Diagnosing issues with your car’s braking system can be crucial for safety. One component that often gets overlooked is the brake servo, also known as the brake booster. This vital part uses engine vacuum to amplify the force you apply to the brake pedal, making braking easier and more effective. When a brake servo malfunctions, it can lead to several noticeable symptoms. This guide will help you understand the common signs of a failing brake servo and how to perform basic checks to diagnose the problem.
Key Brake Servo Symptoms to Watch Out For
Several symptoms can indicate a problem with your brake servo. Recognizing these early can prevent more serious braking issues down the road.
1. Brake Pedal Goes to the Floor with Engine Running
One of the most alarming symptoms is a brake pedal that sinks to the floor when the engine is running, yet feels normal when the engine is off. This suggests that the power assistance provided by the servo is compromised. The original poster in the forum described this exact issue, highlighting a situation where braking effectiveness disappears when the engine is on. This symptom can be particularly dangerous and requires immediate attention.
2. Hard Brake Pedal – Requiring Excessive Force
Conversely, a failing brake servo can also manifest as a brake pedal that becomes significantly harder to press than usual. If you find yourself needing to apply much more force to achieve the same braking power, a malfunctioning servo could be the culprit. While some forum members initially suggested this symptom, it’s important to note that the original poster described the opposite – a softer pedal when the engine is running, indicating a different kind of servo failure. A hard pedal generally points towards a loss of vacuum assist, but in the context of the original question, the pedal going to the floor is the primary concern.
3. Engine Issues – Rough Idle or Difficulty Starting
A vacuum leak in the brake servo system can affect engine performance. If the diaphragm inside the servo unit is damaged, it can create a vacuum leak, leading to a rough engine idle, hissing noises from the engine bay, or even difficulty starting the car. One forum contributor mentioned that a vacuum leak would make the car hard to start and change the idle significantly when the brake pedal is pressed. While not directly brake-related, these engine symptoms can be a secondary indicator of a brake servo problem.
4. No Pedal Drop When Starting Engine
A simple test to check if your brake servo is providing assistance is the pedal drop test. Here’s how to do it, as described by a forum member:
- With the engine off, pump the brake pedal several times. This depletes any vacuum reserve in the servo. You’ll notice the pedal becoming firmer and higher.
- Keep firm pressure on the brake pedal.
- Start the engine.
If the brake servo is working correctly, you should feel the brake pedal drop slightly (a few inches) as the engine starts and vacuum assistance is applied. If the pedal does not drop, it suggests the servo is not receiving or utilizing vacuum, indicating a potential malfunction.
Diagnosing a Bad Brake Servo: Testing Methods
Beyond symptom recognition, there are a few diagnostic steps you can take to further investigate a potential brake servo issue.
1. Vacuum Leak Test
As suggested in the forum, you can perform a vacuum leak test on the servo unit itself:
- Disconnect the vacuum hose from the brake servo.
- Disconnect any other external check valves or T-fittings connected to the servo vacuum line.
- Carefully apply vacuum to the booster through the now-disconnected tube (you can use a vacuum pump or even carefully create suction).
- Observe if the servo holds vacuum. If the vacuum quickly dissipates, it indicates a leak within the servo diaphragm, suggesting a faulty unit.
2. Disconnecting the Booster Test
Another diagnostic approach, also mentioned in the forum, involves temporarily bypassing the brake servo to assess baseline braking performance:
- Disconnect the vacuum hose from the intake manifold and the brake servo.
- Plug or block off the vacuum fitting on the intake manifold. This is crucial to prevent a vacuum leak that can affect engine performance. A simple temporary plug can be used.
- Test the brakes. With the servo disconnected, braking will require significantly more pedal effort as you are now relying solely on manual braking force.
If the brakes function normally (albeit with increased effort) with the servo disconnected, but exhibit the problematic symptoms when connected, it strongly indicates that the brake servo is the source of the issue. Conversely, if the “pedal to the floor” symptom persists even with the booster bypassed, the problem likely lies elsewhere in the braking system, such as the master cylinder or brake lines.
Other Potential Brake System Issues
While the symptoms might point to a brake servo problem, it’s also important to consider other components of the braking system. As one forum member pointed out, issues like improperly adjusted rear brakes or problems with the master cylinder can sometimes mimic Brake Servo Symptoms or be amplified by a failing servo. Therefore, a comprehensive brake system check should include:
- Checking and adjusting rear brakes: Ensure rear brakes are properly adjusted as this can significantly impact overall braking performance.
- Inspecting the master cylinder: Check the brake fluid level and look for any leaks or signs of master cylinder failure.
- Examining brake lines and hoses: Inspect for swelling, leaks, or damage to brake lines and hoses.
Conclusion: Addressing Brake Servo Symptoms
Recognizing the symptoms of a failing brake servo is vital for maintaining vehicle safety. Symptoms like a brake pedal going to the floor, a hard pedal, or engine performance issues can indicate a problem with this critical component. By performing basic diagnostic tests, such as the pedal drop test, vacuum leak test, and booster disconnection test, you can gain valuable insights into the health of your brake servo.
If you suspect a brake servo issue, it is crucial to address it promptly. While some tests can be performed by a DIY enthusiast, brake system repairs are safety-critical. If you are not comfortable diagnosing or repairing brake system components, it is always recommended to consult a qualified mechanic for a professional inspection and repair. Ignoring brake servo symptoms can compromise your braking effectiveness and lead to dangerous driving situations.
