When you have wheel off, Looking at the rotor and caliper, Remove the rotor and remove the outter brake pad and leave the inner brake pad on the brake caliper piston, Use a C clamp to "slowly" compress the caliper. Good Luck!
Make sure you back off the emergency brake adjustment before attempting to compress the piston.
You need to go to your local auto parts store and purchase a special tool. The tool fits onto a rachet and screws the caliper piston into the caliper.
Go buy a 6" C Clamp. You can use that to compress the caliper piston and it is cheaper than a special tool. You can use it for clamping other things around the shop too.
C-clamp won't work, you HAVE TO turn the piston back in with the tool or you could try to put pressure on the piston and turn it at the same time.
ive tried the C-clamp and do not recommend this method!! although upon my first attempt i was unaware that nearly all modern vehicles w/rear disc brakes NEED turned in, like a screw. so i ruined a clamp and the calliper trying to figure it out :( the special tool purchase is not required in most cases because most auto parts stores offer free tool rentals to promote the sales of auto parts, and the tool they offer is usually better than the one most people are willing purchase due to expense probably in the upwards of $50. there is a cheap tool option 3 to 4 bucks kinda looks like a cube w/ a 3/8 ratchet drive hole on each side for a extention to fit to your ratchet. and it has different sized/shaped pegs at the corners of each side to make it more compatible with other vehicles, efficient but difficult to use and i really don't suggest it either but ive used one and it did get the job done. try to find a store that lets you use their tools. AutoZone hasn't had the best service in my experience but it is a good example of a store that practices free tool renals usually nice tools and usually the right one for the job rather than a 3$ junk that's only resulting in sore knuckles // Smallball
This Was answered by Smallball, I put it here because it is the correct way to do the piston. Hope it helps
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