3:31 To 4:10 And Cruise Control

Discussion in '2005 - 2009 Specific Tech' started by mykul68, Feb 17, 2014.


  1. mykul68

    mykul68 New Member

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    Hello all,
    my searches take me to irrelevant threads so my apologies if this has been addressed. I am pondering a 3:31 to 4:10 gear swap on a 2008 GT with auto trans. According to Ford parts site the cruise control will not work afterward. Can anyone confirm if this true after tuning the transmission to adjust shift points and speedometer.

    Thanks in advance for any input,
    Michael Marshall

    00v0v_dOPidSzAOxc_600x450 edited.jpg
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  2. timjimmy

    timjimmy Active Member

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    That doesn't make any sense at all. You recalibrate your speedo using a programmer, and they don't even specifically ask for a rear gear ratio. The outer diameter of the rear tire and the gear ratio determines how many revolutions per mile the tire spins, and that number gets used to adjust shift points, speedometer, and cruise.
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  3. mykul68

    mykul68 New Member

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    Didn't make sense to me either. Maybe Ford meant that would be the case if the speedo wasn't recalibrated. Dunno. Reckon I'll find out soon enough
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  4. retfr8flyr

    retfr8flyr Member

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    Ford doesn't offer 4.10 gears as an option, so that's why they say it doesn't work. With an auto the shifting is based both on rpm and mph. When you change to 4.10's you can change the gear ratio in the tune and the speedometer mph will be correct but the rpm will be off. For best results you need the tune for the automatic functions modified for drive ability, based on the 4.10 gears.


    Earl
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  5. racerraj

    racerraj Founding Member

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    I'm inclined to believe shifts are based more on load and RPM than speed. It is possible the computer senses data out of parameters (Load and RPM relative to speed) if the speedo isn't calibrated. I would be too curious, I would want to test it on the road before calibrating.
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  6. timjimmy

    timjimmy Active Member

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    I thought RPM was controlled by the crankshaft position sensor?
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  7. racerraj

    racerraj Founding Member

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    I was saying the shift points are analysed by the computer using the engine RPMs and the Load on the engine. The crank position sensor would provide the RPMs to the computer and ignition timing reference. The actual RPMs are controlled by your foot of course.
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  8. timjimmy

    timjimmy Active Member

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    Ah, misunderstood what you said. Yes, this is what I was thinking as well, which leads me to believe that 4.10s wouldn't be an issue as long as the car was programmed with the proper revolutions per mile.
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  9. Steve491

    Steve491 Member

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    If you flash the ECM with a "tune" you should not have a problem with speedo. Any decent programmer will allow for gear changes and/or tire size.
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