brakes wont release

[Chris111]

car: 93 240sx

all four of the calipers wont release from the rotors. i wanted to check to see if anyone had any ideas other than the master cylinder. we started with the rear brakes apart to see if anything was wrong but everything looked ok and the pads look brand new. we took the pads out of the rear to see if the rotors turn freely which they did. we also noticed that the piston in the right rear caliper wasn't going back into the caliper....is this normal? so i'm kinda stumped and we haven't even gotten to the front yet. i plan on replacing the master cylinder tomorrrow with a new one and hopefully a caliper if i can find one. i'm hoping that will be the fix however i'm asking for more input.

thanks for the help, chris

[Newcastle82]

Ok, be very careful when you put the caliper pistons back into the rear calipers. They do not just 'force' right in, the way you're supposed to vice or channel-lock the fronts in. They have a special pattern on the mating surface of the piston, and you've got to get the tool that matches that pattern. They are 'screwed' back in, essentially; rotated.

As far as the brakes locking up like that, is your car ABS, or non ABS ? If it's non abs, my reccomendation would be to pull the rears off and remove the lines from them. Then depress the brake pedal while the lines are off, and securely placed over a catch container of some kind. This will suck a lot of air back into the lines when you release the pedal, and should get the fronts to 'unlock'. They, take the fronts off, replace your master cylinder (and the slave also, ALWAYS good to do them at the same time so they wear together). Then tear the fronts apart and get a rebuild kit, replace the rubber, clean them up a little. Put it all back together, bleed the system THOROUGHLY, and you're good to go. Good luck =)