Vacuum seal between master cylinder and booster missing or damaged,
shutoff valve line came loose.
Both issues are easy to fix.

__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

OK, so I checked the vacuum hose just before the booster with all vacuum accessories attached. Vacuum at the hose is 20" hg. Plugged the same line and tried to turn the key to shut off engine - engine shuts off fine. So - that leaves the seal b/t the m/c and the booster, or the booster itself. Is there any other diagnostic to descriminate b/t the two? Or should I just get a new booster? I assume any further testing will require the removal of both the m/c and the booster. Please verify. thanks in advance.

It is very simple.
Remove the nuts holding the master cylinder to booster.
Ease the master cylinder away from the booster.
Replace the vacuum seal between them.
Install the master cylinder to booster.
Install and tighten the nuts.

Test the system.

Yeah..I bet you find the Indy forgot to put that O-ring between the mastercylinder and the booster.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

OK, so I pulled the MC away from the booster. No sort of rubber ring to be found. A-Ha! You guys are the best. There are a couple of grooves on the M/C where it touches the front face of the booster, and then there's the cylinder itself that sticks into the booster. Which location does the o-ring go to? and, who knows what size ring I need? The haynes manual doesn't say, and the steaky site is down . I asked at Autozone, and of course their computer sez "we don't carry that seal..." If this is something I can buy @ a generic place that would be great, since this car is my daily driver. Thanks againg for all your help.

it fits over the protusion of the mastercylinder....measure that and you have the size you need from your hardware store. I don't have one I could measure right now.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Attached pictures.

Attached Thumbnails

   

Our 83 had no seal ring of any kind when we took off the M/C, but the brakes worked fine, and were VERY powerful. What does that mean?

We are putting one on when we reinstall it however...

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)