You require the pistons to be still in good shape to attempt doing them with a kit. That means you have to remove them from the caliper to inspect. Be careful if you attempt to do this. Your climate is as rough as mine on calipers if left sitting.

On a 123 type ate or bendix are the caliper suppliers. As long as you buy both sides substitution is fine. Ate is usually cheaper. Your 220 may be simular but you should check.

Right now I am trying to get a set of caliper pistons to retract or slide a little easier. I have a method that has worked for me several times over the years. I cannot recommend it though as brakes are critical.

On a mercedes two piston caliper I pull the pad on one side. Using a much thinner than the pad pry bar in the resulting space. . Then I press the brake pedal about four times driving the sticking piston partially out.

I then load a syringe that is available to any junky at a drug store. Inject a silicone lubricant into the top of the boot. I then pry the piston back in as far as it will go. Repeat this several times to see if less effort is required with each try. If the piston is getting as loose or sliding in as I think it should I replace the pad and do the other piston by removing its brake pad in a simular fashion.

I used to use brake fluid but became aprehensive of its hydroscopic tendencies. The brake fluid seemed to eat the rust though if a small amount was present. The silicone is not hydroscopic but is not compatable with normal brake fluid either. I never had a caliper leak or develop repeat problems either.

So I now suspect dot 3 or 4 brake fluid I used to use produces better results. Since otherwise the calipers are history usually it costs nothing but some time to attempt this. If substantial rust had developed on the piston I think it has become too late for this approach. This is obvious as the pistons will not free up properly though. To determine how things are progressing use a laser thermometer to measure the disk temperature after a short drive.

Another good test on a two piston mercedes caliper when you think it is about loose enough. Using pliers if you compress one piston by squeezing back the pad tangs the opposite piston should tend to move its pad out a little. Fresh rebuilt calipers are easier to deal with of course.

Again I cannot recommend this approach although it has worked many times on many of my cars. Brakes are just too critical a function to deal with. I get away with it without any complications.

Others may not have my judgement on this method though. You really have to decide if a locked up caliper might occur for example. Not worth the risk if you do not have a feel for this.

A working mechanic does not have the time to even attempt this approach. You want the piston to slide back in pretty easily remember. I really do not know if the average member is observent enough to do this in a safe way. There is no doubt if things are not progressing as I feel they should I stop. Then rekit the caliper or replace it.

Thought I would just bring this old thread forward as it is pretty quiet and dragging calipers are a somewhat constant problem with cars that have sat around a lot.