I had to do a fix to the exact same bolt, same side. First, did the bolt that came out still have any threads showing on it? The hole that bolt goes into is actually larger than the bolt by a good amount and the threaded part in the frame/subframe are quite a ways up into the hole.
My solution was to get a bolt with threads just bigger than the large hole, before the threads the OEM bolt broke off in. When you remove the U-bracket, you can get an idea as to what I am describing. I believe the bolt I used was a very coarse thread 9/16. I basically cut the threads with a bolt, then used a new bolt once the threads were cut. I didn't have a coarse 9/16 tap so, I would cut a turn or so, then remove it, oil it, and cut another. If I recall, the bolt was about 2.5-3 inches long. The head on the bolt was huge as well, somewhere in the 7/8 range.
If you want, you could try to drill it out and use a reverse thread on it, but considering the size of the OEM bolt, I kinda went with the notion it wasn't going to come out. The oversized bolt I used is working great. It even tightened in excess of 50 pounds when I got it finished. Took about 15 minutes.
/brox
