Originally Posted by dennislarock

Headed out to install new modulator and pressure test/adjust.

Here's a little diddy on the *Blue Flying Saucer* of the '85 (and why I like it) should I go that route....

The vacuum modulator with high vacuum softens the shifts at a low throttle response and a modulator with lower vacuum firms up the shifts with more throttle. This is predicated only on throttle position and no other variables.

On the 1985 models, Mercedes engineered a transmission vacuum system that didn’t just rely on throttle position to control the softness or firmness of shifting. It also relies on turbo boost pressure which becomes dependent on engine load and temperature.

The vacuum transducer/amplifier (blue flying saucer) works in relation to turbo boost pressure and engine temperature. Unlike the prior years, the system now starts off at a high vacuum of 12-17 Hg to the modulator. It now leaks down five inches when full throttle travel is given. When the turbo boost pressure goes up, the boost applies an input to the vacuum transducer. This produces an upward deflection of the transducer diaphragm, lowering the amount of full vacuum applied to the modulator valve to zero. The hydraulic modulating pressure in the transmission is increased which firms up the shifting.