HOW TO: Remove broken bolts
I recently broke 6 of those 10mm bolts that hold on the splash shields under the front of my car. The failure mode was the same in every case. I was able to get the bolt started but the corrosion on the exposed threads would cause it to jam until I broke off the head off the bolt. I got them all out using the following technique:
First you need to loosen the bolt since you won't be able to put a lot of torque on it with the head broken off. Apply heat from a propane torch for about 15 seconds and then quickly spray some liquid wrench on it. The benefit is twofold. The heating and rapid cooling expand and contract the bolt plus the liquid wrench will get into the threads to lubricate it. Be careful with the heat if there are plastic or rubber parts nearby. Tapping the part may also help to work the lubricant into the threads.
Now assess how much of the bolt is exposed. The best case scenario is when you can access the rear of the bolt and there is enough exposed to get a good grip on it with pliers. Since the head of the bolt is now gone you can thread the bolt INTO the part and remove it from the rear. This is easiest because you won't have to drag the corroded threads through the part. If you can't get the bolt out from the rear see if you can get a pair of pliers on it from the front and remove it that way. To get a good grip on the bolt you can try using locking pliers (vice-grips). I've also had good luck with robo-grip style pliers.
If you can't get the bolt out with pliers then you will have to drill it. Use a punch to mark the center of the bolt and to keep the bit from wandering. As you start the hole you will inevitably be off center so angle the drill and then straighten it once you are centered. If you have them use left handed drill bits and run the drill in reverse. This will sometimes cause the bolt to back itself out while you are drilling it. [NOTE: I've only tried this once using a set that I picked up at Auto Zone for $10. It did remove the bolt but I ended up breaking the bit in the process.]
After the hole is drilled use an extractor with a tap handle to remove the bolt. I use the square fluted design that you can pick up at Sears. These are better than the screw design for two reasons. It won't try to work itself deeper into the hole as you turn it. This can cause the bolt to expand and become jammed. It will also bend to give you ample warning before you break it. Make sure the hole is drilled to the correct size for the extractor and then drive the extractor into the hole with a mallet. If it is not gripping try taking it out, rotating it a little, and then driving it back in a little harder with the mallet.
If you are having trouble try repeating the heating/lubricating/tapping process. Take your time. If you do manage to break off an extractor inside the bolt then you will have a very hard time drilling it out. [NOTE: I've done it but it took a long time with a dremel tool and a diamond grinding bit.] It's also worth pointing out that this process is a lot easier while the head is still on the bolt. If you are removing a corroded bolt and it's getting harder instead of easier to turn it then heat/lubricate/tap it before you break the bolt.
First you need to loosen the bolt since you won't be able to put a lot of torque on it with the head broken off. Apply heat from a propane torch for about 15 seconds and then quickly spray some liquid wrench on it. The benefit is twofold. The heating and rapid cooling expand and contract the bolt plus the liquid wrench will get into the threads to lubricate it. Be careful with the heat if there are plastic or rubber parts nearby. Tapping the part may also help to work the lubricant into the threads.
Now assess how much of the bolt is exposed. The best case scenario is when you can access the rear of the bolt and there is enough exposed to get a good grip on it with pliers. Since the head of the bolt is now gone you can thread the bolt INTO the part and remove it from the rear. This is easiest because you won't have to drag the corroded threads through the part. If you can't get the bolt out from the rear see if you can get a pair of pliers on it from the front and remove it that way. To get a good grip on the bolt you can try using locking pliers (vice-grips). I've also had good luck with robo-grip style pliers.
If you can't get the bolt out with pliers then you will have to drill it. Use a punch to mark the center of the bolt and to keep the bit from wandering. As you start the hole you will inevitably be off center so angle the drill and then straighten it once you are centered. If you have them use left handed drill bits and run the drill in reverse. This will sometimes cause the bolt to back itself out while you are drilling it. [NOTE: I've only tried this once using a set that I picked up at Auto Zone for $10. It did remove the bolt but I ended up breaking the bit in the process.]
After the hole is drilled use an extractor with a tap handle to remove the bolt. I use the square fluted design that you can pick up at Sears. These are better than the screw design for two reasons. It won't try to work itself deeper into the hole as you turn it. This can cause the bolt to expand and become jammed. It will also bend to give you ample warning before you break it. Make sure the hole is drilled to the correct size for the extractor and then drive the extractor into the hole with a mallet. If it is not gripping try taking it out, rotating it a little, and then driving it back in a little harder with the mallet.
If you are having trouble try repeating the heating/lubricating/tapping process. Take your time. If you do manage to break off an extractor inside the bolt then you will have a very hard time drilling it out. [NOTE: I've done it but it took a long time with a dremel tool and a diamond grinding bit.] It's also worth pointing out that this process is a lot easier while the head is still on the bolt. If you are removing a corroded bolt and it's getting harder instead of easier to turn it then heat/lubricate/tap it before you break the bolt.
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