1. Rust and Corrosion: This is the most frequent culprit. Rust prevents the piston from moving smoothly.
* Solution: Clean the piston: Use a wire brush (brass is best to avoid scratching) to remove as much rust as possible. Then, try using a penetrating lubricant like PB Blaster, Kroil, or Liquid Wrench. Let it soak for a while (even overnight) before attempting to retract the piston. A small amount of solvent on a clean rag can also help remove grime.
2. Seized Piston: The piston might be seized due to corrosion or lack of lubrication.
* Solution: Continued lubrication and gentle persuasion: Keep applying penetrating lubricant and try gently pushing the piston back in. You can use a C-clamp or piston compression tool (highly recommended), but *apply pressure slowly and evenly*. Avoid jarring it. If it's still stuck, you may need more aggressive methods (see below).
3. Brake Pad Wear Sensor: The brake pad wear sensor's wire might be interfering with piston movement.
* Solution: Carefully inspect the area around the piston for the wear sensor wire. Make sure it's not caught or obstructing the piston's path. Gently move it out of the way.
4. Caliper Internal Issues: The caliper itself might be damaged or internally seized.
* Solution: This is less common but possible. If you've tried everything else, you may need to replace the caliper.
Tools & Techniques:
* C-clamp: A C-clamp is a common tool for retracting pistons. Important: Wrap the piston with a piece of wood or thick cardboard to prevent damaging the piston's surface. Apply pressure slowly and evenly. Never force it.
* Caliper Piston Compression Tool: These tools are specifically designed for this job and provide better control and prevent damage. They are strongly recommended.
* Brake Caliper Rewind Tool: A tool that uses a small rotating pin that pushes the piston back into the caliper.
* Air Compressor (Use with Caution): Some mechanics use compressed air. However, this carries a higher risk of damage and should only be done with extreme caution and proper equipment, including a suitable adapter to avoid damaging the seals.
Important Safety Considerations:
* Never attempt to push the piston back in without removing the brake pads first. This prevents damage to the pads and caliper.
* Always wear safety glasses and gloves.
* If you are unsure about any step, consult a professional mechanic. Improperly retracting a caliper piston can lead to brake failure.
If you've tried all these and the piston still won't move, it's time to take your Mustang to a mechanic. Attempting to force it could cause further damage and create a safety hazard.
