Originally Posted by jack1526
First, problem I ran into for myself was that I couldn't get the caliper off the front rotor because the old brake pads had made a groove into the rotor (which obviously need resurfacing now) basically giving it a nice outside lip on the rotor which pretty much kept the caliper from being remove because it lock up with the pads. So, I needed more space between the pad and rotor, which I accomplished by placing my C-clamp onto the piston within the groove where the brake sensor comes out and basically push the piston back just enough to give some space for the brake pads to get past the lip on the rotor.
Did you measure the thickness of the rotor?
I have 51k on my E90 and never had the front brake done before, measured the front rotors and it's at the min. limit so got new rotors waiting to go on along with new pads and brake sensor.
Since you mentioned the lip that was formed on your rotors, it may be due to be replaced since it worn out to it's min. limits. The limit is also stamped on the rotor hub itself.
20.4mm is the min. thickness to scrap the rotor.
You do have to compress the piston back into the caliper before removing it from the disc. This goes for the same for most disc brakes.