Change Your Brake Pads
By Scott MemmerNothing is more important than your car's ability to stop itself.
Even race car drivers will tell you that a car's braking capacity takes precedence over its acceleration. Putting a car through a wall is not nearly as much fun as touching the brakes slightly, banking into a turn, and scooting out the other side. Nor as safe.
But braking systems often fail us -- usually from our own neglect. Even Formula One cars won't stop as effectively with worn brake pads. It's the equipment, folks, not the driver.
In the case of braking, it's essential that we maintain optimum friction pad depth to insure maximum performance of the braking system. In layman's terms: change your brake pads!
In previous articles at Edmunds.com we've discussed the ins and outs of braking systems. The link below provides an excellent primer on the differences between drum and disc brakes. You might want to read it before going any further.
Okay, here's the deal. We're not going to
go into some long, drawn-out discussion about the advantages and
disadvantages of various braking systems, drag coefficients, friction
rates, kinetic versus thermal energy, etc., etc. What we're going to do
here is roll up our sleeves and do a brake reline. Leave that other stuff
to the armchair mechanics, the sideline slackers.
As always with our How To columns, we suggest that you own a basic tool
kit and have the time to commit to the task. This will take a few hours.
In exchange, we hope to teach you a little something about braking systems
and what makes them tick.
As we said at the outset, nothing is more important than your car's
ability to stop itself. Learning about the braking system -- how it works,
ways to maintain it, when to fix it, what to look for while you're in
there -- will not only make you a smarter driver, but a safer one too.
Since we have a limited amount of space
here, we're going to focus exclusively on changing the front brake pads.
Ninety percent of the brake pad changes you make during the life of your
vehicle will be to the front pads.
You can check for brake pad wear by viewing the pads from outside the
front tire. On most cars, you can look through the openings on the outside
of the wheel/rim assembly to see the pads. (Of the six cars we looked at
for this story, all but one had the pads clearly visible. On rare
occasions, you may have to remove the wheel to see the pads.) The outside
pad should be staring you in the face. Look at it from above. The pad will
be pressed against the shiny metal rotor. See it?
Now, there are two way to determine whether the pads need replacing.
First, visually. If the pad depth is less than ¼ inch, plan on replacing
it soon. If it's less than 1/8 inch, you're getting close to damaging the
rotor, so do it ASAP. This varies slightly from car to car, but is a good
general guideline.
Second, by ear. They build these little noisemaking shims into the brake
assembly to tell you when the pads need changing. Are you hearing a
screeching sound when you apply the brakes, like a mouse trying to escape?
You're overdue for a reline. (If the sound is more a scrape-y metal rasp,
you've already damaged your rotors and need to fix the brakes
immediately.)
Okay, you've determined that the front pads are due for replacement.
Remember the rule here: better too soon than too late, which can result
not only in more expensive repairs, but unsafe driving conditions as well.
So let's go...
STEP ONE: Comfort first. Park the car in a cool, shady spot.
STEP TWO: Now safety. Block the rear wheels so the car won't roll
once you jack it up. Put the car in park and set the parking brake firmly.
STEP THREE: Lay out your tools. Grab a tire iron and go to the
front wheels. The tire iron is that long metal rod with a socket on the
end of it that usually comes with the vehicle. You can also buy a really
cool one (called a spinner) that looks like a metal cross -- in fact, it
is a metal cross -- with different-sized sockets on each end.
What we want to do here, before jacking the car up off the ground, is
loosen the lug nuts on the wheels just enough to break them free. So go do
that. Work them off just enough until they loosen their resistance and
become easy to turn with the tire iron. Now slip the jack under the car.
There are several places to safely jack up the car. If you have a
floorjack, you can roll it all the way under to the center of the engine
and jack it up using the K-member that holds the engine. Be careful not to
use the oil pan, as you might damage it. If you have a smaller, single
floor jack, you'll have to do one side at a time. Look for flat spots on
the frame, immediately to the rear of the front wheels, or on the end of
each axle.
CAUTION: Always use jack stands. Never attempt to work on an
elevated vehicle held in place only by a hydraulic jack.
Okay, raise the front axle off the ground. Put your jack stands under each
end of the axle, and lower the car onto the stands. A jack stand (see
illustration) is a metal tripod with variable height adjustments. You
should own two.
STEP FOUR: Remove the lug nuts and the wheel (the tire will be
attached). Best to work on one wheel at a time, leaving the other side
intact as a point of reference. As a safety precaution, roll the
wheel/tire assembly under the front-center of the car, between the jack
stands, and plop it down beneath the engine's K-member. In the event of a
faulty jack stand, this will break the vehicle's fall and could possibly
save your life.
STEP FIVE: Okay, take a breather. Now let's look at what we have
before us.
A disc brake assembly is composed of the following elements: a caliper,
two brake pads, a rotor, and some bolts and clips to hold it alltogether.
It's a very simple design. Here's how it works.
The caliper comes in two flavors -- floating or fixed. Each works
on a similar principle. The caliper's job is to squeeze the brake pads
toward a centrally located metal plate -- the rotor -- producing friction,
which in turn slows the car. Think of a hand slowly clamping down on a
spinning record (or a CD, for you youngin's who've never heard the term
"record" before).
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The brake pads hover on either side of the metal plate. They attach
to the inside of the caliper, depending on your car's design, with clips
or bolts. They are composed of heat-resistant material that rubs against
the rotor. When the brakes are applied, the pads move toward one another,
gripping the rotor between them and slowing the wheels.
The rotor is that shiny metal disc staring you in the face right
now. You can almost see your reflection, right? Get your eyes level with
it. If you can't see your face, or at least its general outline, it may
mean that the disc needs servicing or replacement. Below, we'll show you
how to check this disc for scoring or marring, and what to do about that.
STEP SIX: Back to work. Remove the bolts holding the caliper in
place. Gently slide it out and away from the rotor. Inspect the inside of
the caliper. See the pads? They will be held in place by a bolt or a
series of clips, sometimes both. Remove the bolts or clips holding the
pads in place (remember, you left the other side intact to use as a
reference) and work them free. Examine the pads. Is there any
"meat" left on them, or are they worn down to the screws? If
they're completely worn, you should've been hearing a metallic scrape for
a while every time you applied the brakes.
Lay the pads aside and inspect the rotor. Can you see yourself in it? If
the pads were worn into the metal, your rotor will be scored; you'll have
trouble seeing yourself. Run your fingernails along the surface of the
rotor -- careful, though; if it's been less than 20 minutes since you last
drove the vehicle, they might still be hot -- first the side facing you,
then the side facing away. Is it scored? Deeply? This next point is very
important. If the rotor has any grooves at all in it, remove it at
once. Now you have a decision to make.
If you have a scored rotor, you must decide whether to have it
"turned" or to replace it. If you're short on money, take it to
a local mechanic and ask him to "turn" it for you. What they do
is put it on a special metal-cutting lathe and shave off several
thousandths of an inch of metal until the disc is shiny again. Remember,
though, one of the real advantages of disc brakes over drum is their
heat-handling capability. By removing metal, you reduce the system's
thermal transfer capacity. We recommend turning the discs only when you
are short on bucks. The better way is to take the disc to the auto parts
store, match it up with a replacement, and buy a new one. Last time we did
this, it only cost us twenty bucks for a new rotor, a cheap investment in
safety. You have to go there anyway to buy the new brake pads, as well as
a few other things, so why not make it one trip. In fact, here's your
shopping list:
- new rotor, or rotors, if needed
- new brake pads (bring the old ones, to match them)
- brake pad grease (comes in little packets; they're cheap, so buy two)
STEP SEVEN: Go home and have a
lemonade.
STEP EIGHT: Before you go any further, you must move the piston
back to its "full open" position. The piston? you ask. Ah, we
didn't tell you about that one, did we? Remember the hand-and-record
analogy. As the fingers push down (equivalent to the brake pads wearing)
the distance between the brake pads shortens. Now that we have brand new
pads, we must return the system -- the hand -- to its original
"open" position, to accommodate the new pads. There are several
ways to do this.
First, find the piston. It is located along the back (closest to the
engine) portion of the caliper. It's usually about three to four inches
across, and resembles a small metal promontory with a flat top. See it?
Depending on its condition and age, there are several things you can do to
move it back (toward the center of the car). If it's new, try pushing it
in with the heel of your hand. Doesn't work? Okay, then try a channel lock
or a vise grip. Still won't budge? Then here's a suggestion. A neighbor of
ours turned us on to this once, and it works great. Get a large C-clamp,
place a thin piece of wood or cardboard over the face of the piston to
protect the surface from marring, and work it back that way. As you turn
the handle on the clamp, it will increase pressure on the piston, until it
becomes flush with the surrounding metal. Then loosen and remove the
C-clamp.
STEP NINE:Install the new rotor, if necessary. Remove the old brake
pads from the caliper (usually held in place by several clips), but,
before putting on the new ones, you must do something. Remember the little
packets of grease you bought? These are used to lubricate the brake pads.
Careful now -- not on the front of the pad, which comes in contact
with the rotor, but on the back. The pads attach to the caliper via
a plate-and-clip arrangement. The lubricant goes between the plate
and the back of the brake pad. Got it?
Don't overlook this. If you don't do it,
you'll get a horrible screeching sound every time you apply the brakes,
like a dinosaur in heat (and you know how horny those velociraptors used
to get). After you apply the grease, attach the pad to the plate and slide
the whole thing into place.
STEP TEN:. Basically, at this point, just reassemble the system in
reverse order of the way you took it apart. Now do the other side. Take
the car for a test spin. Sometimes, with new brakes, you can get some
weird scraping and scratching sounds; these will usually go away in a few
days. Clean up, and you're done.
Don't underestimate the importance of a brake reline. As we said at the
outset, absolutely nothing is more important than your car's ability to
stop itself. Knowing more about your car's braking system -- getting in
there and actually seeing what's going on -- empowers and informs you in a
way that going to the corner mechanic doesn't.
For more automotive information, visit www.edmunds.com.