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Thread: Speedo Re-calibrated

  1. #1
    Club Member 91Bird305's Avatar
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    Default Speedo Re-calibrated

    Ever since I did my swap, my speedo has always been off by +15-20mph. Is there anyway to re-calibrate the speedometer to display the correct mph? Car is a 91 Firebird w/ an 87 GN motor swap, 700r4 still and a Dana 60 rear.

    Thanks!
    '91 Firebird - LC2 3.8, 6776S Turbo, Alkycontrol, S60 Rear, ProBuilt 700

  2. #2
    Club Member AutoRoc's Avatar
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    You must have changed gears or tire size. The only way to change the MPH readout (because it is cable driven) is to change these little plastic gears in the tailshaft of the 700R4 trans. Getting them, installing them, getting the correct ratio gears? Goodluck with that part, im sure the info is out there.
    Denny Villemure
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    Vortec 4200 Turbo IROC-Z on 15psi
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  3. #3
    Club Member mustangmike6996's Avatar
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    There are a few speedo drive vs driven gear calculators that will get you within a tolerance. You need to know your rear axle ratio. Knowing the tire size (if different from stock) will help get even closer.

  4. #4
    Club Member Sledder's Avatar
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    Seen this out there if it's any help.

    First I saw this page...........
    http://www.firebirdcentral.com/Articles.asp?ID=258

    Then there was this link on that page about speedo gears
    http://www.v8volvo.se/mekartips/arti...eedo-gear.html

    I Drag Race Because It's Fun, Not Because I'm Good At It.

  5. #5
    Forum Member Detroit Gearbox's Avatar
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    91 is about the year they went electronic.
    If you have plastic gears you are in luck. I have every gear & housing in stock & can calibrate what you need with tire height & gear ratio
    If its electronic I need to know if the vehicle has a Drac module under the dash (pictured below)
    If it has a drac you either need a new one made or one with dip switches installed like the one pictured.... I had several made for this issue with older vehicles.
    If it has no drac I think you can recalibrate on the back of the dash.... its been years since I seen one of those.





  6. #6
    Club Member 91Bird305's Avatar
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    I guess I should wait to do this after I swap the rear tires again. This is good stuff though. I found this thread on TGO as well - https://www.thirdgen.org/forums/tech...r-way-off.html.

    It's not electrical. Sounds like I need to do some measuring and find the right driven gear size. @Detroit Gearbox I'll hit you up as soon as I figure out my numbers and what I need.

    Thanks, everyone!
    '91 Firebird - LC2 3.8, 6776S Turbo, Alkycontrol, S60 Rear, ProBuilt 700

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