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-   -   79 300sd vacuum line question (http://www.peachparts.com/shopforum/diesel-discussion/399661-79-300sd-vacuum-line-question.html)

jabbene 06-23-2019 02:46 PM

79 300sd vacuum line question
 
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.

Diesel911 06-23-2019 11:07 PM

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.

jabbene 06-24-2019 12:21 AM

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

Squiggle Dog 06-24-2019 10:13 AM

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.

Squiggle Dog 06-24-2019 10:24 AM

2 Attachment(s)
This is the line pushed into the black plastic clip on the transmission:
http://www.peachparts.com/shopforum/...1&d=1561386231

And this is the shift modulator to which it attaches:
http://www.peachparts.com/shopforum/...1&d=1561386237

Diesel911 06-24-2019 10:35 AM

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.

jabbene 06-24-2019 11:01 AM

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

tyl604 06-24-2019 05:25 PM

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


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