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Air In Brake Lines
Why is there air in my
brake lines?
BY JOSH BRIGGS
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.
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