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c6 shifting troubles

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Old Dec 19, 2011 | 09:15 PM
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c6 shifting troubles

i have a 77 f150 shortbed 4x4 i just got done redoing rebuild the 400. the problem is the tranny now. if you shift it manually it works good till you get to 3rd then it slips for a little bit. but it wont shift very well if its in drive. i was wondering if it was due to the truck sitting for the last 7-8 years not running and it just needs to be driven a little bit? or if i have to find a differentone or get it rebuilt
 
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Old Dec 19, 2011 | 09:53 PM
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Put in a new vacuum modulator or check the setting on the one in there. Could be vac hose fell off too or not hooked up.
 
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Old Dec 20, 2011 | 08:06 AM
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My vacuum line came off and did the exact same thing your describing.
 
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Old Dec 20, 2011 | 08:55 AM
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My c/6 sat around about 6 years and gave the same problem. New one fixed it. They never had the correct one in stock so i got one with a different color of stripe on it. It turned out to be better as i had changed rear gear ratios and it made it shift better than the old one did before it quit. But if it shifted correct before ,then i would recommend getting one just like whats in it. I think there are about three or more of them and you can adjust them ,at least the ones i have used you can.
 
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Old Dec 20, 2011 | 06:52 PM
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Yes, start with a modulator. When yoou pull it out some oil will run out. I started parking my trucks on a steep hill or jacking up the rear end and doing it then to avoid the exxon valdez coming through. If that doesn't fix it, i would recommend a fluid change to get the valve body De-gunked as much as possible. A modulator would be cheaper and easier.

I prefer the ones with the adjustment inside. those you can adjust and tune and set it where you like it.
 
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Old Dec 20, 2011 | 07:21 PM
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Make sure the shift down linkage is working properly ...After you change the modulator ...
 
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Old Dec 20, 2011 | 11:52 PM
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My C4 was doing the same thing about a month ago, I followed the suggestions, changed the modulator and adjusted the intermediate band, but it didn't help at all. And F250 Warhorse isn't exaggerating about the Exxon valdez when you take out the modulator either so be prepared. Anyway it didn't help mine at all, I ened up having to pull the transmission and rebuild it, turned out my clutches were toast.

Hopefully just replacing the modulator will work for you though.

You might also want to drop the pan and change the filter along with the fluid change that was suggested.
 
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Old Dec 21, 2011 | 05:49 AM
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i think im going to try modulator and change the fluild my pan leaks anyways
 
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Old Dec 21, 2011 | 12:02 PM
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that is where I would start. jsutton is on to something too. wore clutches will act as described if it has a lot of miles or has been overheated. I would do the modulator and fluid both probably. On the leaking pan, those are prone to leaking but they have been overtightened and distorted in mine. I like to put a good straight edge all over on the pan and try to get it back to square again with a mallet. Sometimes a block of wood helps too. good luck
 
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Old Dec 21, 2011 | 02:05 PM
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I was also wondering how hard it would be to put a shift kit in it while I had it open I've never done one before
 
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Old Dec 21, 2011 | 02:12 PM
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It wouldn't be too hard, I should have put one in mine especially since I had it out and apart but didn't because I wasn't sure if my rebuild was even gonna work right since it was my first attempt. LOL
 
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Old Dec 21, 2011 | 04:51 PM
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i cleaned off the modulator and i couldnt find anywhere on the outside of it where there is a color marking i dont know if its inside it or not bot what color of one should i get
 
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Old Dec 21, 2011 | 04:53 PM
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Most common is the green stripe. I think people like the black stripe too, IIRC the black stripe makes harder shifts, but not 100% certain on that part.

EDIT: That may just pertain to a C4, I'm sure someone else will be along shortly.
 
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