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  •  » C4 Wont shift into Drive

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    5/04/2014 1:35 PM  #1

    gotstang
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    From: Woodstock Ontario Canada
    Registered: 4/01/2013
    Posts: 60

    C4 Wont shift into Drive

    Hi I have a 1966 mustang coupe with a 289 C4 Automatic Transmission The problem I having is the trans dose not shift from 2nd to drive the transmission oil is full and a nice pink/red color with no burnt smell the vacuum tube is hooked up to back of the engine center head and runs down to the modulator valve everything is hooked up no leaks. It is an green dot shift indicator all linkage is hooked up and moves freely and kick down cable is hooked up and works fine..JUST WILL NOT SHIFT INTO 3RD GEAR(DRIVE) .Can any one point Me in the right direction to fix this problem Thanks Tom

     

    5/04/2014 8:42 PM  #2

    LondonSteve
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    From: London, Ontario, Canada
    Registered: 4/01/2013
    Posts: 136

    Re: C4 Wont shift into Drive

    The modulator valve is adjustable. You can try pulling the hose off and turning the adjuster with a very small flat screwdriver. You may not be getting enough vacuum delivered for it to upshift, the adjustment can help with that. It controls how early or late upshift takes place.

    Also, if work was done to the tranny, it is possible to install the actuator valve backwords that is inside, directly behind the vacuum modulator. If this is the case, it will never upshift. Ask me how I know.

    Hope that is a start in diagnosis. Simple steps that may help the problem without tearing into it.

     

    5/04/2014 9:11 PM  #3

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 11,733

    Re: C4 Wont shift into Drive

    Are you saying that the lever is not capable of moving the transmission selector into D position on the transmission lever or that once you put it in D, the transmission will not move the car?
     

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    5/04/2014 10:21 PM  #4

    gotstang
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    From: Woodstock Ontario Canada
    Registered: 4/01/2013
    Posts: 60

    Re: C4 Wont shift into Drive

    Thanks Guys I will try the adjustment London Steve answered and see what happens cause the tranny has never been apart. As to the Question from Mustang Steve when I put the mustang in Drive it starts out in first shifts to 2nd then that's it wont shift in drive . when I shift the tranny manually only shifts from 1st to 2nd and dose not shift to drive Thanks  Tom

    Last edited by gotstang (5/05/2014 12:19 AM)

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    5/05/2014 12:19 AM  #5

    gotstang
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    From: Woodstock Ontario Canada
    Registered: 4/01/2013
    Posts: 60

    Re: C4 Wont shift into Drive

    London Steve when I adjust this modulator do I turn clock wise or counter clock wise and how many turns to start with Thanks Tom

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    5/05/2014 6:39 AM  #6

    ChrisH IA
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    From: Des Moines, Iowa
    Registered: 4/01/2013
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    Re: C4 Wont shift into Drive

    I dunno which way the adjustment screw needs turned. I DO know that when you have the hose off the Modulator, poke a q-tip in there; if it comes out wet, your Modulator is bad, Modulator controls the severity of the shift, from what I recall. 

     

    5/05/2014 10:33 AM  #7

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
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    Re: C4 Wont shift into Drive

    I have a tranny that did that once and it was the front pump. Another one was because a vacuum line was broken to the modulator.   I would certainly give any adjustments or vacuum fixes a shot first.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    5/05/2014 10:49 AM  #8

    ChrisH IA
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    From: Des Moines, Iowa
    Registered: 4/01/2013
    Posts: 43

    Re: C4 Wont shift into Drive

    Mustang Steve, I would check , after verifying the modulator valve, if the linkage to the downshift mechanism was adjusted correctly. My '68 doesn't have a cable and 45 years later, the only item that has failed is the modulator valve.She has taken me and my wife wherever we have wanted to go. That transmission has only had the fluid and filter  changed in all those years. 

     

    5/05/2014 4:24 PM  #9

    ultrastang
    I FYI 24-7

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    From: Camden, Arkansas
    Registered: 4/01/2013
    Posts: 570

    Re: C4 Wont shift into Drive

    ChrisH IA wrote:

    I dunno which way the adjustment screw needs turned. I DO know that when you have the hose off the Modulator, poke a q-tip in there; if it comes out wet, your Modulator is bad, Modulator controls the severity of the shift, from what I recall. 

     
    If the diaphragm in the modulator is blown, you'll definitely know it by the huge white plume of smoke coming out the tail pipes behind you. That's what happened to my '68 Mustang around 1983 when it still had its stock C-4.

    If the modulator diaphragm on a C-4 ruptures, the vacuum line attached to the valve siphons the transmission fluid out of the transmission and into the combustion chambers of the engine. The result is an embarrassing, huge cloud of white smoke coming out of the exhaust pipes. 

     

    5/05/2014 8:20 PM  #10

    LondonSteve
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    From: London, Ontario, Canada
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    Re: C4 Wont shift into Drive

    gotstang wrote:

    London Steve when I adjust this modulator do I turn clock wise or counter clock wise and how many turns to start with Thanks Tom

    I honestly could not remember, so I Googled it. Quote: Turn the screw clockwise for harder, later shifts. Turn counterclockwise for softer, earlier shifts. Make adjustments one turn at a time, then test drive. Do not adjust more than four turns in either direction.

    For your problem, that means counterclockwise to get an ealier shift, or get a shift at all. In my case, I was not getting any upshift from 1st to 2nd, and definately not third to fourth, and this helped solve the problem.
     

     

    5/05/2014 8:32 PM  #11

    LondonSteve
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    From: London, Ontario, Canada
    Registered: 4/01/2013
    Posts: 136

    Re: C4 Wont shift into Drive

    Just had a thought. Noticed you mentioned green dot in your description. They shift differently than the later C4 valve body. Could this be your problem?Green Dot C4 Actually the green dot works like this:
    L- 1st gear only
    2- second and third only
    3- automatic 1-2-3
    The only way to hold second is start in low,shift to 2 for second gear, than back to low-that will hold the trans in second gear, than back to 2 to shift to third.

     

    5/06/2014 12:57 AM  #12

    gotstang
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    From: Woodstock Ontario Canada
    Registered: 4/01/2013
    Posts: 60

    Re: C4 Wont shift into Drive

    Thanks guys I will be getting under the car tonight to adjust the modulator valve hope this works I will post results later tonight Tom

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    5/06/2014 7:18 AM  #13

    Nasty65
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    Registered: 4/21/2013
    Posts: 118

    Re: C4 Wont shift into Drive

    So your only "feeling" one shift when starting out in "D"?  You say transmission hasn't been apart, but has the linkage been messed with?  How long have you had the car, is this a problem where it worked fine and suddenly started happening?  Are you sure the modulator is getting vacuum?  test gauge on the manifold port you hooked to, possible pin hole in the vacuum line going to the modulator?

     

    5/06/2014 8:04 AM  #14

    hmartin025
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    Registered: 4/01/2013
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    Re: C4 Wont shift into Drive

    My experience with C4's is with modulator inop, shift into drive is very high MPH. Things are screaming
    before last shift.
    Howard 

     

    5/06/2014 3:05 PM  #15

    gotstang
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    From: Woodstock Ontario Canada
    Registered: 4/01/2013
    Posts: 60

    Re: C4 Wont shift into Drive

    Well Guy's got home from work 2 hours ago  Got out my vacuum gauge check the vacuum at idle at the manifold and I have 16 pounds of vacuum at the manifold so I hooked the hose back up and took the mustang for a ride and it is shifting fine now everything working the way it should all gears a working I'm wondering if the rubber hose coming from the back of the manifold was kinked before  and when I unplugged it to check the vacuum it straighten the hose out and everything is working fine now saved me time and money .I want to Thank Everyone that commented and for Everyone's  Advice as to what I should do so Thank You All for taking the time to help Me.Tom

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