Broken caliper bolt

[Topless]

My method, which usually but not always works

Soak the bolt in penetrating oil for 24 hrs. Fill the cavity behind the bolt and gravity works. Tap on the bolt pretty hard with a hammer on a regular basis to loosen and allow penetrating oil to work. On day two, tap hard again and get a firm grip with vise grips. Start by turning it in the last direction it moved (clockwise) to break it free, and then spin it out counter clockwise. Often this will work without heat. If no-go, apply heat to the bolt with map gas torch and get her real hot. Often you will hear a ping when the bolt frees. Tap again with a hammer and back out with vise grips. If the penetrating oil works you will save the hub threads. Too much muscle too soon and the soft aluminum hub threads will strip out.

Good luck!