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Thread: NA speedometer question

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  1. #1
    2,000 rpm - light wheelspin, no bog here! Boo's Avatar
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    NA speedometer question

    I recently replaced my gauges, now I noticed my speedometer is off, from 0-30 it’s about 10mph lower than actual speed, around 50mph it’s dead on 60mph and up starts to be 5-10 mph higher than I’m actually going, I’m going 70mph odometer is reading 80mph, this is my second cluster the other cluster was off by 10 mph at all times, when I start driving the needle doesn’t start moving until I’m already doing around 10mph, completely aggravating, need some advice thanks

  2. #2
    Ninja Messiah kung fu jesus's Avatar
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    There may be other issues at play here: swapped differential, different speedo gear in the transmission. I would bet one or both of those aren't original to your car.

  3. #3
    2,000 rpm - light wheelspin, no bog here! Boo's Avatar
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    Is it hard to change the speedo gear in the transmission?

  4. #4
    Ninja Messiah kung fu jesus's Avatar
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    I don't know your mechanical experience or tools, but it's not much different than changing the transmission fluid. Check around for speed sensor replacement videos.

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    Boo (10-04-2018)

  6. #5
    2,000 rpm - light wheelspin, no bog here!
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    The speed sender is easy to replace. Remove speedo cable (NA) or unhook electrical connector (NB), remove one 10mm head bolt, swap sender, reverse for installation.

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    Boo (10-04-2018)

  8. #6
    2,000 rpm - light wheelspin, no bog here! mazdarati1's Avatar
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    Speedometer

    I have read in a number of places that NA speedometers are notoriously inaccurate, my car is 5 mph low across the scale. You may get an idea how accurate your car is by checking the speedo against a GPS speed read-out.

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    Boo (10-04-2018)

  10. #7
    2,000 rpm - light wheelspin, no bog here!
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    They definitely aren't the most accurate. For example, I swapped to a 6 speed and 3.9 final drive in my NA. I put in a 4.1 sending unit (tallest I had laying around for a cable driven speedo) and my speedo is pretty close (+/- 1mph minus my error in installing the speedo needle) to a GPS.

  11. #8
    2,000 rpm - light wheelspin, no bog here! Boo's Avatar
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    NA speeed sensor

    My speedometer is off by 10 mph, does not move off 0 till I’m going around 10 mph, if I change the sensor do I want more teeth on the gear or less teeth? Thanks

  12. #9
    Supporting Member DarylSibcy's Avatar
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    Is this for one of the NA's in your profile pic??

    If so, the NA speedo's were never mega accurate from the factory anyway. Mine does the same, but I've never worried about it enough to "fix" it, I've always got something else that needs doing first (and usually more expensive )

    As long as your speedo is accurate from 10 upwards, I wouldn't worry personally - someone else might have better advice though HTH
    You want a good car. I want a good miata.

  13. #10
    2,000 rpm - light wheelspin, no bog here! Boo's Avatar
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    I wish that is was but it’s totally off by 10mph every speed you go, except when you go 50mph and after that it’s 10mph faster than the speed your going, totally messed up

  14. #11
    Ninja Messiah kung fu jesus's Avatar
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    There are different speed sensor gears for the three main differential gearsets in the Miatas. They are different colors, too, IIRC.

    You should also list your tire/wheel specs too, as that may also be playing into the issue.

    Please keep all the your questions about this issue in this thread.

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  16. #12
    2,000 rpm - light wheelspin, no bog here! riefdaddy's Avatar
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    More teeth would get it closer, or smaller tires, or a higher gear ratio.

  17. #13
    2,000 rpm - light wheelspin, no bog here! Boo's Avatar
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    If my cluster is not moving till it hits 10mph, l would want a gear with more teeth?

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