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Discussion Starter #1
Need to change my transmission modulation vavle. Auto parts store says they make a single diaphram and double diaphram. What's the difference and how do I tell which one I need? They said they are color coded but I caint tell what color mine used to be. I know I have a push in modulator not a screw in but other than that I'm not sure. :headscratch::headscratch:
 

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Discussion Starter #2
c-4 Modulator valve needle?

I went with the single diaphram valve just guessing from my earlier post. Put it in and it shifts funny. Think I make wrong decision but I think I may have lost a needle that goes in valve. Didn't know it had one. Neighbor came over when he heard me fussing said some cars have a needle in the valve? Said when I pulled the old one out I should have exchanged needle. Anyone heard of this?
 

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You didn't say, but I suppose this would be a C4 on your '66? They usually had the single diaphragm modulators.

The modulator controls a valve inside the C4 control body by pushing on a small steel rod that may, or may not have stayed inside the transmission when you swapped modulators. Without the rod the modulator does nothing except plug a hole to keep fluid from leaking out.
 

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Discussion Starter #4
figured out the green modulator is the best one for performance thanks to the Greek. Did lose the rod to start with but I figured it out.
 
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