C6 Shift Question
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C6 Shift Question
Hello
I have a 1973 ford f250 390 C6 transmission 3.54 rear gearing.
Have anybody ever encountered an issue with transmission shifting rough from a stop(first) through second. I get a rough pull. Its always from a stop, If so what was your remedy to fix. Also, any body know the difference between a dual diaphragm (DAD) and a single diaphragm on C6 transmissions-which is better.
I have a 1973 ford f250 390 C6 transmission 3.54 rear gearing.
Have anybody ever encountered an issue with transmission shifting rough from a stop(first) through second. I get a rough pull. Its always from a stop, If so what was your remedy to fix. Also, any body know the difference between a dual diaphragm (DAD) and a single diaphragm on C6 transmissions-which is better.
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
Are you sure your vacuum modulator is hooked up correctly and the vacuum lines are good? If you pull the vacuum line off the modulator does it have fluid come out of it?
Hotshot
Joined: Apr 2009
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From: Stanley, VA
The dual diaphragm version was an emissions related version, had to do with the EGR system and low speed. The single line is the preferred version. The modulators themselves are interchangeable. If you're swapping a single line version for the dual diaphragm model just connect the vacuum line that goes directly to intake manifold vacuum and cap the other line.
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I checked the routing and it looks good, line connects to the vacuum tree next to the carb. I also checked the modulator for any signs of trans fluid coming out, saw no sign. Rubber lines look good too, I will be replacing them anyway.
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New User
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The dual diaphragm version was an emissions related version, had to do with the EGR system and low speed. The single line is the preferred version. The modulators themselves are interchangeable. If you're swapping a single line version for the dual diaphragm model just connect the vacuum line that goes directly to intake manifold vacuum and cap the other line.
Hotshot
Joined: Apr 2009
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From: Stanley, VA
The modulators are identified by the color of the stripe on them. The "go to" version is one with a black stripe. There is a small screw, accessible through the nipple that the vacuum line connects to, that can be adjusted to fine tune the modulator.
Fleet Mechanic
Joined: Aug 2004
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From: Nevada
If your trans is original to your truck then the modulator should be screw in type I think, they cutoff was 73ish, they are relatively cheap. But first maybe turn the adjusting screw in the back of the modulator, left or out should be shorter shifts from 1-2, right or in should be longer shifts from 1-2...... Replacing the vacuum line would only be a few bucks and a few minutes of your time, also check the tree its connect to, some times caps are cracked and leaking air......
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