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  #1  
Old 10-02-2009, 03:11 PM
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Rebuilding Vacuum Control Valve

Has anyone tried doing this? I've been troubleshooting the vacuum system on my '81 240D and have found the VCV to be broken. No vacuum whatsoever travels through it.

I did some research, with the only solution being replacement. But has anyone attempted rebuilding it? Anyone have one laying around they're willing to sell?

thanks everyone
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  #2  
Old 10-29-2009, 04:48 PM
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In an attempt to recycle a thread, I was wondering if someone could help me with the VCV on my 240D.

I got a VCV from a member here but I'm a little stumped. The vacuum diagrams i've looked at don't show how the lines are connected to it. The line running from the main vacuum pump line goes directly into the side of the VCV. Then the line that runs to the top of the valve cover comes out from the top of the VCV and through the green dashpot.

I attached an image to clarify things.

My questions arise with the following. I understand how the VCV is supposed to work. It leaks vacuum at a controlled rate depending on throttle position. But when i test for vacuum, it only holds vacuum from the TOP of the vcv, not from the side, where the vacuum originates.

If someone could clarify the proper setup of the VCV or even just a picture of a 240D engine bay around the VCV area would be great help!

Thanks guys!
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Rebuilding Vacuum Control Valve-img00208.jpg  
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  #3  
Old 10-29-2009, 05:45 PM
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Quote:
Originally Posted by qpoiz View Post
My questions arise with the following. I understand how the VCV is supposed to work. It leaks vacuum at a controlled rate depending on throttle position. But when i test for vacuum, it only holds vacuum from the TOP of the vcv, not from the side, where the vacuum originates.
Your understanding of how it operates is flawed.

The vacuum source is on the top of the valve. The side of the valve is atmosphere............leads into the cabin as a vent line.

When the valve operates, it draws air from the cabin through the side port, through the valve, and into the line at the top. The line at the top is teed into the transmission line so that the entire line downstream of the orifice will lose vacuum when the VCV opens.

The VCV should hold about 13" vacuum when you use a Mityvac connected to the top port. As you open the rack, this vacuum level will gradually drop toward zero depending on the amount of the opening.
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Old 10-29-2009, 06:07 PM
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There isn't much inside to rebuild. There is an o-ring inside that you can replace. But other than that I don't think rebuilding it is going to really be possible.
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  #5  
Old 10-29-2009, 06:15 PM
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There should not be any vacuum on the side of the VCV. You should have a tee above your dashpot. One is connected to your vacuum source and the other to the vacuum modulator of your transmission.
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Old 10-29-2009, 06:48 PM
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Awesome! Thank you everyone! The VCV makes more sense now.

Things look a lot clearer now, but now I have the round alarm bell-shaped device to the left of the VCV without a line. PO had the T'd line Brian Carlton mentioned plugged to this. From what i see on the vacuum diagram, it just looks like a vent of some sort. Any advice?

thanks again everyone
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  #7  
Old 10-29-2009, 10:08 PM
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Quote:
Originally Posted by qpoiz View Post
If someone could clarify the proper setup of the VCV or even just a picture of a 240D engine bay around the VCV area would be great help!

Thanks guys!
Here are some pics of my 82 240D it does have EGR, so it may have more lines than yours . . .






Edit to add:I just noticed after I posted those pics that there was some blue denim showing in pic #2! So I went out to look, and sure enough I had left that scrap of cloth/rag in between the IP & block, when I was doing my glowplugs about a month ago! (I just took the pics tonight!)
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Last edited by Shawn T. W.; 10-30-2009 at 09:55 AM. Reason: Just noticed something! Duh!
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  #8  
Old 10-29-2009, 10:41 PM
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Originally Posted by qpoiz View Post
Awesome! but now I have the round alarm bell-shaped device to the left of the VCV without a line.
..........properly configured..........that device gets no vacuum attached to it.
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  #9  
Old 10-30-2009, 12:08 AM
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Thanks for the pics! That's how I set it up before I left work. Drove like a charm on my way home.
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