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Modulator Color - C4 Trans


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Presently I have a green band around my modulator for the c4 and it needs to be replaced.  Before I pull it, not sure if it is the correct one and/or if it has an adjustment screw.


I have researched a ton of information as to the colors and basically everyone is all over the place.



Can someone please breakdown the colors?


NPD also offers a modulator with no color band (D2AZ-7A377-A) and it has an adjustment screw.  Do the other colors have an adjustment screw?  Would a modulator with a screw be better than one without?




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The difference in color determines the preset shifting range base on engine manifold vacuum for vehicle and engine type. Also note that certain colors are either screw in or push in. Either color will work but the results in your shifting timing and hardness/softness will vary. If you go with a preset make sure you are getting the correct type such as screw in or push in. Brown, Purple and Green stripped vacuum modulators are for later year applications (72,73) and are of the push in variety. White is screw in (71). I would recommend getting an adjustable one. Note that some of the color modulators are adjustable. If there is a picture of it look at where the vacuum line goes and see if there is a slot in the end of the nipple. If so then it is adjustable. It will give you the opportunity to make adjustments to the shifting speed and smoothness. When higher amounts of engine vacuum act on the modulator, the transmission begins to shift earlier and softer. As engine loads increase vacuum diminishes, causing the transmission to shift later and more firmly. Engine hp and rear end ratio all come into play. Adjusting the modulator will help with getting the best shifting range for your car set up.

Turn clockwise to firm up and delay the up-shift of the transmission. Turn the adjustment screw in a counterclockwise direction to speed up and soften the up-shift. Do one turn at a time and test drive. Do not adjust the screw more than 3 turns in either direction.


The best overall speeds for the shifts on a C4 transmission are: Light acceleration ; 1-2 shift at 5-7 mph 2-3 shift at 10 - 15mph - Medium acceleration; 1-2 shift at 10-12 mph 2-3 shift 20-25 mph - Hard acceleration; 1-2 shift at 15-17 mph 2-3 shift at 28-30 mph - Full throttle extreme; 1-2 shift at 35-40 mph 2-3 shift at 60-75 mph.




"The only dumb question is the one not asked"

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Two basic types, screw in and push in. The adjustable unit gives you the ability to fine tune shift points. https://www.tciauto.com/ford-1966-72-c4-c6-adjustable-vacuum-modulator-screw-in-white-stripe.html is a good starting point. Chuck

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Thank you. I have a push-in type modulator and will be getting the adjustable one first and see how that goes.




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