cylinder is leaking internally, or fluid is
leaking externally. Check all brake fluid
lines and couplings for leaks, kinks,
chafing and corrosion. If no leaks can be
found, the master cylinder is faulty and
should be replaced.
Check brake booster:
Remove vacuum hose (
A
) from
brake booster and install BMW
special tool 34 3 100 between
connection and hose on non-return
valve (
B
).
Start engine and check build-up of
partial vacuum. Switch engine off.
Press brake pedal to set partial
vacuum of no more than 0.8 bar
(11.6 psi). Wait for vacuum value to
stabilize.
When pedal is released, partial
vacuum should not drop by more
then 0.06 bar (0.8 psi) over 1 hour.
-
If vacuum values are not reached:
Check connections of vacuum
hoses.
Replace vacuum non-return valve
(
B
).
Check seal between brake booster
and master cylinder.
If values still cannot be reached,
brake booster must be replaced.
Worn or contaminated brake pads will
cause poor braking performance.
Brakes
http://ebahn.bentleypublishers.com/BMW/3/E46/Repair%20Manuals/3...
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Summary of Contents for 1999-2005 M3
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