I just thought of something after reading another post. I guess that 126 and later-design cars have a pump to keep the vacuum up when the engine's not running; however, the 123 and older cars rely on residual engine vacuum. I have a factory car alarm that requires that I unlock the driver's (or front-passenger, but that lock doesn't work well) before I open the trunk. Between this and going out to get stuff, I lose vacuum fairly often simply 'cause of the frequency that I open the doors (AFAIK, the vacuum system works fine).

So, I was thinking...would it be possible or feasible to install a vacuum pump on a 123 (or even an earlier vehicle)? Other than simply maintaining originality, is there a good reason not to?

Just brainstorming...thanks!

__________________
2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

I keep reading this and thinking about it.. Yes it would work.. I have no clue how to wire it..
But you know.. I spent years with these systems.. and got most of my experience with my wifes old 115 240D.. and have had a few problems with her 300CD . I have found that the pump system on the Diesel works well.. I can lock my doors and they will still unlock after setting for weeks.. I can open and close them 10 times or so with out starting the engine.. they work fine.. and when I start the engine the system pumps down fast... I have to wonder if you do not have a bad pump.. leaking valve or some thing like that.. The leaks are usaly small.. The most common are at the front of the doors where the tube is bent each time you open and close the doors.. I usaly just cut them there and put a hose over the bend area.. Works fine..

Ken

10 times? That's actually about what I can do; maybe a few less, but it's definitely within what the manual says is normal. Just, sometimes, I need to go out to the car and back that often before re-starting the engine (I can be a bit absent-minded at times ). Any vacuum that may have gone away is restored almost immediately on engine start, so I think it's safe to say the pump's fine.

__________________
2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

I'm way less than 100% sure of what I say here so take it accordingly.

The W116 and W123 system has two hoses to each door lock mechanism because it uses vacuum to lock and unlock the doors.

The W126 and W124 system has one hose to each door lock because it use vacuum to lock and pressure to unlock.

It seems like a lot of work to adapt a later system to a W123. More work than adapting electric locks. You could use a vacuum pump to empty the reservoir when necessary but the triggering mechanism will require some thought.

Maybe all you need is a W126 or W124 trunk key switch that activates/deactivates the alarm.

Keep in the trunk a MightyVac plumbed into the vacuum reservoir so you can recharge it when necessary. Better yet, attach the MightyVa lever to the trunk lid so opening and closing the trunk builds vacuum

Sixto
91 300SE
87 300SDL
83 300SD

Thinking it all over again... Why not just pick up an extra vacuum tank from an old wreck.. and install it some place.. It would double the capacity... its cheap... its not a real problem.. the ones on the TD are mounted just in front of the rear bumper.. they are big and easy to find..

Food for thought..

Ken