who's idea ws this
 

i have read quite a few threads concerning the switch-over valve mounted up there by the brake booster.
it seems that it is common practice to disconnect it,including mb shops.
what is the purpose and what is the reasoning behind this practice. and what is they trying to accomplish. i got my 300sd about 7 months ago. when giving her a once over soon after i found this valve bypassed. thanks to the help provided from you guys i was able to find out the way it is supposed to be. all i know is that the improvement in miles to the gallon was a welcome addition. just curious :confused:

Watch out
 

As I understand it acts as an emergency vacuum relief in 2 ways. First in prevents excess boost at high rpm (there should be 0 vacuum at WOT) and relieves boost in deceleration and thus prevents excess fuel consumption in deceleration.

flyboy,

It is strictly a safety device to blow off boost to the ALDA and prevent overfueling if the wastegate fails to do it's job and your boost gets too high. It is set ~ 1.1 bar? or such.

No vacuum function at all on your 1982 300SD.