Brake doesn’t hold

• Air in brake line.
  

  
  

• Pad or disk worn.
  

  
  

• Brake fluid leak.
  

  
  

• Disc warped.
  

  
  

• Contaminated pad.
  

  
  

• Brake fluid deteriorated.
  

  
  

• Primary or secondary cup damaged.
  

  
  

• Master cylinder scratched inside.