63 SWC Differential

[Ray C.]

I removed the drive train yesterday from a 1963 340 HP car and I am in the process of cleaning the parts. I cleaned and found the Differential codes on the bottom of the main case CC 7 12 63. The dates align with the build date. I have read that the 340HP engine came standard with 370 gears unless ordered with an optional differential. I have the dealer order sheet and invoice and it list only Positraction Axel $43.05 not a particular ratio. My question is: What was shipped from GM if differential axel ratio was not specified?

[Duke W.]

Re: 63 SWC Differential

Assuming your car is also equipped with the optional four speed, the standard axle ratio was 3.70. If a base three speed the only available axle was 3.36. If Positraction was ordered you had a choice of six ratios from 3.08 to 4.56, but 3.70 was still the default if no ratio was specified on the order.

You axle code of CC indicates a Postitraction axle with a 3.55:1 ratio.

Suggest you get a copy of the '63-'67 NCRS Corvette Specification Guide, which has all you need to know to decode the stamped codes on major components, available drive trains , options, prices, quantities built, etc.

Duke

[Joe L.]

Re: 63 SWC Differential

Ray-----

For a 1963 with 340 hp a 3.70:1 rear axle ratio without positraction would have been originally installed if no other ratio was ordered. However, the "CC" code would indicate that the installed ratio was 3.55:1. That ratio could have been ordered and even though it's not on the dealer-prepared, "in-house order sheet", it must have been on the Corvette order form sent to GM. There was no charge for the optional ratios. However, to get them you had to order positraction.

[Ray C.]

Re: 63 SWC Differential

Thanks!

The date code is perfect for the car and I believe that it is an original differential. When I turned the rear wheel hub and counted the turns of the yoke the ratio seemed to be about 3.5 to 1. I was curious to why it wasn't the 3.70:1. I cleaned the differential and found the CC 712 63 stamping.

Again, thanks for the advice!
Ray #36314