brake pads is one of the easiest jobs to perform on your BMW. In general,
you should inspect your brake pads about every 10,000 miles, and replace
them if the material lining of the pad is worn down enough to trigger the
pad replacement sensor. In reality, most people dont inspect their pads
very often, and usually wait until they see the little brake warning lamp
appear on the dashboard. It's a wise idea to replace the pads, and inspect
your discs as soon as you see that warning lamp.
If you ignore the
warning lamp, you may indeed get to the point of metal on metal contact,
where the metal backing of the pads may be contacting the brake discs. Using
the brakes during this condition will not only give you inadequate braking,
but will also begin to wear grooves in your brake discs. Once the discs are
grooved, they are damaged, and there is almost no way to repair them.
Resurfacing will sometimes work, but often the groove cut will be deeper
than is allowed by the BMW specifications. The smart thing to do is to
replace your pads right away.
Brake pads should only be replaced in pairs replace both front pads or
both rear pads at a time. The same rule applies to the brake discs that
should be checked each time you replace your brake pads.
The procedure for
replacing pads on all the wheels is basically the same. There are slight
configuration differences between front and rear brakes, but in general the
procedure for replacement is similar. The first step is to jack up the car
and remove the road wheel. This will expose the brake caliper that presses
the pads against the disc (Figure 1). Make sure that
the parking brake is off when you start to work on the pads.
If you look inside
the caliper, you will see the brake pads - usually they will look very thin,
as is shown in
Figure 2. Begin by removing the small
plastic cap that covers the caliper guide bolts (Figure
3). The BMW caliper used on the 3-Series (and many other BMWs) is a
single piston caliper design. One piston presses against the side of the
brake disc, and the whole caliper slides on the guide bolt to achieve equal
pressure on the disc from both pads.
To replace the brake pads, you need to remove the caliper. Remove both guide
bolts from the caliper (Figure 4)
with a 7mm allen wrench (thanks to Barney McComas for the tip). Then remove the
brake pad retaining clip (keeps the pads from rattling), shown in
Figure 5. Make sure you wear safety glasses during
this step, as the clip can come flying off if you're not careful. Then, use
a pair of needle-nose pliers to remove the brake pad sensor (Figure
After the guide bolts have been removed, you should be able to simply lift
the caliper off of its mount (Figure 7). Suspend the
caliper using some zip-ties or rope - don't let the caliper hang from its
rubber hose (very bad). See
Figure 8 for details. As
this point, you can pluck the outer brake pad out of the caliper, and use a
screwdriver to pry the inner pad out of the caliper piston. The caliper
Figure 9 when you're done.
Once you have the pads removed, inspect the
inside of the caliper. You should clean this area with some compressed air
and isopropyl alcohol. Make sure that the dust boots and the clamping rings
inside the caliper are not ripped or damaged. If they are, then the caliper
may need to be rebuilt.
At this point, you
should inspect the brake discs carefully. Using a micrometer, take a
measurement of the disc thickness. If the disc is worn beyond its
specifications, then its time to replace it along with the one on the other
side. See our Pelican Technical Article on Replacing BMW Brake Discs for
The installation of the new brake pads is quite easy. You will need to take
a small piece of wood or plastic and push the caliper piston back into the
caliper (Figure 10). This is because the new pads
are going to be quite a bit thicker than the old ones, and the piston is set
in the old pads position. Pry back the piston using the wood, being careful
not to use too much force. Using a screwdriver here can accidentally damage
the dust boot and seals inside the caliper, and is not recommended.
Be aware that as
you push back the pistons in the calipers, you will cause the level of the
brake reservoir to rise. Make sure that you dont have too much fluid in
your reservoir. If the level is high, you may have to siphon out a bit from
the reservoir to prevent it from overflowing. Also make sure that you have
the cap securely fastened to the top of reservoir. Failure to do this may
result in brake fluid accidentally getting on your paint.
When the piston is
pushed all the way back, you should then be able to insert the new pads (Figure
11) into the caliper. If you encounter resistance, double check to make
sure that the inside of the caliper is clean. Simply snap the inner
brake pad into place using your hand (Figure 12).
When firmly mounted, the new pad should resemble
process for assembly is the reverse of the disassembly. Mount the
caliper back onto its mounting bracket, surrounding the brake disc. If
the caliper won't fit, then you need to push in the piston a bit more until
the space in-between both pads is wide enough for the brake disc to fit.
Tighten down the guide bolt using a torque wrench to 22 ft-lb (30 Nm).
If your brake sensors
activated the lamp on your dashboard, they should be replaced with new ones.
Disconnect the sensor (Figure 14), and plug in the
new one. Then snap the new sensor into the small gap in the brake pad
You also may want to spray the back of the brake pads with some anti-squeal
glue. This glue basically keeps the pads and the pistons glued together, and
prevents noisy vibration. Anti-squeal pads can also be purchased as sheets
that are peeled off and placed on the rear of the pads.
When finished with
both sides, press on the brake pedal repeatedly to make sure that the pads
and the pistons seat properly. Also make sure that you top off the master
cylinder brake fluid reservoir if necessary. Brake pads typically take
between 100 and 200 miles to completely break in. Its typical for braking
performance to suffer slightly as the pads begin their wear-in period. Make
sure that you avoid any heavy braking during this period.
Well, there you have it - it's
really not too difficult at all. If you would like to see
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