Most Likely Causes:
* Worn-out Brake Pads or Shoes: This is the most common reason. Low brake pads or shoes cause the caliper pistons to push further out, leading to a thumping sensation as they retract. Inspect your pads and shoes immediately – you should be able to see the thickness of the remaining material.
* Worn-out Rotors or Drums: Grooved or warped rotors (front disc brakes) or drums (rear drum brakes) can cause vibration and thumping when braking. Visual inspection will reveal grooves, and a warped rotor may be slightly uneven.
* Brake Caliper Issues: A sticking or seized caliper piston can cause uneven brake pad wear and a thumping feeling. Sometimes, the caliper slide pins can seize, preventing the caliper from moving freely. This can lead to uneven braking and a thumping or pulsing sensation.
* ABS Problems: The Anti-lock Braking System (ABS) can sometimes cause a thumping sensation, particularly if there's a problem with the ABS pump, sensors, or module. This usually presents as a pulsing feeling rather than a sharp thump. Often, an ABS light will illuminate on the dash.
Less Likely, but Possible Causes:
* Suspension Components: While less common, worn-out suspension components (ball joints, control arm bushings, etc.) *can* indirectly contribute to a thumping brake pedal, usually felt more as a vibration in the whole vehicle during braking.
* Power Brake Booster Issues: A failing power brake booster can lead to inconsistent brake feel, including a thumping or spongy pedal.
* Master Cylinder Problems: A severely damaged or leaking master cylinder is a serious issue, likely accompanied by other symptoms like a soft pedal or brake fluid leaks.
What to Do:
1. Check Brake Fluid Level: Make sure the brake fluid level in the master cylinder reservoir is within the normal range. Low fluid could indicate a leak somewhere in the system.
2. Inspect Brake Pads and Rotors/Drums: This is the most crucial step. Visually inspect your brake pads and rotors (or drums) for wear and tear. Replace worn components immediately.
3. Check for Leaks: Look closely for any brake fluid leaks around the calipers, wheel cylinders, brake lines, and the master cylinder.
4. Test the Brake Pedal: Pump the brake pedal several times. A spongy or slow return indicates a problem with the power booster or master cylinder.
5. Listen for Unusual Noises: Pay attention to any unusual noises coming from the brakes, such as grinding or squealing.
6. Professional Inspection: If you're not comfortable inspecting the brakes yourself or if you suspect a more serious issue, take your Explorer to a qualified mechanic for a professional diagnosis and repair. Ignoring brake problems is dangerous.
The thumping brake pedal is a clear indication that something is wrong with your braking system. Don't delay addressing this issue; your safety depends on it. If you're unsure, have a mechanic assess the problem.
