mk2 8v rear brake calipers

[tris]

Hi there, thought i would do the simple job of replacing rear brake pads this afternoon, turned out to be right nightmare!!!
found the rear left piston had siezed in the caliper, and rear right piston wont retract into the caliper. looking in haynes manual its show i needed to turn the piston using the two cut outs on piston face for it to retract into caliper, but it just turns and wont go in!! any ideas?? also managed to get rear left piston turning but its not moving in or out, do i need new pistons, calipers? would any one know rough price or best plce to get parts from?? i love my gti but it tested my patience this afternoon lol
thanks in advance for help!
Tris

[Steve_B]

did you use a wind back tool to press the pistons back? you could be just turning it without pushing it back. Also, did you undo the cap on the brake fluid reservoir, clamp open the rear bias valve, or open the bleed nipple? would be pretty hard to push the pistons back without doing any of these.

[tris]

i did have the brake reservior cap off, was using a box shaped tool with lugs on that fit the cut outs on piston face and applying pressure whilst using a ratchet to screw back but just turning. first time done brakes on golf, so didnt know about clamping bias valve(where is this located?), also bleed valve not open .will have another go tommorrow, thanks for tips

[Steve_B]

bias valve is in front of rear passenger side wheel, just follow the brake lines 
not sure what would happen if the piston is turning but not retracting, hopefully someone else can fill you in on that. Have heard the box tools don't work too well, sure someone else will know more.

[rubjonny]

sometimes you need the proper tool to get them back in, like this:
http://www.justoffbase.co.uk/Disc-Brake-Piston-Wind-Back-Tool-with-Double-Adaptor-Sealey-VS024?category=113