Beefing Up the 7.625 10 Bolt

After spending the better part of this last year building up the engine in my 92 GTA, and hoping to run low or mid twelve’s in the quarter, I came to the conclusion that the factory rear end will be living on borrowed time this spring when I bolt on my Hoosier slicks and go to the drag strip. This left me with three options:

1. Replace it with a 9" Ford.
2. Replace it with a GM 12 Bolt.
3. Build the hell out of the existing unit with the best parts that I could find.

This was an easy choice for me, given the expense of the other two units, I had to stick with my original 7.625 10 bolt. These rear ends can be built to withstand an amazing amount of drag strip abuse, with the right selection of parts. Here is how I did it.

1. Weld the axle tubes all the way around where they go into the housing. The factory only used two spot welds on each tube. This will help keep the tubes from twisting, which will lead to broken axles. The cost was free for me because I am a professional welder and machinist. If you don’t know how to weld though, any competent welding shop can do it for you for under $25.
2. Use 28 spline alloy axles from Drivetrain Direct. They are rated to be 35% stronger than the OEM 28 spline ones. The factory 26-spline axles should be thrown over the nearest hillside! Phone: 888-5844327 EXT. 116. Part number: KA7A7. Cost: $295, which includes new wheel studs that are already pressed in.
3. Use an aluminum rear end girdle. I chose the one from Summit Racing because it had all the features I was looking for at a very reasonable price. The mounting flange is 1/2" thick which will help increase the rigidity of the housing. It has a fill plug and a drain plug as well. It also has two adjustable allen head studs with large feet on the opposite end that tighten down against the main caps. A lot of places that sell these items will also try to sell you a stud kit for $25 to install it. You don’t need them, just go to your local hardware store and buy 10 X 1-1/2" long, 5/16-18 grade eight bolts and flat washers for about $5. These bolts have a clamping force of about 170,000 psi, which is plenty. Phone: 800-230-3030. Part: SUM730755. Cost: $139.99.

   If you have plenty of money to spend, JEGS also sells a girdle that accomodates an axle tube brace kit which will stop forward movement of the housing tube ends, eliminating case distortion. These two pieces together were a little too pricey for me, but to each his own! Phone: 800-345-4545. Ultimate girdle part number:619-301-7.5G. Cost:$139.99. Axle tube brace kit part number: 619-341-A. Cost:$129.99.

4. Use a solid bearing spacer from Drivetrain Direct in place of the stock crush sleeve. It will really help keep the pinion gear from trying to walk up the ring gear, which is a design flaw of these rear ends. Phone: 888-584-4327 EXT. 116. Cost: $21.95.
5. Use a big BEEFY differential such as the Zexel Torsen available from SLP Engineering. There are two models available: An OEM takeoff from a newer Camaro-Trans Am, which has one conical gear to engage the opposite wheel, or a Heavy Duty unit that has two conical gears. By using this unit your wheels will be solidly locked when you floor it, plus it gives full differentiation in the curves. Also, it never has to be rebuilt because it doesn’t have a clutch pack. Phone: 732-349-2109. Part (for takeoff): 6451T Cost (for takeoff): $99.95. Part (heavy duty): 65002. Cost (heavy duty): $299.95.
6. This next tip is just extra insurance against breaking at the track: replace the stock differential cross pin with one make out of Zytanium. The stock pin has been known to break into pieces on more than one occasion. This pin is not needed when using the Zexel Torsen units because they do not require one. Available from year One Next Generation. Phone: 800-921-9214. Part: D66. Cost: $28.
7. If you are also changing your gear set be sure to use a high quality gear set such as GM, Richmond, Strange, or US Gear. If you use one of those generic gear sets, you will probably regret it later when you come off the starting line and break a bunch of ring gear teeth.
8. Use Redline Synthetic Shockproof gear oil and friction modifier. It comes in three formulations: super light, light, heavy. For our third gen cars, I recommend the light one. Available from Summit Racing. Phone: 800-230-3030. Part (gear oil): RED58404. Cost: $7.95 ea. Part (friction modifier): RED80301. Cost: %5.94.

This is the rear end that I have built for my 92 GTA, which I am confident will last many race seasons. If you are on a tighter budget than this, and your car is running 13.50 or slower, you can substitute the OEM 28-spline axles for the alloy ones, and substitute the H.D. Zexel differential with the takeoff version or your OEM posi unit. But, if you are quicker than that, you had better use the good stuff that I outlined above or you may just grenade your rear end at the racetrack.

Total expense using the good stuff- $806.74 *
Total expense using takeoff posi and OEM axles- $311.74 *

This is a hell of a lot cheaper than $2,000 to $2,500 to have a 9" or 12-bolt custom built to fit our cars!

* These figures assume you already have your gear set.