Question: How can I tell if my power brakes are working
properly?
Answer: Most cars and trucks have vacuum-assist power
brakes. If you've noticed the brake pedal seems harder and requires
more effort to apply the brakes, you may have a problem with the
brake booster.
To check the booster, pump the brake pedal with the engine
off until you've bled off all the vacuum from the unit (the pedal
will feel firmer and you won't hear any sounds from the booster).
Then hold the pedal down and start the engine. You should feel
the pedal depress slightly as engine vacuum enters the booster
and pulls on the diaphragm. If there's no change, the vacuum
hose to the booster may be loose or blocked. If the vacuum hose
is okay, the problem is in the booster and the booster needs to
be replaced.
If your brake booster has failed, your brakes will still work
but will require increased pedal effort. The pedal will feel
much harder and will take a lot more pressure to stop the vehicle.
Driving with a bad booster can be dangerous because the vehicle
may not be able to stop as quickly or in as short a distance.
So don't delay. Have the problem diagnosed and repaired as soon
as possible.
If your vehicle has an "integral" antilock brake
system (where the ABS system is combined with the master cylinder
assembly), power brake assist is provided by pump pressure stored
in the ABS accumulator. (NOTE: If your vehicle has a "nonintegral"
ABS system, it has a conventional vacuum brake booster.) If there's
an ABS pump or accumulator failure, power assist will be lost
and the ABS warning light should come on alerting you that a problem
has occurred.
WARNING: If the ABS warning light is on, the ABS system is
usually deactivated which means the ABS system can't prevent skidding
when braking on wet or slick surfaces. You should have the system
checked out and repaired as soon as possible.
HYDRO-BOOST
Though not as common as vacuum booster power brake systems,
some vehicles are equipped with Bendix "Hydro-Boost"
power brakes. This system uses hydraulic pressure generated by
the power steering pump rather than engine vacuum to provide power
assist.
Pressure generated by the power steering pump is stored in
an accumulator, which is then routed to the master cylinder by
the Hydro-Boost unit when you step on the brakes. Problems can
be caused by leaks inside the Hydro-Boost unit, by a worn power
steering pump, slipping or broken pump drive belt, or hose connections.
A simple way to test the Hydro-Boost system is to pump the
brakes five or six times with the engine off to discharge the
accumulator. Then press down hard on the pedal (about 40 lbs.
of force) and start the engine. Like a vacuum booster, you should
feel the pedal fall slightly when the engine starts, then rise.
The leakdown of the accumulator can be checked by pumping
the brakes several times while the engine is running, then shutting
it off. Let the car sit for about an hour, then try the brakes
without starting the engine. You should get 2 or 3 soft brake
applications before it takes more effort to push the pedal.
