My question in concerning a vacuum line that I cannot figure where it should connect. There is a Y that comes out of the top of the VCV. One connection couples with another Y. The other is a black line that goes left behind the valve cover and is just hanging loose under the engine compartment.

The transmission is also shifting rough and I was hoping this was related to this disconnected vacuum line.

I have looked at many diagrams and cannot figure it out. FYI this is not the vent line that goes under the dash. I am fairly certain this line should connect somewhere.

If anyone could help I would really appreciate it with any pictures of where this should connect. Thank you.

On my year of W123 the Black line is not supposed to be connected to anything. It is a vent line that is supposed to go to the inside of the car but it remains open.

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84 300D, 82 Volvo 244Gl Diesel

There is a black line that comes out of the SIDE of the VCV and enters the dash on the driver side. From what I have researched, without removing the dash board, this is the vacuum vent line.

I am asking about the black line coming from the TOP of the VCV and I suspect connects to the transmission somehow

That line should go down and connect to the shift modulator on the right side of the transmission. Also, this black vacuum line should snap into a black plastic clip which is located on the top of the transmission, just behind the bellhousing, and on the left side.

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DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles

This is the line pushed into the black plastic clip on the transmission:


And this is the shift modulator to which it attaches:

Attached Thumbnails

   

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Stop paying for animal enslavement, cruelty, and slaughter. Save your health and the planet. Go vegan! I did 18 years ago. https://challenge22.com/

DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles

Concerning the transmission module when I accidently disconnected that line there was only a tiny extra harshness on up shifts but it was the down shifts that were extremely hard. Again I have a different year, model and Transmission.

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84 300D, 82 Volvo 244Gl Diesel

Thank you Squig and 911 for your help. Real clean engine there Squig. I'll get there someday.

I'm gonna reconnect that line and hopefully I see a big difference

Diesel911 - you are exactly right - vac only needed for downshifts.