* Master Cylinder Issues: A failing master cylinder is a primary suspect. It might be leaking internally, causing low pressure and the spongy feeling you describe. A leaking master cylinder also poses a risk of complete brake failure.
* Wheel Cylinders (Rear Brakes): These are small cylinders in the rear brake assemblies. If they're leaking or sticking, they can cause the brakes to drag and feel like they're pushing back. This is more common in drum brakes (if your Explorer has those in the rear).
* Caliper Pistons (Front Brakes): Similar to wheel cylinders, but for disc brakes. Seized or sticking caliper pistons can create drag and prevent the brakes from releasing fully. This is particularly noticeable if one wheel is more affected than others.
* Brake Lines: A kinked, collapsed, or internally corroded brake line can restrict fluid flow and cause inconsistent braking, including the pushing back sensation. This is less likely to be the sole cause, but could contribute.
* Vacuum Booster: The vacuum booster assists in brake pedal pressure. A leak or failure in this system will result in a very hard brake pedal and reduced stopping power. This might *feel* like pushback, because you need to push harder to stop.
* Brake Pedal Return Spring: A weak or broken return spring can prevent the pedal from returning fully to its resting position. While not directly causing the brakes to *push back*, this adds to the feeling of resistance.
What to do:
1. Do NOT drive the vehicle until this is resolved. This is a significant safety issue.
2. Have a qualified mechanic inspect your brake system immediately. They will be able to diagnose the problem accurately and make the necessary repairs. Attempting brake repairs yourself is strongly discouraged unless you have significant experience and the correct tools.
3. Inspect the brake fluid level. A low level suggests a leak somewhere in the system.
4. Check for leaks around the master cylinder, calipers, and wheel cylinders. Look for wet spots or brake fluid stains.
Ignoring this issue could lead to brake failure and a serious accident. Get it checked out professionally as soon as possible.
