Common Culprits:
1. Air in the System: Power bleeding is usually effective, but it's possible there's still air trapped in the lines.
* Check for Leaks: Carefully inspect all brake lines, hoses, and connections for leaks. Even a tiny leak can introduce air.
* Rebleed with a Vacuum Bleeder: A vacuum bleeder can be more thorough than manual bleeding. It pulls fluid from the system, forcing air out.
2. Master Cylinder Issues: The master cylinder is crucial for applying brake pressure.
* Low Fluid: Check the master cylinder fluid level. It should be at or near the "Full" mark. If it's low, you might have a leak or a damaged master cylinder.
* Damaged Master Cylinder: The master cylinder could be worn or damaged, preventing it from building proper pressure.
* Stuck Piston: The master cylinder piston could be stuck, preventing it from moving freely.
3. Faulty Brake Booster: The brake booster assists the master cylinder in providing braking power.
* Vacuum Leak: A leak in the vacuum hose connecting the booster to the engine can prevent it from working properly.
* Damaged Booster: The booster itself might be malfunctioning.
4. Other Issues:
* Caliper Problems: Although you replaced the brake pads, make sure the calipers are working correctly.
* Wheel Cylinders (Drum Brakes): If you have drum brakes, the wheel cylinders might be leaking or sticking.
* Faulty Brake Line: A brake line could be kinked, pinched, or have internal damage.
* Electrical Problems: A problem with the brake light switch or the power brake system's electrical components could prevent the booster from engaging.
Troubleshooting Steps:
1. Check for Leaks: Examine all brake lines, hoses, and connections for leaks. Look for fluid drips or bubbles.
2. Fluid Level: Ensure the master cylinder fluid level is full.
3. Bleeding: Bleed the brakes again, using a vacuum bleeder if possible.
4. Master Cylinder Check: Observe the master cylinder piston while applying the brakes. It should move smoothly. If it's stuck, you'll need to replace the master cylinder.
5. Vacuum Booster Check: Start the engine and check the vacuum hose for leaks. Also, listen for a hissing sound from the booster while applying the brakes.
6. Check for Electrical Issues: Test the brake light switch and any other relevant electrical components related to the brake system.
Safety First:
* Do not drive the vehicle without brakes! It's extremely dangerous.
* If you're not comfortable working on brakes, seek professional assistance.
* Wear safety glasses and gloves when working on brake systems.
* Always refer to your car's owner's manual for specific instructions.
Important Note: If you suspect a problem with your master cylinder, brake booster, or brake lines, it's best to consult a qualified mechanic. These repairs can be complex and require specialized tools.
