You can buy new pistons for these ! I have serviced both d21 and d22 and you can buy cups/pistons- try p b r and any major brake suppliers ... i'll search my paper work and find the company I got my d21 piston from.. Have you got the piston cups out ? there is a trick to it - the bottom piston will be the one ceased ... Danm I should have made a video on how to.... The trick is once the calliper is off the car and in a soft jaw vice fill the calliper up with brake fluid and then wrap the calliper in a big rag covering all of the calliper except the hole where the line connects to. You will need a compressor with a fitting you can hold against the fluid line hole a give it short burst of air this will pop the top piston.. make sure the rag goes in between the piston and the body of the calliper so you don't damage a good piston when it comes out - and it will, at a hundred miles an hour so be careful .. now replace the piston and place a 1to 1and 1/2" block of wood in front of the top piston wrap again fill and apply air off on off on and this will put all the pressure on the bottom piston and in doing so will pop the lower piston out.. with any luck it wont be rusted but being a d21 you may be out of luck as it's now 20 years of rubber residue, water and crap.. I was lucky with the d22 but the d21 had a rusted piston that had to be replaced and from memory it was under $40 bucks.. keep us posted on how you go fella and good luck ,') oh and anyone that doesn't FULLY service the callipers every 150000ks is mad !even if the lower piston is not ceased the rubber residue will make the lower piston slower than the top , and this will over heat the rotors because you are now putting the pressure of both pistons onto only one ! and if you have ever boiled your fluid you know your in deep shite as the brakes will fail !!! And believe me as one hot day showed me as I ran through an intersection with nothing more than gears and hand brake to come to a stop - danmmmmmm lucky indeed. so if I buy a car it's one of the first things I do- SERVICE THE BRAKES FULLY NOT JUST CHANGE FLUID AS THAT DOES NOT REMOVE THE WATER AND CRAP SITTING AT THE BOTTOM OF THE CALLLIPER SUROUNDING THE LOWER PISTON CUP! ALL THE BEST FELLA !
