I was looking for vacuum leaks, and came across this thing on the top, back of the injector pump. It leaks regularly on and off in spirts at idle (you can hear it hissing), but when the engine is up, it hisses, and drains the vacuum from the rest of the car. I unhooked the vacuum line from the top, and went around the block with the car...no problems.

Is this a necessary part of the car? Any known benefits to keeping it hooked up?

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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

its a vacuum device for the transmission..

That is your transmission shift control valve. It is necessary.It is linked to the Injection Pump and controls the vacuum signal to the transmission modulator for shift control.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=28E03YYRB28G0QVVFE&year=1982&make=MB&model=300-DT-001&category=D&part=Inj.+Pump+Vacuum+Valve

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Is the other side of it suppossed to be routed to the interior of the car for fresh air?

__________________
My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

the black line is the vent line.. its typical for the black vent lines to go to the interior

As mentioned above, it's the vacuum control valve for the automatic transmission.

The line on the side of the device is a vent line and is routed into the cabin to draw "fresh" air.

However, the line for the supply vacuum and the line to the transmission is missing from the valve. The top port is the supply/transmission line and without a connection at that port, the transmission has no vacuum control.

I'd presume that your shifts are all quite firm in such a condition.

It's purpose is to create a vacuum signal similar to that of a gasoline engine. Keep in mind that the same transmission used in this car is the same tranny used in the gasoline car. The diesel engine does not make vacuum so it uses a vacuum pump and this device is used to create a decreasing vacuum signal as the throttle is applied. Put a vacuum gauge on the line coming off of it and going to the transmission. With the engine running operate the throttle. The vacuum signal going to the transmission should be reduced (less vacuum) as the throttle is applied.

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Jim

Wow, I have been looking at the way my system is set up, and I am thinking that somebody really messed up my system before. The only two lines coming out of that are the breather, and the supply to the vacuum.

I have also been checking out some of the vacuum diagrams, I may be reading them wrong, but it looks like this thing is suppossed to be tied into the emissions equipment.

__________________
My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

It was reducing the vacuum on my whole system. So much so that it is closing the vents in my hvac system. The way it is done currently is two supplies (one on top, and one on the bottom) of the component pictured below (blue top). The one on top, on the side is routed to the transmission. There is another on the bottom (clear line), going to the second component pictured (mounted on the injector pump). Currently the transmission is supplied a steady 15-20 in/hg.

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__________________
My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

I did not pick up on the fact that it was an 85 (which is indicated by the round blue item you have attached a pic of). The round blue thing is supposed to smooth out the transmission shifting more than if you were just running the controller at the back of the IP.

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Jim