[barenekd]

Most of the time just having dirt in the slot around the piston is what causes them to stick. Usually just blasting the crack with brake cleaner is enough to get them working properly.The rolling action of the oring as the piston is pushed out is what is supposed to retract the piston as the oring tries to return to its previous position. The same dirt can cause the piston not to be self adjusting as it should slide out incrementally as the pad is used up. IF the dirt is heavy enough it will keep the oring from sliding. the quick ay to adjust the travel is to hold the brake lever back as hard as you can for several seconds, repeatedly if necessary. It's a good exercise at long red lights! This will force the piston assembly out closer to the disc and return the lever to its shorter travel mode.
Bare 

[Arizoni]

Some time back, we did have another member who had noted that his front brake seemed to be applied even when the brake lever wasn't being touched.

The "fix" was to bleed the excess fluid off by opening the bleed valve on the caliper.

Trying to figure out how/why this could happen I came to the conclusion that the rectangular cap on the master cylinder fits the rubber gasket that is under it so tightly that it won't let air into or out of the area above the reservoir.

If the reservoir is filled to capacity and then the gasket and lid is installed and tightened this could produce a pressure in the system that will cause the calipers pistons to slightly apply the brakes.  That is why I suggested slightly "bleeding" the system to relieve any pressure that may exist.

[Ducati Scotty]

That rubber cap is supposed to be a retracting bladder that follows the level of the brake fluid.  If you look at it you can see it's a sort of accordion.  The mounting surface below it (on the master cylinder) should be smooth.  The mounting surface above it (on the cap) should have a small notch or hole somewhere.  The lower surface of the bladder sits on top of the brake fluid and seals it from the outside air.  The upper surface lives inside the cap but the notch/hole should allow air into the space.  That way when the pads wear and the fluid level in the reservoir drops, the bladder can drop along with it keeping the fuid chamber sealed but not causing a vacuum under the cap which would retract the pads too far.

Sometimes the notch/hole can get clogged, it will need to be cleaned.

Scott

[D the D]

And someone mentioned the collapsing brake hose.  You can't see it if the hose inner lining separates and collapses.  Doesn't seem to make sense at first , but it does if you know the mechanics.  When the brake lever is released, the piston in the master slides back, a slight suction is placed on the fluid, the hose lining then collapses before the pistons move and the pistons don't retract.
Check the other stuff first, this isn't likely the problem, but something to check before you get frustrated and get a sledge hammer.

[REdmonton]

I was finally able to get a chance to try draining off a bit of the brake fluid like Arizoni suggested. It seems to have worked. I took the bike for a quick spin and I couldn't hear any squeaking.

[High On Octane]

Sweet!!!

[D the D]

Great it was something with a simple fix!

[Arizoni]

Glad to hear it worked.

Ducati Scotty's description of how a master cylinder is supposed to work is quite correct but I think something more is coming into the picture on some of these Royal Enfields.

If the factory worker overfills the unit with fluid and then places the rubber diaphragm or bladder in place we would have the diaphragm against the fluid holding the cap slightly elevated.
If the mechanic then tightens the caps screws, the cap will shove the rubber down into place which will displace or compress the fluid down into the brake caliper.
That, in effect would lightly apply the brake pads.

By opening the bleed valve and allowing the compressed fluid to escape the caliper pads will be able to relax their grip on the disk.

Actually if I were doing this I would move the brake lever just slightly to blow out just a bit of fluid before I tightened the bleed screw to be sure there was no residual pressure in the system.