C6 shifting issues
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Junior User
Joined: Sep 2009
Posts: 54
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From: Salem OR
C6 shifting issues
hoping someone here can point me in the right direction. I have a 78 Ford F250 4wd with a 460 and a C6 transmission. I just puchased the vehicle. Currently when starting out from a dead stop it takes off ad shifts from 1st to 2nd very fast. It will be in 2nd for the right amount of time and shift smoothly into 3rd. If I manually shift it will stay in 2st until I shift. Fluid level is good. This makes take off real sluggish. I plan on changing the fluid and filter this weekend.
Thanks all
Thanks all
Post Fiend
Joined: Jan 2005
Posts: 8,402
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I`m with 85e, you probably have a vacuum problem. Pull the pipe off at the trans and check for signs of trans fluid, if any found replace the modulator. Check the condition of the pipe right back to the motor.
Also when you do the fluid change don`t forget to drain the torque converter as this is where the most of the old fluid will be.
Also when you do the fluid change don`t forget to drain the torque converter as this is where the most of the old fluid will be.
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Junior User
Joined: Sep 2009
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From: Salem OR
Thanks
Thanks for the info will check these things this weekend when have some time. How do I make sure I get all the fluid out of the torque converter? Been awhile since done any tranny work.
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Junior User
Joined: Sep 2009
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From: Salem OR
Well checked the line and modulator. No fluid in the line and the line is connected at both ends. The top of the line connects to the manifold vacuum not the carb. Most of the line is metal tubing with rubber at both ends to connect. Any other thoughts or ideas? I did not change the fluid yet. Can a modulator be bad and not leak? Does the line need to connect to the carb and not the manifold. Engine is a stock (I believe) with an eldebrock intake and performer carb. Thanks again.
Post Fiend
Joined: Jan 2005
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The line needs to see manifold vacuum so that is OK.
Modulators are not expensive so, if it was me , I think I would replace it and see if that solves the problem.
Look for a colored stripe on it and get the same color if you decide to do that.
Modulators are not expensive so, if it was me , I think I would replace it and see if that solves the problem.
Look for a colored stripe on it and get the same color if you decide to do that.
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Junior User
Joined: Sep 2009
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From: Salem OR
Update
Well changed fluid and removed the modulator. Could not find a colored strip on it. Went to auto parts store and ended up with a green striped one. While comparing the two I noticed that the little adjustment screw where the vacuum hose connects was far inside the housing on the old one. Was feeling confident I found the issue. Filled up tranny and converter with fluid took it for a test drive and the same issue as before. It seems I got a little farther down the road before it shifted but not much. Seems to still shift quickly up tp third gear. before thought was only going from 1st to 2nd but i think it is going from 1st to 3rd within 10 feet of take off.
Going to test drive with vacuum hose removed and if nothing changes replace the vacuum line that is there.
This is so puzzling. Like i said before it manually shifts ok and the kick down works. Any further ideas would be much appreciated.
Well changed fluid and removed the modulator. Could not find a colored strip on it. Went to auto parts store and ended up with a green striped one. While comparing the two I noticed that the little adjustment screw where the vacuum hose connects was far inside the housing on the old one. Was feeling confident I found the issue. Filled up tranny and converter with fluid took it for a test drive and the same issue as before. It seems I got a little farther down the road before it shifted but not much. Seems to still shift quickly up tp third gear. before thought was only going from 1st to 2nd but i think it is going from 1st to 3rd within 10 feet of take off.
Going to test drive with vacuum hose removed and if nothing changes replace the vacuum line that is there.
This is so puzzling. Like i said before it manually shifts ok and the kick down works. Any further ideas would be much appreciated.
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Post Fiend
Joined: Jan 2005
Posts: 8,402
Likes: 10
From your description it sounds like someone else had the same problem and screwed the modulator screw in to try to correct it. A new modulator has not fixed it either.
I would think that you have a defective governor which, unfortunately, is on the back of the trans inside the output shaft housing.
But get a second opinion before you do anything there. Maybe a local trans shop that you know to be honest.
I would think that you have a defective governor which, unfortunately, is on the back of the trans inside the output shaft housing.
But get a second opinion before you do anything there. Maybe a local trans shop that you know to be honest.
Post Fiend
Joined: Jan 2005
Posts: 8,402
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The short answer is I don`t know. It may have a effect on line pressures.
However if the shifts are positive and you don`t notice any slipping in any gear I would think you would be OK.
But a second opinion would be nice.
However if the shifts are positive and you don`t notice any slipping in any gear I would think you would be OK.
But a second opinion would be nice.
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Junior User
Joined: Sep 2009
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From: Salem OR
Back again with this issue with new Information
Ok if you read above my '78 F250 4x4 with 460 and C-6 shifts quickly into 3rd gear when starting from stop.
Recently it started shifting the way it should. Had to get the revs up to get it to shift to 3rd (3000 rpm or so). With just a small amount of throttle it would kick down. The kick down lever has a small extension bolted onto the end of it so it will connect to the eldebrock carb. I found the extension loose and the kickdown rod was not in line with it and the kickdown lever was in a wrong position. I tightened the nut on the extension and took for a test drive and it was back to shifting quickly into 3rd but the kickdown worked the way it was supposed too.
So my question is if the kickdown lever is out of position will it effect the shifting of the trans? Do I need the extension or should the kickdown lever attach directly to the carb? Since this is obviuosly an engine swap did they maybe put on the wrong kickdown lever?
Any thoughts or ideas are much appreciated. I have a used C-6 to put in but would not want to go thru the bother if just gonna have same issues due to linkages.
Recently it started shifting the way it should. Had to get the revs up to get it to shift to 3rd (3000 rpm or so). With just a small amount of throttle it would kick down. The kick down lever has a small extension bolted onto the end of it so it will connect to the eldebrock carb. I found the extension loose and the kickdown rod was not in line with it and the kickdown lever was in a wrong position. I tightened the nut on the extension and took for a test drive and it was back to shifting quickly into 3rd but the kickdown worked the way it was supposed too.
So my question is if the kickdown lever is out of position will it effect the shifting of the trans? Do I need the extension or should the kickdown lever attach directly to the carb? Since this is obviuosly an engine swap did they maybe put on the wrong kickdown lever?
Any thoughts or ideas are much appreciated. I have a used C-6 to put in but would not want to go thru the bother if just gonna have same issues due to linkages.
