I just changed the front disc brakes in my car. Had to replace the right caliper after taking it apart, as it was leaking. I'm wondering how exactly the piston works. I guess that the hydraulic aspect of the brakes pushes it out when necessary, but doesn't it need to draw back when you let off the brakes? How does this happen (it seemed that the piston is very hard to move, so it doesn't seem like it would settle back on its own). I'd like to know better how this works. Thanks,

Andy

 

My understanding is that there is always some level of contact b/w the brake pads and the rotors though the pressure is only induced once you press the brake pedal.

 

It only needs to move back a tiny amount so the pads don't quite touch after you release the brake pedal. The rubber seal between the piston and the cylinder has a special design so it springs back slightly when pressure is released. Moving the piston back more than that amount, such as when replacing the brake pads, does take some force.

 

Thank you guys. Only having to move it back a tiny bit and this being able to happen through the rubber action of the inside seal makes sense. I have another question now that I'm driving my car. I checked the rotors after driving about 10 miles (mostly highway) to see if they were hot to the touch (I had always heard that they should not get very hot if they are working properly - don't know if that is true or not). Well, they were both of equal temperature, but were very hot. The tip of my finger felt a bit singed after about one second of contact. I am hoping that this is normal, but defianately wanted to check. I will be doing driving tomorrow that requires a great deal of mountain type braking. Hope I hear back by then. Thanks again,

Andy

 

Interesting. So the rubber seal compresses when the brake pedal is depressed and when the pedal is released the seal re-expands, thereby causing the pads to move away from the rotor?

 

Drive for several miles without using the brakes at all, then stop once and get out to check. They should not get hot at all from driving, only stopping. I never tried touching the rotor itself though, just general heat around the wheel area.

If the wheel (not just the rotor) is too hot to touch after this test, you have a problem. Major causes for dragging brakes are stuck calipers, partially blocked hose, or improperly adjusted master cylinder. Only the last one would cause problems on both sides.

 

The wheel area itself is not hot. It is just the rotors themselves.