Calipers: Pistons
The pistons are likely to be hard to get out, but can be removed without special tools.
- After detaching the caliper from the bike but before disconnecting the brake line, remove the pads and put a piece of wood 1/2" or 3/4" thick in the caliper, so the pistons won't come all the way out.
- Using the brake lever, pump both pistons out until they are stopped by the wood. Chances are you can then pull them both out. (Don't use pliers or anything that could burr or distort the pistons.)
- If necessary, put in a thinner piece of wood and repeat, or, if one is stubborn and one loose, block just the loose one till the stuck one comes out.
- Remove the seals and clean any crud out of the inside of the caliper using a small wire brush, steel wool, fine emery cloth, etc. and brake fluid, then wash with hot soapy water, rinse, and dry thoroughly with a hair dryer or compressed air.
Unless you really know what you're doing, you probably shouldn't use a hone. The caliper body is aluminum & it would be too easy to overdo it. If you do use a hone, be very careful to remove only the crud, not any metal.
- Be sure to get any crud out of the seal grooves. (You can make a little scraper out of something like brazing rod for this.) Clean up the pistons with hot soapy water or brake fluid and a brush or nylon dish scrubber or the like.
- Don't use coarse abrasives on stubborn deposits or superficial corrosion; use crocus cloth or very fine wet-or-dry paper such as 1000 grit with water or brake fluid. The pistons are hard chromed and polished, and if there is deterioration of the surface that cannot be readily polished out, they should be replaced.
- Lightly lubricate the new seals and the pistons with silicone brake grease and reassemble.
Cleaning the Seal Grooves Tip: The September, 2002, issue of Rider had a Tech Tip in Andrew MacDonald's column which addressed the sticky piston situation:
- "One of the chores of a caliper rebuild is scraping that corrosion out of the O-ring groove with a pick or fine, flat-blade screwdriver. Part-time mechanic Dutch Palmer (officially he's retired but still turns wrenches) noticed me doing this once and said, "You know, if you heat that caliper up with a propane torch, that corrosion turns to powder and scrapes out easily." Within seconds I had a torch burning a flame into the piston bores. You don't have to heat the caliper to where it's a fireball, just get it hot. And Dutch is right--the stuff darn near fell out. There, I told you this tip was a beaut."
Caution: Any brake fluid nearby will ignite in a quite stupendous fashion. Be careful!