The fluid in both the rear axle and, if equipped, the front drive axle should be checked at each oil change. The fluid in the rear axle should be changed at the truck's first engine oil change and thereafter at intervals of 7500 miles (vehicles through 1986) or 15,000 miles (1987 and later vehicles). Changing the front drive axle fluid on these vehicles usually requires it's removal and partial disassembly. The fluid in the front drive axle should not need to be changed unless the axle is removed for repair.
The fluid is checked by removing the filler plug, but keep in mind the the truck must be sitting level or an incorrect fluid level will be indicated. Maintain the fluid at a level 3 / 8 in. below the filler plug hole.
Always use SAE 80W-90 GL5 gear lubricant, part number 1052271, or equivalent.
See Figures 1 and 2
When checking the fluid, the vehicle must be level. If it was necessary to raise and support the vehicle to access the filler plug, the vehicle must be supported at sufficient points (all wheels or 4 points on the frame) so it is sitting level and is not tilted forward/backward or to one side.
- If necessary for access to the filler plug, raise and support the vehicle safely using jackstands, but make sure the vehicle is level.
- Remove the filler plug, located at the side of the differential carrier.
- Check the fluid level, it should be 3 / 8 in. below the bottom of the filler plug hole.
- If necessary add fluid through the filler plug opening. A suction gun or a squeeze bulb may be used to add fluid. Most parts stores will carry a small, hand operated pump which will greatly ease the task of adding fluid.
- Install and tighten the filler plug.
- Remove the jackstands and carefully lower the vehicle.
DRAIN AND REFILL
See Figures 3, 4, 5 and 6
- Run the vehicle until the lubricant reaches operating temperature.
- If necessary for access, raise and support the vehicle safely using jackstands; but make sure that the vehicle is level.
- Use a wire brush to clean the area around the differential. This will help prevent dirt from contaminating the differential housing while the cover is removed.
- Position a drain pan under the rear axle.
- Unscrew the retaining bolts and remove the rear cover. When removing the cover, a small prytool may be used at the base of the cover to gently pry it back from the axle housing, breaking the gasket seal and allowing the lubricant to drain out into the container. Be careful not to use excessive force and damage the cover or housing.
- Carefully clean the gasket mating surfaces of the cover and axle housing of any remaining gasket or sealer. A putty knife is a good tool to use for this.
- Install the rear cover using a new gasket and sealant. Tighten the retaining bolts using a crosswise pattern to 20 ft. lbs. (27 Nm).
Make sure the vehicle is level before attempting to add fluid to the rear axle or an incorrect fluid level will result.
- Refill the rear axle housing using the proper grade and quantity of lubricant as detailed earlier in this section. Install the filler plug, operate the vehicle and check for any leaks.