However, if you're determined to do it yourself, understand you're taking a risk, and this is a simplified overview and may not cover all variations or potential issues:
What you'll likely need:
* New transmission fluid: The correct type and amount are crucial. Consult your owner's manual for the exact specification (Dexron-II or equivalent is a common possibility for this era). You'll need significantly more fluid than a simple drain-and-fill. A transmission fluid exchange machine is ideal.
* Drain pan: A large capacity pan to catch the old fluid.
* Wrench(es): To remove the drain plug from the transmission pan.
* Transmission pan gasket: You'll likely need a new gasket when reinstalling the pan.
* Funnel: To add the new fluid.
* Jack and jack stands: Essential for safe working conditions. Never work under a vehicle supported only by a jack.
* Torque wrench: To tighten the drain plug and pan bolts to the correct specification (consult your service manual).
* Gloves: To protect your hands from the old fluid.
* Shop rags or paper towels: For cleanup.
* Optional but highly recommended: A transmission fluid exchange machine. This is the best way to completely replace the fluid. Failing that, multiple drain and refills are needed, though this is less effective.
Simplified Procedure (Again, highly risky without experience):
1. Safety First: Engage the parking brake, chock the wheels, and raise the vehicle securely using jack stands.
2. Locate the transmission pan: It's usually located at the bottom of the transmission.
3. Drain the fluid: Carefully remove the drain plug (it might be slightly warm) and let the fluid drain into your pan.
4. Remove the pan: Once drained, carefully remove the transmission pan. Be prepared for some fluid spillage.
5. Inspect the pan and filter: If there is a filter accessible (not always the case on these older transmissions), replace it. Clean the pan thoroughly.
6. Replace the gasket: Install the new gasket onto the pan.
7. Reinstall the pan: Carefully put the pan back on and tighten the bolts to the manufacturer's specifications using your torque wrench.
8. Reinstall the drain plug: Tighten to the correct torque specification.
9. Add new fluid: This is where it gets tricky without a machine. You'll need to add fluid through the dipstick tube. If you're not using a machine, you'll need to drive the car for a while, then repeat steps 2-9 several times to flush as much old fluid as possible. Checking the fluid level on the dipstick and adding more is essential throughout the process.
10. Check the fluid level: Once the fluid is replaced, check the fluid level with the engine running and the transmission in park (or neutral, consult manual).
Again, this is a simplified procedure and may not be accurate for your specific vehicle. Consult a repair manual specific to your 1985 Buick Century for detailed instructions and torque specifications. Improper fluid levels or incorrect fluid type can severely damage the transmission.
Strongly consider taking your vehicle to a qualified mechanic for this service. The cost of professional service is significantly less than the cost of a transmission repair or replacement.
