Brake Pad Wear: Over time, the brake pads on any motorcycle can wear down due to regular use. If the brake pads become excessively worn, it can cause the brake calipers to extend further than usual, leading to contact between the brake disc and the pads. This could result in scraping or rubbing noises.
Brake Caliper Misalignment: If the brake caliper is not properly aligned with the brake disc, it may cause uneven contact and scraping. This misalignment can occur due to various factors, such as improper installation, loose caliper mounting bolts, or impact from a fall or accident.
Bent or Warped Brake Disc: A bent or warped brake disc can cause irregular contact with the brake pads, leading to scraping. This can happen if the bike has been involved in an accident or subjected to excessive heat. A bent or warped disc should be replaced to restore proper braking performance.
Caliper Piston Seizure: If the caliper piston becomes stuck or seizes, it can cause the brake pad to constantly press against the disc, resulting in scraping. This situation may occur due to contamination, moisture, or corrosion within the caliper assembly. Proper cleaning and maintenance of the brake caliper are essential to prevent piston seizure.
Suspension Issues: In some cases, suspension problems can affect the brake system's performance. If the front suspension is too soft or improperly adjusted, it could cause excessive fork dive during braking. This can lead to the front end of the motorcycle squatting and the brake pads making contact with the disc prematurely.
It's important to note that the above reasons are general possibilities and may not specifically apply to the KTM Duke model you mentioned. If you're experiencing scraping issues with your motorcycle's front disc brake, it's recommended to consult with a qualified technician or a KTM service center to diagnose the problem accurately and take appropriate action.