2004 GMC Sierra Buildup - Performance In Mind

Project Novakane Part IV: Traction = Action

Dan WardNov 1, 2010
As a grown man, I can't explain it, but the sound and smell of a burnout makes me smile. It's a phenomenon we're sure you can relate to. With that said, nothing is worse than trying to do a burnout, only to suffer the "one-wheel-peel" shame. Most 1/2-ton trucks leave the assembly plant with an open differential sending power only to the passenger-side rear wheel and tire. If you're lucky, or if you checked off the options box at the dealer, your truck may have a posi or locking differential and your truck benefits from sure-footed traction. If not, don't sweat it because this month's installment of our Project Novakane '04 GMC Sierra buildup is for you.
Photo 2/32
To get our Sierra to hook up while at the track, dragstrip, and in poor weather conditions, we contacted 4Wheel Parts and ordered a complete rear differential overhaul. Every part we replaced, we did so with an upgrade in performance in mind. These upgrades included: a new Eaton Detroit Truetrac limited slip, 3.73 gears (from the factory 3.42 gears) and master overhaul kit from G2 Axle & Gear, Mag-Hytec aluminum differential cover for our 10-bolt, and high-performance 75-90W gear oil from Royal Purple. Rather than cut any corners on the install, we went to one of SoCal's leading differential companies, Unitrax, in Anaheim, California. These guys have been giving cars and trucks better traction for 25 years, and they know axles inside and out. Whereas the install does require a press for installing the pinion and differential bearings, once that hurdle is overcome, you can do this install in your own driveway. If your truck could use improved traction and performance, this upgrade is a must.
FROM THE DRIVER SEAT
After just six hours, our GMC was dramatically improved. We followed the instructions and kept our foot out of the throttle for the first 500 miles, but once the gears were broken in, we proceeded to beat on the rearend as hard as we could. It held up and didn't even break a sweat. This parts combo should hold up to around 500 hp before new axles will be needed, but these core parts will be good to go for the long haul. We chose the 3.73 gear ratio to help our "out of hole" times and initial acceleration and they did just that. The shorter gears get our engine in its power band more quickly, with the only downside being 250 higher rpm on the highway (although we haven't seen any large drop in mileage). Smooth best describes the Eaton Detroit Truetrac, as it seamlessly engages when both wheels need to propel the truck. Extra fluid capacity, thanks to the Mag-Hytec diff cover, will keep everything cooler longer, and our entire setup will last for the remainder of the truck's life.
Photo 32/32
YOUR QUESTIONS ANSWERED
Time Spent Working: 6 Hours
Degree Of Difficulty: Advanced
Tools Needed:
Pinion depth tool, press for bearings, 11mm wrench, 13mm, 15mm, 17mm, and 19mm socket, torque wrench, pliers, marking paste, digital caliper, drain pan
Parts Used:
Eaton Detroit Truetrac limited slip for 8.6-inch 30-slpine 913A481 $430.99
G2 Axle & Gear 3.73 gears for GM 8.6-inch 30-spline 10-bolt G/22-2021-373 $217.99
G2 Axle & Gear master overhaul kit for GM 8.6-inch 30-spline 10-bolt $93.99
Mag-Hytec aluminum diff cover for GM 10-bolt GM10-8.5 $250.99
Royal Purple 75-90W high-performance gear oil $15.99 (3)
Total: $1,038.93
(prices from 4wheelparts.com and do not include tax, shipping, or installation)

Sources

4Wheel Parts erferer
Compton, CA 90220
877-474-4821
www.4wheelparts.com
Mag-Hytec
Van Nuys, CA 91402
818-786-8325
www.mag-hytec.com
Royal Purple
Porter, TX 77365
888-382-6300
www.royalpurple.com
Eaton
Cleveland, OH 44114
800-328-3850
http://www.eaton.com
G2 Axle & Gear
Compton, CA 90220
310-900-2687
www.g2axle.com
Unitrax
Anaheim, CA 92806
800-622-4327
www.gounitrax.com

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