Look after your brakes and they will return the favour…
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A caliper contains moving parts and over time they need cleaning and servicing. Typically the parts that need cleaning are the main body of the caliper, the pistons and the bore in which they slide. The serviceable parts are the dust and fluid seals, and the O-ring/s that seal the two halves of the calipers. The parts should be original replacements.
The brake pads need to be removed from the caliper, if they are worn low then it’s a good time to replace them with new. Make a note of how the pads are retained, there is often a pin that goes through the pad and a sprung anti-rattle shim. If you are re-using the pads it is good practice to make a note of which side of the caliper they were fitted to.
Prior to stripping the caliper in half, give it a clean with bike cleaner and a brush. Treat it like a pre-clean; the idea is to remove the heavy deposits of road dirt and dust. Soak it with cleaner, agitate the dirt until it yields, then rinse off with water. If you are re-using the pads don’t use the cleaner on them, simply give them a light brushing over with a fine wire brush.
The pistons in the calipers need to be removed for cleaning, the easy way to remove them is to ease them out with an airline via where the brake hose fits. Exercise a bit of caution whilst doing this, use a relatively low pressure to ease the pistons out and place something like a spanner in the middle of the caliper to prevent the pistons popping out altogether.
Put the caliper in a vice and then undo the bolts that secure the two halves. Note which bolts go where. Just before you have the two halves split keep an eye out for any O-ring/s in the centre of the bodies. These are going to be replaced, but keep them to make sure the new ones match.
Completely remove the pistons using a piston extractor. Make sure you don’t use excessive force or its possible to damage the surface. Be prepared for residual fluid to spill out. Remove all of the pistons and then using a fine pick or very small flat-bladed screwdriver ease out all of the seals.
Now clean the inside of the caliper. Look for any corrosion build up behind the seals. This can be tricky to remove, so use a small, tough nylon brush, or a scotchbrite pad soaked in brake cleaner. Clean any area in the bore that looks like it has started to corrode. Avoid cleaning the machined area where the two halves meet, as it should already be free of contamination.
The brake pistons will mostly be in good condition, it’s usual for the top part that is exposed in the air to get dirty and tarnish. This can be cleaned up by using a metal cleaner like Autosol, you can also use a mop on a drill at a low speed to help speed the process up a bit. Once the cleaner has been applied, switch to a buffing mop and finish off by polishing all over.
Prior to fitting the new seals give the caliper a blast of brake cleaner and then blast with an airline. There are two seals per piston; the one at the top is the dust seal, this is usually thinner and has a double lip. The other thicker seal is responsible for keeping the brake fluid in the caliper. Refer to the workshop manual as sometimes the brake fluid seal has an ‘up’ side.
Push the cleaned pistons back into place, a very light smear of brake fluid on the lower seal is all that should be used to help them in. Insert them all the way. Then using the new O-ring/s join the halves together and tighten up evenly. Use a torque wrench set to the spec to tighten the bolts up. Replace the brake pads and retaining pins.
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