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Broken hex bolt removal

theres an M8x30 hex head bolt which I broke the head off of stuck in my transmission case mount. there is about one hex nut’s worth of thread exposed on the broken head side. the opposite end of the bolt is flush with the piece it is screwed into, however, it could in principle go all the way out either end. I can drill from the broken end, but not the opposite end.

I have broken off a screw extractor tool inside the bolt already. I (think) I used a 7/64" black and decker removal screw (#3). so it is not like I drilled the bolt right down to the threads. there’s some meat there. I tried heating the bolt by using a soldering iron inserted in the drill hole.

before I destroy the threads with vise grips, I wanted to post here. I am wondering if I can get two thin nuts on the threads, tighten them together, then use that as a head. or some other way to install something to grab onto on the threads. another thought is to epoxy something onto the broken end. meanwhile, the bolt is soaking in penetrating oil.

I am not enthusiastic continuing with more screw extractors because drilling will be more difficult now - though of course I might have to do it.

if I ought to take a pic, if my description isn’t good enough, let me know.

I wouldn’t worry about it. There’s enough bolts holding the transmission to the engine that the transmission isn’t going anywhere. I’ve seen many vehicles come into the shop with a missing/broken transmission mounting bolt.

But if you must get it out, take the proper size nut and with a torch burn the coating off the nut. Drive to a local muffler shop and have them thread the nut onto the broken bolt. Then have them weld the nut to the broken bolt thru the center of the nut. Make sure the battery is disconnected before they start welding on the vehicle.

Sometimes it’s just better to pay somebody twenty dollars to do a simple task for you, rather than going through the aggrevation and time with methods that don’t usually work.


ok thanks @Tester - so although the premise was “this bolt has to come out”, I will say now that its a transaxle car, being the Porsche 944. oh also the tranny is actually at this moment on my garage floor, so…

have them weld the nut to the broken bolt

that’s an interesting idea, so yeah, I know a welder - perhaps I can put the tranny in my other car and drive it over. so I suppose that means any epoxy I can find is not going to work?

The weld the nut to the bolt option is far better is success rate than an ez out. Lovin Tester, thanks again for helping the peeps.

Epoxy will just break off. If you want a joint, it needs to be welded. And a soldering iron is unlikely to provide enough heat. You need a torch to heat the bolt up enough to make it move easily.

While I am still working on this, here’s some interesting links I found:

Machine shops have special drills that will drill around a broken extractor. I concur with the comment above, this is a case where it makes sense – time and dollar-wise – to call in a pro who has the appropriate tools for the job. I wouldn’t make further attempts as doing so may damage something that isn’t now broken.

someone flagged this as off-topic, so just wondering what that would be specifically? the links?

Not off topic.

I didn’t flag your post OP, but yes, I expect whoever did was referring to the links being off topic. Not the OP itself. By the way, let us know the result, it is an interesting problem you post, and one that all of us may have to face from time to time.

I am wondering if the bolt was broken off going in or coming out?

@MrHandy2013 out.

I will also reiterate : the end of the bolt is open - that is, it is screwed into a threaded hole that is open at both ends.

gonna get a propane torch, I think… maybe MAPP (or whatever it is now) - not oxy/acetylene yet (out of my league).

There’s a good thread from a while ago here about techniques posted by the experts here used to remove stuck fasteners. I don’t know how to find that old thread, but maybe somebody else here knows how to search for it and will post a link. I think it was about a year ago or year and a half ago.

I used the Car Talk Community search box. Who woulda thunk it would be so easy? lol … Anyway, here’s the link for tricks offered up by posters here on removing stuck fasteners. There’s a lot of good ideas in this thread. Maybe something here might work for the OP. Best of luck.

Gotta disagree with the test results of that first link. No way in my experience that Liquid Wrench is better than PB Blaster. I’ve still got a quart of LW on my shelf that I haven’t used in 20 years because 90% of the time the bolt just broke instead. Since I switched to PB Blaster though, I don’t remember breaking anything of any consequence. Need to let it sit for a while though.

If you have access from the back of it, why not just drill into the bolt a ways, tap it for a course thread, and screw a high grade bolt in it. Then just start tightening that bolt down and it should turn the other bolt out. One question though is how it got that stuck in the first place? Rust? Dirt? I’m a little concerned with heat depending on what you are working on. Not aluminum is it?

Can’t help but to chuckle reading @Bing above … because I’ve got a can of Liquid Wrench sitting in my garage that must be 20 years old. Maybe 30 years. And it’s still half full. That’s how often I use it. Well, and you can’t use very much of it per bolt. Use too much, it drips away from the threads. To show you how little I know about DIY thread penetrants, until recently, I thought Liquid Wrench was all that there was. Thanks to Bing, next time I go to the auto parts store for something, I’ll buy some PB Blaster and give it a try.

@Bing wrote:

One question though is how it got that stuck in the first place? Rust? Dirt? I’m a little concerned with heat depending on what you are working on. Not aluminum is it?

how it got stuck - well, I don’t know. the bolt is on top of the transmission which is gets further bolted up underneath, so it is better hidden than most fasteners. the “block” it is in is some type of aluminum I think. I do not think it is magnetic. It is hard to see the interface clearly, but it seems a whitish dust is coming off. A further chapter to this might be the two other long non-rotatable bolts that are also frozen in the same block, and have a similar whitish residue dust/slime coming out. However, all observations do not suggest it is rust. I am hoping to have two more interesting tests to post here soon, though the results might be uninteresting.

also about the screw extractor result : I am thinking more now that the drilling stage must clear out some 15-30% of the bolt material such that the extractor will sit inside so that it gets covered well over 1/2 way up its thread. You would think the instructions would provide clear guidance in this regard, but no. Last time I googled for this technique, the best I found was a video where the person mentions how it might not work, then it works perfectly, and there is no clear explanation.

I think that’s aluminum and a steel bolt. The whitish material is corrosion-like rust but not rust. Its the reaction between the steel and the aluminum. Aluminum melts at something like 1400 degrees or so (can’t remember) but a low tech butane torch is enough to melt it. I’d be very careful with any heat and use repeated applications of PB Blaster instead with hammer blows to spread the Blaster from time to time. After a week or two of repeated applications and hammer blows, you should be able to work the bolts loose. Just cranking on them is a recipe for breaking them.

something I thought of while sorting through the pile of ideas:

choose from “plan A” ideas, usually only one. e.g. one that can lead to destruction of the threads. e.g. using vise-grips.

choose from “plan B” ideas, like left-handed drill bit. I think using a LH drill bit should come before using a bolt extractor, because the LH drill bit itself might have a chance at grabbing the bolt enough to remove it.

choose from “plan C” ideas which assume a destroyed/nonexistent thread. e.g. drill hole through, use extractor.

a couple ideas for the grab-bag that I thought of, being unable to use or pay for proper welding.

  • install a stud through the bolt, attach nuts/washer on either side of bolt - use nut to rotate entire bolt.
  • cut slot into threaded piece that extends outside block - use a slot of some type to rotate. I figure this will break the bolt.
  • drill hole in bolt, then install a plain sheet metal screw. direction of rotation is same as bolt to go out opposite end.
  • think about left-handed drill bits (while running drill in reverse)
  • a bolt with a hole down the center can shrink more than a solid bolt
  • damaged/stripped nut removal tool mashed onto the end of the bolt. these things look like nuts, but with LH threads inside to cut into a damaged nut.

and, some inspiring videos (THIS IS EMBEDDED AUTOMATICALLY - TELL ME IF THIS IS OK I don’t know how to shut it off yet):

hopefully I can report back soon. oh, the thing I tried before was freeze-off. wasn’t cold enough - also makes a mess with the oil. upside-down dust-off can gets very very cold, but runs out fast.

update: the bolt now has a bolt extractor fused inside, and I have drilled and ground the bolt as much as possible (so far) to remove it. so now it has one end with a deep dimple, and the other with a hole, with the hardened steel extractor mashed in the middle.

I used a rotary tool with a tungsten carbide bit, then a bulky grinder. I think next is a trip to the store to get a narrow rasp/grinder to stick in the dimple and clear a hole again, or get a carbide bit - which seem to be not as easy to find as cobalt.