BMW 3 (E46). Manual — part 171
water, as brake fluid will remove
paint.
Always use new brake fluid from
a fresh, unopened container.
Brake fluid will absorb moisture
from the air. This can lead to
corrosion problems in the braking
system, and will also lower the
brake fluid's boiling point.
Dispose of brake fluid properly.
Do not reuse self-locking nuts,
bolts or fasteners. They are
designed to be used only once
and may fail if reused. Always
replace them with new
self-locking fasteners.
Table b. Brake system troubleshooting
Symptom
Probable cause
Repairs
Brake squeal
Incorrectly installed
brake pads or
parking brake shoes,
or brake parts.
Check component installation. Check/replace
anti-rattle springs.
Brake pad carriers
dirty or corroded
Remove brake pads and clean calipers.
Brake pads
heat-glazed or
oil-soaked
Replace brake pads. Clean rotors. Replace
leaking calipers as required.
Wheel bearings worn
(noise most
pronounced when
turning)
Replace worn bearings. See
310 Front
Suspension
or
330 Rear Suspension
.
Pedal goes to floor
when braking
Brake fluid loss due
to system leaks
Check fluid level and inspect for signs of
leakage.
Master cylinder or
electronic control
system faulty
Replace master cylinder. Diagnose electronic
control system using factory or compatible
diagnostic tool.
Symptom
Probable cause
Repairs
Low pedal after
system bleeding
Master cylinder faulty Replace master cylinder.
Pedal spongy or
brakes work only
when pedal is
pumped
Air in brake fluid
Bleed system using factory or compatible
diagnostic tool
Master cylinder or
electronic control
system faulty
Replace master cylinder. Diagnose system using
factory or compatible diagnostic tool.
Excessive braking
effort
Brake pads wet
Use light pedal pressure to dry pads while
driving.
Brake pads
heat-glazed or fluid-
soaked
Replace brake pads and rotors. Replace leaking
calipers.
Vacuum booster or
vacuum hose
connections to
booster faulty
Inspect vacuum lines. Test vacuum booster and
replace as required. Test vacuum non-return
valve for one-way flow.
Brakes pulsate,
chatter or grab
Warped brake rotors
Resurface or replace rotors.
Brake pads worn
Replace brake pads.
Brake pads
heat-glazed or
oil-soaked
Replace brake pads. Clean rotors. Replace
leaking calipers.
Uneven braking,
car pulls to one
side, rear brakes
lock
Incorrect tire
pressures or worn
tires
Inspect tire condition. Check and correct tire
pressures.
Brake pads on one
side of car
heat-glazed or fluid-
soaked
Replace brake pads. Clean rotors. Replace
leaking calipers. .
Caliper or brake pads
binding
Clean and recondition brakes.
Worn suspension
components
Inspect for worn or damaged suspension
components. See
310 Front Suspension
or
330 Rear Suspension
.
Brakes drag, bind
or overheat
Brake caliper or
brake pads binding
Clean or replace caliper.
Master cylinder or
electronic control
system faulty
Replace master cylinder. Diagnose electronic
control system using factory or compatible
diagnostic tool.
340-2
Bleeding brakes
Brake bleeding is usually done for one
of two reasons: Either to replace old
brake fluid as part of routine
maintenance or to expel trapped air in
the system that resulted from opening
the brake hydraulic system during
repairs.
Always use new brake fluid from an
unopened container. It is important to
bleed the entire system when any part
of the hydraulic system has been
opened. Be sure to have the special
equipment needed before beginning
the job.
WARNING!
E46 cars require special BMW
service equipment to properly bleed
either the ABS/ASC or the ABS/DSC
system. For safety reasons, the
brake system on these cars must not
be bled without the use of a factory
diagnostic computer.
When bleeding the brakes, start at the
wheel farthest from the master cylinder
and progress in the following order:
right rear brake
left rear brake
right front brake
left front brake
Pressure bleeding brakes
-
Top off brake fluid in reservoir and
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