How to Change the Rear Differential Fluid on a 2003 GMC Sierra

Changing the gear oil in the rear differential of your GMC truck will extend the life of the gears, bearings and seals in the rear end. Along with lubrication, the gear oil cools the gears and conditions the seals in the rear axle housing. There are several different options for the rear ends on the GMC, but the process of changing the oil is the same. Be sure to consult the dealer or an auto parts professional for the correct gear oil to use in your truck.

Things You'll Need

• Oil drain pan
• Socket set
• Ratchet
• Putty knife
• Gasket scraper
• Shop rag

Instructions

1. Position a drain pan under the center of the rear axle housing then remove the bolts holding the cover on the differential with a socket and ratchet. Pry the cover loose from the differential housing with a putty knife and allow the gear oil to drain into the pan.

2. Scrape off the old gasket material from the axle housing and from the cover with a gasket scraper or putty knife. Wipe down the cover and mounting surface on the differential housing with a clean rag, removing any oil or debris on the surfaces.

3. Position a new gasket on the differential cover then place the cover against the differential housing. Install the mounting bolts by hand then tighten them using a criss-cross pattern with a socket and ratchet.

4. Unscrew the fill plug from the differential cover using a ratchet and socket and fill the differential with new gear oil. GMC trucks use different gear oils depending on the options in your differential. Posi-lock and open differentials have different requirements so check with the dealer for the recommended gear oil.

5. Insert the tip of the gear oil bottle into the hole in the cover to fill it. The differential is full when the gear oil just starts to run out of the hole. Install the plug and tighten it with a socket and ratchet. Wipe down the cover with a rag then remove the drain pan from under the truck.

6. Dispose of the used gear oil properly. Most auto parts stores have a program in place for recycling used oil, and it is often free if you bring in the oil.

References

• "Haynes Repair Manual 1999 to 2006 Chevy and GMC pickups, 2WD and 4WD;" Ken Freund; 2008