I have a 81 F350 and I have to slam the door as hard as i can to get it to shut. Not sure why at this point other than it's a Ford. I seriously have to use all my might to get the door to latch.

 

usually a problem i see on chevys. Check the alignment, most likely its off as the door hinges havent been properly maintained and are worn and sagging.

 

Sounds like something is slightly out of alignment or the latch mechanism is in serious need of some lubrication.

If you keep slamming it eventually it's going to crack the sheet metal where the latch pin is mounted, so you might want to figure it out before that happens.

 

this happened to my toyota, worn out hinges, try lifting the door up and see if there is any play

 

I don't think it's the alignment. It must be the product.

 

door pins and bushings are probably shot from 30 years of use

 

Probably by using the door help himself into the truck. I'm sure we all do it (I do) but are really not aware of it. I have to remind myself to grab the "oh-****" handle.

 

If you're sure it's not the alignment, check the lock pin.
I'm not sure how an '81 Ford's is mounted, but most have adjustment built in to their mount, allowing them to be positioned further inboard or outboard.

If the driver, as a habit, slams the door even when it's not needed to get it to latch, it can knock the pin inboard, requiring you to slam it to get it to latch.

 

Mine is slowly getting worse, my bets are that the hinges are sagging, mine is starting to and it causes this

 

I shouldn't have to adjust a damn thing! BUT I understand adjustments must be made on an inferior product.