3 Symptoms of a Bad Brake Booster Check Valve

The braking system of a vehicle is often built with an extra feature called a vacuum brake booster. The purpose of the brake booster is to create more pressure in the braking system.

For instance, when you step on the brake pedal to slow down the vehicle, the brake booster ensures that the brake master cylinder receives a steady flow of brake fluid. This boosts the braking pressure in order to make the brake pedal more sensitive when you step on it.

That way, you don’t need to step hard on the brake pedal to get the vehicle to slow down fast. Most cars, trucks, and SUVs on the road these days utilize a brake booster.

What Does a Brake Booster Check Valve Do?

brake booster check valve

One component of the brake booster is the check valve. When the brake booster has air trapped inside of itself, the check valve works to extract the air by sucking it out of there. This prevents the air from accessing the brake master cylinder.

If air were to get into the cylinder, you could have air bubbles in the brake lines. Then your braking performance would be greatly diminished.

A check valve is the link between the brake booster and the vacuum hose. It is what keeps these braking components functioning properly so that your brakes function properly when you step on the brake pedal.

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Bad Brake Booster Check Valve Symptoms

The brake booster check valve should last for a long time. However, there will come a point when the check valve does wear out entirely. You’ll know when this happens because it won’t work anymore.

Of course, the check valve is not often checked when your brakes are inspected, so you won’t have time to prepare for a failing check valve. All you can do is recognize the symptoms for when it does go bad.

Here’s what to look for:

1) Firm Brake Pedal


When you step on the brake pedal, it should not be difficult to push the pedal down with your foot. In fact, it should only take a little bit of foot pressure to push it down smoothly. This is what happens when the check valve is working just fine.

But if the check valve is worn out and no longer working, then it might cause your brake pedal to become more difficult to push down. The pedal will suddenly feel firm and it’ll take a lot more foot pressure than normal to push it down.

This happens because the brake master cylinder has more pressure building up inside of it. Without a check valve to regulate the pressure, it causes this to happen.

2) Spongy Brake Pedal

If you have air bubbles in your brake lines because of the bad check valve, you may notice your brake pedal feeling a bit spongy. Your brake pedal may even go all the way to the floor. This happens when the air bubbles actually go into the brakes and reduce the pressure in them.

Anytime you have less braking pressure, you’ll have a soft and spongy brake pedal. It may be easy to step on the brake pedal when it’s like this, but don’t expect the vehicle to slow down quickly. It will still take longer to slow down under this condition.

3) Poor Brake Performance

how limited slip differential works

If brake fluid cannot reach the brake master cylinder consistently because of a bad check valve, then your braking performance is going to suffer for it. Aside from the firmness of the brake pedal, it’ll still take longer for the vehicle to slow down once you do press the pedal down.

The longer this goes on, the more likely that your brakes will stop working altogether. You’ll obviously be forced to do something about it then because you’ll likely crash your car into something to stop it.

Don’t let the problem get to this point, though. Just replace the check valve and restore the functionality of your brakes.



3 thoughts on “3 Symptoms of a Bad Brake Booster Check Valve”

  1. i am installing a booster check valve in-line in my 1978 fj40 Toyota Land Cruiser resto-mod. which way do i install it? flow to the booster or flow away?

  2. My 2009 nissan versa 1.8l brake pedal just became hard while driving and all wheels are locking up. This started as I was replacing a brake bulb. Pumping the pedal as I had my wife tells me if the brake lights are working. Before changing the bulbs all was well. I then changed out brake pedal switch, brake hoses in front and both calipers. Master cylinder and booster. Adjustment nut is not the problem, because the manufacturer had set it. Also as I said, all was well before the brake bulb problem. While testing out the car, the brake become lock up on all wheels of 20 minutes of driving, also before I had changed out any parts at all.


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