I needed to change the rear brakes on Renault Megane IV. They are not like normal brakes used to be, so I want you to spare some troubles.
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It is impossible to change the brakes like on other cars with Megane 4, because the piston cannot be pushed back as done normally. IMO the brakeshoe has to be removed. For that, fist unhinge the hand brake cable. Be careful when unscrewing the brake line - it is advisable to loosen the bolt, then rotate the brakeshoe instead of the bolt to avoid stress on the brake line.
WARNING: YOU NEED TO BLEED THE BRAKES AFTER YOU ARE DONE!

Here is a picture of (half) the brakeshoe with the piston already screwed in:

After having removed the brakeshoe, it is necessary to screw in the piston clockwise with significant pressure.
(Buy a special tool) or use a hook spanner wrench with two pins, something like this:

Apply pressure on the piston/wrench while screwing it in. Otherwise there will not be enough clearance for the new brake pads (as they are thicker and it is impossible to push back the piston).

Why is it this way? I was told, it is because the parking brake is part of the mechanism. I have unscrewed the piston to understand but I still don't fully. (Unfortunately, I have not taken any pictures :/ ) - do not unscrew the piston if you have no special oil for the sealant. The hand brake pushes the lead screw mechanically. The piston is screwed on the studbolt which has a steep thread. I can only guess that the bolt is screwed out by the hydraulics to automatically readjust the clearance.
I hate that there is no servicing manual available, I hope that this changes some time with future cars again (doubt it though, prove me wrong). Who ever designed this without documenting it should be fired immediately.