Disc brake pads

Like all mountain bike brakes, disc brakes rely on friction pads that gradually wear and need replacing.  At first glance it seems more awkward than the more obvious pads for V or cantilever brakes, but the truth is that it’s a simple procedure.  As always, the details I give here are for my brakes.  There are variations in exactly how it works, but the principles in each step are identical – it may just be a case of looking at your own brakes to work out what needs doing.

Stuff you’ll need:
Replacement brake pads.  These come in a number of shapes and sizes, although from what I’ve gathered, if it looks right it probably is.  Don’t try sticking circular pads into a rectangular slot, but if it looks the same then it’s probably the right one.  Take your old pads in and match them up would be my advice.  After that there’s a choice of sintered (metal) or organic pads.  Supposedly they act differently, but my experimentation hasn’t yielded an appreciable difference.
Pliers.  Ones with a thin nose.
Hex keys.  You don’t have hex keys?  How on earth are you maintaining your bike?

Step one: Get access to the pads.  You can’t change the pads with the rotor between them, so you need to either take the wheel off the bike (which means you don’t have to align the brakes afterwards as nothing has really changed), or take the caliper off the frame (which means you can wave it about and get at the pads easier).

Step two: Free the pads.  There will be some device that locks through the pads and prevents them from just dropping out.  In my case there’s a split pin that threads through a hole in the caliper, through the brake pads and leaf spring, and through another hole in the caliper.  Straighten the ends of the split pin and draw it out from the other end.  Other designs have a screw here that’s locked with a split pin, or something else.  Work out how it comes out and have it out.

Straighten and remove the split pin...

Straighten and remove the split pin…

Step three: Remove the pads.  On my brakes they’re removed from the other side of the caliper from the split pin.  Squeeze them together slightly and draw them out from the caliper.  Keep hold of them – you’ll have three things in your hands: two brake pads and a leaf spring between them.

Remove the pads...

Remove the pads…

Step four: Push the pistons back into place.  The pistons automatically adjust for wear in the pads, so you’ll never be able to jam the rotor back between your new pads if you skip this step.  Stick something between the pistons in the gap where the pads were, and push them back until they’re pretty well flush with the caliper itself.  Push on the edges of the pistons not the middle – there’s nothing much there to push on and you could easily rupture the diaphragm at the other end of the piston.

Push the pistons back...

Push the pistons back…

Step five: Insert new pads.  Open your new pad pack and make a sandwich of the two pads facing inwards with the leaf spring seated between.  It should be obvious how it goes, since it’s the same shape as the pads, and should fit nicely around the friction surface of the pads.  Pinch them together from the fat end and insert them into the caliper the same way the old ones came out.  They should seat nice and firmly in the caliper.

Step six: Lock them into place.  Reinsert the split pin you took out earlier, making sure it goes through the two holes in the caliper, both brake pads and the leaf spring as well, and then bend the end of one of its arms to hold it in place.

Step seven: Put stuff back where you found it.  Put the wheel back on, ensuring that the rotor sits neatly between the pads, or reattach the caliper and set it up carefully.  Job done!

Step eight: If your new pads are organic ones, you need to bed them in properly.  It’s recommended that you do twenty or so sharp stops at speed (read the sections on braking to make sure this doesn’t mean twenty graceful dives over the handlebars).  Otherwise you could end up peeling the braking compound away from the back plate.

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