Just did a front brake on my auto, that I recently bought. It had not been ridden for years and the front brake was jammed on.
As TT and Patrick stated above, the fluid after time, firstly goes to a gel like substance and then hardens up to a scale like substance. My caliper and master cylinder were full of a combination of both. I cleaned the master cylinder reservoir out and filled it with fresh fluid then let it sit overnight. This did not make it work, but I think it helped it to free up.
I then used a master cylinder to pump it all apart. It was a real mess inside, but cleaned up OK
I keep an old road scarred master cylinder ,just for the purpose of pumping out caliper and master cylinder pistons. I know other people have success with a grease gun, but I have always managed to pump it out with my old master cylinder mounted on an old racing clip-on bar.
If the master cylinder is like this- chances are the caliper piston is the same or worse. In fact I have found that this is the biggest cause for brakes to stay on. The caliper piston seal gets jammed with this hard compound and loses its flexibility to return the piston. Often a good clean will allow the brake to work properly without having to replace the piston seal.
There is a good chance that you will just have to clean up the parts and the recess where the caliper seal seats to get you going again.
But you will almost certainly have to pump out the caliper as well to be sure of having a good brake which does not drag.
Just shows why you need to change the brake fluid every couple of years
Regds Clyde
