Driving with air in brake lines

“It’s happened to every driver at some point. One moment, you’re cruising along without a care in the world. You’re simply making your way from point A to point B and enjoying the relaxing ride in between. Then it happens: Without warning, there’s something in the road ahead. You need to stop, and you need to do it now.

Having to slam on the brakes is a high-drama event that puts the spotlight on your car’s braking system. Car brakes rarely get much attention – that is, until there’s an emergency. Then the system that stop-and-go commuters love to hate is on centre stage. But how do brakes translate the pressure of your foot on the brake pedal into stopping power?

Arguably, one of the most important brake parts in turning pedal action into stopping power is a vehicle’s brake lines. Most cars and light trucks have hydraulic braking systems. That means they use fluid to transfer the braking power from your foot to the brakes. In extremely basic terms, here’s how a typical disc brake system operates: The fluid is stored in the master cylinder. When the brake pedal is applied, it moves fluid from the master cylinder to the brake callipers, forcing them to clamp down on the brake rotors to slow the car. That fluid is carried through the brake lines, making them a rather critical brake part. If your brake lines don’t work, your brakes won’t work and you (and your car) will be in a heap of trouble.”

“Air In Brake Line Symptoms

Power brakes, that are standard in most modern vehicles, rely on brake fluid to work.  When you depress the brake pedal hydraulic force is transferred to the brake callipers.  They in turn press the pads into the brake rotors to slow or stop the vehicle.  Air is much less dense when compared to the brake fluid.  This means if air is in the lines it will compress too easily.  When this happens, your brakes will feel too soft or even spongy.

  • Brakes Feel Spongy
  • Brakes Feel Soft
  • Brake Pedal Depressed Too Far

If you’ve felt any of these air in the brake line symptoms, don’t delay, get your brakes checked out by our professional team of brake repair technicians.

How Does Air Get In My Brake Lines?

While the brake system in modern vehicles is designed to be air tight, over time air does get in.  This is due to your brake pads needing to move further as the pads wear down.  Your brake callipers extend to maintain a uniform distance.  To do this the hydraulic pistons also need to extend, causing a void in the hydraulic system.  As your pads wear down more brake fluid is needed to supply your system.

Most people aren’t closely monitoring their brake fluid so as the system works harder to depress the brake pads, air is unfortunately drawn into the system.  It is this air that causes your brakes to feel spongy or soft.

How To Bleed Brakes: Getting The Air Out

To return your vehicle’s braking system to like new condition will require removing the air.  This is a job some car owners can do for themselves, but many prefer to leave their car’s safety in the hands of Certified technicians.

Professional Brake Bleeding

In the hands of trained professional auto repair technicians your brake system will be completely voided of air in the system and brake lines.  This ensures the function of your primary safety system, the ability to stop.

If you suspect that you may have air in your brake lines, contact our service centre for professional assistance.

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All opinions expressed in this article are not the onus of the publisher nor supplier.

Is your brake pedal feeling a little spongy lately? Is your brake pedal going to the floor while you sit at a red light or when you're braking at low speeds? If so, chances are you have air in your brake lines.

A hydraulic braking system, like the one found in most cars and trucks, relies on brake fluid for pressure. The whole system springs into action the moment you step on the brake pedal. But have you ever wondered why your brake fluid level gradually decreases over time? The fluid isn't magically disappearing. In fact, there's actually a perfectly practical explanation for this phenomenon. As your brake pads wear thinner and thinner over several thousand of miles of use, the distance your brake pads need to travel to make contact with your rotors increases. The hydraulic pistons within the brake calipers slowly extend to keep the brake pads at a uniform distance from the brake rotors as the pads wear. It's only a very small distance, but if you consider that there are four sets of brake pads -- each set wearing down a little bit more every time you touch the brake pedal -- it's easy to see how the system requires more brake fluid as time passes. As you probably already know, your brake fluid level decreases as your brake pads wear down. It makes sense, right? But here's where a somewhat common brake problem begins.

Brake fluid resides in a sealed, air-tight reservoir on top of the master cylinder. As the brake fluid level drops, air moves in to fill the void. Wait a minute -- didn't we just say that the system was air-tight? Well, unfortunately, air does get into the reservoir over time and it eventually makes its way into the rest of the braking system -- including your brake lines. Every time you open the cap to check your brake fluid level, you're letting air into the system. When the fluid is at the correct level, air isn't much of a factor; however, the more worn your brake pads are, the larger the void grows. That's one reason why it is so important to keep the fluid at the proper level.

­Water is another factor that can cause brake issues. Water can actually cause air to accumulate in your brake lines. How so, you ask? Well, brake fluid is hygroscopic -- it absorbs and retains water. The problem arises when the fluid has absorbed as much water as it possibly can -- it becomes saturated. Brake fluid is designed to have an extremely high boiling point; however, if you subject your vehicle to excessive braking, like maybe a trip through the mountains, you can easily cause the brake fluid to heat up to this temperature or beyond. When the brake fluid boils -- especially when there is excessive water in the system -- steam is a by-product. The braking system ultimately compresses this steam and turns it into water. The air separates from the water and before you know it, you have large pockets of air in your brake lines.

A spongy brake pedal is bad news, but there's no need to lose any sleep over it; you probably don't need a complete brake overhaul. What you do need to do, similar to other brake problems, is address the situation immediately. Brakes are one of the most crucial safety components on your vehicle. Obviously, with a shoddy brake system, you're putting your safety and the safety of other drivers at risk. So, what can you do? It's a safe bet that your braking system will be fine after you bleed your brakes. This simple procedure will eliminate any unwanted air from the lines and restore your brake pedal pressure. You can do this at home in your garage or take your vehicle to the local automotive shop to have it done for you. While you're at it, you should probably change your fluid, too. Brake fluid, as we mentioned, becomes saturated and can deteriorate over time so go ahead and replace it while you have the opportunity. With fresh brake pads, all new brake fluid and a properly bled hydraulic system, your brakes should feel firm and as good as new.

For more information about braking and other related topics, follow the links on the next page. They'll provide you with lots more information.

Bleeding the brakes is an inevitable part of DIY automotive repairs. Air can enter the brake system during repairs, but the more common reason is far more insidious. Brake fluid is hygroscopic and readily absorbs water from the atmosphere. Water in the brake fluid lowers its boiling point. Heat boils the brake fluid, and the resulting steam leaves air in the lines. Brake fluid is incompressible while air is easily compressed and manifests as a spongy brake pedal or worse.

Meanwhile, contaminated brake fluid attacks rubber, iron, and steel. Black gunk in the reservoir means the war against hoses, caliper piston seals, and wheel cylinder seals is well underway. Repairs caused by rotten brake fluid let in more air, and all of it leads back to bleeding the brakes, a required and universally loathed task that almost always leaves one pondering a better way while lying under the car in a cold toxic soup of brake fluid and rust.

As such, we’ve put together five different ways to get old brake fluid and air out and fresh brake fluid in. No matter the method, the prep is the same: soak the bleed screws in penetrating oil, siphon as much rotten crud out of the reservoir as possible, add fresh brake fluid, start with the bleed screw furthest away from the master cylinder, and work back to the closest one. Along with being poisonous, brake fluid destroys paint, so keep a large bucket or plentiful supply of cool, clean water nearby and immediately flush any spills.

Mike Bumbeck

Gravity is good

Mike Bumbeck

Gravity is the simplest one-person brake bleeding method. Attach the hose to the bleed screw, open it up, and watch old brake fluid and air flow out of the lines like water through the Aqua Virgo aqueduct on the way to Rome. These inexpensive Bleed-O-Matic type setups work well. The small bottle doesn’t hold a lot of brake fluid, but it does help prevent accidentally running the reservoir dry. The magnet makes it easy to stick the bottle in plain view for a reason. We’re not sure if it’s time dilation or sudden flow changes, but sometimes the bottle seems empty one minute and overflowing the next, so keep an eye on gravity.

Pedal and hold

Mike Bumbeck

For whatever reason, gravity doesn’t always take hold and the two-person method can pick up where gravity fails. One person sits in the driver’s seat and pumps the brake pedal while the other cracks open and closes the bleed screws. Pressurize. Hold. Bleed. Repeat. Loud callouts of “pump it up” or “pressure” and “hold it down” can make the garage or driveway sound like a Sunday morning at the Waffle House, but the two-person procedure is a tried and true way to get the brakes bled quickly. Communication breakdowns or attention lapses can slow the job, so sort out the callouts and procedures ahead of time.

Vacuum pulled

Mike Bumbeck

The idea here is to create a vacuum that draws brake fluid and air out of the bleed screws into a catch container. A hand-operated vacuum gun is a decent option, especially if you already have one around. This Mighty-Vac unit came with all the brake bleeding attachments and is rigged with fresh vinyl tubing. First, hook up the bleed screw adapter, hoses, and catch container. Then pull some vacuum and crack the bleed screw. The procedure can be tricky as air sometimes gets in around the bleed screw threads and creates a tube full of bubbles. Slathering some heavy bearing grease around the bleed screw base can help stop deceptive bubbling.

Pressure-operated venturi

Mike Bumbeck

Another type of vacuum setup uses compressed air and a venturi to draw brake fluid and air out at the bleed screw. This system can create the same bubbles in the line issue as the hand-operated unit, as the venturi-type bleeder gets the job done about the same way. Brake fluid and air gets drawn out of the bleed screw and flows quickly through the hose even if it doesn’t seem that way, so this unit came with a large catch can and a few supply bottles that sit upside down in the reservoir. On the negative side, the venturi bleeder we used here pulls a lot of air through the compressor and was a bit more finicky than the hand-operated setup.

Pressure tank

Mike Bumbeck

Some consider the pressure tank brake bleeder the very best there is. When you absolutely, positively want to push every last molecule of air and rotten brake fluid out of the system, accept no substitutes. The Motive unit shown here is one of many, but the concept is the same. Pressure check the tank-to-master-cylinder connection for leaks with air only, depressurize, fill the tank with brake fluid, pressurize, and take a leisurely walk around the car cracking bleed screws with a wrench and catch can. We’re using the universal round pressure cap, but direct fit adapters are available. In this case, the pressure bleeder sorted out the rear ABS brake modulator under the Starion hood like a champ.

Mike Bumbeck

All of these methods work. Hopefully you won’t have to try several options before you find the one that works best for you.