According to the vaccuum diagram for my 83 300 DT, the black line is a vent into the passenger compartment. Should it be connected to anything in the passenger compartment like a check valve or something? Mine is just hanging and it seems to be the cause of insuffiencient vacuum and a jumpy needle on the MityVac gauge. If I block the line off, the gauge rises to 20" hg, left openm it flutuates between 10 to 15" hg.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

There are vents which attach to nothing...you need to know where it originates from to know if it is correct or not though.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

It comes from the T which goes to the VCV on the IP and the 3/2 valve on the valve cover.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

That line goes nowhere. Nothing to worry about. The 85 model has 2 of them, one with a filter and one without and they both go to "nowhere".

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AJ

1985 300D (SOLD)

Are you saying you can not hold a vacuum without plugging that vent line? That probably indicates a defective valve in that circuit but I'm not sure which. Maybe someone else has an idea.

BTW, I put a filter at the open end of mine. I can't hurt and I thought it might help keep dust, etc. out of the vacuum system.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html

The 3/2 valves on the valve cover would be at the top of the list of probable suspects.

I disconnected the 2 lines to the 3/2 valve and eliminated 2 vac T's. I now have 20"hg at the vac pump and 16" hg at idle at the line going to the transmission modulator, it drops to 6" hg at WOT. Problem was big clunk noise when downshifting from 2nd to 1st gear coming to a stop. The clunk is much softer now but not totally eliminated. What do I have to adjust to get the vacuum to 10" hg at idle and 0" hg WOT? Is it something in the VCV or the transmission modulator? Thx!

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked