I have a warped rotor on the back and have the parts to replace it. I tore into it last weekend and got the caliper off and pads removed then the problems started. I was ready for a Torx bit bolt but it looked to be a 17mm bolt head. I got the 17mm socket but it wouldn't fit the head so I got 18 and it was to big. My friend gets a 11/16 and it doesn't fit either. Is there a "special" socket from gm to get these out?