Replace disc brake pads
New pads mean strong braking again and a disc that lasts. The job takes twenty minutes and mostly calls for cleanliness: a pad touched with greasy fingers will never brake well.
What you need
- Pads that fit your caliper (part number in the manual, or on the old pads)
- A hex key, or pliers for the retaining pin
- A plastic tyre lever
- Isopropyl alcohol and a clean rag
- Disposable gloves (recommended)
When to do it
- When the pad material reaches the manufacturer's limit: 0.5 mm for Shimano, 3 mm including the backing plate for SRAM (see Check your brakes). Have new ones ready at about 1 mm.
- When the brake grinds metal on metal: the backing plate is already rubbing on the disc, replace them right away.
- When the pads have been contaminated (oil, brake fluid): they squeal and barely brake, and no cleaning will save them.
Always replace both pads in a caliper together.
Choosing pads
The shape depends on the caliper model: it's the part number that matters (for example Shimano "L03A", SRAM "Level"). For the friction material, there are two main families:
| Material | Pros | Cons |
|---|---|---|
| Organic (resin) | quiet, strong bite when cold, gentle on the disc | wears faster, fades on long descents |
| Metallic (sintered) | lasts a long time, copes with mud and heat | noisier, needs a compatible disc |
How the caliper works
In the caliper (1), pistons (2) push the two pads against the disc (7). Each pad has a metal backing plate (4) and friction material (3), facing the disc. A butterfly spring (5) pushes them apart at rest, and a pin (6) holds them in place.
Steps
1. Remove the wheel
Open the quick release or unscrew the axle, and take the wheel out. Position the bike so you can see into the caliper from above.
2. Remove the pin
Depending on the model: straighten and pull out the split pin with pliers, or remove the small clip and then unscrew the pin with a hex key. Keep it: it can be reused if it isn't damaged (new pads often come with one).
3. Take out the old pads
Pull the pads and their spring out through the top of the caliper, noting which way round the spring was fitted (a photo helps). On a few calipers, the pads come out through the bottom: you then have to remove the caliper, see the manual.
4. Push the pistons back
The pistons have crept forward as the pads wore: you need to push them right back to make room for the new, thicker pads. Slip a plastic tyre lever between the pistons and lever gently and evenly until they're fully back.
5. Fit the new pads
With gloves or clean hands, without touching the friction material, put the two pads and the spring together the same way round as the old ones. Slide the assembly into the caliper, friction material facing inwards, and refit the pin (and its clip, or bend its split end).
6. Clean the disc and refit the wheel
Clean both sides of the disc with isopropyl alcohol on a clean rag. Refit the wheel, guiding the disc between the two pads, then tighten the axle.
7. Bring the pads in
Pump the lever about ten times: the pistons move out until the pads touch the disc. The lever should feel firm again. Spin the wheel: if it rubs constantly, centre the caliper (loosen its two bolts, squeeze the lever, tighten the bolts with the lever held, to 6 to 8 Nm for Shimano).
8. Bed the pads in
New pads brake weakly until they're bedded in. Somewhere clear, do 10 to 20 progressive stops from a normal riding speed (20 to 25 km/h) down to walking pace, never locking the wheel, then a few harder ones. Bedding in lays a thin film of pad material on the disc, which is what gives the bite. The braking becomes noticeably more powerful.
Check it's done right
- The lever is firm and stops well before the bar.
- The wheel spins freely, with no constant rubbing.
- After bedding in, the bike stops cleanly, without squealing.
Common mistakes
- Touching the pad material or the disc with greasy fingers or degreaser.
- Squeezing the lever with the wheel out, then forcing the disc back in.
- Forgetting the pin's clip: the pin can work loose while riding.
- Braking hard straight away: pads that aren't bedded in can catch you out with their lack of bite.
What next
Log the pad change in your logbook, with the part number: you'll know what to buy next time. Check the disc thickness now and then: a minimum is engraved on it (often 1.5 mm), below which it must be replaced. If the lever stays soft despite new pads, the brake needs bleeding, at a bike shop.
Sources
This guide was checked against the following documents:
- Shimano, disc brake technical documents (wear, torques)
- SRAM, brake bed-in procedure
- road.cc, How to clean disc brakes (contaminated pads)
Values vary between models: your part's manual always takes precedence.