I know it's been mentioned already, but with ford doors my first thought is always pins. Theye are notorious for loosening up and causing slack. HOWEVER, I had a similar issue with my passenger side as well, after much investigation, I found one of the front passenger quarter panel mounts was broken causing it to droop slightly, which threw the door geometry off. Must have broken while mudding somewhere. Fixed that and the door lined up.

 

Just joined this site to thank the posts related to door rattle. I have a 90 f150 and 89 ranger. Both have the problem. I tried to adjust the striker pin first before finding this site. Only had a little success. Read posts here and found out I was missing the plastic part on the striker pin. At work I found a hard rubber tube. Cut it down to size and it worked. Not sure how long it will help, but now I know what the problem is. After I put it on. I found a hard flexible plastic tube that will work better. When the rubber one fails. I will switch it out. Saved time and money finding these posts. I was going to replace the weather stripping. No need to now. You can make your own. For future readers. My 90 f 150 sounds like a new truck going over bumps and pot holes. Along with train tracks. Thank you! Everyone who helped with previous post. You guys are great. I made my own and they work.

Someone made a comment about how good they must be because they fail about the same time. While mostly using the driver side door. I think I know why.

The door is kind of resting on the plastic around the pin at all times. When you go over bumps. The doors rattle and bounce on both pins. While the driver side does get more stress with opening and closing the door. They receive about the same while parked or driven. That's why I think they break close to the same time.

Happy New Year Ford Owners!!