TRANSMISSION WON'T UPSHIFT !
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More Turbo
Joined: Nov 2011
Posts: 508
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From: PNW
I should add that the vacuum pull seems weak at the modulator, and didn't change the idle when I unhooked it... Line looks good and has new rubber on the modulator end.. Confused
i ain't rite
Joined: Mar 2005
Posts: 65,507
Likes: 5,564
From: Marlboro Mental Hospital.
also check what controls vacuum signal. i never messed with an PSD /C6 combo so do not know if they use a VRV or not.
but i will second the check downshift linkage comment also. i had a 79 F350 4X4 given to me 20 years ago to use for parts because "the trans was blown"
he lent the truck out and it came back with a no upshift condition.
i loaded it on the trailer and brought it home. once here i took it for a ride to see what was wrong.
saw it would not shift out of first and pulled over, popped the hood, and smacked the kickdown after noticing it was stuck in pass position.
the person that borrowed it mashed the throttle and jammed the kickdown linkage in pass. once i got it unstuck it worked perfectly.
i have since put over 100,000 miles on that truck
but i will second the check downshift linkage comment also. i had a 79 F350 4X4 given to me 20 years ago to use for parts because "the trans was blown"
he lent the truck out and it came back with a no upshift condition.
i loaded it on the trailer and brought it home. once here i took it for a ride to see what was wrong.
saw it would not shift out of first and pulled over, popped the hood, and smacked the kickdown after noticing it was stuck in pass position.
the person that borrowed it mashed the throttle and jammed the kickdown linkage in pass. once i got it unstuck it worked perfectly.
i have since put over 100,000 miles on that truck
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,722
Likes: 2,648
From: SE Florida
A stuck governor is about the only thing left that can do this. It was always either the modulator or the governor. I always check the modulator first, both because it is much easier, and it causes many more problems than the governor.
Was the pin that the modulator pushes on inside the trans in place? I've seen the pin get lost and then it doesn't matter what the modulator does it won't make the trans shift.
Was the pin that the modulator pushes on inside the trans in place? I've seen the pin get lost and then it doesn't matter what the modulator does it won't make the trans shift.
i ain't rite
Joined: Mar 2005
Posts: 65,507
Likes: 5,564
From: Marlboro Mental Hospital.
because they did not trust the overdrive trans.
the C-6 was available as an option on all engines until 1997.
i ran across quite a few C6 trans trucks while i was buying at auction with all the different engines available.
the C-6 was available as an option on all engines until 1997.
i ran across quite a few C6 trans trucks while i was buying at auction with all the different engines available.
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More Turbo
Joined: Nov 2011
Posts: 508
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From: PNW
Problem solved
This takes us back to the keep it simple stupid philosophy... I should've checked the basics EXTENSIVELY first! But since the symptoms were far from familiar I started looking too deep too soon. It was the vacuum source from the start... Someone had messed with the vacuum connection when the modulator failed. Double check your vacuum with a GAUGE! 
. Thanks for all the input!
. Thanks for all the input!
Senior User
Joined: May 2010
Posts: 292
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From: Atlanta, GA
A VSS code will cause stuff like this to happen. IT won't throw a flash code but will make your PCM hate you until you clear it out or it clears itself out. Done enough 20-25 PSI boosted launches to know all about that code. Do my launch, plug in my creader, clear out all the codes in threw, turn the truck off, restart... Everything is as it was before.
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