TH400 Transmission Fluid: How to Choose and Change It

The Turbo Hydra-Matic 400 (TH400) is renowned for its durability and reliability, but to ensure it performs at its best, using the correct transmission fluid and maintaining it properly is crucial. Here’s a comprehensive guide on how to choose the right fluid for your TH400 transmission and how to change it effectively.

Choosing the Right Transmission Fluid

Selecting the appropriate transmission fluid is essential for maintaining the performance and longevity of your TH400. Here’s what you need to know:

1. Type of Fluid:

• Type F Fluid: Originally, the TH400 used Type F transmission fluid, which is specifically designed for certain automatic transmissions. Type F fluid has different friction properties compared to other fluids, which can affect shifting performance and overall transmission behavior.
• Dexron III/Mercon: In many cases, modern TH400 transmissions are compatible with Dexron III or Mercon fluids. These fluids offer better lubrication and have been improved over the years to enhance performance and protection.
• Synthetic Fluids: Synthetic transmission fluids offer superior performance, including better high-temperature stability, improved lubrication, and enhanced protection against wear. They can be a great choice for performance applications or extreme conditions.

2. Manufacturer Recommendations:

• Always refer to your vehicle’s service manual or manufacturer recommendations for the specific type of transmission fluid required. Using the recommended fluid ensures compatibility and optimal performance.

3. Performance Fluids:

• For high-performance applications, such as racing or heavy towing, specialized performance transmission fluids are available. These fluids are formulated to handle higher temperatures and provide better protection under extreme conditions.

How to Change TH400 Transmission Fluid

Regular fluid changes are essential for maintaining the health of your TH400 transmission. Here’s a step-by-step guide on how to change the transmission fluid:

1. Gather Necessary Tools and Supplies:

• Transmission Fluid: Ensure you have the correct type and amount of transmission fluid. Check your vehicle’s manual for the exact capacity.
• Transmission Filter Kit: This typically includes a new filter and a gasket for the transmission pan.
• Tools: Wrenches, screwdrivers, a drain pan, a funnel, and possibly a torque wrench.
• Safety Equipment: Gloves and safety glasses.

2. Prepare the Vehicle:

• Raise the Vehicle: Use a jack to lift the vehicle and place it on jack stands. Ensure the vehicle is securely supported before proceeding.
• Locate the Transmission Pan: The transmission pan is typically located on the underside of the transmission.

3. Drain the Old Fluid:

• Remove the Transmission Pan Bolts: Carefully loosen and remove the bolts securing the transmission pan. Be prepared for some fluid to spill out, so position your drain pan underneath.
• Drain the Fluid: Allow the old transmission fluid to drain completely. If you’re also replacing the filter, remove the old filter at this stage.

4. Replace the Filter:

• Install the New Filter: Remove the old filter and replace it with a new one. Ensure it is properly seated and secured.

5. Clean and Reinstall the Pan:

• Clean the Transmission Pan: Thoroughly clean the transmission pan and the mating surface on the transmission. Remove any old gasket material.
• Install the New Gasket: Place the new gasket on the transmission pan. Make sure it is aligned correctly.
• Reattach the Transmission Pan: Position the pan back onto the transmission and secure it with the bolts. Tighten the bolts to the manufacturer’s specifications.

6. Refill the Transmission:

• Locate the Dipstick Tube: Find the transmission dipstick tube or fill plug. Use a funnel to pour new transmission fluid into the transmission.
• Check the Fluid Level: After adding some fluid, use the dipstick to check the fluid level. Add more fluid as needed until it reaches the correct level.

7. Check for Leaks and Test Drive:

• Check for Leaks: Start the engine and let it idle while checking for any leaks around the transmission pan and fill plug.
• Test Drive: After ensuring there are no leaks, take the vehicle for a short test drive. Shift through all the gears to ensure smooth operation and check the fluid level again. Add more fluid if necessary.

8. Dispose of Old Fluid:

• Properly dispose of the old transmission fluid at a designated recycling facility or auto parts store that accepts used fluids.

Tips for Maintaining TH400 Transmission Fluid

1. Regular Checks: Periodically check the transmission fluid level and condition. Low or dirty fluid can indicate potential issues.
2. Fluid Color: Healthy transmission fluid is usually red or pink. If the fluid appears dark brown or has a burnt smell, it may need changing or indicate other problems.
3. Fluid Changes: Follow the manufacturer’s recommendations for fluid change intervals, especially if you frequently tow heavy loads or engage in performance driving.
4. Monitor Performance: Pay attention to any changes in shifting performance or unusual noises. These can be signs that the transmission or fluid needs attention.

Conclusion

Choosing the right transmission fluid and performing regular maintenance is crucial for the performance and longevity of your TH400 transmission. By selecting the appropriate fluid and following the proper procedures for changing it, you can ensure that your transmission continues to operate smoothly and reliably. Regular checks and timely fluid changes will help you get the most out of your TH400, whether you’re using it for daily driving or high-performance applications.