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Bad Brake Booster: Signs, Symptoms, and Replacement Cost

A brake booster is usually known for making the brake pedal easier to depress. It certainly does this, but few remember that in doing so, it also decreases stopping distances. As a result, they make your vehicle more controllable and safe.

If a brake booster is bad you might experience an unusual brake pedal feel, unusual brake noises, fluid leaks, increased stopping distances, and even engine issues.

What Is a Brake Booster?

A brake booster is a device that applies pressure to your vehicle’s brakes by multiplying the force with which you depress the brake pedal. This makes it easier to depress the brake pedal and stop the vehicle. There are three main types of brake boosters: Vacuum, hydraulic, and electronic.

vacuum brake booster servo

Vacuum brake boosters are the most common type, and they utilize the air that flows through the intake manifold to flow into the booster, creating a pressure difference on one side of a diaphragm within the booster. This pressure difference is what multiplies the force to the brakes.

Hydraulic brake boosters use the hydraulic pressure from the power steering system to assist in braking power. Electronic brake boosters utilize sensors and computers to control and assist with braking power. 

Common Signs and Symptoms of a Bad Brake Booster

Many of the signs and symptoms of a bad brake booster could probably be assumed to be connected to brake feel and function, and most are, but one or two symptoms might surprise you. If you notice any of these signs starting to occur, you should have your local mechanic look into the problem since a bad brake booster pose a potential safety hazard to you and others.

Leaks

bad brake booster symptoms
Brake Booster and Master Cylinder

Leaks can signal problems for many different components, and leaking brake fluid is no exception. Although a brake fluid leak is usually a sign of a master cylinder issue rather than an issue with the brake booster itself, hydraulic and electronic brake boosters can both leak fluid when they go bad. 

Unusual Brake Pedal Feel

Whenever your vehicle’s brake pedal starts to feel differently than it usually does, it should be inspected immediately. You know your vehicle best, and issues should not be ignored, regardless of how small they seem to be. If the brakes become stiff and hard to push, or if they become especially spongey, you could have a bad brake booster.

Additionally, when the brake “bite” point is higher or lower than usual or the pedal is slow to return to its normal position, this could also be a sign of a bad brake booster.

Learn More: Signs and Symptoms of Bad Brake Pads

Increased Stopping Distance

When your brake booster goes bad, and it is no longer able to multiply the power that you use to depress the brake pedal, the result is usually longer stopping distances. This can be frustrating, but it can also be unsafe. It will also most likely be accompanied by a different brake feel than usual. 

Usually, increased stopping distances are accompanied by more difficult brake depression, but depending on the problem, it could be the opposite. The opposite problem could be if the brake pedal feels like mush, and it is still not stopping the vehicle. This is often the sign of a different braking system issue; Neither should be ignored.

Strange Noises

In vehicles with bad brake boosters, there will often be a hissing noise that comes when the brake pedal is depressed. This is a result of the diaphragm within the booster having a leak, allowing higher pressure air to leak to the side with lower pressure. 

Hydraulic and electronic brake boosters can make a whining noise when they start to go bad. Occasionally, they will make other types of noises, but whining is the most common noise. Any bad brake booster, regardless of the type, has the potential to make unusual noises, even if it is not the noise most commonly associated with each type. 

Engine and Fuel Economy Issues

A bad brake booster can actually cause a vehicle’s engine to run poorly and its fuel economy to suffer. This is because the air intake used by the booster is connected to the intake manifold, the same channel through which air has to enter to be used by the engine. If the booster is using too much air, it can actually “steal” from what the engine needs.

This usually only occurs with vacuum brake boosters, and it will be most apparent at low speeds or at idle. Misfires, poor acceleration, rough idling, and even stalling can all occur if the booster has a vacuum leak that causes an excess amount of air to vacate the engine intake. 

Check Engine or ABS Light Illumination

There are so many things that can cause the check engine light to come on, but with a bad brake booster, it usually comes on as a result of an “upstream” issue caused by the brake booster. In other words, the check engine light will often come on as a result of a vacuum leak that robs the engine of air rather than a direct brake booster issue. 

The ABS light could also come on as a result of any braking issue, again, not because the brake booster is directly linked to the ABS system, but rather because it causes another issue within the braking system that ultimately leads to ABS problems.

What is the Expected Lifetime of Brake Booster?

pneumatic vacuum brake booster

Brake boosters are usually quite resilient, and vacuum boosters, being simple devices with very few moving parts, are expected to last well past 100,000 miles. Most will last the lifetime of a vehicle with only one replacement possibly being necessary for the entire duration of its life. 

The most common thing that causes premature booster failure is a leaking master cylinder or a torn diaphragm from an especially dry climate. Hydraulic and electronic brake boosters usually fail sooner and more often than vacuum boosters because of their added complexity, but all types usually have very few problems unless an engineering flaw causes premature failure.

How Much Does Brake Booster Cost to Replace?

Brake boosters themselves are not usually that expensive. Many usually cost from about $100 to about $300 for larger vehicles that require larger boosters. Labor costs are what make brake booster replacements more expensive jobs than other simple replacements. Typical labor costs can run from $300 to well over $500. This is dependent on how much is involved with parts removal for access.

Additionally, when replacing the brake booster, other items within the braking system need to be worked on to supplement the replacement. Brake bleeding and sometimes line replacement often accompany booster replacement, adding to the overall cost. 

Total costs for a complete booster replacement can range from $300 to over $1000 in the most extreme situations. Brave DIY-ers can tackle the replacement themselves to lower costs, but this should be done carefully since working with the braking system is important to the safety of yourself and the vehicle. 

Final Thoughts

Brake boosters not only make it easy to depress the brake pedal in your vehicle, but they do this by multiplying the power of your own pedal depression, helping stop the vehicle safely. Faulty brake boosters are not that common, but when they fail, you could experience strange brake noises, longer stopping distances, excessive pedal resistance, spongy brake feel, brake fluid leaks, or even engine running issues. 

Richard Reed
I've been a General Manager of a moving company and I've also been a Professional Mover for over 30 years. I've driven flat beds, reefers, dropdecks, moving vans, heavy machinery, etc. In my time as a Mover I've driven over 1,000,000 safe miles. My days of moving and driving truck are past me but The Vehicle Lab allows me to share the knowledge I've gained over the past 40 years.
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