ISUZU TROOPER 1998 Service Repair Manual

POWER ASSISTED BRAKE SYSTEM 5C – 23
VACUUM BOOSTER
This booster is a tandem vacuum unit with a diaphragm effective diameter 205 mm + 230 mm (gasoline
engine model) / 180 mm + 205 mm (diesel engine model). 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 one side of each
diaphragm to provide the power assist. When the service brake is released, the atmospheric air is shut
off from the one side of each diaphragm. 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 – 24 POWER ASSISTED BRAKE SYSTEM
DISC BRAKES
The disc brake assembly consists of a caliper, piston, rotor, pad assembly and support bracket. The
caliper assembly has a single bore and is mounted to the support bracket with 2 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 service operation 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 acts equally against the piston and the bottom of the caliper bore to move the piston outward
and to move (slide) the caliper inward resulting in a clamping action on the rotor. This clamping action
forces the linings against the rotor, creating friction to stop the vehicle.
Front disc brakes
Rear disc brakes

POWER ASSISTED BRAKE SYSTEM 5C – 25
ON-VEHICLE SERVICE
BRAKE HOSE REPLACEMENT
1
24
2
3
12
4
5
3
Front/Rear Caliper Brake Hose
Removal Steps
1. Brake pipe
2. Clip
3. Bolt and gasket
4. HoseInstallation Steps
To install, follow the removal steps in the
reverse order.
Rear Axle Brake Hose
Removal Steps
1. Brake pipe
2. Clip
3. Brake pipe
4. Bolt
5. HoseInstallation Steps
To install, follow the removal steps in the
reverse order.

5C – 26 POWER ASSISTED BRAKE SYSTEM
REMOVAL
Preparation:
1) Raise the vehicle and support it with suitable
safety stands.
2) Remove wheel and tire assembly.
3) Clean dirt, grease, and other foreign material off
the hose fittings at both ends.
Front/Rear Caliper Brake Hose
1. Brake Pipe
2. Clip
3. Bolt and Gasket
4. Hose
Rear Axle Brake Hose
1. Brake Pipe
2. Clip
3. Brake Pipe
4. Bolt
5. Hose
INSTALLATION
To install, follow the removal steps in the reverse
order, noting the following points. After installing the
brake hoses, bleed brakes as described in this
section.
Front/Rear Caliper Brake Hose
1. Tighten the brake pipes to the specified torque.
Brake Pipe Torque N·m(kg·m/lb·ft)
16 (1.6 / 12)
2. Tighten the bolt to the specified torque.
Bolt Torque N·m(kg·m/lb·ft)
35 (3.5 / 26)
NOTE:
•Always use new copper gaskets.
•Be sure to put the hooked edge of the flexible
hose end into the anti-rotation cavity.
Rear Axle Brake Hose
1. Tighten the brake pipes to the specified torque.
Brake Pipe Torque N·m(kg·m/lb·ft)
16 (1.6 / 12)
2. Tighten the bolt to the specified torque.
Bolt Torque N·m(kg·cm/lb·in)
13 (130 / 113)

POWER ASSISTED BRAKE SYSTEM 5C – 27
BRAKE PIPE REPLACEMENT
1
12
Removal Steps
1. Brake pipe
2. Plastic clip
Installation Steps
To install, follow the removal steps in the
reverse order.
REMOVAL
Preparation:
1) Raise the vehicle and support it with suitable
safety stands.
2) Remove wheel and tire assembly as necessary.
3) Clean dirt, grease, and other foreign material off
the pipe fittings at both ends.
1. Brake Pipe
2. Plastic Clip
1 Vehice with LSPV

5C – 28 POWER ASSISTED BRAKE SYSTEM
P & B (PROPORTIONING AND BYPASS) VALVE
Master cylinder
(Primary) Master cylinder
(Secondary)
Rear brakeFront brake
INSTALLATION
To install, follow the removal steps in the reverse
order, noting the following points. After installing the
brake pipes, bleed brakes as described in this section.
1. Tighten the brake pipes to the specified torque.
Brake Pipe Torque N·m(kg·m/lb·ft)
Master Cylinder Side Others
12 (1.2/9) 16 (1.6/12)
The P & B valve contains two sections, each serving a
different function.
The proportioning section of the P & B valve
proportions outlet pressure to the rear brakes after a
predetermined rear input pressure has been reached.
This is done to prevent rear wheel lock-up on the
vehicles with light rear wheel loads.
The valve has a By-bass feature which assures full
system pressure to the rear brakes in the event of a
font brake mulfunction, also full front pressure is
retained in the event of rear brake mulfunction.
The P & B valve is not repairable and must be
replaced as a complete assembly.

POWER ASSISTED BRAKE SYSTEM 5C – 29
P & B VALVE REPLACEMENT
1
3
1yy
2
Removal Steps
1. Hydraulic pipes
2. Bolt
3. P & B valve
Installation Steps
To install, follow the removal steps in the
reverse order.
REMOVAL
•P & B valve is not repairable and must be
replaced as a complete assembly.
•Care must be taken to prevent brake fluid from
contacting any painted surface.
1. Hydraulic Pipes
•Plug the pipes to prevent the loss of fluid or the
entrance of dirt.
2. Bolt
3. P & B Valve
INSTALLATION
3. P & B Valve
2. Bolt
Bolt Torque N·m(kg·cm/lb·in)
13 (130/113)
1. Hydraulic Pipes
Hydraulic Pipe Torque N·m(kg·m/lb·ft)
16 (1.6/12)
After installing the brake pipes, bleed brakes as
described in Bleeding Brake Hydrauric System this
section.

5C – 30 POWER ASSISTED BRAKE SYSTEM
LOAD SENSING PROPORTIONING VALVE (LSPV)
(FOR EUROPE AND SOUTH AFRICA)
to rear wheel cylinder
from front master cylinder
from rear master cylinder
Structure and Operation
The following is an explanation of the structure and
operation of the linkage type load sensing device.
This device controls the fluid pressure to the rear
brakes in accordance with changes in rear axle load
(vertical displacements of the rear axle springs).
•Structure
This device consists of a load sensing lever and a
valve.
The valve is mounted through a bracket to the
frame. One end of the load sensing lever is fixed
to the valve at the frame and the other end to the
rear axle housing through a spring.
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POWER ASSISTED BRAKE SYSTEM 5C – 31
•Operation
1) Outline
When the L.S.P.V. (Load Sensing Proportioning
Valve) detects a change in load weight, the load
sensing lever moves. Its reaction force is
transmitted to the bottom of the load sensing
valve to secure an optimum rear wheel cylinder
fluid pressure break point in proportion to the
actual load weight.
Besides, if the front brake system should fail, the
devices is designed to prevent the master cylinder
fluid pressure from decreasing and to apply it
directly to the rear wheel cylinder to obtain a
sufficient braking performance.
From rear
master cylinder
2) Operation
(1) When the fluid pressure is under the break point.
The fluid pressure of the rear master cylinder
passes through a clearance between the valve
seal and the piston and acts on the rear wheel
cylinder. At this moment, a downward force is
applied to the piston. However, the compression
spring force and reaction force of the load sensing
lever keep the piston in the upper position by
pushing upwards. (See the left figure.)To rear
wheel cylinder
(2) When the fluid pressure is equal to the break
point.
As the rear wheel cylinder pressure increases, it
surpasses the compression spring force and
reaction force of the load sensing lever, causing
the pistion to move downwards, so that the
pistion butts against the valve seal to shut off the
fluid line between the master cylinder and rear
wheel cylinder. (See the left figure.)
(3) When the fluid pressure is over the break point.
When the fluid pressure increases further, the
piston moves upwards. The moment the piston
comes apart from the valve seal, fluid pressure is
applied to the rear wheel cylinder and the piston
moves downwards so that the fluid line is shut off
again. This process goes on repeatedly to control
the fluid pressure to the rear wheel cylinder.
C05RW024 C05RW021 C05RW025

5C – 32 POWER ASSISTED BRAKE SYSTEM
(4) When the front brake system fails.
When there is a failure in the front brake system,
the fluid pressure from the front master cylinder
decreases. As a result, the balance between the
front and rear brake side fluid pressures is lost at
the control valve sleeve so that the control valve
sleeve moves upwards.
The control valve sleeve strikes against the piston,
thereby pushing the piston upwards.
Accordingly, the fluid pressure of the rear master
cylinder is not decreased and is applied directly to
the rear wheel cylinder to secure a sufficient
braking performance of the rear brakes. (See the
left figure.)
Valve Maintenance
In the case of fluid leak or other abnormalities, faulty
valve should be replaced.
Note:
The load sensing proportioning valve is not
repairable and must be replaced as a complete
assembly.
ADJUSTMENT PROCEDURE OF LSPV
1. Adjust the rear axle weight by loading the
laggage compartmemt as necessary.
Rear Axle Weight N (kg / lb)
10,300 (1,050 / 2,315)
Note:
The rear axle weight should be adjusted to the
specified value with a man seated in the driver seat.
Rear master cylinder
fluid Pressure
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