It is a bajo bolt if I understand you right. It is the bolt that goes through the end of the brake line. It goes through a round metal hoop on brake line and is a bolt that has threads on end, but in between that and the hex head of the bolt is a fluid passage. You may have broken it. Try pulling it straight out as the fluid passage is not all that strong.
If it continues to spin, the threads on it are probably damaged. The threads on the caliper are harder, so hopefully they are okay. They are a pip thread, so you can't use a standard tap if they are damged, you have to get a pipe thread tap.
To remove the bolt if all else fails, get a hammer and chisel, air hammer with chisel if you have it, and beat the hex head of the bolt off. You can then remove it from caliper and have a beeter angle and will be less awkward to remove the threaded part of bolt. You will also be able to see what is happening to keep it from coming out. If it is bad enoguh, the caliper may have to be replaced as a fix a thread type insert is not advisable for this as it is not designed for pipe threads.
Also, you could remove the hose and caliper to more easily work on it. Especially if you have to take a hammer and chisel to it. Remove the line at the steel hard line. Spray it with WD 40 and/or PB Blaster is even better. Let it soak and wipe it off. If you can let it sit the longer the better. Repeat the soaking it with WD or PB and wipping it at least a few times to loosen up threads as much as possible. If you can get a flare wrench made for lines like this, it is best. If not, use a wrench that is high quality like a Craftsman or Snap on as cheaper wrenches flex and will strip fitting. If you remove this fitting try to pay attention if it starts to strip the hex head as you would have to use vise grips on it if you ever had to remove the hose and it is a pepie and can collapse or get msi shpaen using vise grips. So, be very careful as damaging this fitting will rewuire sawing off end, hoping you have enough steel line to put another end on, getting a flare end kit that is the correct angle for brake lines or towing it somewhere to have it get a new hex head end put on.
I realize taking a hammer and chisel to the caliper is awkward that is why I mention removing the hose so you can take it and caliper to somewhere where it can be supported more easily. Otherwise you will have to get something sturdy to sit the caliper on to pop the hex head off. Try to really get some vise grips on the hex head and pull it straight out first. If it is spinning it has to be close to being able to just pull it out. You might even try putting the vise grips on like you have them now to remove bolt and hit it outwards with a hammer to try and remove it.
The other option now that I come to think of it that will be easier because of the position you have to work onit in. Get a drill and try to get a bit that is surely smaller than the threads of the caliper so you dont hurt it. If you are trying to slavage hose, try to compare it to another one if you have removed any others. Give yourself some room as drilling right donw the middle seldom happens and one you drill into the area where the fluid passage is, stop and try to remove it by pulling on it. By the time you get past the fluid are you probably won, t have to drill into the threads as working on it to break what is left, there won't be much, should eventually break and then you can more easily remove the threaded part. Definatly try the drill first. Stopp before you get to the caliper, you can hold bit next to fitting and see how far you can go before hitting caliper, mark this point by putting tape around bit. Then if pulling or prying does not break it you can try the chisel and hammer. You don't want to damage caliper threads.
I hope it works out. I have been there and it gets to be beyond frustrating once something goes wrong.
Sunday, November 20th, 2011 AT 8:38 PM