[Newbimer]

ATF is one of the best things to help remove rusted parts. If you let it sit, it will wick up the inside between the threads. Not all the way obviously, but it may be just enough to allow it to start turning. It may or may not work, you have nothing to lose by trying.

 

[TobyB]

...and if you want to go nuts, add 50% acetone. Improves penetration.
We all expressed a bit of concern earlier with the possibility of
heat leading to fire...

t

 

[IdahoDoug]

Worth saying you should be happy you have access to try these techniques! Usually when I break a bolt, it's going to require something tedious like removal of the brake master cylinder and then rebleeding the entire system just to get a drill on it, etc. Keep at it! Also don't be shy about applying torque in the tightening direction as well. The whole idea is to break it loose, however minutely. A reverse drill making the hole larger might abruptly loosen it as well since you're applying torque now in reverse (loosening) and vibration and the heat of cutting, etc.

 

[markusmarkus]

The best penetrating oil is a mix of acetone and ATF. I think the ratio is 80% acetone and 20% ATF.

 

[mattman928]

Sorry for the delay. I used the drill to try and widen the hole in the bolt, and then used a much larger extractor kit without success. I heated the bolt hold and the surrounding area with a heat gun and got it to about 200 deg f, then I quench the middle using a can of compressed air upside down so that the super cold gas hit the bolt. I twisted the extractor as hard as I dared without fear of it breaking and making my situation worse. NO LUCK,

The hole is bigger though. I guess next step is to get a plumbers torch and use real heat.

Sapote had asked if the bolt moved at all before it broke, and the answer is NO. When I put the socket and breaker bar to the job, the head just sheared right off and the bolt never budged.