I have a C-4 along with a 1999 Ford Motorsport 302 in my 55 F-100, and it shifts to fast. The C-4 is new from ATI. The rear is the original Dana 44 with 32 gears. I have had the governor cleaned, adjusted the vacuum modulator, and checked intake vacuum, but it stills shifts to fast. It shifts fine manually. When I adjusted the modulator it seemed to help a little bit. Can anyone tell my what's causing this, or what to check next? THANKS

 

I just went through the same thing with my c6. I had the vaccume modulator connected to the manifold vac. port on my Demon carb and couldnt get it to shift right, either too fast or no shift at all. Finally I changed to a direct manifold vac. port (not on the carb) and It shifts great! Easy enough to try and see if it works for you.

Good luck
Nathan

 

Thanks Nathan, but I already have the vacuum modulator hooked to direct vac. port on the intake. Any other ideas? THANKS

 

Try using any different manifold vaccume port that may be available. I never thought it would make a difference, but it sure did.

Nathan

 

they do make anadjustable modulator all you would have to do is mess with it until you get the shifting you want it isn't hard there is a little straight blade screw head inside where the vaccum hose coneects in would be shift later and out would be shift sooner if you can see inside the modulator you might have an adjustablealready if the screw head is in there

 

AZ4,
My C-4 came with an adjustable vac. modulator. I have it screwed almost all the way out. Hardly any change in shifting when it's all the way in or out. What next?

 

If you aren't seeing any change with the adjustment, the Mod. valve may be bad.
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John

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did u screw the modulator IN or OUT? u should screw it in to increase pressure on the shift valve so that it takes more line pressure to overcome it (thus a longer shift). if this does not help u may need a longer rod behind the modulator. some trans builders sell these or you could fab one yourself.

Chris Seay
Bealeton VA

 

You might want to pull the modulator valve out and check to be sure that the pin that goes behind it is in place. If it is missing, the adjustment will have little effect.