Door won't lock

The drivers side door on my 78 is not locking properly. The key turns easily, the locking post goes down, and the door is locked from the inside, but still opens from the outside. I am going to tear into it this weekend, I just thought I'd check here first in case anyone has any advice regarding what I should look for. Thanks

My drivers door (also a '78) just started doing the same thing! Let me know what you find, if I fix mine first I'll post it.

The same thing happened a few years ago on our 1987 Turbo and it was a small plastic clip that holds part of the locking linkage together that had broken and let a rod come loose. The part is only a dollar or two, but it takes a while to get the door panel off and be ablw to get into the door to work on it. If I remember correctly, the rod was up in the cornor where the door handle was located. Good luck.

Thanks for the info about the clip.

Well, I took my door apart today, and here's what I found out. The problem with my door was caused by the linkage bar between the door lock and the interior locking post. The clip was ok, but the rod itself was bent, not alowing the locking mechanism full travel, from locked to unlocked. I think lack of lubrication caused excessive force to put a slight bow in the rod, shortening its length. I was unable to bend it back into any usable shape, so I will need a new one. In the meantime, my door locks wonderfully from outside with the key, but the doorlock post inside is disconnected. Maybe I will add power doorlocks, since this seemed easy after I saw the inside of the mechanism, and would widen my options for replacing the bent piece. The crazy thing is, I've had this car for two years, and only recently discovered this problem. All this time , my door looked like it was locking, but two or three sharp pulls on the handle would still open it. Lucky I found it before a thief did.