Auto Parts: brake caliper, needle nose pliers, wheel drive cars

Question
I have a 2001 nissan sentra.  The rear brake caliper is hard to push in.  I has disc brakes in the back.  The manual i have says to turn the piston with needle nose pliers until it is all the way in.  I have tried this and it does not move.  It is that way on both sides.  Is there another way to push those pistons in.  I have also tried to push them in with a "c" clamp as well like i use on the front calipers, this didnt work either. Thank you for you time.  Chris

Answer
    I never liked this design, but everybody uses it.  When you apply the emergency brake, it turns a screw that runs through the center of the piston.  This has a ratchet-like device in the center that ensures that the piston doesn't retract all the way, allowing for the piston to adjust for pad wear.  When the pads are worn out, in order to make room for the new pads, the piston has to be screwed back in to the caliper housing.  Problem is: front-wheel drive cars do not wear their rear brakes very fast, so they go years and years without having the piston disturbed.  Meanwhile, moisture migrates past the seals around the piston and the screw, reacts with the brake fluid to produce a corrosive acid-like substance, and eats at the ratchet mechanism, bonding it to the screw.  Then, when you want to screw the piston back in, it won't go easily.  Needle nosed pliers are a poor substitute for the proper tool in turning the piston back in (although everyone, including myself, has used them).  If you go to any good parts store, the will have a caliper piston tool which can be used with your ratchet wrench and an extension to properly mate with the holes in the piston and turn it back in.  If you still can't get it to budge, then you will have to replace the caliper with a rebuilt unit.  Make sure that you use the correct brake fluid and be careful to bleed it the way they say in the manual.  If you have anti-lock brakes, you must be careful when turning the piston back into the caliper not to force brake fluid back into the system.  Crack the bleeder screw and fit a piece of tubing to it, submerged in a container of brake fluid, just as though you were bleeding the brakes.  This allows the dirty brake fluid to be expelled from the caliper without going back upstream into the anti-lock system's fine filters and clogging up the whole works.