today,i found two round pieces of metal.the roundness is the equivalent size of a brake caliper piston.
the first piece of metal round,i welded a hex nut dead centre.(welded on the outside of the nut,leaving the thread)
i then drilled a hole,dead centre of the other metal round,and placed a hex nut over the hole,and welded around the outer edge..(so now you have two pieces of round metal,one with a hole right through,the other blanked off...
if you take a long threaded bolt,screw the metal round onto the bolt..
you then screw the blanked off metal round to the end..
you then have a tool you can insert into your brake caliper,the blanked off end to the caliper piston,and the other just inside the caliper(like a pair of brake pads without the disc inbetween)..then
when the bolthead is tightened, this will push the caliper piston back without having to hammer the piston face causing damage..
you could also use worn brake pads instead of finding round,but the round makes it a multi-use tool you can use on any caliper...
hope you get the idea,i havent got my camera with me to photograph,but i am sure you will be able to picture in your mind,what i mean..