C2 rear-end gear ratio?

• posted on January 7, 2007, 5:27 pm
How do I determine the gear ratio in my 63 250hp 4spd- are there #'s on the housing or 3rd member? It don't believe it has posi-track. Thanx- lib

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• posted on January 9, 2007, 5:31 am
There are numbers on the housing but the standard rear gear for the 250-300 hp 4 speed cars was 3.36:1. No it is not posi. All this is off if someone changed the piece.
PDeen

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• posted on January 9, 2007, 7:54 am
lib wrote:

if present it has a stamped 2-letter code indicating the ratio. I think a 63 250hp ordered with a 4spd would have come stock with a 3.08 non-posi., code "CZ". If by chance it originally had a 3-spd (3,540 cars came that way, most of them probably 250hp) and the 4spd was added after purchase, it would have had code "CA", the code for 3.36 non-posi, the most common ratio in '63; "CB for 3.36 posi, "CC" for 3.55 posi, "CD" for 3.70 posi., "CE" for 4.11 posi, "CF" for 4.56 posi, "CJ for 3.08 posi, "CX" for 3.70 non-posi. Don't ask me why they didn't just stamp the ratio plus a "P" where applicable.
Or, place a chalk mark on the sidewall of a rear tire, at the bottom (with the car on level pavement in neutral), and another chalk mark on the driveshaft or a driveshaft U-joint where you can see it if you look under the car. Have someone slowly push the car forward for a count of 3 tire revolutions while you scoot along on a mechanics dolly counting how many times the driveshaft mark makes a revolution; divide the driveshaft revolution count by the tire revolution count and you'll have the ratio. The more tire revolutions you make, the more accurate this method would be. 3 tire revolutions would be 9.24 driveshaft revolutions if the ratio is 3:08, 10.1 at 3:36, 10.65 at 3:55, 12.33 at 4:11. 9 tire revolutions (multiply the above numbers by 3) would be about 27 3/4 driveshaft revolutions at 3:08 ratio, etc. If you jacked the car up from beneath the differential and had 2 friends rotate the rear wheels in unison in the same direction, calling out the revolution count while you count driveshaft revolutions as outlined above, you'd accomplish the same thing, perhaps a bit more safely.... but you may find that the half-shaft U-joints have some interference when the rear wheels are hanging all the way down
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• posted on January 9, 2007, 1:29 pm

The metal tag may have been, but none of my C-2s had one. I've always found the code stamped into the flange where the axle cover mates to the housing - on the bottom surface closest to the roadway.
Here's waving to ya - \||||
Owen ___
'67BB & '72BB
-- not affiliated with JLA forum in any way -- alt.autos.corvette is original posting -- ___
"To know the world intimately is the beginning of caring." -- Ann Hayman Zwinger
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• posted on January 10, 2007, 1:39 am
Thanx for the info. I appreciate it- lib
wrote:

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• posted on January 10, 2007, 2:39 am
snipped-for-privacy@alamedanot.net says...

You can always do what us 'old school' guys do, which is lift the rear end off the ground, put a mark on the driveshaft, and rotate the rear wheel 1 revolution, counting the amount of revolutions of the driveshaft.
Easy and simple.
Chuck