C-6 shifting problem.
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Senior User
Joined: Dec 2002
Posts: 129
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From: Port Angeles WA
C-6 shifting problem.
I just got done replacing the head gaskets in a 76 F-250 with a 390 and a C-6 auto trans. The project went as smooth as possible except for one issue; the C-6 trans does not shift right now. I think this may have something to do with the fact that the trans shifts based on the vacuum pressure from my aftermarket carb. Before the head gasket change the distributor pointed in a different direction then it does now. The timing seems to be correct for the motor but now the truck shifts from 1st to 2nd and from 2nd to 3rd at a very high RPM no matter how much right foot is on the peddle. It also wants to shift all the way into 3rd at a very low speed (20-30mph), which it did not do before. Does anyone know how I can correct this issue? I think that this can be adjusted on the trans but I am not sure how?
Thread Starter
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Senior User
Joined: Dec 2002
Posts: 129
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From: Port Angeles WA
C-6 shifting problem.
So the little hose that comes off the trans modulator should run into the manifold somewhere? Can this connected where the break booster hose goes with an adapter? Also I have an Edlebrock 650cmf carb with the stock manifold does this make a difference its going into the little tube where the vac advance goes in on the other side of the carb right now.
Thanks,
Brad
Thanks,
Brad
Posting Guru
Joined: May 2003
Posts: 1,525
Likes: 3
C-6 shifting problem.
I would not hook up vac modulator directly to the brake booster hose. If the vac modulator fails it would put trans fluid into the booster and damage the diaphram. Surely you have a manifold vacumn source on the manifold somewhere. If you have a vacumn tree with the booster on top with other ports nearer the manifold that would be good.
Thread Starter
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Senior User
Joined: Dec 2002
Posts: 129
Likes: 0
From: Port Angeles WA
C-6 shifting problem.
Yes the break booster line right now goes dirrectally into the manifold so I guess I could place a tree into the line and run the break booster and the trans line from that. I am sure that I will have to recalibrate the trans modulator after I do this because it was never installed this way in the past. Does anyone know how the Ford C-6 trans modulator is adjusted? I understand that there should be a set screw that goes in and out depending on where you want it to shift but do I back this screw off to shift later or push the screw in to shift earlier?
Thanks,
Brad
Thanks,
Brad
Posting Guru
Joined: May 2003
Posts: 1,525
Likes: 3
C-6 shifting problem.
If you have an adjustable modulator, start with the adjustment screw just flush with the nipple. Screwing the screw in will make the shifts later, screwing it out will make the shifts earlier.
