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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.
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