Sounds like your hinge bushings are totally shot. How much can you move the back edge of the door up and down. If its quite a bit, then I'd think about replacing them. I think you can get them under the Help! line at the parts store.
For a temp fix, I'd play with the striker adjustment. Loosen it up with either a bix torx, or put some pliers on the outer edge (where its big around). I had to do this with the '81 to get the door to shut tight. its pretty much a look and see where it needs to go type of deal. Then, when you have it where you want it, tighten it (not all the way, just snug so it wont move when you shut the door), close the door, and if needed try again.
Thats the best I could give ya anyway. Maybe others will chime in.
Yep, I agree the hinges are worn. I was able to compensate for this on one of my vehicles by putting some washers between the door and the bottom hinge. Pick up on the door so it closes properly when you push on it. The distance you have to move it up is approximately how much you want to shim it on the bottom. As long as your hinges aren't totally shot this should fix it. Keep the hinges well lubed to help reduce further wear.
The hinges are tight. The only movement is when I pick up on the back-end of the door, the whole truck moves!!! But really, no play at all. Thats why I was hoping that there was a simple way to just adjust it. Didn't look like I could do it with the striker, but I could be wrong..... I was once before, just don't remember when. LOL
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