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Speedometer Trouble READ PLEASE!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 82Jimmy, Jun 10, 2000.

  1. 82Jimmy

    82Jimmy 1/2 ton status

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    Okay heres my story, my friend has a Jimmy an 83 and he and I were both wondering why his speedometer is off 15-35 mph. He can't get it over 65 but mine pins out at 85 when he is at 65. He has only a 4" suspension lift and has reset his speedometer twice and bought a new one. I can't figure it out. ANYONE ELSE EXPERIENCE THE SAME PROBLEM?
     
  2. Michael

    Michael 1/2 ton status

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    It must not be the speedo if he put in a new one. You might check the drive unit in the trans or maybe the cable is fouled up. Sorry, not much help.

    Michael [​IMG] http://jmartin.net/parker/goose.htm
     
  3. Picard

    Picard Registered Member

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    What did he do when he "reset" the speedo. With big meats (say 36's) 65 would be about 85-90 actual, which is about all an 83 is good for. Unless the pilot gear on the tailshaft and/or a converter (little inline sidewinder gear) was added, no ratio change has been made.

    Good luck on your fix,

    Steve - 90 Warpig
     
  4. 82Jimmy

    82Jimmy 1/2 ton status

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    He has a friend that is a Certified Chevy Repairman (i guess thats how you would put it.) he said there were some gears that needed some replacing yes his tires are 36in.
    he changed almost all the wires himself. A couple he couldn't get to but is in the process of fixing right now. Thanks for the help.


    Bigger is Better
    Cameron Burnett
    82 Jimmy
     
  5. HarryH3

    HarryH3 1 ton status Author

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    The speedo head in the dash only counts revolutions. The gears at the other end of the speedo cable are calibrated to rotate the speedo cable 1,000-times-per-mile, with the tires and wheels that came from the factory.

    Installing taller tires lowers the actual number of times-per-mile that the cable rotates. This causes the speedo to read slow. Changing the gears at the t-case (or tranny on a 2WD) can get your speedo reading pretty close to stock.

    Speedo shops can test your rig over a measured mile and calculate the percentage of speedo error very accurately. They then install a ratio converter inline with the speedo cable (it's a tiny gearbox, think of a single-speed transmission) that will convert the speedo cable RPM to exactly 1,000 rotations-per-mile.

    <font color=black>HarryH3 - '75 K5</font color=black>
    http://ThunderTruck.ColoradoK5.com
     
  6. 82Jimmy

    82Jimmy 1/2 ton status

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    We called a speedometer shop in Amarillo and they said it is a common problem and could repair it in a day or 2. Thanks for the help. I am really thankful for all the replys to my post.


    Bigger is Better
    Cameron Burnett
    82 Jimmy
     

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