I noticed that when I looked up the vacuum modulator for my van it read as follows "C-6 ADJ 10.5-13/EDA 1.71 ". What do these numbers mean? I know C-6 is my transmission and I am assuming that adj means that it is adjustable and I noticed that it has a screw type orifice inside which looks like you can adjust it with a small screwdriver. What does this adjustment do? How do you set it? What is EDA? The new modulator seems to be working, but I am just curious about this.

 

<!--StartFragment -->The vacuum modulator controls upshift, based on intake manifold vacuum when your foot is on the accelerator pedal. Ford calls this the primary throttle valve. This valve is adjustable, which determines upshift and downshift points.
<!--StartFragment -->By turning the adjusting screw (found in the vacuum nipple) counterclockwise, you will lower the spring pre-load. This will cause earlier shifts. By turning the adjusting screw clockwise and raising the spring pre-load, the shift points will go up. The range of adjustability is only a few mph either way.
Stock factory modulators are pre-set and most are sealed.
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