The front differential on a 1999 Chevrolet Silverado takes the input from the transfer case and uses it to turn the front axles and the front wheels when four-wheel drive mode is engaged. Should this differential fail, then the front axles may not turn, and could potentially lock up. Should this happen, you must remove the differential from the Chevrolet and replace it with a new one. This takes a few hours to do correctly.
Park the Silverado and put on the parking brake. Put the drain pan under the front differential. Unbolt the drain plug on the front differential using the 1/2-inch ratchet and socket. Lift the front of the truck with the jack. Take off the front wheels.
Unbolt the driveshaft from the differential with the 1/2-inch ratchet and socket and an open-end wrench and pull it out of the differential. Unbolt the drive axles from the differential with the 1/2-inch ratchet and socket and hang the axles from the frame with the mechanics wire. Unplug all of the electrical connections from the differential with your hands.
Pull off the relay rod connecting the pitman arm and the idler arm on the steering using the 1/2-inch ratchet and socket. Lift the transmission jack up to the differential and wrap the chains from the jack around the differential to hold it to the jack. Unbolt the differential from the drivetrain with the 1/2-inch ratchet and socket and an open-end wrench. Lower the jack down and pull it out of the way.
Remove the old differential from the transmission jack. Set the replacement differential onto the transmission jack. Roll the jack under the front end and lift up the jack. Bolt the replacement differential to the drivetrain with the 1/2-inch ratchet and socket and an open-end wrench. Remove the transmission jack.
Reinstall the relay rod to the steering with the 1/2-inch ratchet and socket. Reinstall the wiring with your hands, then bolt the drive axles to the differential with the 1/2-inch ratchet and socket, then reinstall the driveshaft to the differential with the 1/2-inch ratchet and socket and an open-end wrench.
Fill the differential with the gear oil using the specifications listed in the owner's manual. Replace the front wheels, raise the Silverado slightly, remove the jack stands and lower the Silverado.
