Maximum-Effort Fourth-Gen10-Bolt

After determining the proper pinion depth, installing the pinion, and setting the preload to factory specifications, the replacement differential is pulled out of the box and examined. The Eaton limited-slip differential features a cast-iron case and utilizes carbon-disc clutch packs preloaded by a central-spring assembly located between each differential side gear. The preload from the spring assembly keeps the clutch packs engaged. However, when making a turn, the clutch packs are disengaged to allow one wheel to turn faster or slower than the other.

"Though this be madness, yet there is method in't." Had William Shakespeare been born in the modern age, surely his famous quote from Hamlet, Act 2, Scene 2, would have been used to aptly describe "Maximum-Effort Fourth-Gen 10-Bolt." According to the experts on all the late-model GM Performance boards, only the severely mentally challenged would waste their hard-earned dollars to build up a 10-bolt for their late-model F-body.

But wait just one second: The average Firebird hobbyist isn't putting down over 450 rwhp, hitting the dragstrip on "High School Night," or getting their nitrous bottles refilled on a weekly basis. Most fall somewhere between stock and moderately modified and are quite satisfied with lesser horsepower patinas. Is an expensive aftermarket GM 12-bolt or Ford 9-inch necessary for the majority of these hobbyists? The answer is probably not.

According to Jason Bailey, owner of Texas Drivetrain Performance, "10-bolts can be fortified to handle up to and beyond 425 rwhp. Before recommending what course of action a customer should take as it pertains to upgrading a 10-bolt or purchasing an aftermarket rearend, you must determine the use of the car. Since the 10-bolt has been bashed so much over the years, many owners will step up to an aftermarket rearend to avoid being thought of as either crazy or stupid by their peers. The goal of any rearend build is to know that when the customer leaves, the unit will handle whatever is thrown at it. If I can fortify a 10-bolt to get the job done for a quarter of the cost, everyone wins. By using aftermarket axles and a TA differential cover along with welding the axle tubes, the 10-bolt can be strengthened by 20-25 percent over stock. Owners who modify their Firebirds with the basic bolt-ons, such as headers and a cam, need the extra strength but don't necessarily need to spend thousands of dollars on an aftermarket rearend."

In the first installment, a used housing was purchased and completely disassembled by Texas Drivetrain Performance of Fort Worth, Texas. After detailing the major disassembly steps, the axle housing was taken to Peyton Automotive Performance so the axle tubes could be welded and the rearend straightened. After a quick trip to Enduro Powder Coating for an attractive semigloss-black finish, the housing rebuild began. New parts from Randy's Ring & Pinion of Everett, Washington, were used, and at the article's end, the pinion was reinstalled.

Hang in there as the rearend will soon be outfitted with a new limited-slip differential, and once complete, fitted with Yukon axles and a TA differential cover.

A side-by-side comparison of the Eaton limited-slip differential (left) and the Torsen unit shows the beefier casting of the Eaton. The Eaton unit utilizes two side gears and two spider gears as opposed to the eight worm gears and two side gears on the Torsen. For spirited driving and the dragstrip, the Eaton unit is hard to beat, while a Torsen T2R high-bias differential is the favorite of the road-racing and autocross crowds. A set of additional preload springs (T2 does not contain preload springs) in the T2R differential allows the unit to lock under low-torque settings. This is particularly helpful in start and stop conditions and in cornering.

The differential and the two bearings are taken to the Arcan 20-ton press, and the differential side bearings are pressed on.

The back of the ring gear and the ABS reluctor wheel that were removed from the Torsen differential are cleaned with a grease and wax remover. Next, the ABS reluctor ring is set on top of the ring gear, and both are placed up against the differential. Four of the new supplied reverse-rotation ring-gear bolts (one each at noon, 3, 6, and 9 o'clock) are hand-threaded and tightened in increments using a 31/44-inch socket until the ring gear and reluctor ring are fully seated against the pinion. The four bolts are then removed.

A moderate amount of red Loctite #271 is applied on all 10 bolts; then they are tightened in increments until snug. With the differential mounted on the hydraulic press to keep it in place, the ring-gear bolts are torqued to 89 ft-lbs in an alternating pattern similar to tightening the lugs on your Bird's wheels.