One of my rotors was rusted on. I used a bolt through the caliper mounting hole, using a couple of nuts to hold it straight, and cranked it until it broke the rotor free. You will hear a loud pop as it breaks free.
If you have a really difficult time getting it off, a good smack with a regular hammer or use an air hammer on the face of the rotor between the studs will break it loose. Works everytime. If you are afraid of damaging a stud, thread some nuts onto the end of the stud to protect it from being struck with the hammer.
^ hit it with a big regular hammer in the front between the studs like said above. Your other options are heat and if you don't care about the rotor and plan to replace it just whack the $hit out of it. I Cracked both my rotors trying to get them off last time I did brakes, just beat on them they will come off. remember to put anti-seize on the hub face before putting the rotor back on so you don't have this problem again. Also be careful because you can wreck the hub bearing if you beat them to hard.
Once you do get off the rotor your going to have the same problem getting the hub unstuck from the knuckle after you remove the 3 bolts. Easiest way to do it is put a bolt between the knuckle and hub and crank the steering wheel it will pop it right out. I found that tow hook bolts are the perfect length for doing this let me know if you have any more questions, if you have patience it will all come out rusted or not just don't get frustrated and start beating on things especially if you plan to re-use the rotors.
don't be shy with the anti-seize you will thank yourself next time you do a u-joint.
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