How do I replace bike brake pads?

Pad replacement is one of the few bike jobs that is genuinely straightforward and genuinely important. Most of the difficulty is in identification — brakes take a bewildering number of pad shapes — and in the two steps either side of the swap.

Safety

What you'll need

• Correct replacement pads for your brake
• Allen keys
• Needle-nose pliers (optional)
• Isopropyl alcohol and a clean rag

Step by step

1. Check they really are worn.Rim pads have grooves moulded into the rubber; when those disappear the pad is finished. Disc pads should be replaced when roughly 0.5mm of friction material remains above the backing plate — running to metal destroys the rotor, which costs several times what the pads do.
2. Identify the pad you need.Take the old pad to the shop or photograph the caliper. Disc pads in particular vary by brake model and there is no universal fit. Note whether they are organic or sintered — organic are quieter and bite better cold, sintered last longer and cope better with wet and heat.
3. Remove the wheel for a disc brake.It makes the caliper accessible. Do not touch the lever from this point until the new pads are in and the wheel is back.
4. For rim brakes, note the orientation before removing anything.Many pads are handed left and right, and have an arrow or the word 'forward' on them. A pad fitted backwards can be pushed out of its holder by braking.
5. Slacken the cable or open the quick release before removing rim pads.It gives clearance. On cartridge pads, pull the split pin and slide the rubber out of the holder without disturbing the alignment.
6. Remove the retaining pin and take the disc pads out.Usually a split pin or clip, then a threaded pin, and the pads come out downwards or upwards depending on the caliper. Note how the spring clip sits between them — it only goes back one way.
7. Push the pistons fully back.With the old pads still in place if possible, use a plastic tyre lever or a proper piston press to push both pistons evenly back into the caliper. New pads are thicker and will not fit otherwise. Do this gently and evenly, and never with a screwdriver against a bare piston.
8. Clean the caliper and the rotor.Brush the dust out, and wipe the rotor with isopropyl alcohol. Handle new pads by the backing plate only.
9. Fit the new pads with the spring in place.Then refit the retaining pin and its clip or split pin. That pin is what holds the pads in the caliper — it is not optional and it must be secured.
10. Refit the wheel and pump the lever.Squeeze the lever repeatedly until it firms up and the pads come back to the rotor. Then check alignment and realign the caliper if it rubs.
11. Bed the pads in.About twenty firm stops from moderate speed on a quiet road without coming to a complete standstill, letting them cool between. New pads have very little power until a transfer layer has formed.
12. Test hard before riding properly.Both brakes, at walking pace, then a firm stop. If the lever travel has changed or feels spongy, stop and take it to a shop.

Tips

• Buy pads before you need them. Running to the backing plate on a wet commute costs a rotor.
• Replace both pads in a caliper together, and both wheels' worth if they are close, so the bike brakes evenly.
• Keep the old pads if they have life left as an emergency spare, in a labelled bag away from anything oily.

Common mistakes

• Not pushing the pistons back before fitting new disc pads — The pistons have advanced to take up the wear in the old pads. New, thicker pads will not fit into the remaining gap, and forcing them damages the pad, the piston seal or both.
• Fitting rim pads backwards — Most cartridge pads are open at one end so the rubber can be slid in and out. Fitted the wrong way round, braking pushes the rubber straight out of the holder, and the first you know is metal on rim.

If it doesn't work

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