1983 300SD door lock question - PeachParts Mercedes-Benz Forum

turbozeke418 · #1 09-09-2012, 10:40 PM

Where does the vacuum come from for the door locks? The trunk locks regularly but the doors do not. The previous owner says they were disconnected but I'm not sure from where. I know there is a vacuum pump in the spare tire well in the trunk. But, does the vacuum come from there? There's an electrical harness going to that also. Thanks.

sixto · #2 09-09-2012, 10:47 PM

The vacuum/pressure pump in the trunk locks and unlocks the doors, trunk and fuel filler flap. The harness is for power to the pump and trigger signals from the key lock switches.

Your TD probably has 2 sets of lines to each lock for vacuum lock and vacuum unlock. The SD on the other hand uses a single line - vacuum to lock, pressure to unlock.

Sixto
87 300D

turbozeke418 · #3 09-10-2012, 03:14 AM

I just tested the line going to the pump in the trunk with a mittyvac and it holds vacuum. I pumped it up and all of the doors locked (For some reason I had the keys with me which never happens). I went to unlock the passenger door with the mittyvac still hooked to it and it wouldn't budge. I disconnected the mittyvac and was able to unlock the door. When I turn the key in the drivers door to lock or unlock I can hear a click from the pump module in the trunk but it does nothing.

sixto · #4 09-10-2012, 12:58 PM

The pump does 2 things - move air, direct either vacuum or pressure to the lock actuators. Seems like it's doing one or part of one thing. Do you have access to a known good pump to test?

Sixto
87 300D

turbozeke418 · #5 09-10-2012, 04:11 PM

I don't have an extra pump. I guess I might just have to look for one on ebay or a JY and just buy it and hope it works.

sixto · #6 09-10-2012, 04:26 PM

You can probably find on in the parts forum. Or start a WTB thread.

Sixto
87 300D

tyl604 · #7 09-11-2012, 08:17 PM

If you get a used pump be careful that the connector matches. My 81 300SD (I killed the pump by taking it apart) had a connector different from what Peachparts sent me; they swapped it out easily after I sent them a picture of the connector.

turbozeke418 · #8 09-11-2012, 08:35 PM

I was hooked up by "Benznut" he offered me a great deal.
We'll see how it goes.

turbozeke418 · #9 09-13-2012, 02:05 PM

OK I got the new central locking unit and still nothing works :/ Any ideas on where to go next? I would guess my unit was still functioning, but the problem lies elsewhere.

tiger64 · #10 09-14-2012, 01:51 PM

I had similar problem and it was a fuse. Mine was #10 fuse. Fuse was not burnt but the contacts needed a sanding.

tyl604 · #11 09-14-2012, 09:14 PM

I do not know what a central locking unit is. Can you post a pic? But each door has a regulator. They are about $25 each and easy to replace. You might have one or two bad. The nipples on the new ones are too short and make it hard to get the plastic hose to stay on but it can be done. The lock system is pretty durable. The plastic hoses almost never malfunction or break. In thirty years I have only replaced one regulator and the pump and the locks work fine. Struggling to picture what you mean by central locking unit.

There are a lot of posts and pics which direct you to the junction in the floor in front of the right front seat. You can hook up the mityvac there and almost always find your leak. And a leak is about the only thing that can keep it from working if you have a good pump.

Let us know what you find.

sixto · #12 09-14-2012, 09:29 PM

Do you hear the same click from the replacement pump module? Are you sure it's the pump that's clicking?

Sixto
87 300D

tyl604 · #13 09-14-2012, 09:38 PM

You can generally hear the pump if you are standing outside the car. Not unusual. It cycles when you turn the engine off.

turbozeke418 · #14 09-14-2012, 11:08 PM

Quote:

Originally Posted by tyl604

You can generally hear the pump if you are standing outside the car. Not unusual. It cycles when you turn the engine off.

I hooked up a mittyvac to the yellow line and pumped it up. All the locks lock and it holds pressure. I used a test light and one of the leads going to the unit has power. I'm not sure what to check or where to go from here?

turbozeke418 · #15 09-17-2012, 12:41 AM

Anyone???