The color codes identify the different spring pressures on the modulators. The black modulator is for special applications (diesel with vacuum pump) and the others are weaker than the green.
So they activate at different pressures? And green requires the most except for black? Is the modulator simply a diaphragm that pushes the little rod when the pressure forces the diaphragm at a specific psi?
The vacuum pulls against a spring inside the modulator - The green stripe has the strongest spring other than the Black stripe. If you want it to shift softer and sooner you can change the length of the rod (maximum length is 1.625" for 70 and later C4s).
With a C4 I always use the green stripe modulator and a 1.625" pin. That is not just the best choice - its MY only choice.
So Paul, I know I asked you this earlier, but going the opposite direction (1.620 to 1.600). Would I see any benfit from making one at 1.650 over my stock 1.620, or am I just getting WAY too picky here? I already have the 8d nail to cut to whatever length you suggest. I also have the stock one at 1.620, so I can easily go up, down, or whatever at this point. At this time, with the stock rod, it is shifting PLENTY hard, just not at the rpm/mph points I want it to. Got new modulator yesterday, but then got inundated with work and broken computers, so I may not get a chance to install the new one until later this week.
If you shorten the rod then the C4 will shift sooner ans softer - not good for performance or transmission life. At low throttle you wouldn't notice much difference and at wide open throttle there wouldn't be a lot of change but at moderate throttle levels it would make the transmission feel like it was slipping or just a factory slush-box. Note: the modulator won't change the shift points at wide open throttle - the governor handles that. The stock governor in or Mavericks will shift at about 4800 rpm. No changes to the modulator will change that at wide open throttle.
Allright! Good description! I will stick with the 1.620 stock rod then. It seems to shift hard anyways, and doesn't need to be firmed up at all.
I heard about the visitor. Hope that works out for the both of you... If he calls me again, I may come and help out next weekend. I just put in the new vacuum modulator, and it is shifting just like it should. Took Anna for the first ride, since I think even before I put in the new motor. She was quite pleased I notice a little miss, so now that I have it actually running and safe to drive, I can start fine-tuning a couple of little minor demons I have (miss, dead reverse lights, etc.)
