Broken differential cover bolt..chevt 12 bolt

[g356gear]

I pulled my cover off and all the bolts came out nicely except the very top bolt. The head twisted off with only about 15 ft.lbs of pressure. I went and bought a bolt extractor tool and tried using that. The tool worked fine until the extractor bit broke off clean to the surface of the bolt. This bit is super strong vanadium material that drill bits don't seem to want to touch it at all. Luckily it is the very top position so I think I will be OK against leaking with a gasket and a little gasket maker between the top 2 remaining bolts. Any advice?

[minendrews68]

you may try a solid carbide bit, not the masonary ones but the ones used in machine shops. There is also a solid carbide starter drill. I do believe either one of these would work do drill out the broken bits. Just be sure to get the holes as centered as you can and keep them that way, you don't want your drill wandering off and going through the threads. If by chance you do mess up the threads, you can always Heli-coil them, they would work fine on something like this. I know there are those that will argue that they would work fine even in critical applications I've just never used them in those situations.

[Chevy]

For really stubborn bolts i have found nothing works as well as a torch. Heat the surrounding area up with a torch before trying another removal.

Also if you don't have any luck with a carbide bit and you really want to get that bolt out, you shoud be able to weld a bolt head on, then use the torch and you can back the bolt out--i did this once successfully, but on a little bigger bolt.

Good luck!
Paul

[Vegas69]

Silicone the cover on and it will be fine.

[68nate]

Smack the broken bolt with a punch and hammer- sometimes that stretches the threads enough you can spin it out by hand, if not- weld a nut to the broken bolt and turn out with a socket and ratchet.

[g356gear]

Apparently the bit that broke off in the head of the stock bolt is made of hardened tool steel and no bits I can find seem to will touch it. I am really leery of trying to weld or beat on the bolt being that the differential center section is cast. I really don't want to risk damage the cars original 12 bolt posi differential.

Has anyone seen a type of bit like a hole saw without the centering drill bit? Then I could drill out the bolt and the threads and re-tap to a larger size bolt.

[68nate]

because it is cast the weld won't stick to it. I've done it several times on engine blocks. Also you might be surprised how little beatin' it takes to free things up, just a few light taps usually works. More likely to screw it up trying to drill it. I speak from experience.

[HILROD]

My 12 bolt did the same thing. I ended up drilling and tapping that one hole for 3/8 16.

[MarkM66]

Silicone the cover on and it will be fine.

Exactly.

It helps being at the top too. It won't leak.

[Bow Tie 67]

If there is enough room you can take a very small drill bit and drill right up against the broken extractor into the original bolt. Then you can try and rock the extractor back and forth with a punch to break it loose. Then try and extract whats left of the bolt.

[MrQuick]

I know there isn't alot of room with a 5/16" broken bolt. But a dremel and carbide bit should do the trick. Just grind around the broken extracter till yu can grab a hold of it and rotate it back out.


If all else fails just seal the cover with RTV. Just hope no one figures out you are running an 11 bolt.

[MonzaRacer]

take heavy flat washer with same size hole as bolt but larger diameter, lay it up, cover gears, weld it to bolt then take a nut and weld it to the flatwasher inside the nutlike say a 1/2 in nut. I like to use a little synthetic oil too if it statrts moving the synthetic oil will run into threads and not burn off as easy. Regualr weld wont stick to cast and heat helps free it up.
Make sure your weld is cranked up (hope you have wire welder) nut should be very cherry red hot when welding is done. let cool a bit to harden(minute or two).
Have had so many issues with removing broken bolts ,small ones, with extractors and unless your deadcenter in bolt,,,,, well you guess results, and I love the square ones better but newer twisty ones (forget name) work great too.

[shep]

if there is any of the bolt sticking out to grab hold of heat it until cherry red with a torch then touch the bolt with a candle. Let cool turn it out by hand. The wax from the candle flows into the threads lubricating them. If it is flush weld a flat washer and nut to it and remove it that way.