Daewoo NUBIRA, User Manual

Page: 163 / 685

HYDRAULIC BRAKES 4A – 5
DAEWOO V–121 BL4
DIAGNOSIS
BRAKE SYSTEM TESTING
Brakes should be tested on a dry, clean, reasonably
smooth and level roadway. A true test of brake perfor-
mance cannot be made if the roadway is wet, greasy, or
covered with loose dirt whereby all tires do not grip the
road equally. Testing will also be adversely affected if the
roadway is crowned so as to throw the weight so roughly
that the wheels tend to bounce.
Test the brakes at different vehicle speeds with both light
and heavy pedal pressure; however, avoid locking the
brakes and sliding the tires. Locked brakes and sliding
tires do not indicate brake efficiency since heavily braked,
but turning, wheels will stop the vehicle in less distance
than locked brakes. More tire–to–road friction is present
with a heavily–braked, turning tire than with a sliding tire.
Because of the high deceleration capability, a firmer pedal
may be felt at higher deceleration levels.
There are three major external conditions that affect brake
performance:
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Tires having unequal contact and grip of the road
will cause unequal braking. Tires must be equally
inflated, and the tread pattern of the right and the
left tires must be approximately equal.
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Unequal loading of the vehicle can affect the brake
performance since the most heavily loaded wheels
require more braking power, and thus more braking
effort, than the others.
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Misalignment of the wheels, particularly conditions
of excessive camber and caster, will cause the
brakes to pull to one side.
To check for brake fluid leaks, hold constant foot pressure
on the pedal with the engine running at idle and the shift
lever in NEUTRAL. If the pedal gradually falls away with
the constant pressure, the hydraulic system may be leak-
ing. Perform a visual check to confirm any suspected
leaks.
Check the master cylinder fluid level. While a slight drop
in the reservoir level results from normal lining wear, an ab-
normally low level indicates a leak in the system. The hy-
draulic system may be leaking either internally or external-
ly. Refer to the procedure below to check the master
cylinder. Also, the system may appear to pass this test
while still having a slight leak. If the fluid level is normal,
check the vacuum booster pushrod length. If an incorrect
pushrod length is found, adjust or replace the rod.
Check themaster cylinder using the following procedure:
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Check for a cracked master cylinder casting or
brake fluid leaking around the master cylinder.
Leaks are indicated only if there is at least one drop
of fluid. A damp condition is not abnormal.
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Check for a binding pedal linkage and for an incor-
rect pushrod length. If both of these parts are in
satisfactory condition, disassemble the master cyl-
inder and check for an elongated or swollen primary
cylinder or piston seals. If swollen seals are found,
substandard or contaminated brake fluid should be
suspected. If contaminated brake fluid is found, all
the components should be disassembled and
cleaned, and all the rubber components should be
replaced. All of the pipes must also be flushed.
Improper brake fluid, or mineral oil or water in the fluid,
may cause the brake fluid to boil or cause deterioration of
the rubber components. If the primary piston cups in the
master cylinder are swollen, then the rubber parts have
deteriorated. This deterioration may also be evidenced by
swollen wheel cylinder piston seals on the drum brake
wheels.
If deterioration of rubber is evident, disassemble all the hy-
draulic parts and wash the parts with alcohol. Dry these
parts with compressed air before reassembly to keep alco-
hol out of the system. Replace all the rubber parts in the
system, including the hoses. Also, when working on the
brake mechanisms, check for fluid on the linings. If exces-
sive fluid is found, replace the linings.
If the master cylinder piston seals are in satisfactory condi-
tion, check for leaks or excessive heat conditions. If these
conditions are not found, drain the fluid, flush the master
cylinder with brake fluid, refill the master cylinder, and
bleed the system. Refer to”Manual Bleeding the Brakes”
or”Pressure Bleeding the Brakes” in this section.
BRAKE HOSE INSPECTION
The hydraulic brake hoses should be inspected at least
twice a year. The brake hose assembly should be checked
for road hazard damage, cracks, chafing of the outer cov-
er, and for leaks or blisters. Inspect the hoses for proper
routing and mounting. A brake hose that rubs on a suspen-
sion component will wear and eventually fail. A light and
a mirror may be needed for an adequate inspection. If any
of the above conditions are observed on the brake hose,
adjust or replace the hose as necessary.
WARNING LAMP OPERATION
This brake system uses a BRAKE warning lamp located
in the instrument panel cluster. When the ignition switch
is in the START position, the BRAKE warning lamp should
glow and go OFF when the ignition switch returns to the
RUN position.
The following conditions will activate the BRAKE lamp:
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Parking brake applied. The light should be ON
whenever the parking brake is applied and the igni-
tion switch is ON.
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Low fluid level. A low fluid level in the master cylin-
der will turn the BRAKE lamp ON.
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As a test of the lamp circuit, vehicles with antilock
brakes will momentarily illuminate the lamp for
about 4 seconds when the ignition