Mini cooper S rear brake job

Try removing the ebrake lever off the caliper, and then reset the piston.

The disc on the caliper has four small holes in it. You need a tool that will fit into the hole. You take a rachet and have to turn the caliper disc like you are screwing it in. Apply pressure while you are cranking it in to get it far enough back to put in the new pads. Using a regular caliper compressor will not work with calipers that have an emergency brake attached. You can crank it as hard as you want and it will not budge, needs to screw in. I just went through this over the weekend. The tool I purchased at autozone was $8 but was the wrong fit so see if you can purchase one at a Mini dealership. Use an 8mm Allen to remove the caliper pins and be sure to clean and regrease the caliper pins.

expensive version of the tool for retracting the caliper.

Autozones is about $9, could not find it on there website but they have it here

it slips onto the end of a rachet. It is a square with different sized pins on each of the six sides. None fit perfectly, one side has 4 pins that don't line up, but if you off center it and use 2 pins of the 4 you can crank it in. My suggestion is to use a grinding wheel on the side of the square that has two pins only that are too large to fit in the caliper. Grind them down a bit and they should line up and fit in perfectly. You need to push it in hard when cranking it to get the caliper to compress.