Many people have heard mechanics talk about bleeding brakes in the course of getting their car maintained, but those same people don’t actually know anything about how the brake system on car works past pressing the brake pedal and hoping for the best.
So how and when do you bleed your brakes? Blakes should be bled at least every two years, and any time the brakes on the car are repaired or replaced. Brake bleeding is accomplished by adjusting the bleeder screw and manually pressing any air bubbles out of the hydraulic brake lines, being sure to replace the brake fluid level in the master cylinder as the bleeding is performed.
It might be scary to find that your brakes have become soft or squishy when you to go move for a stop while you’re driving, but in some cases, this symptom can be easily fixed by a brake bleed. Keep reading to find out more about bleeding your brakes and whether you should do it yourself or hire a professional mechanic for the job.
What Does It Mean to Bleed Your Brakes?
When someone says that you need to bleed your brakes, what they really mean is that you need to remove any trapped air from the brake line system that may have been introduced during a brake repair or as the result of a brake line leak.
A hydraulic brake system is dependent on fluid pressure to perform correctly. If there is any air in the brake line, this changes the pressure in the hydraulic system and can cause it to malfunction or, in some cases, even fail entirely. This is the reason that it’s crucial to make sure your brakes are bled correctly whenever a brake job is performed.
If you replace your own brakes without bleeding them afterward, the air in the brake lines could cause your brakes to momentarily fail on the road, which leaves you liable and looking at damages or even injury in some cases.
That’s one of the main reasons you shouldn’t attempt to undertake a brake job on your vehicle unless you have either some experience in automotive repair or a more experienced mechanic looking over your shoulder and doublechecking your work.
When Should You Bleed Your Brakes?
Most mechanics recommend that the brake lines be flushed and bled as a maintenance service roughly every two to three years. Still, because brake repair is moderately difficult and do-it-yourselfers are less likely to undertake it, this is a maintenance service that often gets neglected until brake replacement requires it to be done.
While brake lines only need to be flushed every few years, your brake lines should be bled of any trapped air after every time you replace your brakes. This is because the act of repairing the brakes on a car introduces air into the closed hydraulic system, which can lead to mechanical failures and malfunctions if left unchecked.
What Is the Correct Order to Bleed Brakes?
In order for brakes to be bled correctly, they need to be bled in the proper
sequence on the car to get all of the trapped air out of the lines. This is one
technicality that can lead many amateur auto repair technicians into trouble
when attempting a brake job for the first time on their own without the help of
a professional mechanic.
When bleeding the brakes, it is important to bleed the wheels furthest from the master cylinder first and then the brakes closest to it.
In cars with a rear wheel drive, the recommended brake bleeding sequence is as follows:
- Right rear wheel
- Left rear wheel
- Right front wheel
- Left front wheel
In vehicles with a front wheel drive system or diagonally split brake lines, the recommended brake bleeding sequence is as follows:
- Right rear wheel
- Left front wheel
- Left rear wheel
- Right front wheel
If this brake bleeding sequence isn’t performed correctly, air can still be trapped in the system, and the entire sequence has to be started all over again. For this reason, it’s vital to get the brake bleeding process correct the first time since it’s already a tedious task, to begin with.
Do You need to Bleed All Four Brakes?
When performing a brake bleed, it is most common for mechanics to bleed all four lines at once since this is the best way to ensure that there is no trapped line anywhere in the brake system. Since it is labor intensive and typically requires two people to perform manually, brake bleeds are one of those jobs where mechanics will do the operation as thoroughly as possible to avoid having to go back into the system again.
However, if you’re only replacing a caliper and your car has independent brake lines for each wheel rather than a single hydraulic system, you can safely bleed the line on whichever wheel you’re working on rather than the lines for the entire system.
If you’re performing a brake bleed as a maintenance service,
it’s just better to go ahead and bleed the entire system at once. Since if you
miss any trapped air you’ll be doing the entire repair over again, it’s just
easier to be thorough the first time when doing a brake bleed.
How Much Does It Cost to Bleed Your Brakes?
The average cost to have your brakes bled by a mechanic is between $94 and $115, according to Repair Pal. The reason this repair service is fairly cheap compared to some other car maintenance jobs is that it doesn’t involve the replacement of any parts. At the most, you might be on the hook for some brake fluid.
Because it is a somewhat complicated repair procedure and doing it incorrectly can be a major safety hazard, the fact that it is so cheap to have your brakes bled (and it has to be done so infrequently) means that in almost all cases, it’s better to leave this particular job to a mechanic who knows what they’re doing.
Not only is it easier for mechanics to perform a brake bleed because they often have tools necessary to do the job correctly, but they’re also experienced enough to realize when the brakes have been bled sufficiently to be safe to drive on.
Any amateur auto mechanic will have to attempt a brake job eventually if they seriously want to learn to work on their own vehicles, but if you’ve never done one before, you shouldn’t start a brake bleed without some serious background in the topic before attempting it. It’s important to read over your car’s repair manual, consult with mechanics, and have some help before you try this repair.
Why Is It Important to Bleed Your Brakes?
The reason that bleeding your brakes is important is that trapped air in the hydraulic lines can reduce hydraulic pressure. While brake fluid can’t be compressed in a high-pressure system, air can, which means that when there is air in a hydraulic system, the pressure can fluctuate wildly.
This leads to what is known as “spongy” feeling brakes, which is a cutesy word for that feeling when you press down on your brakes, and it feels like they go halfway to the floor of the car before you get any braking performance.
In bumper to bumper traffic, this can be more than a little nerve-wracking, as well it should be—in most places, the person who hits someone from behind in a rear end collision is almost always legally at fault. And they should be if they have faulty brakes and don’t get them properly repaired.
That means that air trapped in your brake lines can lead to costly repairs or worse if you lose braking function at high speeds.
How to Bleed Your Brakes
When you’re getting ready to bleed your brakes, the first thing you need to do is check your car’s repair manual and see what kind of brake fluid is required. Different models of cars require different brake fluids, and some models have very specific types that must be used in the system, so this step shouldn’t be skipped.
A second important step that needs to be undertaken is that the car needs to be jacked up and placed on jack stands on level, solid ground. Do NOT try to replace brakes on a car that is only sitting on a car jack. Every year would-be mechanics around the world are crushed and injured or killed by car jack failures. That’s why it’s important to put a car up on stable stands any time it is being worked on from underneath. A car should only be on a jack alone when a tire is being changed on the side of the road, and a jack stand isn’t available. Jack stands are only designed to lift a vehicle up off the ground so that a jack stand can be put into place—they aren’t designed to hold a vehicle’s weight for extended periods.
Once the car is up on a jack stand, conduct the following procedure in order to bleed air out of the brake lines:
- Find the brake bleeder screw. If you aren’t sure
where this is located on the brake system, check your owner’s manual. If you
can’t find the screw or you don’t know where your owner’s repair manual is,
stop and take your car to a mechanic, you don’t need to be working on your own
brakes.
- Get a bleeder wrench and loosen the bleeder
screw. A bleeder wrench is specially designed to lock onto a bleeder screw
without stripping it. If you accidentally strip your bleeder screw, you’re
going to have to get the repair done by a professional who has the tools to
undo your mistake, so try to avoid it. Once the bleeder screw has been
loosened, re-tighten it.
- Place a piece of hosing (aquarium tubing works
well) over the end of the bleeder screw leading down into a jar and fill the
bottom of the jar with brake fluid so that the end of the line is submerged.
Technically this step can be done without tubing, but you’re greatly increasing
your chances of brake fluid squirting everywhere since it’s a high-pressure
line.
- Have someone else manually pump the brake pedal
while calling out their actions (Up! Down!). Once they’ve pumped the brakes a
few times, they should hold the brake pedal down with their foot and wait for
further instructions.
- While the brake pedal is being depressed, the
bleeder screw on the brakes should be opened. If this was set up properly,
you’d see air bubbles rise in the jar of brake fluid as the air is bled out of
the brake lines.
- Before the brake pedal is released, tighten the
bleeder screw again to make sure that no air from outside of the brake line
gets reintroduced when the brake pressure is removed.
- This procedure of pumping the brakes and
removing air from the line should be undertaken several times until no more air
bubbles can be seen coming up in the brake fluid in the jar at the bleeder
screw.
- Once done, the bleeder screw should be
re-tightened, and the brake fluid in the master cylinder should be refilled
back to the Full line. Without this step, more air can be reintroduced
into the brake line from the top of the braking system.
- The brake bleeding procedure should be repeated
on each wheel of the car in a sequence determined by whether the car is a rear
wheel or front wheel drive (as explained in the earlier section of this article
about brake bleed order).
- Once the brake lines on each wheel of the car
are bled, the master cylinder should be topped off one final time, and the car
should be taken for a short test drive (preferably not on any busy streets
where emergency braking may be required). At this point, the brakes should feel
tight and responsive, not spongy at all.
- If the brakes are still spongy, the car should be inspected again. Check to make sure that the master cylinder brake fluid level is at the full mark, and if it is, the car’s brakes will need to be bled a second time. This is not uncommon, as it can be someone difficult to remove all the air from the brake lines. This is one of the reasons amateur mechanics are less likely to attempt a brake bleed than they are more simple repairs such as oil changes or bulb replacements.
If you have the proper tools and some patience, bleeding the brakes at home after a brake repair can be safely performed. But it must be done meticulously, as any break in procedure during a brake bleed can lead to brake failure if the hydraulic system isn’t recalibrated properly after brake repairs are completed.
You can find a more detailed tutorial on how to bleed your brakes in this Popular Mechanics article.
Will Air in Brake Lines Go Away on Its Own?
The answer is no, air in brake lines will remain until it is removed from the system by a mechanic. This is because a car’s hydraulic brake system is a closed system, so the air that gets trapped in a brake line has nowhere to go until it is manually expressed from the line.
Not only can trapped air in a hydraulic line not be removed on its own, leaving it in the system can actually cause the hydraulic braking in the car to become progressively worse. That means that a car should be inspected, and the brakes should be bled at the earliest signs of unresponsive brakes in order to avoid more serious loss of braking function and possibly an accident on the road.
Because the brake system is a closed system, when air is bled from the brakes, the brakes also have to be inspected to see how the air got into the system to begin with. This is usually the result of a leak in the brake lines or some kind of malfunction in the braking system that needs to be addressed to avoid more air in the lines in the future (and additional brake bleeding jobs).
Bleeding the Brakes Is Vital for Car Safety
There are few safety systems on a car more vital than the brakes—after all, without working brakes, a car is just a two-and-a-half-ton missile on wheels. Bleeding the brakes on a hydraulic brake system is one of the lesser-known parts of maintenance in car repair, but it’s one of the most important when it comes to making sure your brakes work like they’re supposed to after a brake job.
Bleeding brakes is one of those repair jobs that is usually easier to outsource to a professional mechanic just because of their access to mechanical lifts and multiple people for manually brake bleeding, but the process is simple enough as long as you’re very careful and follow each step of the process to the letter.