Bringing up my old posting because I now have some additional questions, probably best answered by an NCRS person, but here goes.

Do judges check the coded information on the differential as a part of the NCRS judging guidelines and how do they know it should have had the 3.36 non posi if no one has the build sheet?

And why would a non-posi be HD? And why would a non-posi rear use an F-41 on the same car?
Long ago gone are the car parts that would help with the clues, but I find it fascinating.
Just another mystery unsolved.
David

 

Generally, the date and code on the rear end, are no judged during NCRS judging. This is mainly because it's near impossible to see with the car on the ground. The 80-82 Judging Manual states "It is not possible to see the codes stamped on the bottom flange of the case". The 80-82 manual is the only one that I have nearby, but all of the manuals have similar wording in them.

An open rear would not have come with the heavy duty stub axles. The HD stub axles only came on 427's, and the 427 required Positraction, as a mandatory option. It's much more likely that the stub axles needed to be replaced at some point, and whoever did the work, chose to use a set of the heavy duty ones.

Ordering F41 was not tied to ordering a Posi. They were stand alone options. Are you sure the car actually has F41, or does it just have a rear sway bar. Besides the rear bar, F41 included heavy duty front and rear springs, and a larger front bar too. I've seen lot's of cars with just a rear bar added to the standard suspension. This was a very popular upgrade in the 70's and 80's.

As far as ordering a car with or without Posi, in the 60's and 70's, it wasn't like today where everything comes standard or has to be ordered as part of a package. Back then almost everything was an option, and you could build a car just about any way you wanted. Corvettes weren't the only car that didn't come with Positraction standard, it was optional on Chevelle SS's, GTO's, and most other muscle cars too. Positraction wasn't necessarily marketed as a performance option, but instead as a traction aid for driving in wet, icy, snowy or loose gravel situations. It was needed for drag racing or road racing, but not so much for a daily driver, especially if you lived somewhere that didn't see much ice or snow.

Like most options that eventually become standard equipment, GM made Posi standard in 70, because it was cheaper and easier for them to install it in every Corvette, then to maintain an inventory of parts for the handful of people who didn't order it.