Disc brakes are becoming increasingly more common. Their pads are a bit more delicate than rim brake pads, in that they can easily be contaminated with lubes and solvents, which renders them pretty much dead. They have good wear properties, but just like rim brake pads there are certain muddy and wintry conditions which can just eat them. Don't get caught short on braking power and learn how to change your disc pads. Here's how to do it.
Our guide below shows you what we believe is the best method to fit disc brake pads. We've included a list of the tools and materials that you will need to complete the job and in some cases where you can buy them. If there are others that you prefer then feel free to let everybody know in the comments.
Tools & Materials
Most disc brakes use the same basic layout. A calliper with top loaded pads presses against a rotor mounted on the hub. The pads have a small hole in the outer plate through which the retaining bolt passes and secures the pads in the calliper body. The pads themselves with use a metal spring with four small legs which fit around the inside edge of the pads to separate them.
We're using a SRAM Rival calliper to demonstrate the process, which is the same for all SRAM hydraulic disc brakes. Shimano discs differ only in the type of retaining circlip, which is fitted externally to the very tip of the thru bolt, rather than inside the calliper body.
1 Remove the wheel You can't change the pads with the wheel and consequently the disc rotor still in situ. If you're taking out the rear wheel, shift the bike's rear gears so that the chain is on the smallest rear sprocket. Then undo the quick release lever or through axle bolt as seen here and drop the wheel out. Remove the front wheel in the normal way.
2 Remove the circlip Pick the circlip out with needle-nose pliers. It's possible with fingers, though the edges are sharp and the top face bent flush with the calliper body, so its much easier to use pliers and you're less likely to lose the circlip under the fridge.
3 Undo the retaining bolt With the circlip out of the way, you can undo the alloy through bolt. It requires Torx T10 key. These are found on SRAM bleed kit wrenches and on the CrankBrothers Multi 19 tool we've used here.
4 Pull out the old pads There's now nothing holding the pads in the calliper. Grasp the two small metal tabs at the rear of the calliper top slot; these are the bits the through bolt passed through. Slide the pads upwards and out of the calliper through the slot in the top of the body, as shown.
5 The pads and spring The pads will emerge from the calliper complete with their separation spring intact. It'll look like this or worse if you've really ground the pads back to the base plates. These pads still have plenty of wear in them, though they are being removed as they've been accidentally contaminated with brake fluid. This reduces their effectiveness by more than three quarters, and kills the bite required for hard emergency stops.
6 It is an ex pad You can't really see the damage, but you can feel it when you try and brake. If you've got contaminated pads, throw them away. We've baked and sanded the surface of contaminated pads with reasonable success in the past, but they never quite work as well as they do when properly fresh. Replacing pads that are basically new is a bit financially painful, so take care to keep fluids off them when cleaning and lubing your bike and working with the brake fluid.
7 Two fresh pads and a fitting spring Technically, these have done ten miles to get broken in and then been in our storage shed waiting until needed. These are ready to take the place of the knackered ones. By breaking in spare pads before you need them, you're always ready for that next ride without worrying that your initial power won't be spot on. Remember to clean the rotor when changing contaminated pads, as the contaminant will be on the rotor's braking surface as well as the face of the pad.
8 The spring in place The spring fits on the pad like this. The arms of the pad spring should lightly grip the sides of the raised pad material. This keeps the pads and spring working together as one unit. The second pad fits the same way. The faces with the pad material on them should be on the inside, facing each other.
9 The pads and spring, ready to fit The new pads and spring will look like this when assembled and ready to be dropped into the top slot of the calliper. Note the 'hinge' of the spring is at the top edge of the pads, adjacent to the through bolt tabs/hole.
10 The empty calliper While there are no pads in the calliper, it's a good idea to run a clean rag (and make sure it is clean), though the hole left by the pads. This will remove any braking dust and general grime that tends to build up in there, especially in the winter.
Make sure the pistons are fully retracted. You can just see one of the circular piston heads inside the the calliper. If you need to force the piston back, do so with care and use something made from hard plastic, rather than something metal like a screw driver blade. You're less likely to damage the piston head this way.
11 Fit the new pads Making sure you've orientated the new pads and spring the correct way, pinch them together and work them back into the calliper through the top slot. They can be a little awkward at times. Take special care not to dislodge the little arms of the pad separation spring as you insert the pads. If the arms become dislodged and you don't notice, when you come to refit the wheel the disc rotor will chew the dislodged arm out of alignment and make the spring unusable. Once bent, they're bin material.
12 Seat the pads If you know the pad spring is in correctly, give the pads a last push from the top to make sure both they and the spring are fully home. If they're not then the retaining bolt won't fit because the holes in the calliper and pads won't line up.
13 Replace the retaining bolt The disc pads are correctly fitted, so the retaining bolt will just slide through. Tighten it with the Torx T10, just enough to nip the thread up, remember the circlip will be there to stop it from backing right out.
14 Replace the circlip Use the pliers to refit the circlip. This is a very small part, but it has a vital safety role so you need to make sure it goes back on. We've had retaining bolts without circlips bolts rattle out and then had the pad self-eject. Quite a moment.
15 Replace the wheel Refit the wheel and do the rear quick release, or through axle bolt up to the correct tension. Spin the wheel and test the brakes. There should be no rubbing from the pads and brake lever travel and bite point should be normal.