555E Bleeding Procedure After Replacing the Master Cylinders

[MikePhua]

After replacing the master cylinders on a 555E excavator, it is essential to properly bleed the brake system to ensure that air is fully removed from the hydraulic system. Any trapped air can cause issues like reduced brake efficiency or even brake failure. This article outlines the necessary steps to bleed the brake system and restore proper operation after replacing the master cylinders.
Preparation Before Bleeding

1. Check Hydraulic Fluid: Before beginning the bleeding process, check the brake fluid level to ensure that the hydraulic system has enough fluid. Low fluid levels can prevent proper bleeding and affect brake performance.
   
2. Ensure Correct Installation of the Master Cylinders: Double-check that the new master cylinders are installed correctly, and all fittings are securely tightened. Inspect the hydraulic fluid lines to ensure there are no leaks that could affect the bleeding process.
   
3. Prepare Necessary Tools: Gather the necessary tools, including brake fluid, a bleeder hose, a container to catch the fluid, and appropriate wrenches. Ensure everything is easily accessible.
   

Bleeding Process Steps

1. Start the Engine: Start the 555E excavator and let it run at idle speed. Make sure the engine is functioning properly before proceeding.
   
2. Pump the Brake Pedal: Press the brake pedal several times to build up pressure in the brake system. Pump the pedal slowly until you feel resistance.
   
3. Open the Bleeder Valve: The bleeder valve is typically located on each brake cylinder at the wheels. While pressing the brake pedal, open the bleeder valve. This allows air and old fluid to escape from the system.
   
4. Monitor Fluid Flow: Watch the fluid as it exits the bleeder valve. Ensure that it flows smoothly and without any bubbles. If bubbles are visible, continue to press the brake pedal until fluid flows without any air bubbles.
   
5. Tighten the Bleeder Valve: Once the air has been completely expelled and only fluid is flowing from the bleeder valve, tighten the valve securely. Be sure to check the brake fluid level and add more fluid as needed.
   
6. Repeat the Process: Continue this process for all brake cylinders, repeating the bleeding procedure until no more bubbles are present and the brake fluid flows consistently and smoothly.
   
7. Test the Brakes: After completing the bleeding process, test the brake pedal. The brake pedal should feel firm and responsive. If the pedal feels soft or has an unusually long travel, the system may require further bleeding or additional repairs.
   

Post-Bleeding Checks and Maintenance

1. Check Brake Functionality: Ensure the brake system is functioning correctly. The brakes should engage quickly and the pedal should feel firm. If the pedal is too soft or the brakes aren’t responsive, recheck the system and repeat the bleeding process.
   
2. Check for Leaks: Inspect all connections and fittings in the brake system to ensure there are no leaks. Hydraulic leaks can cause brake failure or reduced braking performance, so it is important to address any leaks immediately.
   
3. Regular Brake Fluid Checks: After bleeding, routinely check the brake fluid level to ensure it remains within the recommended range. If necessary, top up the fluid to maintain the correct level. Periodically replace the brake fluid to maintain its quality and performance.
   

Conclusion
Properly bleeding the brake system after replacing the master cylinders is crucial for ensuring the safe and efficient operation of the 555E excavator. By following the steps outlined in this article and performing regular checks and maintenance, you can keep the brake system functioning properly and avoid issues that could compromise safety. If you encounter difficulties or the brakes still don't perform as expected, it is advisable to consult a professional technician for further diagnosis and repair.