The rear differential in your 2004 Tahoe contains the ring-and-pinion gear set known as the "Final Drive" gear. Power from the drive shaft turns the pinion gear in the differential, which in turn moves the ring gear and carrier that are attached to the wheels through the axles. This provides a way to transmit power from the engine to the rear wheels smoothly, without binding or noise during a turn. Maintenance on the differential, in the form of a fluid change, is required to prevent damage to the gears from heat and pressure developed during operation.
Place wheel chocks against the front tires to prevent movement of the Tahoe while the repair is done. Lift the rear wheels off the ground, using a floor jack positioned under the center of the rear differential. Place jack stands under the rear axles and lower the vehicle onto them to provide support and safety.
Remove the floor jack and place the drain pan under the center of the differential. Loosen the 13-mm differential cover bolts, using a wrench or socket and ratchet. Allow the differential fluid to drain into the pan -- the fluid is very thick and it may take a few minutes for it to drain out completely.
Remove the differential cover bolts when the fluid is completely drained. Slide the cover out from under the Tahoe. Clean the gasket surface, using the gasket scraper to remove all traces of the old gasket. Clean the oily residue off the cover, using spray parts cleaner and a shop towel. Lay the cover aside and clean the gasket surface on the differential in the same manner.
Attach the new gasket to the differential cover, using gasket cement. Reinstall the cover when the gasket cement is dry, and tighten the cover bolts snugly to prevent leaks. Avoid over-tightening and splitting the gasket.
Remove the fill plug on the passenger side of the differential, towards the front of the vehicle, using a ratchet and 3/8-inch drive extension bar. Install the hand pump on the first quart of fluid (synthetic 75w90 gear oil), and place the nozzle of the pump in the fill hole. Pump the fluid into the differential. Continue adding additional quarts of fluid until the fluid level is approximately 1/2-inch below the edge of the fill hole.
Reinstall the fill plug and tighten it securely. Raise the Tahoe off the jack stands and remove the stands before lowering the vehicle to the ground. Test-drive the SUV and check for leaks.
