I'm not sure whether this is old news, so I'll post in case it helps someone.


The vacuum control valve on my '87 190DT was clogged. After an attempt at fixing it, I was unable to get the cap back on without damage. So I tried a VCV from a 124 2.5. Mercedes recommends swapping the green (.7mm) restrictor out for a yellow (1.1mm) restrictor when making this change. But even with this additional mod, the VCV from the later car simply didn't pass as much vacuum as the original. This results in hard shifting at light loads. The vacuum orifice is in the plastic cap, and apparently the black caps have a smaller orifice than the blue caps. Correcting the system to operate on less vacuum seemed like a lot of blind experimenting...there may have been a change to the BUFO or the vacuum modulator, or even a valve body change in the transmission. So I hunted up a used VCV with the blue cap, and now everything is fine. So if you find yourself in need of a new VCV, make sure you find one with the correct cap.

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