Speedo Gears

Discussion in 'Got gears?' started by Beamer, Oct 23, 2004.

  1. Beamer

    Beamer Suncoupes Rule !!!

    I am currently running a pegleg 2.56 rear. I believe the speedo is correct, and I can verify soon with my GPS. Does anyone have a table or some type of chart that will tell me which speedo gear I will need for a 3.90 gear rear to have an accurate speedo?

    I know I will need to find out the current gear spline count.

    Thanks any and all...

    Mike

    :TU:
     
  2. 70 gsconvt

    70 gsconvt Silver Level contributor

    Here's a shop that sells everything you'll need at reasonable prices. You could also probably try a local tranny shop. They should have a box or two of this stuff. Look for a shop with old guys and lots of greasy stuff laying everywhere.

    http://www.transmissioncenter.net/speedometer_calibration_______va.htm

    Here's a chart that shows what you probably have in there now:

    http://www.teufert.net/speedo/70-400-gt.htm

    Finally, here are two pages that should help you pick the right speedo gear based on new rear end gear and tire size:

    http://www.chevymania.com/tech/speedo.htm

    http://www.jeeptech.com/javaAps/Speedo.html
     
  3. Beamer

    Beamer Suncoupes Rule !!!

    Thx Phillip,

    I will look it all over and probably pull the gear out today to verify. I am going out here in a few minutes to check the speedo to my GPS for accuracy.

    I appreciate the links and all...

    Mike
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Mike,
    This is real simple. All you need to know is your rear gear ratio, tire diameter, and the # of teeth on the speedo drive gear. The drive gear is located on the output shaft of the trans. When you pop the sleeve and driven gear out, you can count the # of teeth on the drive gear by rotating the drive shaft(wheels off the ground, trans in neutral). Then just plug the #'s in to the calculator here:

    http://www.tciauto.com/tech_info/speedo_gears.htm

    and it will tell you the # of teeth you need for your driven gear.
     
  5. John Eberly

    John Eberly Well-Known Member

    Easy to figure out, can be hard to fix

    Some of the speedo output shaft gears are pressed on. They can be REALLY hard to remove. I gave up and had a tranny shop swap mine, and they had to get a new puller after they broke the one they had!

    I was told (after I put on a new steel gear) that there are nylon type gears that are held on by a metal clip. This is the smart way to go if you're changing gears - then you won't have to deal with the pressed on gear again.
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    I agree John, but he may not need to swap out the drive gear. I originally thought I had an 18 tooth gear in my 67 ST-400. When I counted the teeth, it was only 17 teeth. Had it been 18, I would have had to swap it out because there was no driven gear that would work with my combination. Put the #'s into the TCI calculator. If the driven gear box comes up N/A, you have a problem, and need to change the gear.
     

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