If you have been around third- and fourth-generation F-bodies for any length of time, you probably already understand that the stock 7.625-inch 10-bolt rearend isn't exactly the strongest unit on the planet. In fact, one could argue that the factory 10-bolt is possibly the least capable rearend GM could have used in these high-performance muscle cars. Besides being physically small, the factory rears seem to have an issue keeping teeth on even the stock ring and pinion, a problem that gets worse with every additional ft-lb of torque you throw at it. Replacing the ring and pinion can even make the problem worse, as a steeper gear (numerically higher) means the teeth have to be thinner, further weakening the rearend and making it even easier to break. To add insult to injury, most factory and aftermarket 10-bolts, even in working condition, can exhibit a nasty gear whine, the result of both subpar installations and distortion.
The Eaton limited-slip differential...
The Eaton limited-slip differential (PN ETN-19599-010), our impetus for this project, features race-bred carbon friction clutch packs, an aggressive posi preload, and can be completely rebuilt using easy-to-find parts, which makes it the perfect differential for our all-around street, strip, and road course needs.
So, with all of that in mind, why would anyone choose to risk building a 10-bolt, especially in a car like the STi Killer that will be abused on the dragstrip, road course, and street? Well, first of all, the 10-bolt is very light and less weight means faster turn-in, better handling, and quicker acceleration. The 10-bolt is also efficient, which means it will help us put more horsepower to the ground, instead of soaking it up as drivetrain loss. Options for the 10-bolt have come a long way since the early days and many great companies now offer quality parts for these units at an affordable price. While a $2,000-plus 12-bolt rear was tempting, we just couldn't squeeze it into our budget, a phenomena that is becoming increasingly more prevalent in these tough ecomonic times. And last but not least, we realistically don't plan on putting an earth-shattering amount of horsepower or torque through our rearend and as such, we felt like a quality 10-bolt build would easily be able to handle the demands of our hopped-up GMPP LS6 engine, while offering many benefits over a big, overbuilt drag racing-oriented aftermarket unit.