I had to remove the cross member that is right behind the trnasmision to get the fuel tank out of the truck and three of the four bolts broke . Any ideas on how to remove the studs and keep the threads. They are rusted very badly. and that portion of the frame is boxed in so you cn't get to them.

 

Are there any access holes on the other side? You might be able to drill them out and replace with some good grade 8 bolts. a telescoping magnet is helpful.
Otherwise maybe cut a hole with a hole saw and weld a plate over the hole when youre done.
get some anti-seize on whatever you replace them with for the next poor soul that goes in there

 

There are no access holes in the freme now. I think you are right about cutting the freme and using new bolts and nuts. THanks

 

I would very carefully drill out the existing bolt shanks then retap the same size. Often when drilling out sheared bolts when you get down to the "core size" the remains of the thread wind out and the hole is clean. If you do have to use a tap do not break it in the hole.

 

I broke the bolts off that cross member when I dropped my tank. There was no way I could save the threads when I drilled them out because the broken end did not allow the drill to start in the center of the bolt and the broken end was recessed inside the frame rail. My solution was to drill and tap for larger bolt because the nuts on the inside of the rail are welded on. The new bolts I used were either 5/16 or 3/8” (I don’t remember) and were stainless to prevent the problem from happening again. I hate the New England salt season.