QUESTION:
I’ve begun hearing a faint squealing noise from my car
— in the front, I think. It increases as I speed up
and sometimes goes away if I use the brakes. With the
holidays, this isn’t the best time for a car repair.
Is it important that I fix this right away?
—Doreen
H.
ANSWER:
There’s a good chance the noise you’ve so nicely
described is a brake-pad wear sensor beginning to sound
off. These are little metal tabs attached to the inner
brake pad that come into contact with the brake rotor
when the pad’s friction material wears thin. While the
nail on a blackboard sound will become increasingly
annoying and embarrassing with further driving, the
early warning of worn brake pads can head off some
expensive damage. If a brake pad loses most or all of
its friction material, its steel backing and/or the
rivets attaching the friction material will cause severe
damage to the brake rotor, along with decreased stopping
ability.
Audible
wear sensors are found on some but not all brake pads.
Higher-end vehicles typically use an electrical sensor
that illuminates a warning light when pad thickness
significantly decreases, rather than subjecting the
driver to an awkward sound. This probe-type of wear
sensor requires replacement after activation for about
$10-$40 apiece. Other warning light-type sensors are
embedded within the brake pad, making replacement more
straightforward.
A
tab-type sensor can make noise in the way you described
because brake pads ride just a hair away from the brake
rotor, and flexing of both parts while driving or
braking can cause intermittent contact. As your pads
wear further, the noise will become louder and more
continuous, to the point you won’t want to drive the
car. The good news is you still have perhaps a month of
driving remaining before this happens, and at least
several more months of unimpaired brake operation.
If
you’re considering a brief delay in having the brakes
looked at, I’d feel better knowing the cause was in
fact a wear sensor rather than something else that may
require more immediate attention. Many wheels have
sufficiently large gaps between the spokes to allow a
nice view of the brake caliper and rotor. If so, the
edge of the outer brake pad is usually visible if the
wheel is rotated just right. Thickness of the friction
material on a new brake pad is a bit greater than that
of a pencil. If you see it’s less than one-third of
this dimension, or if the gap between the pad’s metal
backing and the rotor if the friction material isn’t
visible, there’s a good chance a wear sensor is
signaling or will be soon. Inner brake pads typically
wear at a slightly greater rate than the outers, so a
sort-of-thin outer pad means it’s time for brakes now.
NOTE:
I received several reader inquiries regarding where to
purchase brake fluid test strips. The strips I
recommended are made by Phoenix Systems and are
available in two quantities: a sample pack containing
two for about $10 and a tube of 100 for about $67. You
can find them at Walmart.com, eBay.com or Phoenix
Systems’s own website, http:///
