Is it Necessary to Bleed Brakes or Open the Master Cylinder When Changing Brake Pads and Rotors?

QuestionsCategory: Ask An ExpertIs it Necessary to Bleed Brakes or Open the Master Cylinder When Changing Brake Pads and Rotors?
Sophia Jones asked 6 months ago
I recently watched a Chrisfix video where he changed brake pads and rotors without bleeding the brakes or opening the master cylinder. He mentioned that opening the master cylinder cap is optional, especially if the piston doesn't need much compression. I've seen other videos suggesting bleeding brakes or always opening the master cylinder cap, leading to my confusion. Some say it's essential, others suggest it's unnecessary. Could you clarify this for me?
1 Answers
Zack Norman Staff answered 6 months ago
Hello there, Sophia! The necessity of bleeding brakes or opening the master cylinder when changing brake pads and rotors can vary based on a few factors:
  1. Piston Compression: If the brake piston doesn't require significant compression to fit new pads, you may not need to open the master cylinder cap. However, opening it can prevent potential back pressure on the system.
  2. Brake Fluid Condition: Some mechanics suggest opening the bleeder valves to avoid pushing old, potentially contaminated brake fluid back through the system. This is more crucial if your brake fluid is old or if the vehicle has a sensitive ABS system.
  3. Vehicle Specifics: Some vehicles may require specific procedures. For instance, certain cars with complex ABS systems might need special attention to avoid costly repairs.
  4. Maintenance Practices: Regular brake fluid flushing (every 4-6 years) is recommended, especially in humid climates. Doing this during pad and rotor changes can be convenient.
  5. Air in the System: You generally need to bleed brakes if air enters the system, like when replacing calipers. If you're just doing pads and rotors without opening the system, bleeding might not be necessary.
  6. Safety and Precautions: Even if not strictly necessary, some prefer to open the master cylinder as a precaution. It's also important to pump the brakes after reassembly to ensure the pedal feels firm.
In conclusion, while not always mandatory, opening the master cylinder or bleeding brakes can be beneficial, especially for older or less maintained vehicles. Always consider the specific needs of your car and when in doubt, consult a professional. I hope that answers your question! Zack - Motor Verso Mechanics Team