fuel tank just rests on the skid plate??

[GREASE FIRE]

i am trying to fix the sending unit/fuel pickup on my 89 f250 with a 15 gallon rear tank (i think) and i pulled the two-piece skid plate off today just to check it out and see how to remove the tank. Once i had the skid plate off it seemed like the tank could be slid back and forth a bit and even lifted up a little, and i realized the only thing keeping it from falling was the ledge that it sits on. I could not get my head up there to see if the same bolts that held the skid plate on also bolted the outer edge of the tank in place - but it did not seem like it to me. I am trying to figure out if something is missing here and the tank has just been sliding and bumping around or what. Anyone know?

also, the gauge really moves around a lot - it was showing 1/4 tank (which is actually empty because it does not pick up fuel below that point) and then i shut if off for a few minutes, then came back out and started it and it showed close to 1/2 tank. Anyone know what that is about? Need a new sender or what?
Or if there is a thread that explains all this and how to fix it could you post a link?
thanks,
Paul

 

[93turbo_animal]

yes the tank just sits on the skidplates theres usually a rubber or 2 sided tape strip on each side