Needed to get around and finally replace the fuel tank on my Cobra (non-stang) due to a dent. Easy job getting it out, but when I removed it, there was a loud rattle when I moved it around. After taking the fill tube out, I looked in, moved the tank, then just laughed! It seemed my 35yr old tank got the sump dislodged and broke free of it's soldered or silver soldered factory job. The only thing remotely keeping it in place was the fuel pump, because it could only move as far as the pump would allow. Never heard the rattle, most likely due to the 4" sidepipes.
Modified my new tank for sway bar clearance and straightened seam tab so it'll fit the chassis. Along with that, my Autometer gauge wasn't reading correctly so I checked that circuit, called Autometer and sent them the gauge and sender to check. Sender is fine, circuit fine, bench tested and sender at full read 3/4 tank. Installing new tank today and will drive without a gauge. Just have to remember how much fuel I put in.