right amount of "pull" for your hand. Adjust this, not at the lever like ordinary brakes, but at the wheel, using the adjustment disk to move the pads towards or away from the disk.

If you like the brake lever to be closer to the handlebar at rest (a closer starting position), locate and turn the adjusting screw. On this brake, the adjusting screw is recessed in a hole in the brake lever itself.