* Bleeding the brakes: This is the most common cause. Air in the brake lines will significantly reduce braking power, or even prevent it entirely. You *must* properly bleed the brakes after replacing any brake component in the hydraulic system. Failure to do so thoroughly is the most likely explanation. Bleeding should be done in the correct order (usually starting with the furthest wheel from the master cylinder).
* Incorrect bleeding procedure: There are specific procedures for bleeding brakes, depending on the system. Using an incorrect method can leave air trapped in the system.
* Master cylinder installation: The master cylinder may not be installed correctly. Even a slight misalignment can affect performance.
* Wheel cylinder installation (rear brakes): Similar to the master cylinder, incorrect installation can lead to poor or no braking. The wheel cylinders need to be properly seated and adjusted.
* Caliper issues (front disc brakes): While you mentioned new rotors and pads, the calipers themselves might be sticking, seized, or have internal issues. Make sure the calipers are moving freely and not binding. Consider replacing the caliper seals or even the calipers if needed.
* Brake lines and hoses: Internal corrosion or damage to the brake lines or hoses can restrict fluid flow, reducing braking effectiveness. Inspect them closely for rust, kinks, or bulges. If any section is suspect, it should be replaced.
* Proportioning valve: This valve regulates the braking force between the front and rear brakes. A malfunctioning proportioning valve can lead to inadequate braking.
* Low brake fluid: Even after replacing the master cylinder, it's crucial to ensure the brake fluid reservoir is full.
* Brake booster: This component assists in applying the brakes. A faulty brake booster will reduce braking power significantly. Check to see if the booster is working correctly.
* Parking brake: Ensure your parking brake is fully released. A partially engaged parking brake will significantly reduce braking power.
What to do:
1. Bleed the brakes properly: This is the absolute first thing to try. Get a friend to help pump the pedal while you bleed each caliper/wheel cylinder. Use a clear tube to ensure you're actually getting fluid and not just air.
2. Inspect all brake components: Carefully examine all brake lines, hoses, calipers, wheel cylinders, and the master cylinder itself for damage or leaks.
3. Check brake fluid level: Make sure the reservoir is topped off with the correct type of brake fluid.
4. Test the parking brake: Make sure it's completely released.
5. If the problem persists after bleeding and inspection: Take your vehicle to a qualified mechanic. There might be a more complex issue, such as a faulty proportioning valve or brake booster.
Ignoring a brake problem is extremely dangerous. If you're not comfortable working on your brakes yourself, please take your truck to a professional mechanic immediately. Your safety depends on it.
