Chasing down those pesky leaks in central locking system

[nhdoc]

Well, after finding three badly leaking diaphragms on the door actuators and replacing all of 6 them, then finding that the master vacuum switch in the driver's door was also leaky and temporarily fixing it with some white-lube injected into it I then found that the vaccum reservoir had a nick in it which looks like it was done a while back by someone doing some body work possibly.

So, I used some JB weld like stuff over it and patched it up. Now, I can charge the system with my mightyvac and it loses less than 1" of HG per hour without the check valve in the system...with the check valve it loses all its "charge" in under an hour...so the check valve is also bad and is now on order ($10). That should do it.

The 1" per hour is probably attributable to the master switch which is still leaking a little I think. Still, it should hold vacuum overnight at that rate since it starts with 15" or so and the 1" per hour is measured at full charge which means it should bleed down more slowly as it drops off.

Does anyone know who (other than the MB dealer) sells those VDO master vacuum switches?

[MikeTangas]

I would hit the salvage yard, the master vacuum switches are fairly hardy and you should be able to get one for cheap.

[Tomguy]

Are you sure that's what's leaking? Try bypassing it - hook the vacuum source line directly to the lock or unlock line. It will tell you for certian whether or not it's the switch. You might have a cracked hose elsewhere - those plastic lines get brittle with age and can wealr through (especially at the spot where the driver's door opens and closes repeatedly). Just can help save a few $$ if yours is still good.

[MikeTangas]

Tomguy...you jarred a memory. I'm having a little difficulty adjusting to midnight shift after 10 years of mostly days so I get a little fuzzy.

How did you determine that the master valve was leaking? I thought mine was too at one time because of the sound it makes when actuating. Sort of a short sucking whoosh. Not really leaking but rather a controlled leak and the sound comes from the felt (filter) covered end.

As Tom suggested, check the flex points at the door jams, plus be sure to replace every connector at the vacuum diaphrams as well as any repair connectors along the vac lines. The system should hold vacuum over night without problem.

[nhdoc]

I had narrowed the leak to the valve by disconnecting the outlets at the valve and plugging the outlet ports, then I applied vacuum to the inlet and saw the gauge bleed off over a few minutes at each setting. The "unlock" setting bled faster than the lock setting fortunately so it should hold the car locked overnight.

The line to the inlet was fine as I checked that first by disconnecting it and plugging it. Then I removed the filter material from the vacuum switch and put some whitelube (lithium grease) in there which has fixed the seal for now but I don't know how long that will last. I think the sealing o-rings in the valve have just worn out from 33 years of use.