The correct lubricant to use in the manual transmission varies depending on model year and transmission. Refer to the list below for the lubricant that should be used in your vehicle. In some instances you must know the RPO code for the transmission in your truck. This code can be found on the Service Parts Identification label located on glove box door or on the fenderwell.1980-81
Check the lubricant level at the interval specified in the maintenance chart.
- With the truck parked on a level surface, remove the filler plug from the side of the transmission case. Be careful not to take out the drain plug at the bottom.
- If lubricant begins to trickle out of the hole, there is enough. If not, carefully insert a finger (watch out for sharp threads) and check that the level is up to the edge of the hole.
- If not, add sufficient lubricant with a funnel and tube, or a squeeze bulb to bring it to the proper level.
- Replace the plug and check for leaks.
DRAIN AND REFILL
On 1986 and 1987 trucks equipped with the four speed (RPO M73) transmission, four speed transmission with overdrive, or the five speed transmission the transmission lubricant should be changed every 30,000 miles (50 km). No intervals are specified for changing the transmission lubricant for trucks built prior to1985, but it is a good idea on a used vehicle, one that has been worked hard, or one driven in deep water. The vehicle should be on a level surface and the lubricant should be at operating temperature.
- Position the truck on a level surface.
- Place a pan of sufficient capacity under the transmission drain plug.
- Remove the upper (fill) plug to provide a vent opening.
- Remove the lower (drain) plug and let the lubricant drain out. The 1980 Tremec top cover three speed transmission is drained by removing the lower extension housing bolt.
- Replace the drain plug.
- Add the correct lubricant with a suction gun or squeeze bulb.
- Reinstall the filler plug. Run the engine and check for leaks.