Door latch mechanism will not open from the in or outside ..is this a common problem?

no info generic answer remove door panel and examine the latch and linkages

I see you are ale to see the cables and rods how and when they operate. When you to open the latch from the outside and the inside. Are you able to see if they move the mechanism up or down as you try to open the door working the latch outside and the inside door handle. Sounds like your door latch broke internally, the only thing I was able to do was from the inside with somebody holding the outside latch up to open. Kick it hard in the area where the door latch is. Lay on the sit and kick it hard while the outside individual lifts the latch and pulls. It should pop open. Good luck.

This appears to be a fairly common problem on your vehicle 2 seperate occurences the electronic locks will not operate and also the mechanical latch not operating both resulting in an inoperative back door condition. It seems the only way to open the door is to remove back door panel and manually operate the latch mechanism and then find why it will not operate normally for instance the linkage no longer being attached to latch mechanism or electronic connector not making connection both have been found to be common in gmc yukons

You probably either have a piece of linkage that has come loose inside the door or the latch mechanism is stuck halfway between "lock" and "unlock" (fairly common on some vehicles). You will need to remove the driver's seat to make room to work so the driver's door panel can be removed if you cannot open the door from either the inside or the outside.

If you can get the door open, then the door panel should be removed to inspect the linkage and latch mechanism.

sounds like the rod from the outside hande is no longer attached to the latch. probably broke at the handle. you will need to remove the inner door panel and inspect.you should be able to isolate the problem then.

Your latch mechanism in between door and door frame is stuck. Need re-greasing or a new latch.

Sounds like the door latch mechanism is worn out.

The door latch mechanism for your door is operated by rods, from the inside door handle, and the outside door handle.
It is highly unlikely, (Though not impossible), that all those two rods have fallen off. (Spring clips hold the rods in place. Opening Rod Control Clip. In the link below they are shown as Item E)

With the window all the way down, carefully use a long flat tip screwdriver, to push down on the lever for the door latch mechanism, to open the door. Make sure the lever for the door lock, in the door latch mechanism, is in the fully unlock position.

This link may help show you the inner door hardware, I'm referring to above,

http://www.mamotorworks.com/corvette-c3-door-hardware+1968+1982-inner-1-106-9491.html

You can see that when you pull out on the inner door handle, it pulls a rod forward. This rod is attached to a Bellcrank. The Bellcrank in turn pulls down on another rod, which pulls down on a small lever in the door latch mechanism, to release the door latch.

When you push down on the outside door handle, it pushes a small rod that is attached to that same lever as the inner door handle. Looking down through the window opening in the door, it is that lever that you're trying to push down, to open the door.

Viewing down through the window opening, try to operate the outside door latch a little. Watch to see what lever it tries to move. That's the lever you have to move Down, with the flat tip screwdriver.

With the door open, it is a matter to check out,

1.The Inside Door Opening Control, (The inside door handle is attached to it), to see if the locking part of it is functioning correctly. Make sure that it goes to the full Unlocked position.

2.The Door Latch Mechanism. Make sure it is functioning correctly. It, along with the various door hardware parts inside the door, needs to be lubricated at specific intervals. The more it's used, the higher the interval rate goes up. (I find that owners seem to Skip this task a lot! I use Lubriplate White Lithium spray)

To replace the door latch mechanism, I suggest you buy a manual for your car, so you can view all of the door hardware to remove, to remove the door panel. Then view how the spring clips come off of the rods, and the three screws come out of the door latch mechanism.

Manually UNLOCK the door button or slide. HOLDING the OUTSIDE DOOR HANDLE in the OPEN position, with your other hands finger, LIFT OPEN the latch, and close your door. Hope this helps.

There is NOT a mechanical connection to the outside door handles on the front doors. There is an electronic "door popping solenoid" This is a electronic problem. I think there was a recall on this.

When the actuator moves the latch up, it connects the outside door handle to the opening mechanism. When the latch is down, the outside door handle is disconnected from the mechanism so that it cannot be opened. So in this case your latch needs to be replaced, the latch or one of its parts is malfunctioning. the outside handle is never beening disconnected from the latch. remove the door panel visually inspect for damage, and take the proper repair