If you are referring to the bolt that holds the caliper support bracket, I would suggest the following..
These are in there pretty tight. 3/8 drive ratchets are NOT the tool to remove them. You need either a large box end wrench or a 1/2 drive ratchet and the proper socket.
If all else fails, use a breaker bar with a pipe slid over it for additional leverage. If you do not have a breaker bar, you could use the ratchet as long as it is 1/2 inch drive, anything smaller will simply break. If you do use the pipe and ratchet system, slide the pipe on as far as it will go. The closer to the head the less the spring leverage is exerted to the tool.
Good luck...