A quick search of this forum brought up no information on the purpose of the vacuum reservoir in my 1987 300D Turbo (W124, OM603). The reservoir is located with the coolant overflow bottle in the right wheel well. [Yes, the overflow hose is disconnected. The picture was taken a couple of years ago when I opened up the wheel well to replace the hose, which was rotten.]





The vacuum diagram shows the reservoir is connected to the 'blue flying saucer' that, with the VCV, controls vacuum to the transmission. In the following diagram, the reservoir is #9 while the blue flying saucer is #123.





Unlike W123 cars, engine vacuum is not used for door locks. I can only imagine that the reservoir helps keep the transmission vacuum steady. Maybe the transmission modulator requires more vacuum for a second or two than the pump can supply. Anyone have a better guess?

Jeremy

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"Buster" in the '95

Our all-Diesel family
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