In my quest to conquer the lock system, I have been thinking:

So, does vacuum only go from the vacuum resevoir to the rest of the locking ONLY system during the short time that the doors are being locked or unlocked? The system will then stay in one spot (locked or unlocked) until "sucked" the other way without the addition of extra vacuum?

In other words, when I am not either locking or un locking, my master vacuum switch in the drivers door should completely hold vacuum no matter what the state of the system is beyond it? All the lines could be disconnected, but it should still hold vac, right?

Thanks - just trying to really understand how this works.

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Not quite, the door lock system is made up of a lock circuit and an unlock circuit. When the doors are n the locked position, the locked circuit is "aligned" to the main vacuum system and the unlocked circuit s vented. So, the locks only "use" vacuum when they are moved, and they will stay locked even if vacuum is lost, but a leak in the "lock" door lock circuit will cause the vacuum to be lost when the doors are left locked. Similarly, a leak in the "unlock" circuit will cause vacuum to be lost when the doors are left unlocked. Hope that helps.

So when the doors are in the locked position, the is vacuum present in the locked circuit...and if there's a leak in the lock circuit, then vacuum is eventually lost. Is that right? I'm trying to understand as well before tackling mine.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

That is correct, it is controlled by a 3-way switch in the drivers door. There is a solid yellow vacuum line to this switch and a locked (yellow/red) and unlocked (yellow/green) line from the switch to the other doors. If the leak is in the locked circuit, you should only lose vacuum when the doors are left locked.

Thanks Craig for clearing this up.

For a minute there I was thinking it might not be necessary to chase every little last leak in the system. But now I realize it is. I have a 1mmHg every 10 minutes type leak somewhere in my unlock.

That's kind of dumb...they should make it so that no vacuum is applied when there isnt a change in the lock state occuring. The locks hold their state with or without vacuum anyway. This way a little tiny leak wouldnt drain the vacuum resevoir. Oh well, Im sure there is a reason the zen masters of vacuum didnt do it this way...

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Well, I can kind of see why they did if I understand the system correctly. Its all mechanical. The drivers door always has vacuum supplied to it, moving the the lock knob up and down just diverts the vacuum to the "locked" hoses or the "unlocked" hoses. So the drivers door has no idea whether the other doors have locked or unlocked, it just knows that the valve is open to either the locked or unlocked circuit.

There would have to be some kind of delay to open the valve to "locked" or "unlocked" for some length of time, and then have the valve close to both circuits. That would prevent a small leak in the system from draining the vacuum reservoir. Maybe that was impractical to do.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

Part of the reason that it is impractical is that the selector valve and the vacuum reservoir are not co-located. In order to work effectively, the valve would need to be at the reservoir. As designed, the valve is a one end of the system, the reservoir is at the other, and all the "leaks" are in between.