Broken bolt problem - northeast salt belters only

Subframe on a 2000 Subaru has rotted out, it has a recall on it but the dealer laughed as the car is 14 years old.

Got a nice clean one out of Oregon, new bolts from dealer.

2 rear bolts spun right out. 2 front bolts - cheap impact no go, brother in laws' IR than can snap wheel studs off no go. Both of us on a 6 ft cheater pulling for all we had with air hammer on the subframe no go. Finally snapped the bolt off while its still in the captive body nut, hidden rusted threads protruding about 3/4" above the nut inside body not wanting to go back through the captive nut. This is all working overhead next to the gas tank and everything is coated with a very combustible undercoating btw.

I welded a washer to the stump, then a nut, worked back and forth for 30 mins with impact, got 1/4 rotation with lots of penetrating oil. We got greedy and put the bar on it and got another 1/4 rotation before it snapped off flush.

I then ground the top flat, centre punched and drilled the bolt and got up to a 17/32" bit but I'm off centre about 1/8". Into the threads one side, bolt left on other side.

Tried punch to get the half moon to move, no luck.

Options now are:
Try to blow it out into the body cavity with torch and try not to burn car up.
Cut open body to heat cherry red so I can turn it out, again try not to burn up car.
Drill out all the way, weld up the damage to nut and retap the body nut.
Push welding rod up as far as possible into the drilled hole and attempt to weld my way out to heat the bolt and quickly get a nut welded to this mass while hot.
Diamond grinding bit and spend hours getting over to the threads.

Anyone want to speak up? I've done lots of this before, the normal thing is to chop open the unibody and heat the remains of bolt with the torch but the steel is very heavy in this area and not rusty so I hate to chop it up.

bolts like that are a devil. if you can come in from the side with a hole saw and cut an access, then go in with a carbide burr on an air grinder and hog out the fastener. sometimes you need to go in from the top and hole saw down to get access. mig weld the patch back in. you will need to scrape off all that undercoating so as not to start a fire. keep water and a blow gun handy. there is a scraper attachment for a sawzall that works pretty good. standard sawzall works better than a super, the super has too long of a stroke.

If it were me...I would get a diamond bit in my dremel and split the thickest part of the bolt thats left...I would split it from the drilled side right into the threads so the remaining pieces can be chiseled together and then should just fall out.

Its in a very complex part of the body too, multiple lap joints, 3 layers of steel. Nut is at bottom of a angled 2" wide but 8" tall space.

Brother in law wants to cut it open, I did my drilling and didn't do it well so I'm low man right now.

Gonna pick up some small carbides tonight, I can get a decent size one in there, better than a 1/8" diamond bit.

Just a suggestion.....
I had a similar problem in removing a subframe on a FWD car some time ago. I found that the captive body nut is accessible from the top from inside the car - at least on many models. I pulled back the floor mats and rugs, and found a plastic body plug that I removed and got access to the captive nut.
One cause of this problem that I have seen on several occasions is that there are semi-exposed threads on the topside of the captive nut. Salt or salt water gets to the exposed threads and causes rust to scale up in the threads. Then when you try to remove the bolt, the rust flakes jam up the threads. Pushing the bolt the other way may also work to just let id drop into the cavity where it will do no harm.

Good luck!!!

If you have a recall go and push that to the limit, try another dealer. Demand that they follow through, complain to the manufacture or National Highway safety people.
Don"t be bashful

Unfortunately no body plugs. There is a 3/8" hole with plastic plug underneath from previous rustchecking jobs. All it lets me see is the threads past the nut and that they are rusty.

I'd be miles ahead if I could have somehow threaded it in rather than out.

(quoted from post at 19:25:20 02/04/14) Unfortunately no body plugs. There is a 3/8" hole with plastic plug underneath from previous rustchecking jobs. All it lets me see is the threads past the nut and that they are rusty.

I'd be miles ahead if I could have somehow threaded it in rather than out.

Click to expand...

For three 5/8" dia broken off studs, flush to the surface, I drilled a center hole through the stud, placed a nut over the stud, turned up the mig welder to 3/16" T setting and plug welded the nut to the broken off stud. Welding shrunk 2 of the studs enough to come out, the 3rd had to be drilled and re-tapped. On that miserable 3rd stud, to keep the hole on center for drilling, I started with smaller sized bits, stepping up in size. If off center, took a small carbide burr in a die grinder and ground the thicker side of the hole. By the last drill size which was the tap drill size, the hole could be tapped out and works fine. A very tedious job.

Sears has a carbide bit for the Dremel tool that may help you get back on center. The trick is to not get off center.Snap-on has an extractor set with pilots to keep on center when drilling. { Another trick is don't buy cheap cars from our WW2 enemies.]

Yup welding works great when you don't have to run another
inch of rotten threads through the nut. I prefer a washer first
so you can get good penetration around perimeter.

Car says built in Indiana on it, our other Japanese car was built in Ontario canada. I think our ford truck was Mexico.

They all rust the same up here.

I think I'd use a top down approach at this point... Open it up. I might just torch the whole damn mess right out and weld a new nut back into the hole too...

Rod

Hi Ken,
How did you make out with the bolt? I found your post very interesting and informative.
Martin

Got the other side loose this am, cut it off and cut a slot in stub, going to screw it up into the body cavity tonight after work.

Other side is still fighting me, need a new carbide bit. Burned up my diamond bits being too impatient.

Subframe is all loaded up with the control arms new bushings diff etc waiting on these last 2 bolts.