'73 450SEL door lock system

I am looking for info on the vacuum system of door locking on my beast. Without getting too detailed, I'll say that when I lock the driver's door the others don't go down.
Any help would be very appreciated.

[420SEL]

Sounds like a leak somewhere. Do you have the shop manuals with the system diagrams? Maybe someone here with experience on your model can give you likely failure spots. I would check all the connections inside the driver's door to start with.

[cth350]

Rocky,

You'll have to start with a handy vacuum pump and the driver's side door panel removed. Each door has a double acting chamber to move the locks. One or more can be leaking. Also, each door has a vacuum switch, one or more can be leaking. Lastly, there are one or two unions in the system. One or more of which can be toast.

You REALLY want the factory shop manuals. They can be acquired on CD here at the parts shop or on paper (used) on ebay. The paper route is far more expensive, but many people like to hold the books in their hand rather than read them on a screen. Me? I have both.

-CTH

[jas2wa]

I am going to have my driver's door apart to renew the window regulator- while I am in there, I was thinking I should just r&r all of the vacuum lines and etc. I plan to go door to door, cleaning and lubing all the regulators and fixing the vacuum locks at the same time- does anyone have a handy list or pic of what vacuum pieces are in the doors? Perhaps getting a vacuum tester and only replacing faulty bits is a more cost effective way to do it...any suggestions?

I have a 108/109 factory manual, but cannot seem to find these vacuum diagrams and etc.

Thanks,

JAS

[psfred]

JAS:

The vac lock system is in the body manual, not the shop manual.

They are easy -- there is a yellow plastic line going from the intake manifold to the driver's door and to a plastic tank behind the left front wheel (behind the splash panel). This line provides vad to the whole system.

On the driver's door there is a vac switch operated off the lock. In the unlock position vac is supplied to the lock side of the servos in the other doors, the trunk lock, (but NOT the gas filler lock) via the yellow with green stripe vac line.

In the lock position, vac is supplied to the lock side of the servos via the yellow with red strip vac line.

To troubleshoot, you must have a vac source -- the best one is the MitiVac hand pump (sold under other names, too). First check that the line in the engine compartment is connected and intact -- if not, no locks.

Attach the vac pump to the yellow line and pump. You should get vac enventually -- you are evacuating the resevior, too, so it will take a while. If no vac accumulates, have a helper listen for hissing at the front left fender tank, the door boots where the lines go, and at the kick panels where the Ts are.

If you cannot locate the leak this way, take the driver's door panel off and try pumping down the two servo lines. If the locks work, the switch is bad, replace it. If they don't, or only one side (lock or unlock) works, you will have to dig around under the dash and find the rubber Ts in the lines. Disconnect and try individual sections -- the left rear door lines T on the driver's side, the right front at the passenger side kick panel, the rigth rear door at the base of the B pillar.

What usually happens is that the upper (lock) diaphram in the doors is gone, they are exposed and when the window seals get bad, the collect dust and dirt.

New diaphrams are available, $5 each, get them all. Trunk lock and gas filler lock (lock only) you will probably have to get the whole servo for, as they use different diaphrams.

The lines can break in the door boot, too -- Performance Analysis in TN has both lines and diaphrams.


Peter

[jas2wa]

Thanks Peter- I will be ready to tackle this chore soon, hopefully- your directions are very helpful-

-JAS

[zambo]

Great feedback here on this topic - I am new to the 108 (and MB's for that matter) family so am encountering the classic newbie problems as I go.

My central locking works when the motor is going and will lock all doors, but not open them again. I test this by being in the drivers seat, doors closed, motor running. I push the drivers door lock down and all up locking buttons obey! But when I raise the drivers door lock manually, the others do not move. Also, nothing locks as soon as the motor is switched off. I have a feeling there could be a few problems here, but would again appreciate any feedback offered.

Regards

Richard Zammit

[psfred]

Richard:

Start with the yellow plastic vac line in the engine compartment, next to the brake booster. There is a check valve in it (blue and black plastic), and if this is bad, you won't have any vac with the engine off.

Check the condition of the yellow line, the rubber connector on the intake manifold (way down in the rear center), and the T to the vac tank under the fender. You may get lucky and have just a bad connector and check valve.

Get a MitiVac hand pump, it will save countless hours.

Once you get the hand pump, attach to the yellow line and pump down by hand. If you never get any residual vac, you have a leak (as I suspect you do), and you will have to locate it. Check the vac tank (I don't remember where the T is at the moment), but if that isn't it, pull the door panel on the driver's door and check from there.

I suspect the vac switch on the driver's door is gone, they wear and start to leak vacuum. Replacement is easy (two screws). While in there, you can check the rest of the system by applying vac to the red striped line (lock -- this one works anyway, but does it hold vac indefinitely?) and the green strip line (unlock). If both hold vac, it's for sure the switch.

If not, you will have to find the leak by use of the MitiVac and repair it.

Peter

[zambo]

Thanks for the detailed reply Peter - can I ask one question though. I understand that the vacuum pump will do it's job regarding the valves in the door, etc, on whether it holds the vacuum, but I am wondering how I check the tee valve near the firewall and near the vac tank? Does the pump come into play there or am I listening for leaking air as such. (Hope I've got that description right).

Thanks again for that excellent reply.

Regards

Richard

[psfred]

Richard:

If it is a big leak, you will hear the air hissing in. If it is small, you have to test everything in smaller and smaller sections until you find it.

Usual leaks are the rubber connectors that are exposed to the sun and road dirt (those inside are usually fine) cracks in the plastic lines ditto -- they get brittle with exposure to UV and ozone. The diaphrams crack, usually the top one (the lock side) and the rubber fittings on the vac tank under the fender and shrink and leak.

The pump has a gauge, it's easy to tell if the vac is holding.

Peter