* Improper Bleeding Procedure: Even with new components, incorrect bleeding techniques can leave air in the system. Make sure you're following the correct procedure for your vehicle, ensuring you bleed each caliper/wheel cylinder in the correct order (usually starting with the furthest wheel from the master cylinder). A pressure bleeder is highly recommended for this, as it ensures consistent pressure and is far more efficient than gravity bleeding.
* Leaking Wheel Cylinders: Despite being new, a faulty wheel cylinder is possible. Inspect them carefully for leaks around the seals and boots.
* Leaking Master Cylinder: A new master cylinder can also be defective. Look for leaks at the seals and around the pushrod.
* Master Cylinder Piston Not Returning Properly: The master cylinder piston might not be retracting fully, causing inconsistent brake pressure.
* Proportioning Valve Issues: Your 4Runner likely has a proportioning valve that adjusts brake pressure to the front and rear wheels. A faulty valve can cause braking imbalance or poor performance.
* Restricted Brake Lines: A blockage or kink in the brake lines can prevent proper fluid flow. Check the lines for any damage or restrictions.
* Low Fluid Level: Ensure your brake fluid reservoir is topped off to the correct level *after* bleeding the brakes.
* Caliper Piston Issues (if using disc brakes): Seized or sticking caliper pistons can hinder braking even with new parts.
* Air in the ABS Module (if equipped): If your 4Runner has ABS, air trapped within the module can be very difficult to remove and may require specialized equipment.
Troubleshooting Steps:
1. Re-bleed the brakes using a pressure bleeder: This is the most important step. Gravity bleeding is often inadequate, especially after major brake work.
2. Visually inspect all brake components: Look for leaks at every connection, cylinder, and line.
3. Check for brake fluid leaks at the master cylinder and wheel cylinders.
4. Test the master cylinder's piston return: If it doesn't fully retract, the master cylinder may be faulty.
5. If you have disc brakes on the front, inspect the caliper pistons for smoothness and free movement.
6. If the problem persists after these checks, take your 4Runner to a qualified mechanic. Brake issues are serious and shouldn't be ignored. A mechanic has the tools and expertise to diagnose and repair more complex problems.
Don't drive the vehicle until the braking issue is resolved. Compromised brakes are incredibly dangerous.
