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  #1  
Old 12-10-2001, 09:44 PM
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Diagnosing Vacuum Problems FAQ

Since all of our 1980's diesels (specifically the W123) rely heavily on the vacuum system, why don't we put together a FAQ on a step by step way to find the problem?

I have a digital camera. I'm having a vacuum problem and I hate to spend $$ at my indie mechanic if I don't have to.

I'm sure if we put our heads together, we can come up with a great FAQ.

Craig

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  #2  
Old 12-10-2001, 09:59 PM
drivesme
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Great idea!

I have a million of them!!!
Can you buy the lines buy the foot or do they come
all ready cut? What are the size's to ask for?
Does it have to be the hard lines or can you use something else?
And most of all Where do you start???!!!
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  #3  
Old 12-10-2001, 10:46 PM
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I'll answer a few:

1) The lines I replaced today were connections between hard plastic tubing and a switch or some other device. I got the rubber connections with a 90 degree bend in them, from the dealer at $20 for 8.

2) I think you can but the rubber lines by the foot, but the most common problems occur at rubber connections or at a diaphragm. There are very few straight rubber lines in the car.

Craig

Please correct me if I'm wrong. But the question we all really want to know is:

Where do we start? I bought a Sears version of a Mighty Vac. I stand next to the car with vac. tester in hand, and I don't know what to do.
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  #4  
Old 12-10-2001, 11:03 PM
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I couldn't accomplish anything on my vacuum issues without the MityVac. This piece of test gear gives you two things, a measuring instrument (vaccum gauge) and a vacuum source.

Troubleshooting most systems is a matter of "divide and conquer". This lets you eliminate things quickly that are not a problem. The worst thing you can do is try to test every single component individually.

Secondly, you need to know how the system works in theory so you can find what's wrong. I could have hooked gauges up to my transmission vacuum modulator all day long and not been able to figure out what I should see without a lot of help from this forum. (Part of my problem was incorrectly hooked up lines.)

Different problems are going to require different FAQ starting points and diagnosis paths. However, there are a few very basic things you can check with MityVac right away that will tell you if you have major problems.

Basically, they are:
1) Are you getting a vacuum from the vacuum pump? (Fix or Repair)
2) Do you have a leak? (Find it)

The rest gets into a lot of details that you can find here by using the search function on your particular problem.

Ken300D
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Old 12-11-2001, 12:31 AM
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Thanks Ken300D-


1) I assume that if there wasn't any vacuum at all, the car wouldn't run (engine would), or if it did, very poorly.

2) Being that something doesn't work, like the door locks, we can assume we have a leak.

So my questions are:

1) How to find the offending part.

2) Where do we start to look? Example: Where do I test the locking fuel filler door?

You said to test each component. My problem is, I don't know where to look, and a step by step, linear way of going about it would save a lot of time.

I just finished changing 8 'L' rubber hoses on the drivers side of the engine compartment. I also looked under the passenger seat and saw a loose blue vacuum hose. When I looked under the drivers seat to get an idea where it might go, I found one loose there also.

My indie mechanic told me that there are 5 places (junctions) to test to diagnose a vacuum leak. Unfortunately, I didn't get the locations.

I'm sure I could search the entire forum for the answers, and find them. I only thought that a central location would be a good idea.

Larry Bible helped me the other week when I posted a question about my trans not shifting. He told me to look on top of the valve cover at the vacuum junction. Unfortunately, I have a 1985 California version and I don't have that junction. I thought it was a vacuum leak. After an evening of searching the forum, I think I found the answer, and it wasn't a vacuum leak. I think it's a sticky kickdown switch. I ordered one from Randy at EPS today. He said he rarely gets requests for these, but thanks to this forum, I found the answer.

This forum is fantastic. Any answer can be found, and it has saved me thousands of $$.

Just as there is a proceedure for changing a door check on a 124, or removing the radio on the same model, I think a vacuum testing proceedure would be very helpful.


Thanks everyone for your help. I'm not sure I'd own a Benz without this forum.

Craig
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1972 & 1974 BMW 2002tii's.
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  #6  
Old 12-11-2001, 12:49 AM
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Craig.

Several months ago, my door locks were not operating properly and Icesailor helped me out by posting a step-by-step process of elimination to determine where the leak was. My question was regarding my air-conditioner of all things, but because of his post, my door locks work just fine now. The beauty of this method is that you don't even need a vacuum gauge. The other thing is that once you try it this way it helps you understand how to isolate other areas of concern in the vacuum system. Anyway, here's the link: 82 300TD A/C problem
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  #7  
Old 12-11-2001, 01:10 AM
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Dave-

Thanks for that thread. I saved it.

Vacuum leaks REALLY make me nuts. I had a 1985 300CD for a year and learnd a lot. I missed it so much I bought another on Saturday. I feel comfortable tackling almost any problem, except for vacuum problems.

I am urgently trying to fix the problem because 1) my AC/heat isn't working properly, 2) transmission is shifting harshly.

I don't know if these can be related to a vacuum leak. I do know that the transmission does have a vacuum connection and the flow of air through the AC system is controlled by doors activated by vacuum.

I'll find the answer, thanks to everyone, I just want to find it before I cause more stress to my tranny than I need to.

Craig
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1972 & 1974 BMW 2002tii's.
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  #8  
Old 12-11-2001, 01:45 AM
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What happens if my locks don't lock or unlock?

Craig

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