2002 ISUZU AXIOM Brake fluid

5C±3 POWER±ASSISTED BRAKE SYSTEM
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. The master cylinder is not repairable. If found
defective, it must be replaced as a complete
assembly.
2. 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.)
3. The torque values specified are for dry,
unlubricated fasteners.
4. Perform service operations on a clean bench free
from all mineral oil materials.
Brake Booster
331RS001
This booster is a tandem vacuum unit with a diaphragm
effective diameter 205mm (8.072 in) + 230mm (9.056 in).
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
A05RW001
Rear Disc Brake (4y4 Model)
A05RW002
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 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.

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
ªNeutralº, 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 ªMAXº 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
ªBRAKEº warning light should turn on and go off when the
ignition switch returns to the ON position.
The following conditions will activate the ªBRAKEº 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 ªBRAKEº light on.
3. During engine cranking the ªBRAKEº light should
remain on. This notifies the driver that the warning
circuit is operating properly.

5C±8
POWER±ASSISTED BRAKE SYSTEM
Condition CorrectionPossible cause
Excessive Brake Pedal TravelAir in hydraulic circuit.Bleed the hydraulic circuit.
Level of brake fluid in the reservoir
too low.Replenish brake fluid reservoir to
specified level and bleed hydraulic
circuit as necessary.
Master cylinder push rod clearance
excessive.Adjust
Leakage in hydraulic system.Correct or replace defective parts.
Brake DragMaster cylinder pistons not returning
correctly.Adjust the stop light switch and
vacuum booster push rod. If
necessary, rebuild.
Restricted brake pipes or hoses.Check for soft hoses or damaged
pipes, and replace with new hoses
and new double±walled steel brake
piping.
Parking brake maladjusted.Adjust
Parking brake lining clearance
insufficient.Adjust
Brake pedal free play insufficient.Adjust the brake pedal height or
power cylinder operating rod.
Piston in the master cylinder sticking.Replace
Piston in the disc brake caliper
sticking.Replace piston seals.
Brake pads sticking in caliper.Clean
Return spring weakened.Replace
Parking brake binding.Overhaul the parking brakes and
correct.
Front hub bearing preload incorrect.Adjust or replace.
Parking brake shoes not returning.Correct or replace the brake back
plate and brake shoe as necessary.
Obstructions in hydraulic circuit.Clean
Rotor warped excessively.Grind or replace.
Rear brake drum distorted.Grind or replace.
Parking cable sticking.Grind or replace.
Grabbing or Uneven Braking Action
(All conditions listed under ªPullsº)Malfunctioning vacuum booster.Check operation and correct as
necessary.
Binding brake pedal mechanism.Check and lubricate, if necessary.
Corroded caliper assembly.Clean and lubricate.
Brake NoisyBrake pads are worn.Replace
Brake pads are hardened.Replace
Brake pads are in poor contact with
rotor.Correct
Brake disc(s) warped, worn or
damaged.Grind or replace.
Disc brake anti±squeak shims
fatigued.Replace
Front hub bearings are loose or
preload is incorrect.Adjust or replace.
Brake disc is rusted.Grind or replace.

5C±9 POWER±ASSISTED BRAKE SYSTEM
Condition CorrectionPossible cause
Poor Brake ActionMaster cylinder faulty.Correct or replace.
Vacuum booster faulty.Correct or replace.
Level of brake fluid in reservoir too
low.Replenish and bleed.
Air in hydraulic circuit.Bleed
Disc brake caliper faulty.Clean or replace.
Water or oil on brake pads.Clean or replace.
Brake pads in poor contact with the
rotor.Correct
Brake pads worn.Replace
Brake disc rusted.Grind or replace.
Check valve in vacuum hose faulty.Correct or replace.

5C±10
POWER±ASSISTED BRAKE SYSTEM
Hydraulic Brakes
Filling Master Cylinder Reservoir
CAUTION: Use only specified brake fluid. Do not
use any fluid which contains a petroleum base. Do
not use a container which has been used for
petroleum based fluids or a container which is wet
with water. Petroleum based fluid will cause swelling
and distortion of rubber parts in the hydraulic brake
system. Water mixed with brake fluid lowers the fluid
boiling point. Keep all fluid containers capped to
prevent contamination.
Always fill the master cylinder reservoir when the en-
gine is cold.
Never allow the brake fluid to come in contact with
the painted surfaces.
The master cylinder reservoir must be kept properly
filled to ensure adequate reserve and to prevent air
and moisture from entering the hydraulic system.
However, because of expansion due to heat ab-
sorbed from the brakes and the engine, the reservoir
must not be overfilled. The brake fluid reservoir is on
the master cylinder, which is located under the hood
on the left side of the cowl. Thoroughly clean reser-
voir cap before removal to avoid getting dirt into res-
ervoir. Remove the diaphragm. Add fluid as required
to bring level to the ªMAXº mark on the reservoir
tank. Use ªDOT 3º Hydraulic Brake Fluid. If the fluid
cap diaphragm is stretched, return it to the original
position before installing.
Deterioration of Brake Fluid
Using any other brake fluid than specified or brake fluid
with mineral oil or water mixed in will drop the boiling point
of brake fluid. It may, in turn, result in vapor lock or
deteriorated rubber parts of the hydraulic system. Be sure
to change the brake fluid at specified intervals.
If the rubber parts are deteriorated, remove all the system
parts and clean them with alcohol. Prior to reassembly,
dry the cleaned parts with air to remove the alcohol.
Replace all the hoses and rubber parts of the system.
Leakage of Brake Fluid
With engine idling, set shift lever in the neutral position
and continue to depress brake pedal at a constant pedal
application force.
Should the pedal stroke become deeper gradually,
leakage from the hydraulic pressure system is possible.
Perform visual inspection for any signs of leakage.
Bleeding Brake Hydraulic System
A bleeding operation is necessary to remove air from the
hydraulic brake system whenever air is introduced into
the hydraulic system. It may be necessary to bleed the
hydraulic system at all four brakes if air has been
introduced through a low fluid level or by disconnecting
brake pipes at the master cylinder. If a brake pipe is
disconnected at one wheel, only that wheel
cylinder/caliper needs to be bled. If the pipes aredisconnected at any fitting located between the master
cylinder and brakes, then the brake system served by the
disconnected pipe must be bled.
1. For 4±Wheel Antilock Brake System (ABS) equipped
vehicle, be sure to remove the ABS main fuse 60A
located at the relay and fuse box before bleeding air. If
you attempt to bleed air without removing the main
fuse, air cannot be let out thoroughly, and this may
cause damage to the hydraulic unit. After bleeding air,
be sure to replace the ABS main fuse back to its
original position.
2. Set the parking brake completely, then start the
engine.
NOTE: The vacuum booster will be damaged if the
bleeding operation is performed with the engine off.
3. Remove the master cylinder reservoir cap.
4. Fill the master cylinder reservoir with brake fluid.
Keep the reservoir at least half full during the air
bleeding operation
5. Always use new brake fluid for replenishment.
6. When replenishing the brake fluid reservoir, carefully
pour in the brake fluid to prevent air bubbles from
entering the brake system.
When the master cylinder is replaced or overhauled,
first bleed the air from the master cylinder, then from
each wheel cylinder and caliper following the
procedures described below.
Bleeding the Master Cylinder
7. Disconnect the rear wheel brake pipe (1) from the
master cylinder.
Check the fluid level and replenish as necessary. If
replenished, leave the system for at least one minute.
8. Depress the brake pedal slowly once and hold it
depressed.
9. Completely seal the delivery port of the master
cylinder with your finger, where the pipe was
disconnected then release the brake pedal slowly.
10. Release your finger from the delivery port when the
brake pedal returns completely.
11. Repeat steps 8 through 10 until the brake fluid comes
out of the delivery port during step 8.
NOTE: Do not allow the fluid level in the reservoir to go
below the half±way mark.
12. Reconnect the brake pipe (1) to the master cylinder
and tighten the pipe.
13. Depress the brake pedal slowly once and hold it
depressed.
14. Loosen the rear wheel brake pipe (1) at the master
cylinder.
15. Retighten the brake pipe, then release the brake
pedal slowly.
16. Repeat steps 13 through 15 until no air comes out of
the port when the brake pipe is loosened
NOTE: Be very careful not to allow the brake fluid to come
in contact with painted surfaces.

5C±11 POWER±ASSISTED BRAKE SYSTEM
330RW012
17. Bleed the air from the front wheel brake pipe
connection (2) by repeating steps 7 through 16.
Bleeding the Caliper
18. Bleed the air from each wheel in the order listed
below:

Right rear caliper or wheel cylinder

Left rear caliper or wheel cylinder

Right front caliper

Left front caliper
Conduct air bleeding from the wheels in the above
order. If no brake fluid comes out, it suggests that air
is mixed in the master cylinder. In this case, bleed air
from the master cylinder in accordance with steps 7
through 17, and then bleed air from the caliper or
wheel cylinder.
19. Place the proper size box end wrench over the
bleeder screw.
20. Cover the bleeder screw with a transparent tube, and
submerge the free end of the transparent tube in a
transparent container containing brake fluid.
21. Pump the brake pedal slowly three (3) times
(once/sec), then hold it depressed.
22. Loosen the bleeder screw until fluid flows through the
tube.
23. Retighten the bleeder screw.
24. Release the brake pedal slowly.
25. Repeat steps 21 through 24 until the air is completely
removed.
It may be necessary to repeat the bleeding procedure
10 or more times for front wheels and 15 or more
times for rear wheels.
26. Go to the next wheel in the sequence after each wheel
is bled.
Be sure to monitor reservoir fluid level.
27. Depress the brake pedal to check if you feel
ªsponginessº after the air has been removed from all
wheel cylinders and calipers.
If the pedal feels ªspongyº, the entire bleeding
procedure must be repeated.28. After the bleeding operation is completed on the each
individual wheel, check the level of the brake fluid in
the reservoir and replenish up to the ªMAXº level as
necessary.
29. Attach the reservoir cap.
If the diaphragm inside the cap is deformed, reform
it and install.
30. Stop the engine.
Flushing Brake Hydraulic System
It is recommended that the entire hydraulic system be
thoroughly flushed with clean brake fluid whenever new
parts are installed in the hydraulic system. Approximately
one quart of fluid is required to flush the hydraulic system.
The system must be flushed if there is any doubt as to the
grade of fluid in the system or if fluid has been used which
contains the slightest trace of mineral oil. All rubber parts
that have been subjected to a contaminated fluid must be
replaced.
Brake Pipes and Hoses
The hydraulic brake system components are
interconnected by special steel piping and flexible hoses.
Flexible hoses are used between the frame and the front
calipers, the frame and rear axle case and the rear axle
and the rear calipers.
When the hydraulic pipes have been disconnected for
any reason, the brake system must be bled after
reconnecting the pipe. Refer to
Bleeding the Brake
Hydraulic System
in this section.
Brake Hose Inspection
The brake hose should be inspected at least twice a year.
The brake hose assembly should be checked for road
hazard, cracks and chafing of the outer cover, and for
leaks and blisters. Inspect for proper routing and
mounting of the hose. A brake hose that rubs on
suspension components will wear and eventually fail. A
light and 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.
CAUTION: Never allow brake components such as
calipers to hang from the brake hoses, as damage to
the hoses may occur.

5C±15 POWER±ASSISTED BRAKE SYSTEM
P & B (Proportioning and Bypass) Valve
P & B (Proportioning and Bypass)
Valve Sectional View
350RW014
Legend
(1) Master Cylinder (Secondary)
(2) Master Cylinder (Primary)
(3) Rear Brake
(4) Front Brake
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±pass feature which
assures full system pressure to the rear brakes in the
event of front brake system malfunction. Also full front
pressure is retained in the event of rear brake
malfunction.
The P&B valve is not repairable and must be replaced as
complete assembly.
Removal
1. The 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.
2. Remove hydraulic pipes (1) and plug the pipes (1) to
prevent the loss of fluid or the entrance of dirt.
3. Remove bolt (3).
4. Remove P&B valve (2).
350RW026
Installation
1. Install P&B valve (2).
2. Install bolt (3) and tighten the bolt to the specified
torque.
Torque: 22 N´m (16 lb ft)
3. Install hydraulic pipes (1) and tighten the bolt to the
specified torque.
Torque: 15 N´m (11 lb ft)
4. After installing the brake pipes, bleed the brakes as
refer to
Bleeding Brake Hydraulic System in this
section.