Vacuum door locks question

[clackclack]

I have an 83 300SD and the door locks and all associated locks won't work. I tried to pull vacuum at the firewall to no avail. I looked in the boots that run from the fender to to the door and it looks like only wires in there. Is the lock an electrical servo that transmits to the vacuum under the dash or what not? Thanks.

[tangofox007]

On a W126, vacuum for the door locks is supplied by an electric vacuum pump in the trunk.

[clackclack]

I have a big line going into the firewall that I can't get vacuum on. Wonder what that is?

[toomany MBZ]

Originally Posted by clackclack

I have a big line going into the firewall that I can't get vacuum on. Wonder what that is?

Pics?

[tyl604]

Search the forum; there is a lot of info on the door locks and vacuum. There is a major junction box under the carpet at the front passenger's feet. Generally you go here to start working with the Mityvac to see where you do and do not have vacuum. If every lock is not working, you may very well have a bad vac pump in the rear tire compartment or a hose problem back there. If they all work and one or two just go out, it is generally a $25 actuator which is inside each door.

[cdplayer]

Hi. I know there is an electrical lead in each of the front door handles. If you look at the area near the door latch, pull the round plastic cup that cradles the connection. This is one area to look for a bad connection. However it is possible that the lock cylinder has worn the electrical contact internally. That is a worst case scenario.
Have you confirmed your vacuum pump is still working? If not,take a look in the trunk, lower right hand side of the spare tire well. Remove an 8mm bolt. Pull out the vacuum pump. If your central locking system stops working, most cases the problem is a seized vacuum pump motor. Broken welds, rust, or torn diaphrams cause these to fail.
You can test your pump with a battery charger. Negative cable to the brown wire. Positive to one of the other leads. If the pump does not work, try starting the positive cable on another lead. Just depends on the cycle of the pump at last use.
If the pump still will not start, replacing it may be the next step.
Unless you are handy with a soldering iron and ohm meter.
I have a vacuum pump that will work on your car now on Ebay,item # 370325491006. This is one of four designs used for the year/models I mention in the listing.
The vacuum pumps found in the 1981 to 1984 W126 chassis and the 1983 and 1984 W201 190E and D are interchangeable. Same electrical lead, and single port vacuum.
I hope this info helps.