That happens to all of us. Just shove it back together and rebleed it.
Well, actually, don't just SHOVE it back together. Nothing serious has happened yet. There is a lip seal that must be pushed in sideways to prevent catching the edge and ripping it, but from your pictures it hasn't come out yet. It is on the inside of the piston which is what you're seeing. A spring inside is pushing the two pistons apart so those two lip seals don't fall over. That spring is what pushed the piston out. The dust boot holds them back in.
The shoes hold the pistons in too. If you were pedal-bleeding, the pressurized break fluid is what pushed the shoe and piston out if the drum was off. Still, no harm done. If no brake fluid ran out, the lip seal isn't out far enough to cause a worry. That's what it appears in the pictures. Just push the piston back in and pop the dust boot back in place. This is less likely to happen with an old wheel cylinder because rust forms on it that "glues" the dust boot in place.
Monday, May 21st, 2012 AT 5:49 PM