Brakes Stuck Pbr Calipers (how To Fix Them)?

Discussion in 'SN95 4.6L Mustang Tech' started by 67rcks, Oct 17, 2012.

  1. How is it best to release stuck pistons in 2002 gt (twin piston) caliper so that there would be somewhat lesser drag between piston and seal?
    (the problem - passenger side wheel is dragging with engine off too)

    Has anyone attemted to do this with success instead of buying new/rebuilt calipers?

    Do I have to disassemble the piston off the caliper to clean it or is there some less-invasive trick?

    For others, do not use pliers to pull the piston off the bore - the pistons have a ceramic layer that cracks once you grab it with pliers!!!
  2. Are you talking about the 13" Cobra style caliper or the 11" GT /V6 caliper ?

    Either way, if the caliper is dragging, you will need to push the piston back in. Do you have an old set of pads ? What sort of break service tools do you have ?

    Crack the bleeder valve when you do this so the fluid goes out the bleeder and not backwards through the system.

    What is the condition of the rubber dust seals around the pistons ? Are they soft and pliable or are they hard/dry ? Have they come away from the caliper body or piston ? You can rebuild these yourself if you get your hands on a new set of seals. Likely what has happened is the dust seal failed and you now have junk in the caliper bore and it is causing your pistons to stick. Most people don't want to rebuild calipers because if you get it wrong, well brakes no workie....

    When is the last time you bled the brakes ?
  3. These are PBR calipers (not cobra)
    I took the pistons off (inner seal too) and was quite surprised to find out they sit really tight in the bore in the operating range!
    I have new rotors and brake pads whose total width is some 52.5 mm (2 1/16"). Is this the correct width? The piston is possible to freely move in the bore if the width of rotor and two pads is up to 51 mm. No wonder this caliper causes wheel dragging!
    If you have just bought new pads and rotors can you please measure their overall width for me?
    Just trying to find out what is wrong - either pistons, too thick brake pads, too thick rotors or caliper.
    Why its bore is trapezoidal?? i.e has a larger diameter at the seal than at the bottom? Is it normal?
  4. Most caliper bores I've seen are cylinders all the way down.

    If the piston moves freely in the bore all the way in and out you are ok there, the pistons aren't going to be off in size.

    It is most likely the pads being slightly too thick.

    The rotor, you can check with a c-clamp type caliper.
  5. It turned out to be the sheet-metal pistons became slightly oval in the upper part (closer to the pad).