Hissing Sound When Braking
A well-maintained braking system is crucial for vehicle safety. Among the various issues that can arise, a hissing sound when braking is a common yet concerning symptom. This article aims to help you identify, understand, and resolve the issue of a hissing sound when braking.
What is the Hissing Sound When Braking?
The hissing sound when braking typically occurs when there is an issue within the braking system. You might hear it while pressing the brake pedal, especially when the car is idling. This sound can emanate from inside the vehicle or from the brake components themselves.
What causes a hissing sound when I brake?
Several issues can cause a hissing sound when braking. Understanding these causes is the first step in diagnosing and fixing the problem.
Vacuum Leak in Brake Booster
The brake booster uses vacuum pressure to help you apply the brakes. A vacuum leak can disrupt this process, causing a hissing sound. Symptoms include a hard brake pedal and increased stopping distance.
Worn Brake Pads
Worn brake pads can cause a variety of noises, including a hissing sound. This is due to the metal parts of the brake pads coming into contact with the brake rotor. Signs of worn brake pads include squealing noises and reduced braking efficiency.
Air in the Brake Lines
Air in the brake lines can cause the brake pedal to feel spongy and may produce a hissing sound as the air moves through the system. This typically occurs if there is a leak or if the brakes have not been properly bled.
Brake Fluid Issues
Brake fluid is essential for hydraulic pressure in the braking system. Low or contaminated brake fluid can cause various issues, including hissing sounds. Regular checks and proper maintenance of brake fluid levels are vital.
Malfunctioning Master Cylinder
The master cylinder is a critical component that generates the hydraulic pressure needed to operate the brakes. If it malfunctions, it can cause a hissing sound and lead to brake failure. Symptoms include a sinking brake pedal and uneven braking.
Diagnosing the Hissing Sound
Proper diagnosis is crucial to addressing the hissing sound when braking.
Initial Inspection
Start with a visual and auditory inspection. Listen for the hissing sound while pressing the brake pedal and check for any obvious signs of wear or damage in the brake components.
Testing the Brake Booster
To test for vacuum leaks in the brake booster, turn off the engine and repeatedly press the brake pedal until it becomes firm. Hold the pedal down and start the engine. If the pedal sinks slightly, the brake booster is working correctly. If not, there might be a vacuum leak.
Checking the Brake Pads and Rotors
Inspect the brake pads and rotors for wear and damage. Worn brake pads should be replaced immediately to avoid further damage and ensure safety.
Bleeding the Brake Lines
Bleeding the brake lines removes any air trapped in the system. This involves opening the brake bleeder valves and allowing the brake fluid to flow until it runs clear and bubble-free.
Inspecting Brake Fluid and Master Cylinder
Check the brake fluid level and look for signs of contamination. Inspect the master cylinder for leaks and other issues. If the fluid is low or dirty, a brake fluid flush might be necessary.
Case Study: Resolving a Hissing Sound When Braking in a Mercedes C-Class
Braking issues can be a significant concern for vehicle owners, impacting both safety and comfort. In this case study, we explore a real-world example involving a Mercedes C-Class with a customer’s complaint of a hissing sound when braking. We detail the diagnostic process and the steps taken by a qualified technician at a Mercedes dealership to resolve the issue.
Customer Complaint
The owner of a 2011 Mercedes C-Class reported a persistent hissing sound when applying the brakes. Concerned about the safety implications, the owner brought the vehicle to a certified Mercedes dealership for a thorough inspection and resolution.
Initial Assessment
Upon arrival, the vehicle was assigned to a qualified technician with expertise in Mercedes-Benz models. The technician began by confirming the customer’s complaint through a preliminary test drive, during which the hissing sound was indeed noticeable when the brakes were applied.
Diagnostic Process
Visual Inspection
The technician started with a visual inspection of the brake components:
- Brake Pads: The brake pads appeared significantly worn, with minimal friction material remaining.
- Brake Rotors: The rotors showed signs of severe wear and scoring, indicating that they were past their serviceable life.
Detailed Component Check
- Brake Booster and Vacuum System: The technician checked the brake booster and vacuum lines for any signs of leaks or damage but found them to be in good working condition.
- Brake Fluid: The brake fluid levels were within the acceptable range, and there were no signs of contamination.
Intervention
Replacing Worn Brake Pads and Rotors
Based on the inspection results, the technician determined that the worn brake pads and rotors were the primary cause of the hissing sound. The following steps were taken to address the issue:
1. Removing the Old Components
- The technician safely lifted the vehicle and removed the wheels to access the brake components.
- The worn brake pads were removed from the calipers, and the old rotors were detached from the wheel hubs.
2. Installing New Components
- New, high-quality OEM brake pads were installed into the calipers.
- New brake rotors were fitted onto the wheel hubs, ensuring proper alignment and torque specifications.
3. Reassembly and Testing
- The technician reassembled the brake components and wheels.
- A brake fluid check was performed to ensure optimal levels and no air in the brake lines.
Test Drive
After replacing the brake pads and rotors, the technician conducted a test drive to verify the repair. The hissing sound was no longer present, and the braking performance was restored to optimal condition.
Outcome
The replacement of the worn brake pads and rotors successfully resolved the hissing sound when braking. The vehicle’s braking system was restored to factory specifications, ensuring both safety and comfort for the owner.
Customer Feedback
The owner was highly satisfied with the service and the prompt resolution of the issue. They appreciated the thorough inspection and the detailed explanation provided by the technician.
Conclusion
This case study highlights the importance of addressing brake issues promptly and thoroughly. In the case of the Mercedes C-Class, the hissing sound was due to worn brake pads and rotors. The qualified technician’s expertise and systematic approach ensured a successful resolution, restoring the vehicle to safe operating condition.
Regular maintenance and timely replacement of brake components are crucial in preventing such issues and ensuring the longevity and reliability of the braking system.
Brake replacement
Brake rotor change
To change the brake rotor, follow the next steps;
Step 1 : Deposit and set down
- Remove the brake caliper (3) with the brake pads (5) and secure them to the vehicle with the cables connected without applying stress.
- Detach the screw (1) from the upper sliding pin (11) and remove the brake caliper (3).
- Detach and remove the screws (10) from the brake caliper bracket (2).
- Detach the locking screw (12) from the wheel hub and remove the brake disc (7).
Step 2 : Clean
- Clean the contact surfaces and the fitting areas of the brake disc (7).
- Lightly grease the fitting areas of the brake disc (7).
- Perform the installation in reverse order.
Brake pads replacement
Check and replace the brake pads
To check and replace the brake pads, follow the next steps;
Step 1 : Deposit and set down
- Unscrew the cap of the brake fluid reservoir and extract a small amount of brake fluid.
- Remove the corresponding front wheel.
- Unscrew the screws (11) from the brake caliper bracket (2).
- Remove the brake caliper (3).
- Remove the brake pads (5).
- Push back the brake piston using the resetting tool (01).
- Extract the wear sensor from the right front brake pads (S10/2) from the pad wear sensor holder of the brake pads (5).
Step 2 : Checking
- Check the wear and condition of the brake pads (5).
- Check the wear and condition of the brake discs (7).
- Check the condition and proper installation of the sealing boot (9), as well as the proper mobility of the guide sleeve (10).
Step 3 : Cleaning
- Clean the contact surfaces of the brake pads (5) on the brake caliper (3) and on the brake caliper bracket (2).
- Perform the installation in the reverse order.
How long brake pads should last ?
Brake pads typically last between 30,000 to 70,000 miles, though this range can vary based on several factors. These include driving habits, vehicle type, brake pad material, and driving conditions. Aggressive driving, frequent stop-and-go traffic, and heavy loads can wear out brake pads more quickly. Conversely, highway driving and less frequent braking can extend their lifespan. Regular maintenance and inspections are crucial to ensure brake pads are in good condition and replaced timely to maintain vehicle safety.
Preventative Maintenance
Preventative maintenance can help you avoid the issue of a hissing sound when braking.
Regular Brake Inspections
Conduct regular brake inspections to catch issues early. Look for signs of wear, damage, and fluid levels.
Timely Replacement of Brake Components
Replace brake pads, rotors, and other components as recommended by the manufacturer to maintain optimal braking performance.
Keeping Brake Fluid in Check
Regularly check and replace brake fluid to ensure it is clean and at the correct level. This helps maintain the hydraulic pressure needed for effective braking.
Proper Brake Use
Avoid heavy braking and maintain a steady braking pattern to extend the life of your brake components.
Conclusion
Addressing a hissing sound when braking promptly is crucial for your safety. Regular maintenance and timely repairs can prevent most issues. If you encounter persistent problems, don’t hesitate to seek professional help.
