Unless you’re a professional athlete with tree trunks for legs, be grateful that
your car has a brake booster nestled between the brake master cylinder and firewall
on your car. Your brake booster doesn’t make any noise, and it doesn’t use
any electricity or gasoline, but it ensures that you can stop your car with only
a light touch of the brake pedal. Things weren’t always like that: before the
invention of the vacuum brake booster, cars still stopped. It’s just that you
had to really stomp on the brake pedal. The modern brake booster is an ingenious
device that operates using something that your engine generates whenever it’s
running: vacuum. The brake booster takes engine vacuum via a rubber hose that
runs from the intake manifold, and the brake booster uses that vacuum to amplify
the pressure you put on the pedal. A light application of the brakes is translated
by the brake booster into significantly more pressure on the brake master
cylinder, ensuring that your car stops quickly.
So what happens to
the brake booster if your car stalls, resulting in a loss of engine vacuum? Early
designers realized that gas engines were hardly foolproof, so they designed
a little check valve into the brake booster circuit. The brake booster stores
enough vacuum to provide full boost for two or three pedal applications even after
the engine dies. The check valve on the brake booster is what keeps that vacuum
from leaking out. And speaking of leaks, that’s the reason most brake booster
units have to be replaced. As your brake booster ages, the rubber seals and
diaphragms that hold the vacuum tend to wear out and crack. If the brake booster
can’t hold vacuum (despite the check valve’s best efforts), its time is up
and you’ll need a new or remanufactured new brake booster. |
