Does anyone know what the piston to bore clearance is normal on the 86 Fiero calipers? What is the piston diameter supposed to be? I had to use high pressure to get the pistons out and I had to freeze the pistons and warm the calipers to reassemble them but now the rotors are running hot. I put new seals in and there was not any sign of corrosion or damage of any sort. The car only has 37k miles on it but it did remain unused for a long time. I can free them up (front) but as soon as I press the brake and release it the wheel will not turn by hand. The pistons look to be phenolic resin or a plastic material. Are there any aftermarket aluminum pistons? Can the pistons be resized? (probably hard to do as there is no way to chuck them up without doing one end at a time and re-dialing them in)

Something is not right. You should need no more than a 'C' clamp to move the piston.

https://www.fiero.nl/forum/A...120111-2-093933.html

the caliper & piston must be cleaned meticulously., perfect,imaculate the plastic pistons are designed for the aluminum caliper & fit tight
before you install check to see if piston will go in ,it is a tight fit & when you check the piston must be perfectly centered do not push it all the way in check caliper for score marks
the fiero store rebuild calipers are far superior to what you get from online rock auto parts price is not the object here some time you gotta pay
many rebuilt calipers are bad,read the "any one have success rebuilding rear calipers' -dennis la grua
you will have an easier time if your go to search feature at top of page & enter =""caliper piston"" then ""caliper plastic piston""

after you read the appropiate post ,, go to the ogre site & read his wise informative brake repair post
just click on the ,,Orange OGRE name in some of the post

the fiero store use to have the last supply of GM caliper pistons ,,they must all be gone by now but call & ask
if they have the GM pistons

the front calipers, when quality pads are installed like thermo quiets will stop the Fiero very well,,many/most
fiero owners install cheap pads !! a NO No ..do not scrimp cheap with your brakes , when you use top quality
brake pads,your Fierowill stop much quicker...flush out dirty fluid & make sure the wheels rotate with similar resistance
sop old dirty fluid outof master add clean & flush
A wheel that you can not get to equal the freer resistance of the oposite, is often a defective hose ,,
after a long drive you feel the wheels to see if one is hotter!
a small amount of grease on the bleed valve will pay dividend next time,,clean mating surface of bleed valve & do not
overtighten
you should have more success after reading the many post on calipers ,,when buying rebuilt?? go with fiero store

[This message has been edited by uhlanstan (edited 01-03-2014).]

First make sure it is the calipers. Get the brakes to stick again. Open the bleeders. If still locked, it's the caliper. If they free up, most likely restricted brake hoses. Phenolic pistons will show little blisters when they seize.

Thanks to everyone that replied to the front brake caliper/piston issue. There was a lot of good ideas and help with the wisdom of each of the responses. As it turned out I had to replace the calipers. The pistons measured at 1.930 inches and the caliper bore measured nearly the same but the calipers had a .002 out of round that caused the piston to "rock" as it entered the bore. One of the pistons had a small chip taken out of it as it entered in to the caliper with the use of a C-clamp. I had to drill/tap a banjo bolt for 1/8 inch npt and put a grease zirc to use the grease gun to push the piston out. It came out without too much force but 110 lbs. of air pressure would not move it. Anyway the car will be back on the road tomorrow. Thanks again!