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Symptoms of a Bad or Failing Vacuum Brake Booster Check Valve

brake booster check valve

Diesel vehicles typically employ the services of a vacuum brake booster in order to provide additional power to the braking system. It's designed to provide consistent flow of hydraulic fluid to the brake master cylinder while increasing brake pressure and helping heavy vehicles stop easier. However, this component is also common on Volkswagen, Audi, and other diesel-powered consumer cars, trucks and SUV's. From time to time, this mechanical part is susceptible to damage or typical wear and tear. This includes the brake booster check valve.

The check valve is designed to suck air that is trapped in the brake booster and does not let additional air enter the cylinder. This protects the brake lines from developing an air bubble which can seriously impact the performance of brakes. This part connects the body of the brake booster to the vacuum hoes and is a safety solution that still allows the brakes to work – even if the engine is shut off. Typically the vacuum brake booster check valve is not inspected during regular maintenance, but is examined by specialized diesel mechanics; especially on big rigs in fleet applications.

There are times when this part can show signs of wearing out or that the booster check valve has failed entirely. Here are a few of those warning signs to you can determine if a potential problem with your vacuum brake booster check valve exists. Remember, these are common warning signs that should be professionally diagnosed by a certified diesel mechanic and properly repaired.

1. Brake pedal is difficult to engage

When the vacuum brake booster check valve is working correctly, applying pressure to the brake pedal is easy and very smooth. When the check valve is not working correctly, the operation of the brakes becomes much more difficult. Specifically, the pedal goes from smooth and soft to aggressive and very difficult to press down. This is due to the excess pressure inside the master cylinder; which the check valve is designed to regulate. The inconsistency of the brake pedal is a quick warning sign that a potential safety issue exists with the brakes and should immediately be inspected by a certified diesel mechanic.

2. Brakes feel spongy

As the problem with the vacuum brake booster check valve increases, the symptoms will progressively move down the brake lines and to the brakes themselves. In this case, the air that is supposed to be removed by the check valve enters the master cylinder and then into the brake lines. This causes a reduction of pressure inside the brake lines and can cause the brakes to be applied softly. While driving you'll feel as if the brake pedal is spongy, however, the brakes will also take longer to stop the vehicle.

This situation calls for an immediate inspection of the brake system. When air enters the brake lines, it typically becomes trapped due to the fact that brakes are hydraulically controlled. In order to remove the air from the brake lines, the brakes will have to be bled professionally. As such, when you experience a problem like this with your diesel powered vehicle, stop driving the vehicle as soon as possible and have the entire brake system professionally examined.

3. Brakes stop working

The worst case scenario occurs when the vacuum brake booster check valve completely breaks and eventually leads to a brake system failure. Hopefully you never get to this point; but if you do, safely stop the car, have the vehicle towed back home and contact a diesel mechanic who is certified with brake system inspections and replacement. Depending on what actually broke, the repairs can range from simply replacing the vacuum brake booster check valve to complete brake system repair and replacement.

The vacuum brake booster check valve is important to your braking system, and acts as a safety feature. It's due to these facts that the problems and symptoms above should not be ignored or put aside for another day. Take time to contact a certified ASE or diesel mechanic to inspect, properly diagnose and make appropriate service adjustments to your brakes.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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