Page 681 of 2100

5C±1 POWER±ASSISTED BRAKE SYSTEM
AXIOM (Vehicles Produced Before July/31/2001)
BRAKES
POWER-ASSISTED BRAKE SYSTEM
CONTENTS
Service Precaution 5C±2. . . . . . . . . . . . . . . . . . . . . .
General Description 5C±2. . . . . . . . . . . . . . . . . . . . .
Diagnosis 5C±6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General Diagnosis 5C±7. . . . . . . . . . . . . . . . . . . . . . .
Hydraulic Brakes 5C±10. . . . . . . . . . . . . . . . . . . . . . . .
Filling Master Cylinder Reservoir 5C±10. . . . . . . .
Deterioration of Brake Fluid 5C±10. . . . . . . . . . . . .
Leakage of Brake Fluid 5C±10. . . . . . . . . . . . . . . . .
Bleeding Brake Hydraulic System 5C±10. . . . . . . .
Flushing Brake Hydraulic System 5C±11. . . . . . . .
Brake Pipes and Hoses 5C±11. . . . . . . . . . . . . . . .
Brake Hose Inspection 5C±11. . . . . . . . . . . . . . . . .
Front Caliper Brake Hose 5C±12. . . . . . . . . . . . . . . .
Front Caliper Brake Hose and Associated
Parts 5C±12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±12. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±12. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rear Axle Brake Hose 5C±13. . . . . . . . . . . . . . . . . . .
Rear Axle Brake Hose and Associated
Parts 5C±13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±13. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±13. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Brake Pipe 5C±14. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±14. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±14. . . . . . . . . . . . . . . . . . . . . . . . . . . .
P & B (Proportioning and Bypass) Valve 5C±15. . . .
P & B (Proportioning and Bypass) Valve
Sectional View 5C±15. . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±15. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±15. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±16. . . . . . . . . . . . .
Brake Pedal 5C±17. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Checking Pedal Height 5C±17. . . . . . . . . . . . . . . . .
Checking Pedal Travel 5C±17. . . . . . . . . . . . . . . . .
Brake Pedal and Associated Parts 5C±18. . . . . . .
Removal 5C±18. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±18. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stoplight Switch 5C±19. . . . . . . . . . . . . . . . . . . . . . . . .
Parts Location 5C±19. . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±19. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±19. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±20. . . . . . . . . . . . .
Fluid Reservoir Tank 5C±21. . . . . . . . . . . . . . . . . . . . .
Fluid Reservoir Tank and Associated Parts 5C±21Removal 5C±21. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±21. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Master Cylinder Assembly 5C±22. . . . . . . . . . . . . . . .
Master Cylinder Assembly and Associated
Parts 5C±22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±22. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection and Repair 5C±22. . . . . . . . . . . . . . . . . .
Installation 5C±23. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±24. . . . . . . . . . .
Special Tools 5C±24. . . . . . . . . . . . . . . . . . . . . . . . . .
Vacuum Booster Assembly 5C±25. . . . . . . . . . . . . . .
Vacuum Booster Assembly and Associated
Parts 5C±25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±25. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection and Repair 5C±26. . . . . . . . . . . . . . . . . .
Installation 5C±26. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exterior Components 5C±28. . . . . . . . . . . . . . . . . . . .
Exterior Components and Associated Parts 5C±28
Removal 5C±28. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection and Repair 5C±29. . . . . . . . . . . . . . . . . .
Installation 5C±29. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vacuum Booster Overhaul 5C±29. . . . . . . . . . . . . . . .
Vacuum Booster 5C±29. . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±30. . . . . . . . . . . . .
Special Tools 5C±31. . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Disc Brake Pads 5C±32. . . . . . . . . . . . . . . . . . .
Front Disc Brake Pads Inspection 5C±32. . . . . . . .
Front Disc Brake Pads and Associated
Parts 5C±32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±33. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±33. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Disc Brake Rotor 5C±35. . . . . . . . . . . . . . . . . . .
Inspection 5C±35. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replacing Brake Rotors 5C±35. . . . . . . . . . . . . . . .
Refinishing Brake Rotors 5C±35. . . . . . . . . . . . . . .
Front Disc Brake Caliper Assembly 5C±36. . . . . . . .
Front Disc Brake Caliper Assembly and
Associated Parts 5C±36. . . . . . . . . . . . . . . . . . . . . .
Removal 5C±37. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±37. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Disc Brake Caliper 5C±39. . . . . . . . . . . . . . . . .
Front Disc Brake Caliper Disassembled
View 5C±39. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Disassembly 5C±39. . . . . . . . . . . . . . . . . . . . . . . . . .
Page 682 of 2100

5C±2
POWER±ASSISTED BRAKE SYSTEM
Inspection and Repair 5C±40. . . . . . . . . . . . . . . . . .
Reassembly 5C±40. . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±42. . . . . . . . . . .
Rear Disc Brake Pads (4y4 Model) 5C±43. . . . . . . .
Brake Pads Inspection 5C±43. . . . . . . . . . . . . . . . .
Brake Pads and Associated Parts 5C±43. . . . . . .
Removal 5C±44. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±44. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rear Disc Brake Rotor (4y4 Model) 5C±46. . . . . . . .
Inspection 5C±46. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replacing Brake Rotors 5C±46. . . . . . . . . . . . . . . .
Refinishing Brake Rotors 5C±46. . . . . . . . . . . . . . .
Rear Drum (In Disc) Inside Diameter Check 5C±47
Rear Disc Brake Caliper Assembly
(4y4 Model) 5C±48. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rear Disc Brake Caliper Assembly and
Associated Parts 5C±48. . . . . . . . . . . . . . . . . . . . . .
Removal 5C±48. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±49. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rear Disc Brake Caliper (4y4 Model) 5C±50. . . . . .
Rear Disc Brake Caliper Disassembled
View 5C±50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disassembly 5C±51. . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection and Repair 5C±51. . . . . . . . . . . . . . . . . .
Reassembly 5C±51. . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications (4y4 Model) 5C±53
Brake Lining 5C±54. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Brake Lining and Associated Parts 5C±54. . . . . . .
Removal 5C±54. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Brake Lining Inspection 5C±55. . . . . . . . . . . . . . . .
Installation 5C±55. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Drum Brake Adjustment (4y2 Model) 5C±56. . . . .
Servicing The Brake Drum 5C±56. . . . . . . . . . . . . .
Wheel Cylinder Assembly (4y2 Model) 5C±57. . . . .
Wheel Cylinder Assembly and Associated
Parts 5C±57. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 5C±57. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 5C±57. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Disassembled View 5C±58. . . . . . . . . . . . . . . . . . . .
Disassembly 5C±58. . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection and Repair 5C±58. . . . . . . . . . . . . . . . . .
Reassembly 5C±58. . . . . . . . . . . . . . . . . . . . . . . . . .
Main Data and Specifications 5C±60. . . . . . . . . . .
Service Precaution
WARNING: THIS VEHICLE HAS A SUPPLEMENTAL
RESTRAINT SYSTEM (SRS). REFER TO THE SRS
COMPONENT AND WIRING LOCATION VIEW IN
ORDER TO DETERMINE WHETHER YOU ARE
PERFORMING SERVICE ON OR NEAR THE SRS
COMPONENTS OR THE SRS WIRING. WHEN YOU
ARE PERFORMING SERVICE ON OR NEAR THE SRS
COMPONENTS OR THE SRS WIRING, REFER TO
THE SRS SERVICE INFORMATION. FAILURE TO
FOLLOW WARNINGS COULD RESULT IN POSSIBLE
AIR BAG DEPLOYMENT, PERSONAL INJURY, OR
OTHERWISE UNNEEDED SRS SYSTEM REPAIRS.
CAUTION: Always use the correct fastener in the
proper location. When you replace a fastener, use
ONLY the exact part number for that application.
ISUZU will call out those fasteners that require a
replacement after removal. ISUZU will also call out
the fasteners that require thread lockers or thread
sealant. UNLESS OTHERWISE SPECIFIED, do not
use supplemental coatings (Paints, greases, or other
corrosion inhibitors) on threaded fasteners or
fastener joint interfaces. Generally, such coatings
adversely affect the fastener torque and the joint
clamping force, and may damage the fastener. When
you install fasteners, use the correct tightening
sequence and specifications. Following these
instructions can help you avoid damage to parts and
systems.
General Description
Master Cylinder Assembly
330RS001
Page 683 of 2100

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.
Page 684 of 2100

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.
Page 685 of 2100
5C±5 POWER±ASSISTED BRAKE SYSTEM
Leading/Trailing Drum Brakes (4y2 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 contact 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.
Page 686 of 2100

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.
Page 687 of 2100

5C±7 POWER±ASSISTED BRAKE SYSTEM
General Diagnosis
ConditionPossible causeCorrection
Brake PullTire inflation pressure is unequal.Adjust
Front wheel alignment is incorrect.Adjust
Unmatched tires on same axle.Tires with approx. the same amount
of tread should be used on the same
axle.
Restricted brake pipes or hoses.Check for soft hoses and damaged
lines. Replace with new hoses and
new doubleªwalled steel brake
piping.
Water or oil on the brake pads.Clean or replace.
Brake pads hardened.Replace
Brake pads worn excessively.Replace
Brake rotor worn or scored.Grind or replace.
Disc brake caliper malfunctioning.Clean or replace.
Front hub bearing preload incorrect.Adjust or replace.
Loose suspension parts.Check all suspension mountings.
Loose calipers.Check and tighten the bolts to
specifications.
Brake Roughness or Chatter
(Pulsates)Excessive lateral runout.Check per instructions. If not within
specifications, replace or machine
the rotor.
Parallelism not within specifications.Check per instructions. If not within
specifications, replace or machine
the rotor.
Wheel bearings not adjusted.Adjust wheel bearings to correct
specifications
Pad reversed (steel against iron).Replace the brake pad and machine
rotor to within specifications.
Excessive Pedal EffortMalfunctioning vacuum booster.Check the vacuum booster operation
and repair, if necessary.
Partial system failure.Check the front and rear brake
system for failure and repair. Also,
check the brake warning light. If a
failed system is found, the light
should indicate failure.
Excessively worn pad.Check and replace pads in sets.
Piston in caliper stuck or sluggish.Remove caliper and rebuild.
Fading brakes due to incorrect pad.Remove and replace with original
equipment pad or equivalent.
Vacuum leak to vacuum booster.Check for ruptured or loose hose.
Check the direction of check valve
within vacuum hose.Correct vacuum hose direction.
Grease on the brake pads.Replace or clean.
Page 688 of 2100

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.