* Rust and Corrosion: This is the most common culprit. Rust builds up on the caliper mounting bracket, the caliper slide pins, and even the rotor hat. This prevents the caliper from sliding smoothly. The caliper may be binding on the rust, preventing it from being pushed onto the rotor.
* Stuck or Seized Caliper Pins: The caliper slides on pins that are lubricated. If these pins are seized due to rust, corrosion, or lack of lubrication, the caliper won't move. They might even be broken.
* Worn or Damaged Caliper Slide Pins: Even if not completely seized, worn or damaged pins can prevent smooth caliper movement. The pins may be pitted or scored, preventing them from sliding properly in their bores.
* Bent Caliper Bracket: The bracket that holds the caliper might be bent, misaligned, or damaged, preventing the caliper from seating correctly. This is less common but possible after a collision or hard impact.
* Caliper Itself is Damaged or Seized: The caliper piston might be seized inside the caliper, preventing it from retracting properly. The caliper itself might be warped or damaged.
* Incorrect Parts: While less likely, ensure you have the correct caliper for your Mustang model year.
* Rotor Problems: Though less likely to prevent *sliding on*, a severely warped or damaged rotor could indirectly interfere with caliper placement.
Troubleshooting Steps:
1. Clean Everything: Thoroughly clean all surfaces with a wire brush, brake cleaner, and a degreaser. Pay close attention to the caliper mounting brackets, the caliper slide pins, and their bores. Remove any rust and debris.
2. Lubricate the Slide Pins: After cleaning, lubricate the caliper slide pins and their bores with high-temperature brake caliper grease. Do *not* use general-purpose grease.
3. Inspect the Slide Pins: Check the slide pins for wear, damage, or seizure. Replace them if necessary. If they are difficult to remove, use penetrating oil and a slide hammer to carefully extract them.
4. Inspect the Caliper Bracket: Check the caliper bracket for any bends or damage. If it's bent, it might need to be replaced or straightened (difficult and often not recommended).
5. Inspect the Caliper: Try to retract the caliper piston using a C-clamp or specialized brake caliper tool. If it's seized, the caliper likely needs to be rebuilt or replaced.
6. Inspect the Rotor: Ensure the rotor surface is clean and free of significant damage. Warped rotors can make the process more difficult, but unlikely to be the primary cause of this problem.
If you've addressed these points and the caliper still won't go on, you may need to consult a mechanic. Brake work requires precision and safety; if you're unsure about any step, seeking professional help is advisable.
