Note: this information was inspired by a post to the ST1100 list by Tim Shevlin. Thanks, Tim.
When relining the brakes, you may notice that the caliper pistons are very difficult to retract into the caliper. Cleaning the pistons and seals will solve this problem. Remove the pistons one at a time to clean them. To get them out, I put a block of wood to restrain one piston while applying 100 psi air pressure with a rubber tipped nozzle to the caliper inlet port. If you haven't disconnected the hydraulic hose, you can use the hydraulic system to accomplish this. Whatever you do, do not grab the piston with pliers, because you will ruin it for sure.
Now clean each piston before you shove it back into the caliper. There will be some pretty stubborn deposits on them. Don't use anything harder than a fingernail to scrape them. This means no files, sandpaper, etc. Use alcohol as a solvent. If you use another solvent, wash the piston with soap and water to remove all traces, which may be incompatible with the rubber seals.
I then put a very light coating of SilGlyde silicone grease (from NAPA) on them to ease the re-installation. The seals will squeegee most of the grease off the piston. This grease isn't harmful to the rubber. The shop manual suggests using brake fluid for this purpose. I reasoned that the silicone grease would help keep road grime from building up on the pistons.
BTW, this silicone grease is the same lubricant used for the caliper slide pins.
I used a bit of anti-sieze on the threads on the pad pin and the pad pin plug, because I had a devil of a time loosening the plug. I ended up heating the caliper with an electric heat gun to assist in getting the plug loosened. If the caliper can stand enough heat to boil the fluid, anything I can hold onto won't be too hot for the components. Do not use an impact driver, because the components are too delicate.
Here's some added information from George Catt:
"The grooves for the dust seal seem to build up some corrosion over time, causing the dust seal to "shrink" against the piston. Part of the rebuild (new fluid seals and dust seals) should be to scrape all the crap from the grooves before re-assembly. Probably needs to be done every other pad change or so."
A useful tip from Eric Russell:
"Pay particular attention to the grooves in the caliper where the rubber seals reside. There are no 'return springs' for the brake pistons. They depend on the slight distortion of these rubber seals to pull the pistons back when you release the lever. If there is any build up of dirt or corrosion in the grooves, the seals will grip the pistons too tightly. The hydraulic force when you apply the brakes will push the piston out but then they cannot retract.
"In the future, when you next replace the brake pads, first carefully extend one piston at a time and clean off the exposed area of the piston before pushing them back into the calipers. You only need to extend them a fraction to allow you to get them clean - don't push them out too far. I use a strip of rag about 1/2" wide and 6 - 8" long dampened with brake fluid wrapped around the piston to clean them 'shoe shine' fashion.
I like to use popsicle sticks that I whittle into scrapers to clean out said grooves. The wood will not scratch the metal of the caliper but it will clean out the gunk. Next I scrub them with alcohol pads (like the nurse uses before you get an injection) and then scrub & rinse with brake fluid."
The September, 2002, issue of Rider had a Tech Tip in Andrew MacDonald's column which addressed the sticky piston situation:
"Here's how this beauty of a tip came about: I had a 19-year-old bike come in for rear-brake pads. The make and model doesn't matter, because old brakes are the same on any bike--there're all a pain to work on. My first clue of an impending can o' worms was that I needed a C-clamp to press the two pistons in the caliper and make room for the new pads. Normally, thumb pressure alone will force a piston back in a healthy brake system. I bolted the caliper back up, pumped up the rear-brake pedal and the pistons locked up the rear wheel solid. Time for an overhaul.
"Two things cause brake pistons to jam up. The first is old, sludgy brake fluid that plugs up the tiny return orifice in the master cylinder, constantly holding line pressure. The second is the O-ring that seals around the piston, and while they do turn rock hard with age, it's the corrosion formed in the recessed groove behind the O-ring that's the real problem. Water can creep into those alloy calipers, creating corrosion that forces the O-ring out of its groove and mashes it against the piston.
"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."
Thanks Andy and Dutch. Perhaps some silicone grease in those O-ring grooves will help retard that corrosion.
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Last updated on January 27, 2014, 2004 © 2002-2014 M. E. Martin, All rights reserved