All vehicles use a multipurpose gear oil in the manual transmission. The recommended types are: API GL4 or GL5 with the viscosity SAE 75W90 or 80W90.
The oil in the manual transmission should be checked at least every 7500 miles (12,000 km) and replaced every 25,00030,000 miles (40,00048,000 km). Even more frequently if driven in deep water.
- With the truck parked on a level surface, remove the filler plug (usually 17mm) from the side of the transmission housing. A gasket will also have to be removed and replaced.
- 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 somewhat easier, though not always simple.
- Install the filler plug with a new gasket. Run the engine and check for leaks.
DRAIN AND REFILL
The oil in the manual transmission should be changed at least every 30,000 miles (48,000 km).
- The transmission oil should be warmed to normal operating temperature before it is drained.
- Raise and safely support the truck on safety stands 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. It is usually on the passenger side on four speeds, and on the bottom center of five speeds. Place a pan under the drain plug, and then 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 then install it, tightening it until just snug.
- Remove the filler plug from the side of the transmission case. It is usually on the driver's side of four speeds, and on the passenger side on five speeds. There will be a gasket underneath this plug. Replace it every time the bolt is removed.
- Fill the transmission with gear oil through the filler plug hole.
- 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.
- Install the filler plug and gasket, lower the truck, and then check for leaks. Dispose of the old oil in the proper manner.