Hockeynut, I believe there is a controlled leak, or the orofice in the small plastic inline fitting sets the vacuum. I was advised to change my fitting from yellow to green, the size of the small opening is all that changes from one to the other. I can't tell you where the vacuum drops but I'll try to figure this out. All I know is the shift points up shifting are set by the valve and coming down I believe its the leak that determines the shifts. This is so simple its mysterious!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!