spug,

I am just learning about the vacuum system. Here's what I know about the nonlocking seatbacks...they are vacuum controlled. On the 300cdt 1982 model the baby blue vacuum line bundled with the yellow lines just in front of the firewall on driver's side is responsible for the seatbacks locking. Yellow lines are for door locks. Get a mityvac hand pump and test for vacuum seal on the baby blue line. No seal means you have to go downstream...into the cabin of the car...I assume you have the 300cdt? The seatback vacuum line is baby blue in the coupes. The lines run under the floorboard to the seats...I've read that you have to pull out the seats in order to get to the vacuum lines under the seats to test them...My guess is that removing the seats is a lot of work...Before removing the seats I plan on removing the underdash and looking for where the lines enter into the cabin...perhaps there's a loose connector under the dash that needs reconnecting or replacing?...Much easier that pulling the seats. If there's nothing under the dash, then next step is to go under the seats to find the leak...not sure if you can easily pull the connector under the seat in order to test vacuum seal with mityvac. From what I understand you are best starting upstream by the vacuum pump and going down until you find the leak. Any leaks that you find, you should plug with a golf tee or appropriate sized nail until you can buy new connectors or check valves, as they will not only affect the related system, but can also screw up everything else that runs on vacuum...ie, shut-off, transmission, etc...

I'm new at this, but have spent the better part of this weekend researching and understanding the vacuum line diagrams. You should find a schematic for the vacuum system and EGR either front right or front left above headlights. Vacuum systems changed regularly sometimes several times during early 80 years. Looking at somebody elses diagram of the same year car could only confuse you as yours could be different. The diagram for my car was on the front left lip just behind the headlight assembly facing up.

The fact that your car holds vacuum seal for five days likely means your vacuum resevoir is solid functioning...getting ready to test mine this afternoon.

Again, I am a newbie, and would welcome any feedback...still not sure if there should be a check valve on the seatback vacuum line...I have one and it looks jerry rigged...half the check valve is plugged...probably needs replacing...no vacuum post valve to seats...the mystery continues to unfold.