Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 1184

POWER-ASSISTED BRAKE SYSTEM

5C–3

The master cylinder contains two pistons that supply the
hydraulic pressure for a dual–circuit braking system.
The primary piston provides the fluid pressure to the
front brakes, while the secondary piston provides the
fluid pressure to the rear brakes. If the pressure is lost
from either system, the remaining system will function to
stop the vehicle.

CAUTION:

1. If any hydraulic component is removed or

disconnected, it may be necessary to bleed all
or part of the brake system. (Refer to Bleeding
Brake Hydraulic System in this section.)

2. The torque values specified are for dry,

unlubricated fasteners.

3. Perform service operations on a clean bench

free from all mineral oil materials.

Brake Booster

331R200001

This booster is a tandem vacuum unit with a diaphragm
effective diameter 205mm + 230mm (8.07in + 9.06in). In
normal operating mode, with the service brakes in the
released position, the tandem vacuum booster operates
with vacuum on both sides of its diaphragms. When the
brakes are applied, air at atmospheric pressure is
admitted to both sides of the diaphragm to provide the
power assist. When the service brake is released, the
atmospheric air is shut off from both sides of the
diaphram. The air is then drawn from the booster
through the vacuum check valve to the vacuum source.

CAUTION:

1. If any hydraulic component is removed or

disconnected, it may be necessary to bleed all
or part of the brake system.

2. The torque values specified are for dry,

unlubricated fasteners.

3. The vacuum booster is not repairable and must

be replaced as complete assembly.

5C–4

POWER-ASSISTED BRAKE SYSTEM

Disc Brake

Front Disc Brake

A05R200001

Rear Disc Brake (4

´4 Model)

A05RW002

The disc brake assembly consists of a caliper, piston,
rotor, pad assembly and support bracket. The caliper
assembly has a fornt dual bore, rear single bore and is
mounted to the support bracket with two mounting bolts.
The support bracket allows the caliper to move laterally
against the rotor. The caliper is a one–piece casting with
the inboard side containing the piston bore. A square
cut rubber seal is located in a groove in the piston bore
which provides the hydraulic seal between the piston
and the cylinder wall.

NOTE:

1. Replace all components included in repair kits used

to service this caliper.

2. Lubricate rubber parts with clean brake fluid to ease

assembly.

3. If any hydraulic component is removed or

disconnected, it may be necessary to bleed all or

part of the brake system.

4. Replace pads in axle sets only.

5. The torque values specified are for dry, unlubricated

fasteners.

6. Perform the service operation on a clean bench free

from all mineral oil materials.

Operation

Hydraulic pressure, created by applying the brake
pedal, is converted by the caliper to a stopping force.
This force creates a clamping action of the piston
pressing towards the rotors (outward) and the     caliper
slides inward toward the vehicle. This clamping action
forces   the linings against the rotor, creating friction to
stop the vehicle.

POWER-ASSISTED BRAKE SYSTEM

5C–5

Leading/Trailing Drum Brakes (4

´2 Model)

A05RS003

This drum brake assembly is a leading/trailing shoe
design. Both brake shoes are held against the wheel
cylinder pistons by the upper return spring and to the
fixed anchor plate by the lower return spring. When the
brakes are applied, the wheel cylinder pistons expand
pushing both shoes out contacting the drum.
With forward wheel rotation, the forward brake shoe will
wrap into the drum and becomes self-energized.
With reverse wheel rotation, the rear brake shoe is
self-energized. Force from the brake shoes is
transferred to the anchor plate through the braking plate
to the axle flange. Adjustment is automatic and occurs
on any service brake application. Also, with leading/
trailing brakes, it is normal for the front shoe to wear at a
faster rate than the rear shoe.

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 where 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. Braking without locking the
tires will stop the vehicle in less distance than braking to
a skid (which     has no brake efficiency). More tire to
road friction is present while braking without locking the
tires     than braking to a skid.
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   lower than the “MAX” mark if the front and
rear linings are worn. This is normal.

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.