Isuzu N-Series. Service manual — part 198
SERVICE INFORMATION 00-9
Notice:
• When the brake pedal is operated after the engine
is turned off and the oil pump stops, during a few
operations a fluid sound due to the flow of high-
pressure oil or a sound of movement by the charge
spool may be produced, but this sound is not ab-
normal; it merely indicates that boosting by the ac-
cumulator (accumulator operation) is proceeding
normally.
Also, a similar fluid sound is produced during quick
operation of the brake pedal even if the engine is
on, but this too is normal.
• If the pressure of the oil in the accumulator drops
with operation of the brake pedal after the engine
is turned off or when the engine has been off for a
long time, then immediately after the engine is
turned on, fluid sound during charge valve opera-
tion or switching sound when charging ends will be
produced, but this sound is not abnormal; it merely
indicates that the accumulator is being normally
charged.
Also, a similar charging operation sometimes oc-
curs and sound is sometimes produced when the
pressure inside the accumulator drops even when
the engine is on and charging has ended, due to
such causes as rapid operation of the brake pedal,
internal leakage that is too slight to affect brake
performance, or a change in temperature; this too
is normal.
• When the brake pedal is pressed strongly as far as
the booster full load region while the engine is on,
sometimes sound is produced by the flow of hy-
draulic oil discharged from the oil pump, but this is
not abnormal. Also, pressing the pedal in as far as
this booster full load region can cause a significant
increase in the oil temperature inside the oil pump
and can lead to a failure, so keep the pedal
pressed for no longer than 5 seconds.
Warning buzzer contin-
uously sounds
1. Faulty hydraulic booster assembly
• Faulty pressure switch
• Leakage inside the charge valve
• Confirm that the electric devices (pres-
sure switch, relay, buzzer, etc.) are
working correctly.
• If all are working correctly, pump the
brake pedal at least 10 times after turn-
ing the engine off to reduce pressure in
the hydraulic booster.
Start the engine, and release the park-
ing brake. Check to see if the alarm
stops within ten seconds (if it does, the
electrical devices are working properly).
• When testing the electrical devices, al-
ways keep your foot on the brake pedal
with just enough pressure to prevent
the vehicle from moving.
If the alarm does not stop, the hydraulic
booster assembly may have to be re-
placed.
Charge operation
remains in effect
1. Bad charge valve operation
• Bad valve switching operation
• Turn the engine on, and without press-
ing the brake pedal, check whether any
charging sound continues, such as the
sound of the fluid.
• If it continues and will not stop, replace
the hydro boost assembly as neces-
sary.
PROBLEM
POSSIBLE CAUSE
CORRECTION
00-10 SERVICE INFORMATION
Brake Lining
PROBLEM
POSSIBLE CAUSE
CORRECTION
Poor Contact at the
Center of Shoe
1. Bell-mouthed drum.
2. Distorted mounting plate.
3. Bent brake shoe.
4. Undersize linings.
5. Loose wheel bearing.
1-5. Repair or replace as required.
Unequal Wear on the
Shoes in the Same
Brake
1. Brake linings not a balanced set.
2. Sticking wheel cylinder piston.
1-2. Repair or replace as required.
Material at the Center
of the Shoe Exces-
sively Thin
1. Undersize linings.
2. Oversize drum.
1-2. Repair or replace as required.
Lining Tapered across
the Width
1. Bell-mouthed drum.
2. Bent shoe.
3. Distorted mounting plate.
1-3. Repair or replace as required.
Lining Worn at One
End
Bent mounting plate.
Repair or replace as required.
Linings Glazed
1. Grease on lining.
2. Wrong type lining for service involved.
1-2. Repair or replace as required.
Rivets Tear Loose
1. Improper set rivet.
2. Improper setting of the rivet.
3. Enlarged rivet holes in the shoe.
1-3. Repair or replace as required.
Unequal Wear
Opposite Brakes,
Same Axle
1. Weak shoe return spring.
2. Obstructed hydraulic line.
3. Stuck wheel cylinder piston.
4. Brake drum surface in poor condition.
5. Loose wheel bearing.
1-5. Repair or replace as required.
Linings at Scored
1. Scored drum.
2. Abrasive material between the lining
and drum.
1-2. Repair or replace as required.
Cracks at Rivet Holes
1. Wrong type rivets.
2. Rivets not properly set.
3. Dirt or rust on the shoe table.
4. Wrong size lining.
1-4. Repair or replace as required.
Elongation of the Rivet
Holes
1. Loose rivets.
2. Wrong size rivets.
1-2. Repair or replace as required.
Wear on the Edge of
the Lining
1. Wrong width lining.
2. Holes improperly drilled.
3. Loose wheel bearing.
4. Bent shoe.
1-4. Repair or replace as required.
Groove on the Edge of
the Lining
1. Lining too wide.
2. Worn drum.
1-2. Repair or replace as required.
SERVICE INFORMATION 00-11
Brake Drum
Exhaust Brake
PROBLEM
POSSIBLE CAUSE
CORRECTION
Brake Drum Heat
Checked in Spots
1. Out-of-round brake drum.
2. Eccentric mounting of the drum.
3. Loose wheel bearing.
1-3. Repair or replace as required.
Drum Uniformly Heat
Checked
1. Improper friction materials.
2. Overworked brake.
3. Driver abuse.
1-3. Repair or replace as required.
Excessive Scoring of
the Drum
1. Improper friction materials.
2. Overworked brake.
3. Abrasive material between the lining
and drum.
4. Soft drum.
5. Bent or warped shoe.
1-5. Repair or replace as required.
Excessive Drum
Cracks
1. Drive abuse.
2. Weak drum.
3. Wrong friction material.
4. Overworked brake.
1-4. Repair or replace as required.
PROBLEM
POSSIBLE CAUSE
CORRECTION
Exhaust Brake does
not Operate
1. Blown fuse.
1. Replace.
2. Improperly adjusted or faulty accelera-
tor or clutch switches.
2. Adjust or replace.
3. Poor connections or corroded terminals
at switches or control valve.
3. Clean or replace.
4. Improperly adjusted or seized exhaust
brake valve.
4. Adjust, or repair.
5. Vacuum lines kinked, restricted, or
plugged with ice.
5. Repair.
6. Seized vacuum chamber.
6. Repair.
7. Valve linkage broken.
7. Repair.
8. Chamber or control valve jammed with
ice.
8. Melt ice and drain lines of water.
9. Faulty control valve. Valve should open
when approximate battery(s) voltage is
applied to terminals.
9. Replace.
10. Faulty vacuum chamber.
10. Replace.
11. Broken wire in wiring harness.
11. Repair.
Exhaust Brake SIow to
Operate
1. Tighten exhaust brake valve or linkage.
1. Free up and lubricate.
2. Improperly adjusted accelerator or
clutch switches.
2. Adjust.
00-12 SERVICE INFORMATION
Parking Brakes
Insufficient Braking Force
Weak Braking Action
1. Improperly adjusted or tight exhaust
brake valve.
1. Free up and/or adjust. Lubricate as
needed.
2. Tight linkage.
2. Free up and lubricate.
3. Vacuum lines kinked or partially
plugged with ice.
3. Repair.
4. Leaking fittings at vacuum lines.
4. Tighten.
5. Leaky vacuum chamber.
5. Replace.
Exhaust Brake will not
Shut Off (Exhaust
Brake Control Switch
“Off”)
1. Seized exhaust brake valve or linkage.
1. Free up and lubricate.
2. Control valve or chamber jammed with
ice.
2. Melt ice and drain lines.
3. Short in wiring harness (approximate
battery(s) voltage) at control solenoid
regardless of control switch position.
3. Repair.
4. Faulty control switch.
4. Replace.
Exhaust Brake “On”
Continuously when
Exhaust Brake Control
Switch is “On” (not
Controlled by Clutch or
Accelerator Switches)
1. Improperly adjusted clutch or accelera-
tor switches.
1. Adjust.
2. Switches improperly wired.
2. Check wiring against wiring diagram.
Repair as needed.
3. Short in wiring harness.
3. Repair.
Engine Overheats or
Loses Power
1. Engine brake valve stuck partially
closed.
1. Free up and lubricate or replace.
2. Engine brake valve adjusted so that it is
partially closed.
2. Adjust.
PROBLEM
POSSIBLE CAUSE
CORRECTION
Brake lining and drum
clearance
Clearance between the brake lining and
the brake drum excessive
Adjust the brake lining and the brake drum
clearance.
Brake lining
Brake lining worn out
Replace the brake lining.
Camshaft
Camshaft worn out
Replace the camshaft.
Control wire
Control wire stretched
Adjust the control wire length or replace
the control wire.
PROBLEM
POSSIBLE CAUSE
CORRECTION
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