Here's a general outline, but I strongly advise against attempting this unless you have significant experience working on older cars and transmissions:
1. Identify Your Transmission: Confirm the exact type of Hydra-Matic transmission you have. A service manual specific to your car's year and transmission is invaluable. The manual will have the correct fluid type and capacity.
2. Gather Supplies:
* Correct Type of Transmission Fluid: Use only the type specified in your service manual. Using the wrong fluid can severely damage the transmission. Type "A" ATF was common for this era, but verify.
* New Transmission Pan Gasket: Essential to prevent leaks.
* New Transmission Filter (if applicable): Some Hydra-Matics had replaceable filters. Check your manual.
* Drain Pan: To catch the old fluid.
* Socket Wrench Set: To remove the transmission pan bolts.
* Funnel: To add new fluid.
* Jack and Jack Stands: To safely support the car.
* Gloves and Safety Glasses: For protection.
* Rags or Shop Towels: For cleaning.
* Torque Wrench (recommended): To tighten the pan bolts to the correct specification (found in your service manual).
3. Raise and Secure the Vehicle: Safely raise the front of the car and secure it on jack stands.
4. Locate the Transmission Pan: The pan is usually located at the bottom of the transmission.
5. Drain the Old Fluid: Carefully remove the transmission pan bolts and allow the fluid to drain completely into your drain pan. Be prepared for a significant amount of fluid.
6. Replace the Filter (if applicable): Install the new filter according to your service manual.
7. Replace the Gasket: Carefully clean the mating surfaces of the pan and transmission, and install the new gasket.
8. Reinstall the Transmission Pan: Attach the pan and tighten the bolts to the specifications in your service manual, using a torque wrench. Do not overtighten.
9. Fill the Transmission: Use a funnel to carefully add the correct amount of transmission fluid (specified in your service manual). This usually involves filling to a certain level inside the pan while it is still installed. The service manual will have detailed instructions.
10. Lower the Vehicle: Carefully lower the vehicle.
11. Check for Leaks: After refilling, run the engine for a few minutes and check for any leaks around the transmission pan.
Disclaimer: Working on a transmission is complex. Improperly performing this task can lead to significant transmission damage, requiring costly repairs. If you are not comfortable with this process, take your car to a qualified mechanic specializing in classic cars. A service manual for your specific 1964 Cadillac DeVille is crucial for this task and will provide detailed instructions and torque specifications.
