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Far from a car expert here, as may be obvious from my question, but I'm trying to figure out the axle ratio on my 1963 C2 Coupe. Is there an easy way to determine if it has the "special highway axle" of 3:08 to 1? Thanks!
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250hp and 300hp '63s came "standard" with the 3:08 ratio, but required the G81(positrack) AND G91(special highway axle) RPOs on the order unless a different ratio was ordered from the dealer. Look for a CZ, or CJ stamped on the bottom of the diff cover. These are the 3:08 factory codes...assuming the gears have not been changed in the past....
|UPDATED|2/16/2026 9:32:02 PM (AZT)|/UPDATED|
|UPDATED|2/16/2026 9:32:02 PM (AZT)|/UPDATED|
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If you can't determine the ratio by the stamps on the diff, then just put a mark on the driveshaft and rotate a rear wheel 1 full turn. Count the rotations and partial rotation of the driveshaft, looking for about 3.1, 3.3, 3.5, 3.75, or 4 rotations.
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💬F4Gary said:
If you can't determine the ratio by the stamps on the diff, then just put a mark on the driveshaft and rotate a rear wheel 1 full turn. Count the rotations and partial rotation of the driveshaft, looking for about 3.1, 3.3, 3.5, 3.75, or 4 rotations.
That's the "old school way"...!!! 👍
Jim Olson 
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💬F4Gary said:
If you can't determine the ratio by the stamps on the diff, then just put a mark on the driveshaft and rotate a rear wheel 1 full turn. Count the rotations and partial rotation of the driveshaft, looking for about 3.1, 3.3, 3.5, 3.75, or 4 rotations.
💬Norsky said:
That's the "old school way"...!!! 👍
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in Forum: C2 Engines, Driveline and Handling
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