Replacing your rear gearset with numerically higher gears will result in better acceleration at the expense of increased fuel consumption. Gear replacement is a long and involved process that varies from vehicle to vehicle, but generally requires dissasembly of your rear differential. This requires removing your rear brakes, releasing the rear axles, and disconnecting the driveshaft.
Park your vehicle on flat ground and loosen the rear lug nuts. Use a hydraulic jack to raise the rear end, then place your vehicle on jack stands. Remove the wheels followed by the rear brakes. The rear calipers will typically be held to the rear rotor with two bolts. Remove the bolts, lift the calipers off the rotors, then zip tie them out of the way, making sure you are not placing any weight on the rear brake line.
Remove the C-clips that secure the rear axles with needle-nose pliers, then remove the bottom bolts on the rear differential. Allow the fluid to drain out of the differential. Some vehicles may have dedicated drain plugs on the rear differential cover, in which case drain the rear differential via the drain plug, then remove the fill plug on the rear differential cover. Expect anywhere from 1 to 3 quarts of fluid to drain from the differential, so be sure to have a pan to catch the fluid. Remove the rear differential cover by removing the securing bolts, which can number from eight to 12 bolts.
Remove the rear locking bolt with a wrench. This will typically be located in the middle front section of the carrier. Rotate the carrier for the shaft to slide out. Push in the half shafts to remove the C-clips and slide the half shafts away from the center carrier. Remove the carrier caps with a socket and long ratchet. Use a large pry bar to push the carrier up and release it from the housing. With the carrier out, you will be able to release the drive shaft by placing a punch in the locking position, then use a rubber mallet to push the pinion out.
Use a bearing puller to remove the old bearing in the pinion. You may find it easier to do this at a work bench since the pinion is now out of the vehicle. Press the bearing on the new pinion. Install the pinion with a new crush sleeve. Shim the carrier to make sure it is centered. Bolt the new gear into the differential and torque down the retaining bolt. Install the differential ring gear, making sure to shim correctly. Reinstall the caps and torque to your manufacturer's specifications.
Reinstall the axles and reinstall the C-clips into the differential, followed by the spider gear drive pin. Reinstall the differential cover with a fresh gasket, then fill the differential with fresh fluid. Refer to your owners manual to determine the correct amount of fluid, as well as the specified gear oil weight. Most vehicles use 75W-90 oil, but it can vary among manufacturers. Once the vehicle is buttoned up and on the ground, be sure to slowly drive a few figure 8 patterns to assure fluid distributes properly.
