Diagnosis - Isuzu 1999 RODEO Workshop Manual

5C–6
POWER–ASSISTED BRAKE SYSTEM

Diagnosis

Road Testing The Brakes
Brake Test
Brakes should be tested on a dry, clean, reasonably
smooth and level roadway. A true test of brake
performance cannot be made if the roadway is wet,
greasy or covered with loose dirt so that 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 of the vehicle toward wheels on one side or if the
roadway is so rough that wheels tend to bounce. Test the
brakes at different vehicle speeds with both light and
heavy pedal pressure; however, avoid locking the wheels
and sliding the tires. Locked wheels and sliding tires do
not indicate brake efficiency, since heavily braked but
turning wheels will stop the vehicle in less distance than
locked wheels. More tire–to–road friction is present with a
heavily braked turning tire then with a sliding tire.
The standard brake system is designed and balanced to
avoid locking the wheels except at very high deceleration
levels.
It is designed this way because the shortest stopping
distance and best control is achieved without brake
lock–up.
Because of high deceleration capability, a firmer pedal
may be felt at higher deceleration levels.
External Conditions That Affect Brake Performance
1. Tires: Tires having unequal contact and grip on the
road will cause unequal braking. Tires must be
equally inflated, identical in size, and the thread
pattern of right and left tires must be approximately
equal.
2. Vehicle Loading: A heavily loaded vehicle requires
more braking effort.
3. Wheel Alignment: Misalignment of the wheels,
particularly in regard to excessive camber and caster,
will cause the brakes to pull to one side.
Brake Fluid Leaks
With engine running at idle and the transmission in
"Neutral", depress the brake pedal and hold a constant
foot pressure on the pedal. If pedal gradually falls away
with the constant pressure, the hydraulic system may be
leaking.
Check the master cylinder fluid level. While a slight drop in
the reservoir level will result from normal lining wear, an
abnormally low level in reservoir indicates a leak in the
system. The hydraulic system may be leaking internally
as well as externally. Refer to "Master Cylinder
Inspection". Also, the system may appear to pass this test
but still have slight leakage. If fluid level is normal, check
the vacuum booster push rod length. If an incorrect length
push rod is found, adjust or replace the push rod. Check
the brake pedal travel and the parking brake adjustment.
When checking the fluid level, the master cylinder fluid
level may be low from the "MAX" mark if the front and rear
linings are worn. This is not abnormal.
Warning Light Operation
When the ignition switch is in the START position, the
"BRAKE" warning light should turn on and go off when the
ignition switch returns to the ON position.
The following conditions will activate the "BRAKE" light:
1. Parking brake applied. The light should be on
whenever the parking brake is applied and the ignition
switch is on.
2. Low fluid level. A low fluid level in the master cylinder
will turn the "BRAKE" light on.
3. During engine cranking the "BRAKE" light should
remain on. This notifies the driver that the warning
circuit is operating properly.