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  1. #1
    Jr. Apprentice
    Join Date
    Oct 2008
    Montreal, Canada

    Question Erratic Speedo-1991 R2500 Suburban

    Here is the scoop.
    1991 Suburban 6.2 Diesel
    Automatic 4speed overdrive trans.
    139000 kms (86370 Miles).
    Drak has been replaced
    Vehicle speed sensor replaced last week.
    No engine codes.
    Wiring between VSS and body is soft but seems solid.
    My problem is during acceleration, speedo intermittently drops and fluctuates speed causing tranny to downshift, although it doesn't need to. This occurs anywhere between 45 mph up to 70, and more so during humid or wet weather.
    Any ideas or experience on this one?
    GM Fan-through & thru!:glasses:

  2. #2


    this type of thing happened to a friend of mine in an older PowerJoke, the tranny tried to keep up with the bouncing needle and made it shift erratically. He replaced the gauge cluster and now it shifts perfectly.
    1999 GMC Sierra 2500 350 vortec
    1967 Jeep M725 ambulance 230 tornado
    1990 Cherokee Limited- 3 inch lift on 33's
    ...and every one of em has issues

    If you have any questions or problems don't hesitate to send me or any other GMTC moderators a PM

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