FLUID LEVEL CHECK
See Figures 1 and 2
The oil in the manual transmission should be checked at least every 7500 miles (12,000 km) for 1970-78 vehicles, or 15,000 miles (24,000 km) for 1979-88 vehicles and replaced every 25,000-30,000 miles (40,000-48,000 km), even more frequently if driven through deep water.
- With the truck parked on a level surface, remove the filler plug (square head on some models, Allen head on others) from the left side of the transmission housing.
- 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 Figure 3
Once every 24,000 miles (40,000 km) for 1970-78 vehicles, or once every 30,000 miles (48,000 km) for 1979-88 vehicles, the oil in the manual transmission should be changed.
- The transmission oil should be hot before it is drained. If the engine is at normal operating temperature, the transmission 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 transmission. 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 transmission case. It is on the driver's (left) side. There is usually a gasket underneath this plug. Replace it if damaged.
- Fill the transmission 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 transmission.
- 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.
CHECKING WATER ENTRY
See Figure 41986-88 4WD Models Only
After having driven in deep water or mud, the clutch housing should always be checked for water entry. There is a small rubber gasket at the bottom of the left side leading edge of the transmission case where it mates with the rear of the engine block, carefully pry it out and let any water that has collected in the clutch housing seep out.