function have not answered my question regarding the line going from the vacuum control valve(IF i've even got that straight in my mind) to my modulator valve. On my '81 300SD, the line is connected to the 'Y" that comes from the main line from the pump to the brake booster. That 'Y' is also connected thru what I thought was a one-way valve(but I think I read was something to smooth out the pulses in the available vacuum ? ) to the top most port on the control valve.

I would appreciate if someone would identify the top and lower ports on what I have called(in my ignorance) the "vacuum control valve".

The line going out the top right goes to the modulator. The line going out the bottom right comes from the line connecting the pump to the booster. The bolt is plugging up where the line to the box on the valve cover was connected.

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__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

You've got it basically correct.

The top port is the supply vacuum to the vacuum control valve. The valve bleeds off vacuum from the supply resulting in lower vacuum to the transmission. Of course, this only works if there is a restriction upstream of the valve.

The lower port is the vent line. In order to "bleed vacuum", you must add air. So, this line heads into the cabin to provide air for the VCV. In theory, it's preferable to provide clean air from the cabin rather than smelly diesel exhaust from under the hood.

it does not hold vacuum with the mighty vac. I also connected the gauge to the 'Y' where the modulator plugs in and read approx 12" - 13" at idle and 20" - 21" when the rpm's came up. Thought I read somewhere that should be about 17" ?

Could that pulse damper be defective(blocked)?

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car