C6 vacuum system
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C6 vacuum system
I have a 1989 F250 with a 7.3 Diesel and a C6. The problem is the shift points are very high and rough. I am certain it is in the vacuum modulator system, but I think it may be the vacuum regulator on the injection pump. I only get 8 in of vacuum at the modulator valve at idle. The supply to the vacuum regulator is 20 in. Even with the regulator removed from the pump I only get a maximum of 9 in of vacuum on the output side. Should i be getting at least 18 or so at idle, or is this normal for the diesel application?
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C6 vacuum system
All manuals I have consulted do not mention anything specific to the diesel application. The Ford manual would be ideal, but that is one I do not have. Does anybody know how each stripe colour relates to internal spring tension of the modulator valve?
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Joined: Jan 2003
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From: Vincennes, IN
C6 vacuum system
I have an 89 F250 7.3L Diesel with a C6. Mine shifts at approx 2500 RPM. First to second is extremely rough. Second to third is firm but not annoyinly rough like first to second. I've tried everything to get it to shift at a lower RPM or atleast shift smother but I've come to the conclusion that this is just the way this old transmission performs. 
Does yours shift down from third to second when it falls below 35mph?
Does yours shift down from third to second when it falls below 35mph?
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