C6 only shifts manually!!

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Oct 6, 2009 | 12:54 PM

70efftoofifty

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C6 only shifts manually!!

I just recently acquired this 1970 F250 360 C6 auto 2wd. I have already checked the tranny fluid so nobody say anything about that.

If I put it in drive it won't shift out of first. If I pull the lever down to second it will shift. If I immediatly put it back in drive it will stay in second, but will not shift to third. to get it to shift to third I have to be going atleast 35 and put it from 2nd to drive back to 2nd and back to drive. While in drive it will downshift fine, but it will not shift up. If it downshifts while in drive I have to perform my "secret ritual" to get it to shift up again.

Any suggestions? Is there something I can look for/replace or does the pig need to be rebuilt?

Oct 6, 2009 | 07:25 PM

Danger_Dave

Fleet Mechanic

Joined: Dec 2006

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From: UPSTATE NY

that sounds like a fun truck to have! i want to have an extra truck just as a backup thats extra clunky. maybe a 64 or something of that nature.

Oct 6, 2009 | 08:41 PM

70_RangerXLT

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From: Kernersville, NC

Actually sounds like either the governor is sticking or the valve body has a sticking valve.

Oct 6, 2009 | 10:44 PM

hogbus

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Mine has acted up like that too....try replacing the modulator valve on the transmission...its a pretty cheap part and easy to swap out.

Oct 7, 2009 | 10:48 AM

70efftoofifty

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I just ordered a modulator valve for $12.83 at Advance Auto Parts, and I can go pick it up tonight after 4. I'll replace it and let everyone know what happens.

Oct 7, 2009 | 06:15 PM

hogbus

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i hope it works for you....the one in mine has been replaced three times since 1972, its always worked great afterward.

Oct 8, 2009 | 07:27 AM

70efftoofifty

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Ok, so I got the new modulator valve and crawled up under my truck only to find out the old valve wasn't even connected to the vacuum line. There is a steel line going from the engine back to the tranny with a rubber hose connecting it to the carb and the end by the tranny was missing the rubber hose. I replaced the valve anyway since it was only $12 and connected it. It shifts by itself now in drive, BUT now it shifts to 2nd at about 8 mph and 3rd at 15 mph. Also when it shifts to 3rd it hesitates for about half a second allowing the engine to rev up if I'm accelerating as if it shifted into neutral and then 3rd.

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Oct 8, 2009 | 07:46 AM

70efftoofifty

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I'm glad too. I'll try adjusting it tonight and let everyone know what happens.

Oct 8, 2009 | 05:10 PM

#10

70efftoofifty

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Ok I figured out the problem.... When I removed the old modulator the little rod inside fell out into my driveway and I had no idea there was supposed to be one in there (I don't know much about transmissions, especially automatics). I messed around with the adjustment for like an hour and just happened to see the little rod laying in my driveway. I had no idea what it was, but after some searching around online about why my tranny still shifted wierd I found some stuff about a rod inside the modulator. I took the modulator out and sure enough that little rod I found fit perfectly inside. Now the transmission shifts to 2nd at 12 mph and 3rd at about 25 with no hesitation whatsoever.