When troubleshooting your vacuum system you must know where the hoses and lines go
On many diesels the diagram was on a sticker mounted on the front core support of the engine as you see in this picture for a 1980 300SD. But these stickers do come off and you are stuck with finding the right information online or in a manual. These diagrams may or may not help. We also have a number of diagrams and vacuum troubleshooting information in Kent's manual.
Problem & Solution
Common among these chassis:
W116
W123
W126
Non Turbo Late 240D
Non Turbo 300D
1981 to 1984 617 Turbo Diesel