Help me understand the vacuum system...

[WhoWhat]

So, if a vacuum is technically a place where air pressure is lower than atmospheric pressure, how does the vacuum system work on our MBs?

I'm trying to read up and get educated on how the system works, but I'm not catching on very quickly. At it's core, it seems the system is a series of tubes with air flowing through them. The tubes connect to different moving parts of the car, forcing them to move one way or another - i.e. the door lock thingy moves into the up (unlock) position because.....there is a tube leading to that thing with air pushing the thing up?

Or, the reason I started reading all this stuff was to investigate a really hard shift from 1st gear to 2nd gear. Many posts point to a possible vacuum leak.

But, I need to understand the basic premises of the system - help?

TIA,

[ImBroke]

There is a vac pump on the front of the motor. The vac generated goes to a bunch of places to do different things. The big line goes to the brake booster for "power" brakes. Smaller lines branch off of that for climate control, door locks, trans modulator, and shut off being the major ones. For shut off, when the key is on, the vac supply is blocked for the Injection Pump shut off. Turn the key off, and the blockage is removed, supplying vac to the shut off, and the car shuts off. Usually. For the door locks, a vac is supplied to the master lock switch. Lock the door, and a vac is supplied to the yellow with red stripe lines, pulling the lock actuators to the lock position. Unlock, and the vac is removed from the red, and applied to the yellow with green stripe, moving the acutators in the opposite direction. This vac is supplied from the reservoir in the trunk, since the car is off and won't generate a vac like this. Hope this gets you started.

[WhoWhat]

Originally Posted by ImBroke

There is a vac pump on the front of the motor. The vac generated goes to a bunch of places to do different things. The big line goes to the brake booster for "power" brakes. Smaller lines branch off of that for climate control, door locks, trans modulator, and shut off being the major ones. For shut off, when the key is on, the vac supply is blocked for the Injection Pump shut off. Turn the key off, and the blockage is removed, supplying vac to the shut off, and the car shuts off. Usually. For the door locks, a vac is supplied to the master lock switch. Lock the door, and a vac is supplied to the yellow with red stripe lines, pulling the lock actuators to the lock position. Unlock, and the vac is removed from the red, and applied to the yellow with green stripe, moving the acutators in the opposite direction. This vac is supplied from the reservoir in the trunk, since the car is off and won't generate a vac like this. Hope this gets you started.

Roger that - thanks. So, I've had one time over the past few months where my car would not shut off. The rest of the time, it shuts off perfectly. Could there be a small leak in that line going to the IP shut off? And how does the vacuum affect the shifting? What does the vacuum line look like? Always the same looking line? Same diameter or color or material?

[nickofoxford]

if you were to lock your doors for the night using the vacuum lock system, do they unlock with decent speed the next morning? if so then you are holding vacuum pressure and it would turn out to be the switch (usually on top of your engine) that regulates vacuum pressure to the tranny. hope this helps out.

-nick

[toomany MBZ]

Originally Posted by WhoWhat

Roger that - thanks. So, I've had one time over the past few months where my car would not shut off. The rest of the time, it shuts off perfectly. Could there be a small leak in that line going to the IP shut off? And how does the vacuum affect the shifting? What does the vacuum line look like? Always the same looking line? Same diameter or color or material?

Vac lines are hard plastic, and come in many different colors, so you know where they go. The transmission is shifted via vac pressure.
Yes, there could be a leak somewhere that gives you shut off problems, occasionally. Difficult to nail down, as there are many systems that interconnect.

[firemediceric]

I have read of many that have put a filter on their vac lines to keep oil out of the system and prevent problems.

Does anyone have a pic that can be posted showing what type of filter and where it should be located?

Not meaning to hi-jack the thread, but I figured this question was related.

[WhoWhat]

Originally Posted by nickofoxford

if you were to lock your doors for the night using the vacuum lock system, do they unlock with decent speed the next morning? if so then you are holding vacuum pressure and it would turn out to be the switch (usually on top of your engine) that regulates vacuum pressure to the tranny. hope this helps out.

-nick

It unlocks, albeit pretty slow. I guess it depends on what you mean by "decent speed." I'd say within three seconds, all the locks are up.

All the windows work, and move at what i deem to be appropriate speeds...even the sunroof works well.

I'm guessing the fluid and filter has not been changed on my car, since the PO handed it over to me with all kinds of issues. I'll change the fluid/filter when I replace the radiator in this (or next) weekend. I'll report back if I notice any difference in shift quality.

[compress ignite]

Bosch Fuel Filter (OEM VW) works great.[Inexpensive]

Probably pick a handful up at Advance,Autozone or NAPA.

The one you want protection from is the Vacuum Fuel Shutoff on the I.P.

[Palangi]

Those little filters in the vacuum lines are not for "protection". They just allow you to see if there is oil in the system.