Then the axle was carefully...
Then the axle was carefully pulled out of the end of the housing and stored. The process was repeated for the other axle.
In stock form, the six-speed-equipped Formula sheared an axle on drag radials during drag testing. Now that the car pushes over 465 rwhp, only a maximum-effort 10-bolt can withstand the brutal power of the turbocharger. Since the rear-wheel horsepower rating of the Formula is pushing the outer limits of the 10-bolt, it should be noted that the primary use of the car is spirited street driving with very occasional trips to the dragstrip. If the car's use had been primarily at the track, an aftermarket rearend would have been highly recommended.
The teardown and subsequent build-up of a used housing was completed by Texas Drivetrain Performance of Fort Worth, Texas. Texas Drivetrain Performance has been in business for five years and is owned by Jason Bailey. This shop builds and repairs all makes of rearends and manual transmissions but specializes in late-model GM performance, including the 7.625-inch 10-bolt and the T-56 manual transmission. The shop is fully equipped with all of the specific GM Kent Moore service tools necessary to ensure that the rearend is built correctly. Peyton Performance Automotive of Waxahachie welded the axle tubes and straightened the housing, and Randy's Ring & Pinion of Everett, Washington, supplied the rearend components. Now let's get to work.
To remove the differential,...
To remove the differential, a 5/8-inch socket and a 1/2-inch breaker bar was used to break each of the four bearing-cap bolts loose.
Conclusion
Check next month's issue as a replacement Eaton limited-slip differential and Yukon axles are installed along with a TA differential cover. We'll wrap up the 10-bolt build, presenting you with a breakdown of the parts list and cost of building the rearend, and then we'll perform a strength and cost comparison to the aforementioned GM 12-bolt and Ford 9-inch rearends.
| Recommended Tools And Resources |
| Standard socket set Allen wrench set GM Kent Moore differential service tools OTC race driver Pry bar or large screwdriver GM service manual |
| Recommended Parts And Supplies |
| (1) Yukon rearend installation kit (PN YK GM7.5-B, retail $138.21) (2) Yukon axle bearings (PN AK1563, retail $15.20 each) (2) Yukon axle seals (PN 8660S, retail $2.68 each) (2) Yukon axles (PN YAG 26059962, retail $175) (1) Yukon 3.42-ratio ring and pinion set (PN GM 7.5-342, retail $196.35) (1) Eaton limited-slip differential (PN EAT19599, retail $541.04) (1) TA differential cover (PN YPT3-GM7.5, retail $148.11) (1) TA stud kit for differential cover (PN 1815, retail $24.99) (2) Qts. 80W90 gear oil (GM PN 88900329, retail $6.47 each) (1) Bottle GM limited-slip additive (GM PN 1052358, retail $7.65) |
The bearing bolts and caps...
The bearing bolts and caps were removed from the differential housing. A sealable, plastic bag and a permanent marker work great for keeping the items in order for reassembly.
To take the differential out...
To take the differential out of the housing, a large pry bar on a ring-gear bolt was used to extricate the housing. Once the differential starts to move out, it may be necessary to leverage your tool behind one (as shown) or both ends of the differential to remove it. When extricating the differential, the races and shims were kept in side-specific order.
A closer look at the Torsen...
A closer look at the Torsen T2 differential reveals the "Equvex " parallel axis-gear technology that results in a full-time torque-sensing, torque-biasing, differential system. In other words, the differential applies power to the axles to maximize traction. Attached to the differential is a set of GM factory 3.42:1 gears and a reluctor wheel. The reluctor wheel interfaces with the sensor on the top of the housing to provide input for the ABS. On traction-control-equipped cars, each of the axles has a smaller reluctor wheel pressed onto the axle base with sensors residing in the backing plates for the rear disc brakes.
| Five Steps To A Stronger Rear |
For just over $500, including labor, the best investments a 10-bolt owner can make to strengthen the rearend by approximately 20 percent are replacing the weak factory axles, welding the axle tubes to the differential housing, and installing a TA differential cover. Let's elaborate on these mods and provide a few more:
Install aftermarket axles. The factory axles are weak and can break under racing conditions even with stock power levels. Replace the axles with a set from Yukon. Cost: $175 Fully weld the axle tubes to the center housing so they can't rotate. This strengthens the entire assembly. Cost: $85-$100 Use a TA rear differential cover with bearing-cap preload screws. Preloading the bearing caps prevents deflection between the differential and the ring and pinion gears (prevents ring moving away from pinion). Cost: $148.11, plus $24.99 for stud kit Replace the Torsen T2 differential with an Eaton or Auburn unit if you're pushing over 400 rwhp for street or strip applications. The casings on the Eaton and Auburn units are beefier and better able to handle higher horsepower requirements. The Eaton unit is a clutch-type that can be rebuilt at home, while the cone-type Auburn unit has to be sent to the factory for service. For road racing or autocross applications, use a Torsen T2R differential. Cost: $450-$600 Have a high-quality ring-and-pinion set installed. If you're looking to change gear ratios in your rearend, GM supplies numerous ratios, including 3.73 and 4.11. Have a qualified shop set the backlash to factory spec (0.005-0.009) with a footprint in the middle area of the ring gear teeth. Cost: $200, plus $200 for installation and an additional $150 to remove and rebuild the rearend |
With the differential out...
With the differential out of the way, we removed the pinion using a 1-1/4-inch socket on an impact gun to take off the pinion nut. After the yoke was removed, the pinion nut was screwed back onto the pinion about three full turns. Using a 4-pound sledge hammer, the pinion was driven rearward in the housing to free it from the bearings.
The nut was then taken back...
The nut was then taken back off, and the pinion was pulled out of the housing.
By placing a pry bar or large...
By placing a pry bar or large screwdriver under its lip and then prying up, the pinion seal was liberated. Then, out came the outer pinion bearing.
With the bearing removed,...
With the bearing removed, a punch was employed to carefully drive out the outer and inner pinion-bearing races, taking care to not damage the race seating surfaces.
After removing the axle seals...
After removing the axle seals from the ends of the axle housing with a pry bar, a bearing puller with an integral slide hammer was attached behind the axle bearing on the inner edge. Following several hard jolts of the slide hammer, the bearing came loose from its press-fit race.
The pinion gear was set up...
The pinion gear was set up in an Arcan 20-ton press to remove the pinion bearing. After attaching the bearing separator, the bearing was pressed off and the factory pinion shim examined. It is vitally important, even if using new gears, to separate the pinion bearing in order to determine the thickness of the shim, as this is an excellent starting point for reassembly. In this case, a micrometer determined that the shim was 0.033-inch. On average, the 10-bolt uses between 0.030- and 0.034-inch shim thickness. Differences in the shim size are necessary to compensate for minute manufacturing thickness deviations in the inner pinion-bearing race and housing.