Was it possible for the 1970 big block 396 (402) Nova to come with the 10-bolt rear-end installed from the factory? I know the 12-bolt was optional for around $150 from the dealer at the time but that was a lot of money to the car buyer in 1970. Did the factory turn out some 10-bolt rear-ends in the big block Novas from 1970?
Jeff Smith: I’ve learned over the years never to say never because someone will come forward with a build sheet that says otherwise, but as far as I know, Chevrolet always put the 12-bolt behind any big-block Nova in 1970. Remember that in 1970, the 10-bolt was still the spindly 8.2-inch diameter ring gear rear-end used behind a 283 and Powerglide combo. This is a weak rear-axle assembly compared to the 12-bolt’s much larger 8.875-inch ring gear diameter, so it is unlikely that Chevrolet would put the 10-bolt behind even the base 350-horsepower 396 (402). This makes sense because all 1970 big block automatic Novas came with the much stronger TH-400. It simply wouldn’t make much sense to put a 10-bolt behind the TH-400.
Just to broaden your outlook, starting in 1972, Chevrolet converted to the “corporate” 10-bolt in the Nova. This is a 10-bolt but with a compromise 8.50-inch ring gear diameter that is almost exactly in between the 8.2 and the 8.875 sizes. While ignored by enthusiasts, this is a very strong rear-axle assembly that uses the 12-bolt’s pinion shaft diameter. The weakest link is the stock 28-spline axles but there are aftermarket limited-slip differentials that upgrade to 30-spline axles. For example, Eaton offers a Truetrac limited-slip differential that employs 30-spline side gear. The best thing about these rear-ends is that you can still find them used for a cheap price. The same cannot be said for a 12-bolt.
How strong is this 10-bolt? Strength is a relative term, but I have a close friend who still runs a second-generation Camaro in Fastest Street Car racing from time to time that has run as quick as 8-teens at 179 miles-per-hour using the stock, GM 8.5-inch rear axle assembly. He uses much larger spline count axles but the rear-end has lasted for years. That should give you some idea of the 10-bolt’s strength.