How Do Hydraulic Calipers Work?

"This is your master cylinder, which just like any other hydraulic brake system is where pretty much all the power comes from. You see, this is called a push rod, and there's a cam on your brake lever, which is that right there. We're basically looking at this. So, when you pull the brake lever, that pushes in the push rod like that. It's hard to push it in by hand, because it's new and has a firm seal on it. That pushes fluid out that way, down through your brake line, and to your pistons. So when I push on this caliper, it actuates the brake arm like that, and to show you what the difference is between a clean caliper and a dirty caliper, this is the caliper that was relatively well maintained. You can see there's a little bit of corrosion inside the piston bore. This is one that was ridden in snow and ice and much for way too long, and there's just filth everywhere. I just took these off a bike yesterday. So you can see what the difference is. These are both fresh of something. Neither of these worked very well, or as well as something that was new and well maintained, but the caliper here in my right hand, well, it doesn't work nearly as well. There's so much in it that this piston is actually seized and won't move. So that's some of the things that can go wrong with your disc brakes."