* Caliper Piston Not Fully Retracted: The most common culprit. If the caliper piston wasn't fully pushed back into the caliper before installing the new pads, it can cause the pads to drag against the rotor, leading to a whirring or grinding noise. The piston might be seized or sticky.
* Brake Pad Shims Missing or Incorrectly Installed: Shims are metal plates on the back of brake pads designed to reduce noise and vibration. If they're missing or not properly seated, it can cause a whirring sound.
* Damaged Rotor: The rotor (brake disc) might be warped, scored, or have excessive rust. The new pads might be highlighting the existing rotor damage.
* Loose Wheel: A less likely but possible cause. Check that the wheel lug nuts are properly tightened.
* Caliper Issues: The caliper itself could be sticking or have internal problems, even if the piston retracts.
* Something caught in the brake assembly: A small stone or other debris might be lodged between the pad and rotor.
What to do:
1. Check the Wheel: Make sure the wheel is securely fastened.
2. Inspect the Rotor: Carefully examine the rotor for warping, scoring, or excessive rust. If damaged, it will likely need to be replaced or resurfaced.
3. Examine the Brake Pads and Shims: Make sure the shims are present and correctly installed. Check for any debris between the pads and rotor.
4. Verify Caliper Piston Retraction: This is crucial. If you didn't use a caliper piston compression tool, it's highly likely the piston isn't fully retracted. You'll need to use the correct tool to ensure full retraction. If the piston is seized, you might need professional help.
5. Test Drive (carefully): After addressing the above, take a short test drive to see if the noise is gone.
If the noise persists after checking these points, it's best to take your vehicle to a mechanic. Attempting to troubleshoot complex brake issues without proper knowledge and tools can be dangerous. Brake problems should always be addressed promptly.
