The correct lubricant to use is SAE 80W-90 GL-5, or SAE 80W GL-5 for cold climates.
See Figure 1
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
No intervals are specified for changing the transmission lubricant, 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 1976-79 Tremec top cover three speed is drained by removing the lower extension housing bolt.
- Replace the drain plug.
- Add lubricant with a suction gun or squeeze bulb. The correct lubricant is SAE 80W-90 GL-5, or SAE 80W GL-5 for cold climates.
- Reinstall the filler plug. Run the engine and check for leaks.