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Old 03-30-2010, 11:51 AM
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1970 Gto

Anyone know what speedometer gears go with a 70 gto with a 140 mph speedo . I don't have the same trans it came with and its about 40 mph off. Thanks!!!!

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Old 03-30-2010, 11:21 PM
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http://novaresource.org/speedo.htm has the formula you need. You need your tire diameter and rear axle ratio to plug into the formula. Once you find out what speedo gear ratio you need, look at the chart to find out what gear combo will get you the closest. Gears are cheap at your local dealer or online.

http://novaresource.org/speedo2.htm has more gears.
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Old 03-31-2010, 05:46 AM
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70 gto

Would this work with a 140 mph as with 120 like most . Thanks
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Old 03-31-2010, 06:30 AM
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Quote:
Originally Posted by harleygearhead
Would this work with a 140 mph as with 120 like most . Thanks

it does not matter if it is a 85 mph speed-O or a 200 mph unit... the gear ratio for the speed-O gears must be figured by the proper formula as posted by the member here
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Old 04-01-2010, 08:05 PM
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No problem. It even works on Fords.
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Old 04-01-2010, 08:37 PM
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They are right, the speedo doesnt care if its 120, 140 or 160, it just cares how many revolutions the driveshaft and output shaft are turning. If you swap a 120 for a 140 and they are both calibrated correctly, that is the only thing you need to change. It will work and be accurate as long as the gears in the tailshaft are formulated to work with the final drive and tire diameter.
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Old 04-01-2010, 09:33 PM
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If your speedometer was correct with the old transmission, you need the same gear that was in it.
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Old 04-02-2010, 10:44 AM
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1970 gto

Not good in math can't get it to work out for me. I have 3.55 rearend gears 25in tire. Thanks Steve
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