I have a brake booster line from a 1983 240D (apparently same as used in the W123 turbo diesels).

My question is with regard to the second nipple located toward the vacuum pump.
(check valve has 2 nipples)
Is that particular nipple always open or is it closed off? (mine appears closed)
I don't suspect that the check valve can open and close this second nipple.

Does anybody know the function of each nipple?
For example,the first on closest to the brake booster- does it draw vacuum or release..

Likewise the second nipple that I am originally referring to.

Excuse the question if it appears dumb.

Thanks

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

If you look at the base of each nipple oe is slightly larger than the other .

The smaller nipple is used to connect the VCV on the I.P. when fitted with automatic transmission .

Do make sure it's capped off if you're not using it .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Thanks Nate.

"The smaller nipple is used to connect the VCV on the I.P. when fitted with automatic transmission ."

So this lower port (closer to the vac pump) should be open to the check valve interior?
The nipple is shorn off but it is closed inside. Maybe plugged with a hollow plug.

update: I just saw an old performance parts catalog and the 1983 auto trans 240D seems to not utilize the second nipple closest to the vac pump.
But the vac line is basically the same 2 nipple type as the 1984/5 300D turbo

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

As long as it's closed you're good to go .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I think one nipple is on the vac pump side and the other is after the check valve. The check valve locks up vacuum when the engine is off so the door locks and such still work, though they have another check valve downstream, plus the reservoir in the trunk. You wouldn't want the VCV to source vacuum there since it always leaks (by design) so would leak it off. As I recall, the brake booster doesn't have a check valve at its fitting like you see in most U.S. cars, but that is just an open tube, so the check valve in question is mainly/solely to maintain vacuum at the brake booster for one or two more brake-assists after the engine turns off, such as if the engine dies while driving.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Hey Bill what you say makes sense about preserving brake vacuum temporarily but this particular brake booster line has both nipples after the check valve towards the vac pump direction.

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Posting a photo would help. In my 1984 300D, both nipples might appear to be on the same side of the check valve, but I think one has an internal port which routes to the other side.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Here is a picture

https://www.pelicanparts.com/More_Info/1234307429INT.htm?pn=123-430-74-29-INT&bt=Y&fs=0&SVSVSI=3204


edit: just found this thread by accident
here is a quote by 1983 300CD: "If you look closely at the check valve with the two fittings located on the valve they aren't just plain open tubes. There are numbers stamped into the plastic, 0.5 and 0.6. Those are restriction values. One fitting is even color coded with a white ring to signify they are different. A general drill-out repair will get the system closed again and often works fine but if you ever start to notice things like a change in shifting or engine shut down you could possibly adjust it out farther down in the system or you could add in Mercedes' little color coded plastic inline vacuum restrictors to make adjustments. This is just an observation for people who are still experiencing vacuum issues after a repair."



https://www.peachparts.com/shopforum/diesel-discussion/413088-w123-brake-booster-check-valve-replacement-unavailable-2.html

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD