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