The best way to extract the broken stud is to but a 7/16 nut over the broken stud,weld the nut to the to the top of the stud let it cool then weld a bolt to the the nut head down . use a steal plate drill Three holes into the plate that that will Aline with the two adjacent studs to the broken one .I install a1' piece of pipe over both the adjacent studs with a washer and a nut on each stud. Bolt the two end nuts down solid Then install a nut on the nut that has to be pulled and tighten it until the stud pulls .this can be doe on the car . I did this on the side of the road with a acetylene torch to pull the stud on my pickup.