1. Air in the System:
* Most Likely Culprit: Even after bleeding twice, air can still hide in the system, especially in hard-to-reach spots.
* Solution: Bleed the brakes again, meticulously following these steps:
* Proper Order: Start with the farthest wheel from the master cylinder (usually the rear passenger side) and work your way towards the front.
* Pump and Hold: Pump the pedal several times, then hold it down while opening the bleeder valve.
* Close Valve: Close the valve *before* releasing the pedal.
* Repeat: Repeat the process until fluid flows freely and is free of air bubbles.
* Top Off Reservoir: Make sure the master cylinder reservoir is topped off with the correct brake fluid.
2. Worn or Damaged Brake Components:
* Suspects:
* Wheel Cylinders (Rear): Worn seals or internal damage can cause leakage.
* Caliper Pistons (Front): Similar to wheel cylinders, they can leak or seize.
* Brake Lines: Corrosion or damage can lead to leaks.
* Brake Hoses: Similar to brake lines, they can crack or leak.
* Diagnosis:
* Visual Inspection: Look for leaks around calipers, wheel cylinders, lines, and hoses.
* Test for Leaks: Pump the pedal and observe for fluid leakage. If you suspect a leak, try applying pressure to the system with a brake pressure tester (available at auto parts stores) to pinpoint the source.
* Solution: Replace any leaking or damaged components.
3. Master Cylinder Issues:
* Possible: Even a new master cylinder can have issues.
* Investigation:
* Check for Leaks: Inspect the master cylinder for leaks around the reservoir and the pushrod seals.
* Verify Correct Installation: Ensure the master cylinder is properly mounted and the pushrod is adjusted correctly.
* Resolution: If necessary, replace the master cylinder again, ensuring proper installation.
4. Power Brake Booster Issues:
* Consider: If you have a power brake booster, it can contribute to a soft pedal.
* Testing:
* Manual Pedal Feel: With the engine off, pump the brakes. The pedal should feel firm. If it's still soft, the booster likely isn't functioning properly.
* Vacuum Check: Check the vacuum line leading to the booster for leaks or blockage.
* Solution: If the booster is faulty, it'll need to be replaced.
Additional Tips:
* Proper Brake Fluid: Use the type of brake fluid specified for your vehicle.
* Professional Help: If you're unable to resolve the issue, it's best to consult a qualified mechanic.
Let me know if you have any other questions. Good luck!
