C-6 tranny
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Junior User
Joined: Jun 1999
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C-6 tranny
I have a 78 F250 with a 351M and a C-6 tranny. Recently my automatic has become a manual, meaning I have to manually shift from 1st to 2nd but it will not shift up to 3rd, then I have to shift back down again. I'm not familiar with this problem hope someone can help.
Senior User
Joined: Jul 1999
Posts: 228
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From: Poynette Wisconsin
C-6 tranny
Look at the dipstick and check the fluid level. And check the vacume modulator lines, also look for any tranny fluid in the lines.
>I have a 78 F250 with a
>351M and a C-6 tranny.
>Recently my automatic has become a
>manual, meaning I have to manually
>shift from 1st to 2nd but
>it will not shift up to
>3rd, then I have to shift
>back down again. I'm not
>familiar with this problem hope someone
>can help.
>I have a 78 F250 with a
>351M and a C-6 tranny.
>Recently my automatic has become a
>manual, meaning I have to manually
>shift from 1st to 2nd but
>it will not shift up to
>3rd, then I have to shift
>back down again. I'm not
>familiar with this problem hope someone
>can help.
Thread Starter
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Junior User
Joined: Jun 1999
Posts: 50
Likes: 0
C-6 tranny
Thanks for the info. , Ben_e. My fluid level might be a little high. Would this have anything to do with it not shifting? I'm just a beginner at engine work but I also noticed that there is a rod from the tranny that appears to go to some linkage on the carb. that is off. Any help is appreciated.
Elder User
Joined: Jun 1999
Posts: 940
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From: LAT 46.55501° & LON -122
C-6 tranny
This linkage that goes to the carb is for your kickdown. When properly adjusted, it will downshift the transmission one gear depending on vehicle speed and gas pedal position. If the linkage is removed, the transmission will run and shift fine; however, it will not downshift above 25 MPH (approx.) when you "floor it". Just make sure that the kickdown lever on the transmission wants to stay in sprung-up position. If the internal spring for the lever is broken, or if something is always pushing the lever down, it could cause problems such as you are experiencing. (Note: this arm should have a travel of about 3/4in measured at the end.)
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
C-6 tranny
There is a vaccume line from ther rear of the transmission up to the rear of the engine on the intake manifold. Make sure that this is connected. A c6 will not will not shift with this disconnected.
John
John
New User
Joined: Jul 1999
Posts: 16
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C-6 tranny
Todd; the C-6 depends on engine load to shift the piston inside to redirect fluid to the servo. The only way to sense this load is by a vaccumm modulator. it is located at the rear of the tranny oil pan, with a 3/8" hose comming off going to the intake vac port tree.Check to see your getting vac down there, and that the diaphram is good (switch with another). The other problems could be on the fluid side of things. A low fluid flow problem could exist and thus not lock up the drum in Drive (3rd) that is why don't have high gear.Inside the pan is a filter everyone knows about. This could be plugged or restricting your flow. There is another strainer or screen farther up the fluid stream, you must remove the valve body to get to it. It is located on the other side of the body. If this sounds complicated for you I'd suggest looking for someone who has experiance with specifically C-6 workings. If you think you can do it contact me off list, and I'll explain and send pics/instruction.....power of the internet!!
Good luck.....Marvin
meyer@stratford.webgate.net
Good luck.....Marvin
meyer@stratford.webgate.net
Senior User
Joined: Jul 1999
Posts: 228
Likes: 0
From: Poynette Wisconsin
C-6 tranny
>My fluid level might be a little
>high. Would this have anything
>to do with it not shifting?
Not likely, did you check it when it was warmed up like after you have been driving awhile? If not check it again after you have driven it.
>I also noticed
>that there is a rod from
>the tranny that appears to go
>to some linkage on the carb.
>that is off.
You need to hook it back up. Did you check the vacume line going to the modulator. Follow it from the intake manifold down to the back of the tranny to see if it's diconected or if the line is bad.
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Fleet Mechanic
Joined: Jul 1999
Posts: 1,360
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From: Iowa
C-6 tranny
Mine will shift wothout the modulator hooked up, but the rpm's are really high when it does-something like 5500 rpm. It shifts HARD, too!
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Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
C-6 tranny
Jason, You're a big boy, but if the only way your transmission will shift, is to rev it up to 5500 rpms, IMHO you are testing your Ford by fire. Your shifts should come at about a third of that. The FE is past it's tourque curve at those rpms, and even though the engine will likely hold, you are shorting the life of it by doing that.
My statement sould have been, the transmission wont shift properly, with the vacumn disconnected from the modulator.
Get that fixed and Good Ford trucking to You,
John
My statement sould have been, the transmission wont shift properly, with the vacumn disconnected from the modulator.
Get that fixed and Good Ford trucking to You,
John
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
C-6 tranny
Jason, 5500 is kinda high for shifting. The FE is way past it's tourque curve. It should be shifting at about 1/3 of those rpms. You are making that old iron live hard if you are turning it often like that.The vacume is aiding in the shifting, and should be connected.
John
John
