If you don't know what the modulator is, I think you should let a tech make this adjustment.
The modulator is on the side of the bottom of the transmission. Located under the car. It is black, green, or red in color with a small black cap on the top. You have to take off the cap and turn in the key for firmer shifts. You must reinstall the cap correctly for the vacuum to operate.
1992 500E (very soon I hope
1981 280GE SWB
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