this is a little info on your door cracks and what causes them. i own a 99 sc xlt. it has 25g on it and it has had a door crack. my next door neighbor owns and operates a body shop. along with the other body shops around town we together have come up with this hypothesis: door structure and componet integrity. the design on the f150's door is a little shy on the structural side. the bottom half of the door is too weak to support the force of repeated stress. when you shut your door where is your hand? is it btween the door handle and the bottom portion of the glass? if it is then you will likely have a door crack. instead of closing the door the way most people do, try placing your hand below the door handle. this location is just inches away from the outer door support or crash bar. this might save your crack!

 

If you want to get another idea why they crack. Open your door and stand next to it so you can look inside or outside. Look where the body meets the bottom of the window trim on the outside. Now raise and lower the window with the power button. You will see the door skin bow out about 1/2" when the window seats completely on closure. It will amaze you how much movemnet there is. Now imagine every time you lower the window just an inch you get that movement in the door skin.


97 super cab 4x4 black 4.6 auto. 39,000 miles

 

I agree with you Bob J. I read about this some time ago on this forum and found the same to be true on my 99 F-150 SC. Fortunately, I have yet to have cracks appear, but I'm sure in time they will.

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1999 F150 SuperCab, 4.6 (Romeo)