brake fluid flushing BMW 528i 1998 E39 Workshop Manual

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020-24
Maintenance
tions. In general, replacement batteries should always be
rated equal or higher than the original battery.
The battery is held in place by a single hand screw and plate.
A secure battery hold-down is important in order to prevent
vibrations and road shoclt from damaging the battery.
CAUTION-
Prior to disconnecting the baitem read the battery discon-
nection cautions given in
001 General Cautions and
Warnings.
NOTE-
Always disconnect the negative (-) cable first, and connect
it last. While changing the battery, clean away any corro-
sion in or around the battery tray
More battery and charging system information is in 121
Battery, Alternator, Starter.
Brake fluid, replacing
Brake fluid absorbs moisture easily, and moisture in the fluid
affects bralte performance and reliability. This is why
BMW
strictly recommends replacing the bralte fluid every two
years. When replacing or adding bralte fluid, use only new
fluid from previously unopened containers. Do not use brake
fluid that has been bled from the system, even
if it is brand
new. Use only DOT
4 brake fluid.
NOTE-
See 340 Brakes for brake fluid flushing procedures.
Brake pad 1 rotor wear, checking
Disc brakes are fitted at all four wheels. Although the brakes
are equipped with a brake pad warning system, the system
only monitors one wheel per axle. Pad thickness should be
checked whenever wheels are off or brake
worlt is being
done.
4 Disc brake pad wear can be checked through opening in
caliper:
Measure distance
(A) of brake pad "eai' to bralte rotor.
See
340 Brakes. Compare to specification below.

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Tool for bleeding clutch hydraulics (Tool No. 21 5 030)
21 5 030 I
The clutch is hydraulically actuated by the master and slave
cylinders. With the self-adjusting clutch
(SAC), clutch disc
wear is automatically taken up through the self-adjusting
pressure plate springs, making pedal feel consistent through-
out the life of the clutch.
A soft or spongy feel to the clutch pedal, long pedal free-play,
or grinding noises
from the gears while shifting can all indi-
cate problems with the clutch hydraulics. In these circum-
stances it is best to
star? with a clutch fluid flush, followed, if
necessary, by replacement of the hydraulic parts.
NOTE-
The clutch hydraulic system shares the fluid reservoir and flu-
id with the brake hydraulic system.
Clutch hydraulic system,
bleeding and flushing
If the clutchlbralte fluid is murky or muddy, or has not been
changed within the last two years, flush the system and
change the fluid. Flushing the old fluid from the clutch lines is
done using a bralte system pressure bleeder.
- Remove brake fluid reservoir cap. Using a clean syringe, re-
move brake fluid from reservoir. Refill reservoir with clean
DOT
4 bralte fluid.
Worlting inside engine compartment, remove left
interiorven-
tilation filter housing:
Release 3 plastic taps
(A) on duct. Earlier models use a
single release latch.
Rotate duct inward to remove.
Disconnect electrical harness to hood position switch.
Remove filter housing cover.
Release spring lock
(B) on interior ventilation housing and
remove housing.

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Anach pressure brake bleeder to fluid reservoir and pump
bleeder a few times to pressurize hydraulic fluid system.
CAUTION-
* Do not exceed 2 bar (29 psi) pressure at the fluid resenfoil
when bleeding or flushing the hydraulic system.
Brake fluid is poisonous, highly corrosive and danger-
ous to the environment. Wear safety glasses and
rub-
bergloves when working with brake fluid. Do not siphon
brale fluid with your mouth. Immediately clean away
any fluid spilled on painted surfaces and wash with wa-
ter, as brale 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 clutch and
brake hydraulic systems, ;nd will also lower the brake
fluid boiling point. Dispose of brale fluid properly.
- Raise and safely support vehicle.
WARNING-
Make sure the car is stable and well supported at all times.
Use a professional automotive lift orjackstands designed for
the purpose. A floor
iack is not adequate support.
- If necessary, remove transmission splash shield.
Hydraulic system, bleeding
Worlting underneath transmission, connect a hose from
clutch slave cylinder bleeder valve
(arrow) to a container.
Open bleeder valve and allow bralte fluid to expel until
clean fluid comes out, free of air bubbles.
Close bleeder valve and disconnect pressure bleeding
equipment from fluid reservoir.
Slowly operate clutch pedal about
10 times. Fill reservoir
with clean fluid as necessary.
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340-8
1 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.
Read the
Warnings listed below before beginning the bleed-
ing procedure an on any
E39 car. If air enters the ACS or DSC
hydraulic unit, the factory BMW Service Tester MUST be
used in conjunction with a bralte pressure bleeder before the
vehicle is driven.
The BMW
ServiceTester (DISpluslGT1iMoDiC) must be
used to bleed the braltes if:
Any hydraulic brake system components are replaced, in-
cluding bralte lines.
Air has enter the
ABSIASC or ABSlDSC hydraulic unit.
WARNING -
* The ASC and DSC systems use electronic controls and a
sophisticated hydraulic unit Once air enters the hydraulic
unit, it is very difficult to remove using traditional methods.
For this reason, pressure
brake bleeding should be done
in conjunction with the BMW
Sewice Tester (DIS-
plus/GTl/MoDiC). The tester electrically cycles the hy-
draulic unit solenoids in the hydraulic unit while
pressurized brake fluid is forced through the system.
When flushing the brake fluid from the system, use ex-
treme care to not let the
brale fluid reservoir run dry If
air enters the hydraulic unit, the BMW Service Tester
MUST be used to bleed the brale system before the
vehicle is driven.
Always use new brake fluid from an unopened container. It is
important to bleed the entire system when any part of the hy-
draulic system has been opened. Be sure to have the special
equipment needed before beginning the job.
When bleeding the
braltes, start atthe wheel farthest from the
master cylinder and progress in the following order:
right rear brake
left rear brake
* right front brake
left front brake