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SPEEDO GEAR ADJUST

Discussion in 'Trucks and Trailers' started by ERIC, Apr 3, 2000.

  1. ERIC

    ERIC LawnSite Member
    Messages: 10

    THIS MIGHT BE A STUPID QUESTION? I OWN A 1979 CHEVY 4X4 PICKUP WITH A TURBO 400 TRANSMISSION, 40" TIRES, AND 4.10 RUNNUNG GEARS. THE PROBLEM IS WITH THIS SIZE OF TIRES MY SPEEDOMETER IS WAY WAY OUT OF WACK. I KNOW THEY MAKE SOMETHING TO ADJUST THE SPEEDO GEAR RATIO BUT I HAVE NO IDEA WHERE TO FIND THIS ITEM. ANY INFO WOULD BE GREATLY APPRECIATED. THANKS
     
  2. Doug406

    Doug406 LawnSite Member
    Messages: 134

    Your chevrolet dealership. They will have a bunch of different gears for you. what you must figure out is which one. On a 79 you should have a 203 case, there should be a little converter box where the cable goes in the case. Try removing that all together and see what your speedo says, otherwise swap gears (about 7 bucks a pop). There is a mathmatical way of figuring it out, but i can not remember it. Something like old number of teeth on speedo gears / old tire size x uknown new teeth needed/new tire size. Example 32teeth/29" tires times T(unknown)/40" tires. That may be it.
     
  3. mpastor

    mpastor LawnSite Member
    Messages: 6

    The other thing you could try would be to go to a Speedo calibration shop. They could calibrate your speedo to compensate for the larger tire/wheel size.
     

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