Isuzu N-Series. Manual - part 206

SERVICE INFORMATION 00-41

Hydraulic Booster Type

Push Rod Length

• Use a scale to measure the push rod length (push

rod to flange face clearance).
Push Rod Length “L” to 17.95 — 18.2 mm (0.707
— 0.717 in).
If the push rod length is not equal to the specifica-
tion, the hydraulic booster assembly must be re-
placed.

Operating Rod Length

1. Loosen the jam nut at the stop light switch.
2. Loosen the jam nut on the hydraulic booster oper-

ating rod.

3. Turn the operating rod until the distance from the

center of clevis pin hole to mounting surface of the
brake pedal bracket should be set at 109 

± 1 mm

(4.29 

± 0.04 in).

When fixed under this condition, there is no need
to adjust the brake pedal height and free play.

4. Tighten the operating rod jam nut.

Tighten:
Jam nut to 20 N

⋅m (2.0 kg⋅m / 14 lb⋅ft)

5. Stop light switch so that the end of the switch

threaded portion contacts the brake pedal, then
back off the switch 1/2 turn.

Tighten:
Stop light switch locknut to 20 N

⋅m (2.0 kg⋅m / 14 lb⋅ft)

6. Check light pedal operation to be sure that it is op-

erating properly.

• Measure the brake pedal free play, after reduc-

ing the pressure of the hydraulic oil in the accu-
mulator by pedal operations at least 10 times
with engine off.
Brake pedal normal play is between 21 — 24
mm (0.83 — 0.94 in).

• Pressing the brake pedal with a force of 294 N

(30 kg / 66 lb) with the engine on, the clearance
between the brake pedal and floor panel is
more than 35 mm (1.4 in). 

• Brake pedal height “B” is 167 mm (6.58 in) (ref-

erence).

• Brake pedal travel “A” is between 180 

± 5 mm

(7.09 

± 0.2 in) (reference).

N5A0008E

N5A0009E

Legend

1. Accumulator
2. Stud bolt
3. Cover boss
4. Lock nut
5. Clevis
6. Operating rod
7. Guard
8. Flange

N5A0010E

00-42 SERVICE INFORMATION

Brake Bleeding

Brake Bleeding Precautions
Air in the brake hydraulic circuit will result in dangerous
reduced braking efficiency.
The brake hydraulic circuit must be bled whenever the
vehicle has been operated with the reservoir brake fluid
level at an excessively low level or any time the brake
pipes have been disconnected in the course of brake
servicing.
The brake bleeding procedure requires the cooperative
action of two men.

Brake Bleeding Procedure
Bleed the brake hydraulic circuit in the following se-
quence.
LHD
Left-hand rear wheel (vehicle equipped with ABS) 

→

Right-hand rear wheel 

→ DSPV or LSPV → (If so

equipped) 

→ Right-hand front wheel → Left-hand front

wheel
RHD
Left-hand rear wheel (vehicle equipped with ABS) 

→

Right-hand rear wheel 

→ DSPV or LSPV (If so

equipped) 

→ Left-hand front wheel → Right-hand front

wheel

1. Check to make sure that the service area is well

ventilated.
Apply the parking brake firmly. Start the engine and
allow it to run until the vacuum pressure rises suf-
ficiently.

Notice:
Brake booster (master-vac) will be adversely effected if
bleeding operation is performed without running engine.

Legend

A. Pedal travel

(Reference).....180 

± 5 mm (7.09 ± 0.2 in)

B. Pedal height

(Reference).....167 mm (6.58 in)

N5A0011E

N5A0012E

N5A0013E

SERVICE INFORMATION 00-43

If the vehicle is equipped with ABS, be sure to remove
the ABS fuse (60 A) from the fuse box before beginning
the air bleeding procedure. If this is not done, air is not
bled completely from ABS unit, so that ABS unit will be
broken. (Be sure to install the ABS fuse (60 A) in speci-
fied position when the air bleeding procedure is complet-
ed.)

2. Fill the brake fluid reservoir (1) up to the “MAX” lev-

el with clean brake fluid.
It may be necessary to replenish the brake fluid
reservoir several times during the bleeding proce-
dure to maintain the required level of brake fluid.

Notice:
Pour the brake fluid carefully so as not to produce air
bubbles.

3. Remove the right hand rear wheel cylinder (left

hand rear wheel cylinder if ABS is equipped) bleed-
er screw rubber cap and wipe it clean.

4. Connect one end of a vinyl tube (2) to the bleeder

screw.

5. Insert the other end of the vinyl tube into a trans-

parent container approximately 1/3 full of brake flu-
id.

6. Depress the brake pedal (3) slowly 3 times and

hold it depressed.

7. Loosen the bleeder screw (4) approximately 1/2 of

a turn.
This will release the brake fluid with air bubbles into
the transparent container (5).

8. When the brake fluid being released into the trans-

parent container is completely free of air bubbles,
retighten the bleeder screw (4).

9. Slowly release the brake pedal.

10. Replace the bleeder screw rubber cap.

Notice:
In order to bleed the air completely from the brake line,
repeat the above procedures.

Bleeding of the brake fluid circuit should be performed
for front wheel 10 times or more, for rear wheel 15 times
or more.
11. Repeat Steps 3 through 10 for each bleeder

screws as mentioned before.

12. After the air bleeding procedure is finished in all

wheels, depress the brake pedal, and verify wheth-

N5A0016E

N5A0017E

N5A0018E

00-44 SERVICE INFORMATION

er there is no abnormality in operation of the brake
system.

13. After the air bleeding procedure for individual

wheel is completed, inspect the fluid level of the
reservoir tank. If it is insufficient, replenish brake
fluid. Do not overfill above “MAX” level.

14. Stop the engine.

Hydraulic Booster Line Bleeding

Bleeding Precautions
After removing the hydro boost assembly or piping and
making repairs, do not run the vehicle until you perform
the below-described air bleeding and then verify that ev-
erything is normal, including hydro boost boosting and
accumulator operation.
Bleeding Procedure

1. Attach the hydro boost and the master cylinder to

the vehicle and connect the piping.

2. Fill the hydro boost reservoir with hydraulic oil be-

tween its minimum and maximum range.

3. Turn the engine on for about 5 seconds.
4. Then turn the engine off and check the quantity of

hydraulic oil in the reservoir.

5. If the hydraulic oil is below the minimum, pour in

more hydraulic oil so that it is in the range from min-
imum to maximum.

6. Repeat the above steps 2 — 5 until there is no

foaming or change in the level of the hydraulic oil
in the reservoir. But if the hydraulic oil foams during
the above steps, let it stand for a while, wait for the
foam to dissipate, then continue the work.

7. With the engine on, repeatedly press the brake

pedal slowly about five times.

8. Then turn the engine off and check the quantity of

hydraulic oil in the reservoir. If the hydraulic oil is
below the minimum, once again pour in more hy-
draulic oil so that it is in the range from minimum to
maximum.

9. Leaving the engine off, repeatedly press the brake

pedal at least ten times.

10. Verify that there is no foam or change in the level

of the hydraulic oil in the reservoir. If any foam re-
mains, let it stand for a while, wait for the foam to
dissipate, then repeat the above steps 7 — 9.

11. If it is necessary at this time to bleed out the air

from the brake fluid pressure system, such as the
master cylinder or the wheel cylinder, be sure to
first complete step 10 above and make sure that
the engine is on.

12. With the engine on, strongly press the brake pedal

as far as the booster full load region slowly and re-
peatedly about 30 times (for 1 — 3 seconds each
time). When doing so, do not keep the pedal at the
full load region (no longer than 1 second).

13. Then turn the engine off and repeatedly press the

brake pedal at least 10 times.

14. Check the state of the hydraulic oil in the reservoir,

and if there is no foaming or change in the level of
the oil, the operation of bleeding the air out is con-
sidered completed. If any foam remains, let it stand
for a while, wait for the foam to dissipate, then re-
peat the above steps 12 — 13.

Notice:
Precautions when bleeding the air from the brake fluid
pressure system 
When doing air bleeding of the brake fluid pressure sys-
tem, such as the master cylinder or wheel cylinder, ver-
ify that the air has been bled out of the hydro boost, and
make sure that the engine is on.
Be aware that if air bleeding of the brake fluid system is
to be done with the engine off, air bleeding cannot be
done.
If air bleeding of the brake fluid pressure system is to be
done at the same time as air bleeding of the hydro
boost, do so when the operation of the above hydro
boost air bleeding method 10 has been completed.
Supply Parts Replacement

1. The hydro boost is a precision part that operates

with high-pressure hydraulic oil. Never remove any
parts from the hydro boost except replacement
parts.
Trouble may occur if a part other than a replace-
ment part is removed and a non-matching part is
included or the assembly is bad. For example, mi-
soperation may occur and the brake becomes inef-
fective, or a bad seal may allow high-temperature
hydraulic oil under high pressure to spatter and
cause a burn.

2. The hydraulic oil to be used for the hydro boost is

ATF DEXRON

®

 III. Using any other hydraulic oil

could adversely affect the rubber parts and cause
poor operation or oil leakage.
In particular, the hydraulic oil for the hydro boost is
quite different from the brake fluid that is used in
the master cylinder.
Be careful that hydro boost parts do not come into
contact with the brake fluid for the master cylinder,
and that master cylinder parts do not come into
contact with the hydraulic oil for the hydro boost.
Any mixing together of the hydraulic oil for the hy-
dro boost and the brake fluid for the master cylin-
der could cause degradation such as the swelling
of rubber parts, brake failure due to oil leakage or
bad operation, or a serious mishap such as a vehi-
cle fire caused by brake friction.

3. Operation of the pump while the engine is on will

cause the hydro boost hydraulic oil to get hot. In
particular, frequent repeated operation of the brake
will sometimes increase the temperature of the hy-
draulic oil in the hydro boost assembly to 100

°C

(212

°F) or more. Be careful in handling.

When performing work such as removing the hydro
boost assembly from the vehicle, before starting