My 78's passenger door is locked and won't unlock with either the key or the inside manual knob. Car recently had a new handle put on this door, but nothing else was changed. The lock is unresponsive except for a small movement I can see through the window opening (window down). The manual knob and shaft are pretty much the same thing. Tried moving the door handle (in and out) while turning the key, no luck. I can see minute movement of it when you try to use the key. Cannot remove the door card as 2 screws on top are hidden with the door closed. I have removed the arm rest to better fiddle with it. I have tried to lift or move the one lever I can see through the window slot. No luck. My guess is something is bound up lower than the mechanism. There was an older discussion (dated about 10 years ago) not completely helpful and not sure those members are even still members. 

Anyone have thoughts? Anyone have a detailed diagram of the locking system, most of the ones I found so far don't really show much and if they do it's power door locks. Thanks!

Hello, Not sure if the door locks are the same, but on earlier ones, 72-76, there is a small curved linkage between the lock on the door and the mechanism for locking and opening the door. It is out of adjustment. There is to much pressure on the rod. It needs to be removed and threaded up or down to eliminate the pressure. The pressure puts the system out of synchronization. 

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Since it's an old car, I'm thinking a "slim jim" might to the trick 

-Adam Wartell
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Thanks Manchester, I think that's part of the problem because I've just read that there's a tension problem when you put a new door handle on. However, before I can do any of that I have get the door unlocked, so I can get to that adjustment. Thanks for the info.

Thanks Adam, that was my first idea, I made one up and it didn't do the trick. However, I've since found out that this maybe the result of incorrect installation of the new door handle. There's a different lever I need to get too, but it farther up the mechanism(almost under the door handle) and harder than stink to get to it, but I'm working on it. Thanks for the suggestion tho. Milt

Yes, correct. You need to press on the actual door lock assembly. If you have a assembly manual you can see the process and how to locate it. 

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This happened to me n my 78 a year or so ago. You can get the door panel off. Youcan get to all of the screws by moving the seat back & forth.  Then pull panel out.

You should be able to get the the door latch rod and push it out of the latch to see if that is the problem.

If not then the lattch is stuck in the Locked position.

There is a tab on the inside portion of the lock that you can hit to open the latch with the window down.

It will take some force to move the lever.

I never could do it so I took it to my mechanic. He did and put in a new latch.

Don't want to be judgemental, but the handle installer should have verified all the mechanism worked before finishing the door panel installation. The connecting rod MUST insert in both points with NO tension on either points. 

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Perhaps these will help with the visuals...

Joel Adams
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Thank you Everyone, who responded to this posting and your suggestions.. Greatly appreciated!!

In the end the attached YouTube video was the answer to my issue and I was able to open the door. HOWEVER,  it wasn't as easy as the demo in the video showed. There was no way could get a long screwdriver to that lever without the inside door card being somewhat removed. Maybe it was because I have a Silver Anniversary edition (Since repainted black) or what but the guy in demo did not have a door card on that door (besides not having an outside wall (LOL)).

Having looked at the whole mechanism, I WD-40 the heck out it, and will fix what he suggested at the end of the video to stop the problem, but I think I'll treat the car to a new unit all together, but not right now. Thanks!

The video:  https://www.youtube.com/watch?v=BldEzHHDiM0

I saw that video too. I just couldn't hit the tab ard enought to make it come loose.

My mechanic oviously new how hard it had to be hit to make it release.

Hey Len, did you take it to DMS?

Of course. I wouldn't trust anyone else. LOL