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  #1  
Old 11-01-2000, 06:18 PM
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As reported earlier, mt '85 300D is showing sighns of vacuum problems. I purchased a MightyVac tester today. The pump is showing 23# at idle. Revving the engine effects little or no change.

Vacuum going into the shift module is around12# at idle and 15-16# revved.

Also, Pumping 20# of vacuum into the vacuum pump itself holds pretty steady. Seems to loose 1-2# after 5 minutes.

I removed the brake booster hose at the vac pump and could see the check valve. It looked kind of black and sooty (a technical term).

I've read posts by Benzmac that this valve can clog and fail.

Questions:

1. Can I remove this by just wrenching off that fitting on top of the pump?

2. Can I clean this and with what?

3. Does Parts Shop sell a check valve?

4. Am I kidding myself this is the problem or does it sound more like a vacuum pump?

Thanks in advance!

Mr. BILL

90 300SE
85 300D
84 300SD (sold)
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  #2  
Old 11-02-2000, 11:14 AM
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Any help? PLEASE!!
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  #3  
Old 11-02-2000, 02:50 PM
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Join Date: Oct 1999
Location: Culver City, CA, USA
Posts: 62
Mr. BILL,
Are you having a problem with the door Locks?
If so I have the same problem. I found the root cause of my problem to the the Heat/AC system. The green line going into the cabin has a steady leak when the system is off. Unfortunatlly I can not fix this as I have not found a vaccum diagram for the Heat/AC system.
Check your green line for vaccum leaks.
Mark.

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  #4  
Old 11-02-2000, 05:56 PM
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Bill,

One of the check valves is in the fitting where the line connects to the pump. I cleaned mine with denatured alcohol and compressed air. There are two other valves inside the pump body, if you go after these you might as well put in a rebuild kit.

Bob D.
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  #5  
Old 11-02-2000, 10:11 PM
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Thanks Bob,

Do I need to remove the valve from the pump to clean it? Can you give me more detailed information as the the process you followed?

Mr. BILL
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  #6  
Old 11-03-2000, 08:16 AM
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Sure Bill,
I removed the fitting with an appropriately sized wrench and plunked the valve into a small container of alcohol. I swirled it around for a few seconds and then removed it and blew it off with an air nozzle. I wiped it with a rag and put it to my lips first one way and then the other to verify proper operation. Finally, I reinstalled it on the pump connected the line and went on to look for my vacuum troubles else where as the system continued to perform intermittently.

Iíll be spending this weekend again with my new best friends a mighty vac and a hand full of golf tees
Bob D.
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  #7  
Old 11-03-2000, 09:14 AM
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Thanks Bob,

It sounds like you have a fair amount of experience with the old "MightyVac" tester.

Do the numbers in my origional post sound to you like the pump is the source since vacuum doesn't rise upon increased throttle?

Thanks,

Bill

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  #8  
Old 11-03-2000, 01:01 PM
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Bill,

The number from the pump sounds right to me. Check the circuit that runs to the egr control valves on top of the valve cover. I find it better if that bb that keeps "accidentally" falling into egr lines does so before the control valves, as these frequently leak. Also check the line that runs to the vacuum modulator . It should hold a good vacuum. The rubber cap on the modulator dries out and leaks. These are the easy ones. After that you can have many fun filled afternoons with the ac and heat system as well as the door locks.

Bob D.
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