Two Wheeled Warlord
Join Date: Jan 2006
Location: Salmon Arm, B.C.
Rep Power: 1
Calipers off, pads out, hose it with brake clean, wipe with a rag, blast with compressed air, and here's where it gets tricky. Best done with the wheel, fender off, and the bike on a front and rear stand.
Pop the cap off the top of the front brake resi. Put one set of pads back in and use a box wrench to sub for the rotor. You can slip an elastic to hold it place for starters.
Use another box wrench (enclosed end) to push all the pistons in. Pump the front brake lever now and watch them come out. When they get a bit further than normal wipe with more brake clean and shoot with air. Then take a Q-tip and wipe some brake fluid around the piston as close to the seal as you can get. Knock the pistons back and pump out a few more times to work the fluid in and then wipe with clean/shoot with air. Pads back in, and tuck the wrench in to sub for the rotor and do the same for the other side.
Put the cap back on the resi, and put the bike back together. Of course if the fluid is black like vinegar instead of yellow like olive oil it may be time for a bleed, and if your seals are far gone it's time for a caliper rebuild.
The pads must skim the rotor, other wise the airspace would translate to mush when you pulled the lever. Some guys do get a bit nutty with shims, washers and facing the tabs to make the wheel spin like a bicycle wheel.
Oh yeah, your first question. The seals act like spings. The grab the piston and stretch then snap back in. They're not very strong so if there's a lot of dirt then they can't over come that. You can "pre-load" them by slipping a thin card between the pads and rotor, squeezing the lever, pulling the card and squeezing again. That'll have the spring with a bit of tension woun up from the get go.