Fuel tank strap bolt -Weld nut spins

I have the notorious bad fuel pump, caused by driving it down to empty a few too many times. Had to drop the tank, but strap bolts fought hard to stay on. Tried driver side bolts, but couldn't get them out all the way, front interior bolt came out with a little help from some wd40. Rear interior strap bolt got stuck after several turns. Got both hands on it and broke the weld nut free. Now the whole thing simply spins around. Can't seem to find the right sized socket to get in the frame rail access hole for the nut. Welding the nut simply isn't and option for me, since the nut is inside the frame rail & i don't have the skill to bend a stick & weld it in there blind w/ the gas tank still in my way. I've been buying large sized metric sockets. The strap bolt is a 15mm, have tried 13/16 & 3/4" sae sockets on the jam nut, seem to be too small. (can't see what i'm doing in there, going by feel.) Bought a 24mm, seems it's either too large, or i was too wet and tired. It's raining, dark, and I'm nearing my wit's end. If anyone knows the size or can find out, it would save me several trips to the store exchanging sockets to find the proper one.

Come to find out it is a square nut. Go figure. Explains why I couldn't get ANY 6pt. socket on it. Still have yet to figure out how to get it the rest of the way out. i only have 2 threads left above that nut. So close...

After much discussion w/ local mechanics (shadetree and professional), seems cutting the bolt out w/ die grinder or sawzall is the best option. Will have to replace it with another bolt and (what GM should've done in the first place) a SIX SIDED nut in the frame cross-member.

I had the same problem on an Aerostar. Fortunately, Chevy put bolts on both sides of the tank strap. If you can just remove one bolt on each strap, you can still drop the tank; just bend the straps out of the way. The metal bends easily. You could put a piece of rubber between the strap and tank when you put the tank back in to compensate for the slack caused by the loosened bolt, and forget it. I didn't have a side grinder and I'm leary of making sparks around a gas tank, so I fudged a hacksaw in to cut the bolt, and even after removing the tire, I only had a 1" stroke on the saw. Took about half an hour to saw thru. Fun fun fun.
I've learned that when dropping a gas tank, (or any frame/suspension bolt), use WD-40 to saturate the bolt threads as much as possible before putting both hands on the rachet.
:wink: