Broke off a skid plate bolt

+1.. spin it out with channel locks.. just keep going out the back

 

And after it's out, replace with SS bolts. That's what I did shortly after getting my truck or at least anti-sneeze.

 

If/when you do get it out, you should run a tap through the nut to clean the threads. I believe it's M8x1.25. You'll probably want to use the tap on the other ones too, if they are rusty.

I'd probably try heat first. It's a small enough part that a propane torch should be able to get it hot. Ideally you'd heat the nut so it expands and not the bolt. But I think even if you heat both it will still help. Once it's hot use vice grips to turn the stub.

I'm not convinced that penetrating oil does anything in most cases.

 

Replace the bracket or use a time-sert kit.

 

as a guy that uses stainless hardware every day, it MUST be used with anti-seize, and even then, the likelihood of it galling up and doing the same thing but worse is highly likely.

use no more than a grade 3 bolt. you want something soft so that if/when it breaks off again, it's easier to drill out. stainless will gall up, break, and then due to the hardness, be even more difficult to get out.

but really, i suspect this entire thing started because someone decided that non-structural items like skidplate bolts needed to be torqued to the moon. it's holding up a 4 pound hunk of metal. the amount of force one can input via a small 1/4" drive ratchet is more than enough.

if there's fears of the bolt loosening up, some blue thread lock at the same torque would be useful.

 

i DON'T recommend these for this situation. drilling out the bolt should be a separate operation from tapping in this case, though drilling and tapping should be an absolute last resort, as there should be an intermediate step of clearing/cleaning the hole before running a tap through it.

but also, those drill-tap bits are really only designed for thinner 1/8-1/4" thickness materials. the issue here is that the welded nut is at least 1/2" tall, meaning that the tapping portion will start to try to do it's job before the drill portion has finished it's job, which will almost always result in either less threads, a worn thread starting portion which tends to serve to create pre-damaged threads, or introduces additional stresses on the drill-tap which will break it as soon as the tap portion starts to grab. been there, done that, it's why i now own both drill taps, and a drill and tap set...

 

I’ve not tried this, but I’ve of people having good success using reverse thread drill bits. They cut into the material in the reverse direction, so you are both unscrewing the bolt while drilling into it. From what I’ve heard, many times the bolt will just back out.

I might also try the soaking in PB Blaster or Croil, then use a little heat on the bracket to loosen it up.

Did you do the last oil change? I’m kind of wondering if the last person maybe cross threaded the bolt and jammed it. You may be tapping it again regardless

 

that reminds me. last time i had a stuck bolt like that, with access to the back, i ran a standard drill bit through from the back side to spin it out. this is advantageous as many standard drill bits can be had in better qualities than most budget reverse-twist drill bits.