I haven't performed precisely that test, but the booster seems to be working (at least somewhat). With the engine off, I can pump the brakes, getting rid of all the vacuum in the booster, then start the engine. I can feel the booster kick in as the pedal sinks a fraction of an inch as the vacuum comes up.\
I know what a total lack of boost will probably feel like, and it's not like that. I don't have to put both feet on the pedal and push like hell to get it to stop. But on the 85 I can use toe effort to stop the car. The 77 requires foot effort. I wish I had a little scale I could put under my foot to get comparative numbers. Something is not right but it is not completely wrong. I really don't want it to go completely wrong when I'm driving it
It doesn't seem like a master cylinder problem since there is no sponginess and the pedal does not pump up.. It just seems as though I'm getting about half of the boost I'm getting on the 85.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13