C2Dude

The previous owner stated that my 66 has a 3.55:1 posi. While adjusting the parking brakes and with the car on jack stands, when I rotated the drivers side wheel the passengers side rotated in the same direction. I had thought that on a posi, it would rotate in an opposite direction. Is that the case? Must confess, the mechanics of differentials is knowledge I do not yet possess but this would be a start.
Thanks.

Jriver

65GGvert

You've got it you got it backwards. Non posi rotates in opposite directions.

C2Dude

OK, so on a posi, rotating one wheel rotates the other in the same direction. Thanks for the clarification.

vettsplit 63

GUSTO14

In 1966 Positraction was a $42.15 option (G81), ordered on 86% of all corvettes. Yours was either one of the almost 14% in which it wasn't ordered or has been changed out at some point. The 3:55 was only available as an option on the SB with the L79 or standard on the BB, L72, where it was only available with the posi. It's not clear if it was available without the posi in the L79.

If your car is not equipped with the L79 or an L72, and it has a 3:55 ratio, it is very likely it was changed out at some time. Before you jump to too many conclusions, you may want to first verify the ratio is in fact a 3:55.

Check out pages 12 and 18 at this link. https://www.gmheritagecenter.com/doc...t-Corvette.pdf

Good luck... GUSTO

C2Dude

Hi Gusto,
I have crawled under her and the differential has the AN designation which I believe is correct for a posi. She does have (or is supposed to have) the L-79 motor (has the HT designation stamped on the block although it is hard for me to make out "broach marks" on the stamping. I will check out your link. I have not done the spin the wheel 360 degrees while counting driveshaft revolutions yet, plan to do that soon. While I am at it I will check to see if as I hold one wheel, the other is locked up. Thanks

SoCalErv

Gusto: That is a great link. Does anyone have a clean copy. Some of it over age and numerous copies have become a tough read for an old fart.

GUSTO14

The Vehicle Information Kits are actually a combination of a number of documents put together by the GM Heritage Center, including the Corvette Black Book and parts of various official GM documents. If you find a section you are most concerned with you'll need to go online to see if you can find a better copy. Otherwise check some of the earlier and later kits (similar to your car) and you'll find some are better copies than others and many have some of the same information in them.

Good luck... GUSTO

Early66L72

Gusto

look at page 12 PDF and page 68 of the document for the rear end codes. they say the location is rt front of carrier and it lists as 396. interesting. maybe they carried some info over from 65. my early 66 L72 has the code and date on the bottom, back by the rear cover and is " AZ 09 21 65"

GUSTO14

Even more interesting is that some of the documents (re: AMA Specifications) for the '65 Corvette (dated 9-28-64) don't even make mention the 396 (L78) option in the specs... Of course the 396 wasn't available until later, but it almost makes you wonder when the decision to offer it was actually made.

The AMA Specifications issued 2-22-65 (page 74 of 99) are the first mention of the 396 (L78).

GUSTO