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Speedo fluctuates and cruise and jake won't work

Discussion in 'Peterbilt Forum' started by Hertz309, Apr 17, 2017.

  1. Apr 17, 2017 #1
    Hertz309

    Hertz309 Bobtail Member

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    Apr 17, 2017
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    I have an 05 pete 379, my speedometer has been fluctuating from 0 to 40, 50, 10 basically all over the place. I've changed the sensor, the plug on the sensor wires, checked all the wires and the ecm plugs. Everything seems fine there. The cruise won't work cause it's trying to work off the what the speedo is reading, same thing With the jake. I've even unplugged the speedo behind the dash and that doesn't change anything
     
    Hertz309, Apr 17, 2017
    Hertz309, Apr 17, 2017
    #1
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  3. Apr 17, 2017 #2
    GrapeApe

    GrapeApe Road Train Member

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    Jan 7, 2013
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    Make sure that the trans yoke is tight, the VSS tone ring can spin on the shaft when it comes loose.
     
    GrapeApe, Apr 17, 2017
    GrapeApe, Apr 17, 2017
    #2
  4. Apr 17, 2017 #3
    nasriza

    nasriza Road Train Member

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    Chicago, IL
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    Probably like Grapeape Said tone ring is loose
     
    nasriza, Apr 17, 2017
    nasriza, Apr 17, 2017
    #3
  5. Apr 17, 2017 #4
    Hertz309

    Hertz309 Bobtail Member

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    Apr 17, 2017
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    Have checked it and the nut will not budge. Been bouncing down a rough highway today and it suddenly reads right for half a minute or so then goes back down, and when it climbs to my current speed it does it at a steady pace
     
    Hertz309, Apr 17, 2017
    Hertz309, Apr 17, 2017
    #4
  7. Apr 17, 2017 #5
    Kitty power

    Kitty power Light Load Member

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    Apr 12, 2017
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    SWAG I had same problem How many miles on Trans? You ain't gonna like this but a tone ring covered with ground up trans guts will do this some times a rough road knocks some loose. Oh yeah loose plug or wire at trans or rubbed bouncing sensor wire.took trans out and rebuilt installed OOUUCCHH! kittypower
     
    Kitty power, Apr 17, 2017
    Kitty power, Apr 17, 2017
    #5
  8. Apr 17, 2017 #6
    Hertz309

    Hertz309 Bobtail Member

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    Apr 17, 2017
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    Sensor and cog ring are all external though on this tranny
     
    Hertz309, Apr 17, 2017
    Hertz309, Apr 17, 2017
    #6
  9. Apr 19, 2017 #7
    W900AOwner

    W900AOwner Heavy Load Member

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    Jul 2, 2014
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    I'd check the GROUND wire as well before you go too crazy. Electricity is lazy, and no grounds do funny things. If the tach, speedo AND cruise are acting up, I'd go there myself. KW uses ONE common ground wire for everything behind the dash panel, not sure how Peterbilt is configured, but I'd check that soon anyways. Shine up the spot on the main ground where instruments are grounded and see what happens. Worth a shot anyways.
     
    W900AOwner, Apr 19, 2017
    W900AOwner, Apr 19, 2017
    #7
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