TH400 Transmission Fluid: How to Choose and Change It

The TH400 transmission, also known as the Turbo Hydra-Matic 400, is renowned for its strength and durability. However, like any mechanical component, it requires proper maintenance to ensure optimal performance and longevity. One of the most crucial aspects of maintaining a TH400 transmission is selecting and changing the transmission fluid. In this guide, we’ll cover how to choose the right transmission fluid for your TH400 and the steps to change it.

Choosing the Right Transmission Fluid

Selecting the appropriate transmission fluid for your TH400 is vital for maintaining its performance and extending its lifespan. Here are some key considerations:

1. Type of Fluid:
   • Dexron III/Mercon: The TH400 was originally designed to use Dexron III or Mercon transmission fluid. These fluids provide the necessary lubrication and hydraulic properties required by the transmission.
   • Synthetic Fluids: Many enthusiasts prefer synthetic transmission fluids for their superior heat resistance and longevity. Synthetic fluids can provide better performance, especially in high-stress or high-temperature environments.
2. Quality of Fluid:
   • Brand and Specifications: Choose a high-quality transmission fluid from a reputable brand. Ensure that the fluid meets or exceeds the specifications recommended by General Motors for the TH400.  Do also have a look at 68rfe torque converter.
3. Additives:
   • Some transmission fluids come with additional additives that can enhance the performance of your TH400. These additives can improve lubrication, reduce wear, and extend the fluid’s life. However, it’s essential to ensure that any additives are compatible with your transmission and do not void any warranties.

Steps to Change TH400 Transmission Fluid

Changing the transmission fluid in your TH400 is a straightforward process that can be done with basic tools and some mechanical knowledge. Here’s a step-by-step guide:

1. Preparation:
   • Tools and Supplies: Gather the necessary tools and supplies, including a drain pan, socket set, screwdrivers, a new transmission filter, a gasket, and the appropriate amount of transmission fluid (usually 8-12 quarts).
   • Safety: Ensure the vehicle is parked on a level surface and the engine is cool. Use jack stands to safely lift and support the vehicle if needed.
2. Drain the Old Fluid:
   • Locate the Pan: The transmission pan is located at the bottom of the transmission. Place the drain pan underneath it to catch the old fluid.
   • Remove the Bolts: Use the socket set to remove the bolts securing the transmission pan. Start by loosening the bolts on one side, allowing the fluid to drain from that side into the drain pan.
   • Remove the Pan: Once most of the fluid has drained, remove the remaining bolts and carefully lower the transmission pan. Be prepared for additional fluid to spill out.
3. Replace the Filter:
   • Remove the Old Filter: The transmission filter is typically held in place by a few screws or clips. Remove the old filter and discard it.
   • Install the New Filter: Install the new transmission filter, ensuring it is securely in place.
4. Clean and Reinstall the Pan:
   • Clean the Pan: Thoroughly clean the transmission pan and remove any old gasket material. Check for any metal shavings or debris, which could indicate internal transmission issues.
   • Install the New Gasket: Place the new gasket on the transmission pan. Some gaskets may require a thin layer of gasket sealer to hold them in place.
   • Reinstall the Pan: Carefully align the transmission pan and start threading the bolts by hand. Once all bolts are in place, tighten them in a crisscross pattern to ensure an even seal. Be careful not to overtighten the bolts, as this can damage the gasket and cause leaks. Do also have a look at transmission cooler.
5. Refill the Transmission:
   • Locate the Fill Tube: The fill tube is typically found near the back of the engine bay and is fitted with a dipstick.
   • Add New Fluid: Using a funnel, add the new transmission fluid through the fill tube. Start by adding about 4-5 quarts and then check the fluid level using the dipstick.
   • Start the Engine: With the vehicle in park and the parking brake engaged, start the engine and let it idle. Cycle through the gears (P, R, N, D) to circulate the new fluid.
   • Check and Adjust Fluid Level: With the engine still running, check the fluid level again and add fluid as needed until it reaches the correct level on the dipstick.
6. Test Drive and Final Check:
   • Test Drive: Take the vehicle for a short test drive to ensure the transmission operates smoothly and there are no unusual noises or issues.
   • Final Check: After the test drive, check the transmission fluid level one last time and inspect for any leaks around the transmission pan.

Additional Tips

• Regular Maintenance: Regularly check the transmission fluid level and condition. If the fluid appears dark or has a burnt smell, it may be time for a change.
• Fluid Condition: Fresh transmission fluid is typically red or pink and should be free of debris. Dark or burnt-smelling fluid can indicate overheating or internal transmission issues.
• Service Intervals: It’s generally recommended to change the transmission fluid and filter every 30,000 to 50,000 miles, depending on driving conditions and usage. More frequent changes may be necessary for high-performance or heavy-duty applications.

Proper maintenance of your TH400 transmission is essential for ensuring its longevity and performance. By choosing the right transmission fluid and following the correct procedures for changing it, you can keep your TH400 running smoothly for years to come.