My electric vacuum pump retrofit - PeachParts Mercedes-Benz Forum

wolf_walker · #1 04-04-2004, 03:25 PM

I think the w123 at some point was going to get an electric pump just like the S class used. It's just too much of a drop in for it to be coincidence.

Anyway, I now have an electric vac pump from an 86 SDL to run my door locks, fuel filler and trunk lock. It seems to work very well, holding the system at about 12 in inches of vacuum whenever it's kicked on. And it's kicked on every time a door is locked or unlocked. I did this by tapping into the 12v+ lead off my keyless entry module. Worked like a charm too. My drivers door has an electric lock solonoid, this in turns activates all the stock interlocking setup. I have a clicker for the alarm, remote starter and door locks. So whenever I lock/unlock the drivers door with either the clicker or manually, the pump runs till 12 inches of vacuum are achieved.

Here is the pump in testing. Notice it has two power connectors, and two vacuum lines. One of the vac lines doubles as vac and pressure, since the SD system uses both with a single line to the door locks. The other line is a pressure only that ran the orthopedic seats in the SDL(and may soon run some in my 300D).

wolf_walker · #2 04-04-2004, 03:29 PM

Here is the keyless entry/alarm/remote start setup. Visable also is my Kenwood satalite radio reciever and the Music Keg(140 cd's worth of music in that photo). Also notice on the far right, I'm wired for a second battery.

wolf_walker · #3 04-04-2004, 03:31 PM

One has to loop around the line feeding the power locks and the one going to the vacuum tank. This is fairly easy..

wolf_walker · #4 04-04-2004, 03:36 PM

Here is the little harness comeing down from the keyless entry module, where the pump triger lines come from, and from my terminal strip I have mounted back here. What that terminal strip is, is just where I ran a heavy hot wire from the battery to a terminal block back here to power stuff from. Makes it a lot cleaner than running wires to the battery.

Note the little indent in the floor is just right, and the piece of rubber hose serving to protect the bend in the harnes as it goes down in the spare tirel well. And yes, that is duct tape. This is all reasonably temporary, as I do feel the single hose system of the S class cars is superior than the slightly overcomplicated twin hose deal in the w123, and I intend to change over completly.
This will also give me the ability to operate the interlocking feature from the trunk or either front door, which is mildly interisting. Much less so when you have a clicker already.

wolf_walker · #5 04-04-2004, 03:38 PM

Complete harness.

Note my never been on the ground spare tire. The sidewall is like steel on this thing, and it's not from age. No wonder they only needed a 195 series tire.

wolf_walker · #6 04-04-2004, 03:40 PM

The one thing I really did to the car, was drill an access hole for the vacuum tube and put a rubber bushing in it. The outer part to the right was already very open, just had to go through the inner. And there may well have been a hole there, just covered in body sealer.

wolf_walker · #7 04-04-2004, 03:46 PM

Here is the pump, in it's foam shell, fitting like a glove next to the spare tire. You can see the vac line to it, which goes up to a check valve, it then goes to a Y splitter, one is the short piece of tubeing I added going into the vacuum tank, the other is the original piece of tubeing that goes to the front of the car to be looped into the door lock tube.

Another note on the reason for that check valve. It's also there because this pump is designed in such a way that it will pull vacuum on one cycle, and the next cycle HAS to be pressure. It will not do more than once vacuum cycle in a row. However it does auto cutoff at a given pressure and vacuum, so when it hits the check valve, it ceases to try and pressurize my locks system.
Seems to work fine this way. I could have changed this internaly I'm sure, but I really wanted to leave it stock again so that I can swap to the system that uses pressure at a later date.

wolf_walker · #8 04-04-2004, 03:48 PM

This is all on my 83 300D with 253K miles.

About all I'm missing now is power seats, and that's in the planning phase..

Zeitgeist · #9 04-04-2004, 05:58 PM

You've done an impressive bit of work there wolf_walker. I can't tell from your photo, but it appears as if the vacuum pump is quite similar to those used on VW/Audi and Volvo cars for their cruise control systems. These should be in plentiful supply at wrecking yards, if others would like to attempt your retrofit without resorting to using the much rarer MB pump. YMMV

#10 04-04-2004, 05:58 PM

Very cool setup. It's nice to always have functioning door locks.

I'm interested in maybe adding orthopedic seats in the future. It's nice to know that the pump is already compatible with the system.

wolf_walker · #11 04-04-2004, 06:19 PM

Zeitgeist, I'll look at the pump you mention and see if there the same or not. Good idea. I never would have bothered with this if it were not for getting the pump pretty cheap.

VeeDubTDI, This pump at least is compatable, it has a dedicated hose just for pressure. I could not swear about the rest, but I think one could make it work either way.

I have a leak from something I added(as there was no leak before), but even with an almost depleted system the pump alone opened the locks in no more than three seconds.
I'll get the leak worked out of it, it's aparently a very, very small and slow one.