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Educate me on dual diaphragm vacuum modulators on C6 trans

70_Fastback

70_Fastback

Hell Bent for Speed
On the C6 I am about to swap into the rat rod I opted to replace the old gnarly vac modulater. This one is the non-adjustable type with 2 vacuum line connections instead of the normal one. Question is where does the second line connect to? Is one manifold vacuum and the other carb vacuum? Or can I swap that modulator with a single port adjustable type?

Any help would be appreciated. Thanks


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Your best bet would be to install a single port adjustable design modulator. It is supplied manifold vacuum and the shift points can be adjusted to some extent. They are available from Jegs, Summit, and other similar places and probably trans specialty stores also. You will need to know if your trans needs a modulator that is a push-in style or a threaded design mounting type before ordering. The push-in type will have a retainer & bolt holding it in.

The dual port modulators second smaller port was hooked into the EGR vacuum control system- I can't remember exactly how. They were designed and used to help control emissions.
 
This is a push-in style as well. What do the different band colors indicate? Different shif ranges? That is a question all of th parts stores ask as well.
 
The color code is used to identify the different calibrations of shift timing based on year, and type of vehicle. I believe the white or purple one should work fine in your application. Both were used on cars prior to 73 model year.
 
The double that I took off had, what appeared to be, a faint white line around it. So I will go back with white. Thanks!
 
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