Ive checked the vacuum schematics but I cant seem to figure out where this tube goes! It was originally hooked up to a T fitting near the outer (fender) side of the brake booster. It looks to go around the brake booster and off to the passenger side fender. It holds NO vacuum. What gives? In the mean time I disconnected it and joined the remaining two pipes.

Attached Thumbnails

 

__________________

I don't know the SD so will have to guess. Might it lead to a vacuum reservoir in one of the fenders?

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

is there a vacuum reservoir in both fenders?.. are they necessary?

__________________

If there is/are, it/they should show in the diagram. The W123 diesels have a reservoir in the trunk while the W124 diesels have one in the right front (passenger) fender. Note that when I say "in the fender," I mean "in the fender." You cannot see the W124 reservoir until you pull the plastic fender liner from within the wheel well. Sorry I can't comment specifically on your SD but I've never worked on one.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970