Re-Gear and Speedometer Calibration - UpTo Speed

Lower Gears + Tuning = Better Mileage

Brandan GilloglyAug 1, 2008
Photo 2/38
You might recognize this Silverado 1500 from a Fantastic Four article in 2007. This truck was our first GMT-900 to go under the knife, and we really loved the look we got from the Pro Comp lift, wheels, and tires. The JBA headers and exhaust, combined with an AEM intake, boosted power across the rpm range. And, it also gave the truck a couple hundred rpm in the top end before it began to fall off. But even with an extra 25 hp and 23 lb-ft of torque, the truck still was not quite as peppy as it was with its original wheels and tires.
One year later and the added mass of the 35-inch tires was starting to show by way of some rear-end noise. We decided to do what we probably should have done when we first lifted the truck: add new gears. We called Off Road Warehouse in San Diego, to get the truck on a lift and into some new 4.56:1 gears and a Mag-Hytec diff cover. We also decided it was time to correct the speedometer, which we took upon ourselves. When we first lifted the truck, there weren't any programmers available, but now Hypertech has a solution. Check out how we tuned the truck, solved our speedometer issues, and how Bill "Thunder" Hulls, along with the guys at Off Road Warehouse, resuscitated our Silverado.
From the Driver Seat
After the new gears were installed, the noise was gone and the truck felt like it did when it was new. The gears corrected the tire height, and the added power from the programmer, plus the extra power we picked up from the intake and exhaust has woken the truck up. Best of all, the mileage improved from a dismal 12 mpg average to 15 mpg, a 25-percent improvement. That's the mileage we were getting from a stock '07 Silverado! The Mag-Hytec differential cover provided added peace of mind; the increased fluid capacity, cooling fins, and magnets will all help the gears last longer, and the dipstick will make it much easier to maintain. The speedometer calibrator finally made the gauge accurate, but with our new gears we were less than 5-percent off anyway. The real benefit is the ability to change tire sizes and update everything in the matter of an hour.
Your Questions Answered
TIME SPENT WORKING: 7 hours
(6 for both differentials, 5 minutes for the programmer, and 45 minutes for the speedometer calibrator).
DEGREE OF DIFFICULTY: Advanced
(Due to the specialized parts and importance of proper setup, gear installation is difficult. However, anyone can
install the differential cover and programmer.)
Tools Used:
Sockets, an impact wrench, bearing puller, press, dial indicator, and micrometer
PARTS USED:
Hypertech Max Power Programmer PN 32004 $379.99
Hypertech Speedometer Calibrator PN 730102 $209.39
Mag-Hytec GM 10-bolt 8.5-inch cover $250
{{{Sierra}}} Gear and Axle 8.5-inch GM 4.56 $125.40
Sierra Gear and Axle 8.5-inch GM '99-up master bearing kit $78.97
Sierra Gear and Axle 8.25-inch GM IFS 4.56 $148.50
Sierra Gear and Axle IFS install kit $69.63
TOTAL: $1,261.88
(Not including tax and labor)  

Sources

Hypertech
Bartlett, TN 38133
901-382-8888
www.hypertech.com
Mag-Hytec
Van Nuys, CA 91402
818-786-8325
www.mag-hytec.com
Off Road Warehouse
San Diego, CA 92111
800-341-7757
http://www.offroadwarehouse.com/
Sierra Gear and Axle
800-792-2714
www.sierragear.com

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