what does this do? - PeachParts Mercedes-Benz Forum

angst · #1 03-10-2002, 07:12 PM

What does these valve looking things do? This looks like a one way valve of some sort. It is on my vacuum lines near the fuse box (79 300sd)
The vacuum lines seem kind of oily inside and the connection keeps popping off. The engine will not turn off if this disconnected.

mikemover · #2 03-10-2002, 07:39 PM

I think they are some sort of check valve, but I'm not sure exactly what they do...mine has them too. Maybe they regulate the amount of vacuum going to a particular component?...Just a guess.

If there's oil in your vacuum lines, you probably have a failing vacuum pump diagphram, better get it checked, it will eventually ruin your entire vacuum system...Oil eats the rubber vacuum lines!

Mike

tcane · #3 03-10-2002, 07:56 PM

They are one-way check valves that also regulate the amount of vacuum that goes to a particular system (climate control, door locks, etc.).

Mikemover is right on with the analysis that your vacuum pump is failing and allowing oil into the vacuum system. You need to fix this as soon as is practicable.

Good Luck!
Tom

angst · #4 03-10-2002, 11:30 PM

Yikes
I didn't expect such dark forboding! Your replies sent me to my Haynes book which only has about two paragraphs worth on the subject of Vacuum pumps. It said that a fault in the pump will manefest itself in the locks and the brakes. Both of which I am experiencing. The locks are kind or quirky. Also, sometimes when I first start the car the brakes are real hard for a couple minutes, like as if they were manual.
There are a couple other threads going right now on the subject of vacuum pumps that give me the impression that a failing pump will destroy the engine.
My haynes manual does not go into detail on how to replace other than saying you have to remove the radiator and drivebelts.
So, someone please give me an idea of what this could cost me in time and in money? Also is driving it risky untill I replace this part?
thanks
Eric Z
angst at usa dot com

Ducati · #5 03-11-2002, 02:10 AM

I am not sure that a failing vacuum pump will harm an engine -Or Will It?
I have glitchy door locks. My climate controls are starting to act up, as they work only on Defrost now, which I understand is the default for the system. However, the brakes work very well, still. I find this vacuum system to be the most perplexing thing about Mercedes, because it is new to me. What methods and procedures are available to troubleshoot and diagnose problems in the vacuum system? What tools are needed? How does one use a Vacuum Tester? How do I repair my door locks? What is happening to my Environmental Controls?
There! Lotsa Questions.

mikemover · #6 03-11-2002, 10:27 AM

Won't ruin the engine itself, but it will eventually ruin the vacuum system. The oil will ruin the vacuum lines, diaphragms in the climate conrols/door locks/etc. If you have total vacuum pump failure, you will have no power assist on the brakes, climate control will not work, transmission will not shift properly, engine will not shut off without pushing the "stop" lever under the hood, locks will not work...many many issues!

If you're that unfamiliar with the vacuum system, I'd advise taking it to someone experienced. Let them diagnose and repair it, and hopefully you can look over their shoulder and learn a few things about it in the process.

Mike

wheelguru · #7 03-11-2002, 11:50 AM

Last week I lost the vacuum in my car (78 123) no door locks, no heat (at least the defrost keeps it warm), no engine shutoff. I was just going to wait till it got warmer to mess with it, but now I am worried about oil getting in everything. How much longer should I put it off? can I just disconnect the vacuum line from the pump? I assume that I can just get a new diaphragm and put it in the pump, is that all there is to it? thanks, Andy

Nate Stanley · #8 03-11-2002, 12:33 PM

Not trying to scare you, but there is a VERY remote possibility that the vacuum pump can shred the engine, but it has nothing to do with the seals and 1-way valves that you will replace when you rebuild the pump.

Once you get the pump off (get a long allen t-handle to do this), inside you will find a roller bearing that rides on a wavy-shaped cam in the front of the engine. This provides the reciprocating motion to drive the pump diaphragm.

If that bearing goes out, it could drop balls or bearing cage parts into the path of the timing chain, and I'll leave the rest to your imagination.

It's unlikely that this will happen since the bearing is smothered in oil at all times, but be SURE to check it for free rotation and no play before you button it up. And don't blow it dry and spin it with compressed air, either.

Otherwise, it's a pretty straightforward R & R--Let us know how it turns out!
Nate
'79 300D
'84 300D Turbo (pix to follow soon)
'85 F-250 6.9 Diesel
'96 Ford Crown Vic

MikeTangas · #9 03-11-2002, 01:20 PM

Also a bad bellows in the shut down solenoid will introduce oil into the vacuum system.

mikemover · #10 03-11-2002, 01:23 PM

wheelguru,

If you disconnect the vacuum line from the pump, you will have no power brakes, the tranny will not shift properly, and you will have to shut the engine off with the "stop" lever. The vacuum pump is an item you need to deal with right away...The longer you drive the car with vacuum pump problems, the more likely you are to cause other problems and cost yourself MORE money!

Mike

wheelguru · #11 03-11-2002, 06:19 PM

I got 2 1/2 of them already - brakes only a little stiff. I will get a new diapraghm and rebuild this weekend. It is supposed to be warm this week, so I can ride my bike till the weekend. thanks all, Andy

tcane · #12 03-11-2002, 06:42 PM

There are two different types of vacuum pumps:
Diaphragm type in the 300D & CD to engine #12-108987 and 300TD to engine #12-108474
rebuild kit costs about $35;

Piston type in the 300D & CD from engine #12-108987 and 300TD from engine # 12-108474
rebuild kit costs about $55

Either pump can be R&R'd without removing the radiator if you have the right tools and if you can wiggle your way to access the fasteners (19mm nuts on the vacuum lines and 5mm allen head screws on the pump housing). Removing the radiator does make it lots easier to remove the pump though.

Nate is right about the bearing causing major damage, but as he said kind of remote. Check it anyway.

Ducati:

You're asking for a small book worth of info. I suggest you get the M-B shop manauls (on eBay for either the CD or print version) and the Mity Vac tool (to check for vacuum leaks, bleed brakes, pull fluid from hard to reach places, check the engine mechanical condition, and other tests - a very useful tool that costs about $30 for the least expensive version). The vacuum lock diaphragms can be rebuilt for the door locks, trunk, and fuel door.

Good Luck!
Tom

Ducati · #13 03-11-2002, 08:37 PM

Thanks for the advice. MikeMover. Im a little bit more worried now.
So, I will have to buy the tool and the manual. The manual should show me where to connect the vacuum tester, I suppose.
Having never worked with vacuum systems on any other car I have ever had, I am facing a steep learning curve.

My brakes work great so far. The door locks and environmental controls are the only signs that I have impending problems.
I suppose that I have no choice but to get the tester and the manual, or are there other tests and fixes that I can perform in the interim?

angst · #14 03-11-2002, 10:07 PM

I pulled the offending connection apart tonight and put silicone on all potentially loose tubes. There was certanly a small amount of oil in it. It does seem to be a one way valve. It was keeping the oil from getting past and I could blow the oil out.
Here is a picture of the pump. Maybee someone can tell me why the top half would be painted white? Would this be done to indicate a rebuild? Is the one missing screw a potential source of the oil leak? Is the small amount of oil coming from the seals an indication that the part is shagged out?

Ducati · #15 03-11-2002, 10:27 PM

It's too chilly to go outside and look under my hood, but this thing must be the vacuum pump. Where is it located? Can it be rebuilt?