Car Analogy

Its easy to see how this happens. The bolt threads touching the 'nut' in the body are protected, but the threads sticking up past the nut, up inside the body/frame get corroded. So it starts to poosen ok, but as more and more of the nasty threads are worked down into the nut, it gets harder and harder to turn.

Whenever this sort of thing happens, you gotta do as suggested above. Back it in till it gets easy, then back it out a little, working the threads clean a little at a time. Back and forth. Its time consuming, but way less time than breaking a bolt!

Lesson learned, and hopefully a warning to others.

The weld on a nut trick should work, as it'll heat the heck outta the bolt and nut. Heat is very effective. If the bolt breaks off flush, the only solution is to hack the frame, cut a section out to get to the nut, and replace it, welding it in place. Then weld the back the hole you cut open. Undercoat. Its been done. Its about as painful as it sounds.

HotMess

For anybody interested, where does the other end of these sub frame bolts end up? Presumably it's some dead cavity within the bowels of the car?

I've seen people in situations where the captive nut spins or the bolt breaks, where they had to do surgery to get to the other side of the fastner (like here from my vw days: VWVortex.com - Access to rear bolts of front subframe?). I cant imagine this would be easy for any of the fasteners for the subframes (but i don't know)

You'll probably have good luck with the welding trick, but you may want to remove as much of the 1" protruding as possible. If it snaps again, you'll want as much material as possible. Just remember to take it easy, and run the bolt forward to 'clear' the threads from any loose debris. My secret in these cases relies on a decently powerful impact. I've a 3/8 Milwaukee Fuel impact driver, it has more than enough power to remove axle nuts, but not enough to shear a bolt off. Any time i run into a stubborn sub frame bolt, i run it forward/reverse over and over again on it's max power setting. Each time the bolt is backing out, i keep and eye for how far the socket rotates before it slows down/starts seizing. Then i go forward as much as possible, and reverse again, keeping an eye to see how much farther out the socket rotated compared to last time. If the bolt ever gets too hard to turn with the impact, I use a breaker bar to drive the bolt/nut back IN, then resume with the impact.

Remember, once you get your bolt out, you'll inevitably have damaged the threads in the captive nut to some degree. The more careful you were removing the bolt, the lass damage you'll do. I always run a thread chaser through the affected nut repeatedly until a new bolt turns in freely by hand. If you don't do this, you'll risk damaging the new hardware, and risk not getting the proper clamping force (@ the recommended torque settings). I'm cheap, so i make my own thread cleaners from old fastners, but you can but them at princess auto/HF probably. Oh yeah, and put a bit of anti-seize so when those bolts come off in the next 50 years, it wont be an issue again!

Car Analogy

I bought this thread restoring kit on Amazon. One of the best purchases I've ever made. Its not like a tap and die, which cut new threads, removing material. Instead it realigns the threads. Moves the metal back into shape. Sure, if threads are really buggered some metal is removed, but not as much as with tap and die.

The kit I got is for smaller fasteners. Wouldn't work on subframe size stuff. But I imagine there are kits in larger sizes.

Let me find the link for the one I bought...

https://www.amazon.com/gp/aw/d/B000X...IZL&ref=plSrch

Spartarus

For stuck fasteners, use an impact wrench, not a breaker bar.

You will achieve much better results, cause much less damage, and break many less fasteners.

This took me way too long to learn.

Also, the value of PB blaster or equivalent can not be overstated. I use a mix of Acetone and automatic transmission fluid as penetrating lubricant. It works ridiculously well.

bgoetz

Well an update. I finally got the subframe dropped and tried welding with no success. It seems the grade 8 bolts are damn near impossible to penetrate. So the subframe is down and I measure about 1.5" bolt left in the car ~.5" to the fixed nut, .5" I guess in the fixed nut then the other .5" that I bet is all corroded. My next course of action will be drilling it out then trying an extractor bit. I am going to start by marking and trying to punch the center. Then 1/8" bit, then 5/16". From there I am about as big as I want to get and I will try my extraction options, hoping I weakened it enough that it comes right out.

Let this be a lesson to everyone, this is a giant PITA!!

Halfassjack

Don't break off extracter or your done. Let someone mdm it. Some are on site. If it broke the bolt something a third the size will also break.

bgoetz

what is MDM and where do I find someone to do it?

Halfassjack

Metal disentigration machine. Check with local machine shops. They should know who is doing it in your area. Google it. Is the best way. They aren't giving it away.

rpg51

Here are some videos re MDM -

Bugsy

Another technique I've used over the years, when we had a hidden nut, or a seized shaft, we'd take an electric arc welder, and clamp the two electrodes as close together as we could. A few hundred amps for a few minutes will heat the bolt or shaft red hot without a torch.
Used it many times to remove a seized motorcycle swingarm pivot bolt or fused cycle axles
Disconnect your battery if you try this.