What you'll need:
* Brake fluid: Use DOT 3 brake fluid specified for your vehicle. Never mix different types of brake fluid.
* Bleeding wrench: A wrench that fits your bleeder valves (usually 8mm or 10mm).
* Clear hose: A short length of clear tubing to fit over the bleeder valve.
* Jar or container: To catch the old brake fluid.
* Socket wrench: To remove and install the master cylinder (if you haven't already done this).
* Wrench (optional): To hold the bleeder valve. Using a wrench helps prevent rounding off the bleeder valve.
* A helper: Crucial for efficient bleeding.
Bleeding Procedure (Rear to Front):
The proper order is crucial. Air tends to rise, so start with the furthest point from the master cylinder and work your way closer. For a 1991 Explorer, this is typically:
1. Rear passenger side: Have your helper pump the brake pedal slowly and firmly several times. Then, have them hold it down. Open the bleeder valve slightly. You'll see brake fluid with air bubbles emerge into the hose. Close the bleeder valve once the fluid runs clear and without bubbles. Repeat this process several times until there are no more air bubbles.
2. Rear driver's side: Repeat the process for the rear driver's side wheel.
3. Front passenger side: Repeat the process for the front passenger side wheel.
4. Front driver's side: Repeat the process for the front driver's side wheel.
Important Considerations:
* Keep the master cylinder reservoir full: Ensure the master cylinder reservoir always has enough brake fluid. Low fluid levels can introduce air into the system.
* Firm but slow pumping: The helper should pump the brake pedal slowly and steadily, not rapidly. Jerky pumping can introduce more air.
* Consistent pressure: Keep a firm, consistent pressure on the bleeder valve. Avoid opening it too widely; a slow drip is better than a gush.
* Check fluid level: Frequently check the master cylinder reservoir and top it off as needed.
* Air bubbles: Continue bleeding each wheel until the fluid runs completely clear. If you notice that air bubbles are still coming out, repeat the entire procedure again.
* Brake pedal feel: After bleeding, test the brake pedal. It should feel firm and responsive. If it feels spongy or soft, there may still be air in the system.
* Gravity Bleeding (Alternative, less effective): If you're working alone, gravity bleeding is possible, but less effective. Open each bleeder valve and allow the fluid to drain slowly. This method might take considerably longer and might not fully remove all the air.
After Bleeding:
* Test drive: Once bleeding is complete, perform a test drive in a safe, controlled environment. Test your brakes thoroughly before driving at normal speeds.
* Top off fluid: Check and top off the master cylinder reservoir as needed.
If you're uncomfortable performing this procedure yourself, it's strongly recommended to take your vehicle to a qualified mechanic. Bleeding brakes improperly can lead to dangerous driving conditions. Improper bleeding can also damage your brake system. Remember to always prioritize safety!
