QUOTE(Mblizzard @ Jun 18 2015, 07:40 AM)

QUOTE(dabird @ Jun 18 2015, 05:24 AM)

I was thinking about my brakes while driving to work today. Since my pistons are dragging against the rotors it makes sense that the cause could likely be internal swelling of the soft brake lines. I'm thinking a way to test for this would be to open the bleeder and that should release the pressure and allow the pistons to slide back....does that seem like it would work?
This is a new concept to me regarding lines swelling which I have a hard time visualizing. If you think of brake fluid as an uncompressible fluid it basically performs like a rod that transfers the force you put on the pedal to the piston in the caliper. You get a force multiplication by the fact that the psi you put on the pedal is increased by the surface area of the piston.
Others may have more experience with this but unless the lines have completely swelled shut, I would find it hard to see that the rubber wall could hold back sufficient pressure to keep the piston pressed against the rotor indefinitely. I would think that the pressure would have to return to an equilibrium point after a certain amount of time and the pistons would move back. If that was not happening then opening the bleeder screw would release the pressure if it was present. Worth a try.
But I bet if you do it that wont be the problem. There is a procedure for setting the clearance on the pads but as stated earlier if the pistons are stuck they are stuck.
I would get a bunch of brake fluid and flush the system noting the condition of the fluid that comes out. If it is dirty and full of grit then you can be pretty sure internal corrosion is your problem.
The calipers work by having a tiny amount of "kickback" that is provided by the elastomer gaskets on the piston.
Under normal operation the pressure pushes the piston towards the rotor, and when you let off, the force of that rubber elastomer pulls the piston back the few thousandths that keeps the pads from dragging on the rotor.
It does not take much back pressure to keep the piston from pulling back.
The symptom of my problem was that after a long highway drive, you would go to use the brakes and they would go to the floor until you pumped them.
I finally checked and found after a long drive that one of the front wheels was really hot.
The brake was dragging and after a long time, it would boil the brake fluid creating a "gas pocket".
I rebuilt the front calipers three times to try to solve the problem and couldnt figure it out until I tried to purge the lines by pumping them with no calipers installed.
The side that was dragging would barely trickle out while the other side would shoot fluid 10 feet.
I replaced the lines and the problem went away.