Just took off the VCV from the IP for another look in good light at the workbench, looked for a removable cap as akimball442 mentioned above... None found... I then again removed the two screws holding the cover over the coiled flat spring and reconsidered the shaft carrying the 10mm nut with an 8mm jambnut against it.

I had thought that this served to only adjust tension on the spring, a preload of sorts. I then changed its setting with the engine running and a vacuum gauge attached. You're correct - the spring preload determines how much vacuum is dumped before additional valve movement is applied.

I've now set this VCV to begin additional dumping action at 10" vacuum; the transmission modulator now gets its correct baseline amount at idle speed. I reset the VCV's control rod for .5mm clearance at the stop pin.

It's too bad that understanding and knowledge appears usually only after a period of time wasted...

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Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951