I have a 93 and a 96 F150.

Both have the springs "twisted" as shown below.

What causes this?

 

Normal wear and tear. There was a thin strap holding them together. It could run a long time. I have seen where the spring hangs out a lot and is broken off. A c clamp might get it back in place or you will have to loosen the u bolts. After loosing u bolts I would put new u bolts in.

 

Like sam said, loosen bolts, straighten it up, replace the mounting U bolts, then get new "spring rebound check straps". Mine are loose and rattle when I go down brick roads (which we still have a handful around here) so I searched for months for new rebound straps and the only place I could locate them was from the Ford dealership, they were only $22 out the door, I still haven't gotten around to replacing them yet but as soon as I get a couple rainy days in a row it's next on my list. If you need it I can get you the part # off of my box.