When I bought my '84 300SD, the door locks weren't "automatic" because the vacuum pump that serves the locks (in the trunk) was bad - the owner told me that upfront. Right now, I have to unlock all doors manually and only the trunk is unlocked automatically when I unlock the driver door.

I looked around online for this vacuum pump, and most places have it for around $300-400!

That begs another question... Is it possible to take this pump apart to see if I could repair it, or is that out of question? Anyone know where I could get one of these things cheaper than 300-400 bucks (other than ebay, of course...)?

denis,
i haven't done it, but have seen the kit at www.***************

0005861723
Meyle/Effbe
Vacuum Pump Repair Kit
For 0002301365 piston type pump. 1 kit per car. $41.79


For $41 bucks I'd give it a go!

John

__________________
John Hughes, was in Landstuhl, Germany but currently in San Antonio, TX


1978 280CE Astral Silver now 59,xxx miles and counting "Silber-Kugel"
1986 300E Black Pearl Metallic 143,xxx miles 5-spd daily driver w/ blk leather "Schwarz-Schönheit"
1989 190E 2.6 (euro) 5-spd Desert Taupe 112,xxx kms Had to leave behind in Germany!!! "Helga"
1983 300D Pastel Beige now 312,xxx + miles SOLD

OBK#24

Let me get this straight. If the trunk locks and unlocks automatically from the drivers door, then I don't see how can the pump be "bad"? It is a single pump. Check the flex fittings at the pump. Many times a quick replacement of one fixes the problem.

http://mb.braingears.com/ will have a diagram for troubleshooting.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

I don't believe that the kit is for the vac pump that serves the door locks. It says for piston-type pump PN 000 230 1365, but the vac pump I just pulled out of my trunk has PN 000 800 0248.

In fact, I just opened up this little Bosch pump to have a look inside. It doesn't have much you can rebuild. It has a piston in cylindrical housing that has two wires soldered to it (red and black). These wires come off a small circuit board that has a bunch of resistors, some capacitors, a chip, 2 weird spring-loaded transformers, and some other stuff. The 12V power connector from the car hooks up to this little circuit via a 3-prong plug. Also, there are 3 wires that come off the circuit board which operate what looks to me like a valve. The vacuum port from the piston cylinder, the aforementioned valve, and the vacuum output port that connects to the car's locking system are all joined inside the pump housing by a rubber Y-fitting. So what must happen is that the piston generates positive pressure, which raises the locks, and once the locks are undone, the residual pressure in the system is relieved by opening the valve inside pump housing, which lets the air out via the vent holes in the pump housing. When the doors are locked, I presume the piston pulls vacuum, lowers the locks, and the valve is timed to open and let the air in the system to equalize the pressure. Anyhow, this is all my hypothesis.

I think now that I've taken this thing apart, I'll try to hook it up to that electrical connector in the trunk and see if there's power to the board. At the very least, I could do a continuity test for the ground circuit. Also, I could monitor if there is any change in the voltage across the two wires that power the piston cylinder as the doors are unlocked...

So that brings me to the following question. How exactly is the power supplied to the lock pump? Is the lock cylinder on the driver's door connected to a power source that gets bridged and unbridged when the lock cylinder is turned? I guess I'll find out by observing the change in voltage across the pins of a connector that runs to the trunk and powers the pump. But does anyone know?

No, on my car the trunk lock opens and closes via the driver's door lock even with the pumpin the trunk unplugged from the vacuum circuit and from its electrical connector. I presume the trunk lock must be controlled by some other way.

On the 84 300SD with the factory alarm there is a small electric actuator, as well as the vacuum actuator, for the trunk lock. Generally, they work when the alarm is activated (whether the alarm is operational or not) by the driver side key/tumbler alarm microswitch.

Only if the trunk vacuum actuator is in the unock position, will it work as you've described, as it's meant to be a redundant system for the trunk only.

There are two versions of the electric vacuum pump for the 126. You want the early one (81-85, I believe). The later version has two electric plug connectors and doesn't fit the harness.

These pumps show up on Ebay quite often at a reasonable price.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Close.
If you notice on the circuit board there is a pressure/vacuum switch. The basic premise of the pump is that it will run for x seconds or unti line pressure/vacuum exceeds a certain amount. The thought is that is an element in the door blows, the pump will time out instead of runnning forever. If all the elements are good, then once the system locks/unlocks, the system will reach a preset pressure and the pump will turn off.

The bad news is that if the trunk locks/unlocks, your pump is fine. Put it back together and hope you didn't F it up. You'll need to trace the vacuum lines from the pump to the fuel door. I believe it Tees off there and goes to the trunk and inside.

Most likely scenario on your car is that the element(s) in the door(s) failed and rather than replace them, the PO bypassed them.

If you messed up your pump, check eBay for a used one.

but as jbaj007 said, the trunk locks/unlocks without the vac pump. the previous owner said that the door locks stopped working one day, although the trunk never quit. heck, i disconnected the pump and took it out of the car, and my trunk locks are still working - that should say something...

Oh yeah, the electric solenoid in the trunk. Mine does not have that for some reason.

On the 3 wire plug into the pump, Brown is ground, and the blue or yellow get +12 v when the driver's lock is moved up or down.

The Electric Troubleshooting Manual of my FSM only shows the electric solenoid on MY 1985. I suppose it is possible that the MY 1984 w/ alarm came with it too.

On my 84 SD I found that the problem was the plug. The connecters inside of it got corroded due to water in the trunk and they no longer made contact with the power.

Check that out on yours.

I have a new problem where my pump again got flooded overnight and now when it's plugged into power it won't quit pumping. I walked out one morning and my locks were going open...closed....open....closed....

bummer....

haven't had time to take care of that. Won't be a very good move until I find the source of that leak and fix it.

And yes, the SD has the electric selenoid that locks the trunk.

I wish you good luck...I got a replacement pump from a member of this board. He sent me a PM when he read that mine was missing from the car. Maybe you will have the same response from someone else.

__________________
1998 W202 C230 - The money pit of late.
1984 W126 300SD (356,800 miles) Gone to the wrenchapart
1984 W123 300D Gone to the wrenchapart
1972 W108 280SE 3.5 (sold but not forgotten)
1986 Buick Grand National 3.8l Turbo (86k miles)
1966 Glassic Model 'A' Replica http://www.glassicannex.org

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I went out to my car with a Voltmeter just now and worked on testing that plug in the trunk that delivers power to the vac pump.

Here's what I found:

DRIVER DOOR LOCKED (knob down):

Voltage between blue and brown wire: 12.7 V
Voltage between blue and yellow wire: 0 V
Voltage between yellow and brown wire: 0 V

Resistance between blue and brown wire: 110 Ohm
Resistance between blue and yellow wire: open circuit (infinite)
Resistance between yellow and brown wire: open circuit (infinite)

DRIVER DOOR OPENED (knob up):

Voltage between blue and brown wire: 0 V
Voltage between blue and yellow wire: 0 V
Voltage between yellow and brown wire: 0 V

Resistance between blue and brown wire: open circuit (infinite)
Resistance between blue and yellow wire: open circuit (infinite)
Resistance between yellow and brown wire: open circuit (infinite)

So I guess here's a possible problem: thorsen just said in his post that both blue and yellow are supposed to be getting +12V with respect to brown (ground). Yellow isn't giving me any voltage with respect to brown at all. Also, yellow is always open-circuit with respect to blue and brown no matter what position the locks are in. That says to me that either the yellow wire has a bad connector lead that corroded, as Fuzzball was saying, or maybe it has a bad connection to the lock itself.

Are my conclusions correct?

I guess an easy test for the trunk connector problem is to skin/strip a small section of the yellow wire prior to the connector and test voltage and continuity there with respect to other wires. If results are the same, then i would have to trace where these connector wires go... And where do they go??

EDIT:

I did strip a small section of the yellow wire and measured it ahead of the connector - exact same results. This means the connector is fine but the problem must lie on the other end of where these wires are going... Where do these wires go exactly and how do I get there??

Sounds like it's time to take off the driver's door panel and check the door module switch. The door module switch is located near the back edge of the driver's door and connects to the lock/unlock knob. If I remember correctly, the connector on the door module looks very much like the one on the pump.

Check continuity of the blue and yellow wires from the door to the trunk.

On the switch, check the continuity from the black-red wire to the yellow and blue wires. I bet when you pull the knob you you have +12v at the blk/red and the blue wire, but when you push it down you have +12v at the blk/red and 0 at the yellow wire.

If so, your switch is bad.

I didn't buy any repair manuals for this car yet (ebay cd's?? bentley??), so I would really appreciate it if someone could help me with procedures for removing the driver door panel. I am especially afraid to damage the power seat adjustment switch. Where are the screws/tabs/fasteners located for the driver door panel and which tool(s) do i need?

Thanks in advance!!

Search for other threads on here, it's been discussd before. Take your time and go slowly.

For an on-line cd manual try here: http://mb.braingears.com/ Also, I believe I heard that MBCA sells the CD's for $20

Door panels on these MB's are a cinch. Start at the recess behind the inner door handle. Press in and you will see the tabs around the edge, that you will need to pry up to remove. Remove the screws behind it, the ones for the arm rest and then lift up on the panel. Takes about 5 min. less with an electric screwdriver.

(BTW, thanks jbaj007 for the heads-up. I wasn't aware the trunk lock operated like that. I wonder if this is specific to cars with factory alarm wiring?)

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )