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Old 04-09-2007, 05:19 AM
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What speedometer gears do I have?

I am going to need to correct my gears. What I need to know is what drive gears did GM put into 1974 Novas with th350's? I've determined through novaresource.com and my own experience that the original car had a 2.73 differential. (I've got a 3.08 in my camaro and the speedo is 1000rpm/mile and the speedo is going too fast AND I'm going even higher to 3.73's, meaning the original had 2.73 in that nova, the only possible gear lower than 3.08 available for novas that year) BUT using the calculators, I'm somewhat guessing at tire diameter, I put in a 26" which is the standard size the nova would have come with.

Aftermarket companies sell 7,8,9 and 10 tooth drive gears but others seem to suggest GM only put 8 and 10 tooth drive gears in, or only black and purple. Did GM put 7 or 9 tooth in them? What color would these be?

I'll have to change out the drive gear if its anything other than a 7 or 8. I've never done that before, is this the basic procedure?:
-drop out driveshaft
-drain fluid
-remove speedo driven housing/gear
-remove 4 tailshaft bolts
-remove/replace drive gear
more or less?

thanks for any help.

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Old 04-09-2007, 08:28 AM
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The older GM parts books have a big section on which gears for a certain trans, axle ratios & tire by size. I've seen them in the 73-78 book and a newer book, they were truck books but showed your trans, so info is correct.

Easy way is to get the car out on a highway with mile markers, and go 5-10 miles to figure out what percent it is off. Then go to ebay under "speedometer adapter" to find one of those GM factory corrector gearboxes to dial it right in. They list them by how many percent underdrive or overdrive. Some of the buy-it-now are pricey but in regular auction format, you can do better. 2 minutes to install.
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Old 04-09-2007, 01:15 PM
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IF ... you are going to a 3.73 gear ...

just change the driver and driven to the gears you need ...

No big deal ( this is NOT a Turbo 350 but the principal is the same ... )
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Old 04-11-2007, 09:19 PM
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