FLUID LEVEL CHECK
See Figures 1 through 5
The oil in the transfer case should be checked at least every 15,000 miles (24,000 km) and replaced every 25,000-30,000 miles (40,000-48,000 km), or more frequently if driven through deep water or mud.
- With the truck parked on a level surface, remove the filler plug from the side of the transfer case housing on 1980-86 models (720 series), or the rear of the housing on 1986-88 models (D21 series).
- If the lubricant begins to trickle out of the hole, there is enough. Otherwise, carefully insert your finger (watch out for sharp threads!) and check to see if the oil is up to the edge of the hole.
- If not, add oil through the hole until the level is at the edge of the hole. Most gear lubricants come in a plastic squeeze bottle with a nozzle; making additions simple. You can also use a common everyday kitchen baster.
- Replace the filler plug, run the engine and check for leaks.
DRAIN AND REFILL
See Figures 6, 7 and 8
Once every every 30,000 miles (48,000 km), the oil in the transfer case should be changed.
- The transfer case oil should be hot before it is drained. If the engine is at normal operating temperature, the oil should be hot enough.
- Raise the truck and support it properly on jackstands so that you can safely work underneath. You will probably not have enough room to work if the truck is not raised.
- The drain plug is located on the bottom of the transfer case. Place a pan under the drain plug and remove it. Keep a slight upward pressure on the plug while unscrewing it, this will keep the oil from pouring out until the plug is removed.
- Allow the oil to drain completely. Clean off the plug and replace it, tightening it until it is just snug.
- Remove the filler plug from the side of the case. There will be a gasket underneath this plug. Replace it if damaged.
- Fill the transfer case with gear oil through the filler plug hole as detailed previously. Refer to the Capacities Chart for the approximate amount of oil needed to refill your transfer case.
- The oil level should come right up to the edge of the hole. You can stick your finger in to verify this. Watch out for sharp threads.
- Replace the filler plug and gasket, lower the truck, and check for leaks. Dispose of the old oil in the proper manner.