I have searched and followed many suggestions. I have a 1981 300SD.

Very harsh shift and down shift. I have adjusted the vacum modulator all the way in and all the way out to no avail, never once did the tranny flair. I have adjusted the transmission vacum at the IP pump to no avail. Plugged up the vac. line going into the car for ignition shut off, hvac system and doors. No difference. Plugged the line going to the valve cover vac lines to no avail.

I read that not enough vacum will cause hard down shifts. Is the vacum modulator on the transmission the culprit? Yes I changed the hard vacum line and the rubber hose to the control modulator to make sure I didnt have a leak.

I do not have a vac gauge. Sorry.

Thanks for your help.