2004 ISUZU TF SERIES fluid

BRAKES 5C-21


LAOD SENSING PROPORTIONING VALVE (LSPV)
RTW35CMF000101



Structure and Operation
The following is an explanation of the structure and operation
of the spring type load sensing device.
This device controls the fluid pressure to the rear brakes in
accordance with changes in rear axle load (vertical
displacements of the rear axle springs).









Structure
This device consists of a load sensing spring and a valve.
The valve is mounted through a bracket to the frame.
One end of the load sensing spring is fixed to the valve a
t
the frame and the other end to the rear axle housing
through a bracket.

5C-22 BRAKES

RTW35CSH001001






Operation
1) Outline
When the LSPV (Load Sensing Proportioning Valve)
detects a change in load weight, the load sensing spring
stretches.
Its reaction force is transmitted to the bottom of the load
sensing valve to secure an optimum rear wheel cylinde
r
fluid pressure break point in proportion to the actual load
weight.
Besides, if the front brake system should fail, the device is
designed to prevent the master cylinder fluid pressure from
decreasing and to apply it directly to the rear wheel cylinde
r
to obtain a sufficient braking performance.

RTW35CSH001101

2) Bellow cutting point.
The Force (F) keeps the main piston (1) the rest position.
The inlet pressure (A) and outlet pressure (B) are the same
as well as the inlet pressure (C) from front master cylinder.
The bypass piston (2) is kept on rest position by equilibrium
of the pressures (A) and (C) and the bypass spring load (3).

RTW35CSH001201

3) Cutting point.
The cutting point is given by relation between force (F), tha
t
is the load applied by suspension of the vehicle and the
main piston area (1). The cutting point is achieved when the
force generated by hydraulic pressure is upper than the
force (F) given by the load suspension. The main piston (1)
moves from the rest position closing the valve. In this
moment the inlet pressure (A) is upper than the outle
t
pressure (B). The bypass piston (2) continues on the res
t
position by equilibrium of (A) and (C) pressure.

BRAKES 5C-23

RTW35CSH001301

4) Failure on front master cylinder.
In case of failure on front master cylinder the pressure on
the inlet port (C) drop to zero. The pressure from inlet por
t
(A) acts on the bypass piston (2) and move it by comprising
of bypass spring (3). It makes possible the communication
between the inlet port (A) to outlet port (B) through the
bypass system. The outlet pressure (B) reaches the inle
t
pressure (A) and the LSPV is bypassed.


Valve Maintenance
In the case to fluid lead or other a abnormalities, faulty valve
should be replaced.
Note:
The load sensing proportioning valve is not repairable and
must be replaced as a completed assembly.


LOAD SENSING PROPORTIONING
VALVE (LSPV) ADJUSTMENT
RTW35CSH000301

1. Fluid Pressure Measurement
1) Rear axle weight adjustment
With an axle eight meter, adjust the rear axle weight with
a person sitting in the driver’s seat and a weight loaded
in the rear body.
N (kg/lb)

MODEL Adjustment value
4

2 7845 (800/1764)
4
2 HIGH RIDE
4

4 9316 (950/2095)

RTW35CSH000101





2) Installation of a fluid pressure gauge
Remove the air bleeder of the left hand wheel front and
rear brakes. Bleed air out of the fluid pressure gauge
with the measurement hose of the fluid pressure gauge
installed.
Pressure Tester: Brake oil (Fluid pressure gauge)
5-8840-2190-0

5C-24 BRAKES

RTW35CSH000201
3) Rear wheel cylinder fluid pressure measurement
Step on the brake pedal until the fluid pressure of the
front wheel cylinder gets to 9.8Mpa (100kg/cm
2), and
check the rear wheel cylinder fluid pressure. (Read the
value of the front wheel cylinder fluid pressure 2
seconds after the measurement. When measuring the
L.S.V fluid pressure, keep the brake pedal pressed
down without stepping it down twice or releasing it.)
Rear Wheel Cylinder Fluid Pressure MPa (kg/cm
2)

2WD 6.77
0.83 (69.0
8.5)
2WD (With High Ride
Suspension), 4WD 6.77

0.83 (69.0

8.5)

RTW35CSH000401
2. Oil Pressure Adjustment
1) LSPV spring length adjustment
Loosen the adjust nut of the LSPV spring joint, and
adjust the length of the LSPV spring.
When the oil pressure is insufficient, turn the adjust nu
t
clockwise to extend the span “A”. When the oil pressure
is too high, turn the adjust nut counterclockwise to
reduce the span “A”.


2) After adjustment, tighten the lock nut securely.
Lock Nut Torque N
m (kg
m/lb in)
11-20 (1.1-2.0/95-174)

BRAKES 5C-25


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 engine
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 absorbed from the
brakes and the engine, the reservoir must not be
overfilled. Thoroughly clean reservoir cap before removal
to avoid getting dirt into reservoir. Add fluid as required to
bring level to the “MAX” mark on the reservoir tank. Use
“DOT 3” Hydraulic Brake Fluid.

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.
Make sure by visual check that there is no leak.




BLEEDING OF THE BRAKE HYDRAULIC
CIRCUIT
If air enters the bake lines, it will cause poor brake action.
Therefore, bleeding should be performed if the brakes have
been used with the level of brake fluid in the reservoir
excessively low or if brake pipes have been disconnected in
the course of brake servicing.
Bleeding operation calls for co-operative action of 2 persons.

Set the parking brake firmly while bleeding.

Perform bleeding operation with ENGINE RUNNING, to
prevent damage to push rod seal.

Make sure exhaust is suitably ventilated.

Bleed the hydraulic system with the fluid reservoir filled to
the specified level.

Bleed the system starting with the rear wheel cylinde
r
farthest from the master cylinder.

5C-26 BRAKES


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 are
disconnected at any fitting located between the master cylinder
and brakes, then the brake system served by the disconnected
pipe must be bled.

1. 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.
2. Remove the master cylinder reservoir cap.

3. Fill the master cylinder reservoir with brake fluid. Keep the
reservoir at least half full during the air bleeding operation
4. Always use new brake fluid for replenishment.
5. In replenishing rake fluid, take care that air bubbles do no
t
enter the brake fluid.


When the master cylinder is replaced or overhauled, firs
t
bleed the air from the master cylinder, then from each
wheel cylinder and caliper following the procedures
described below.


Bleeding the Master Cylinder
6. 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.
7. Depress the brake pedal slowly once and hold it depressed.
8. Completely seal the delivery port of the master cylinder with
your finger, where the pipe was disconnected then release
the brake pedal slowly.
9. Release your finger from the delivery port when the brake
pedal returns completely.
10. Repeat steps 7 through 9 until the brake fluid comes out o
f
the delivery port during step 7.
NOTE : Do not allow the fluid level in the reservoir to go below
the half-way mark.
11. Reconnect the brake pipe (1) to the master cylinder and
tighten the pipe.
12. Depress the brake pedal slowly once and hold it depressed.
13. Loosen the rear wheel brake pipe (1) at the master cylinder.
14. Retighten the brake pipe, then release the brake pedal
slowly.

BRAKES 5C-27


15. Repeat steps 12 through 14 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.


16. Bleed the air from the front wheel brake pipe connection (2)
by repeating steps 6 through 15.

Bleeding the Caliper
17. Bleed the air from each wheel in the order listed below:

Right rear wheel cylinder

Left rear wheel cylinder

Left front caliper
 Right front caliper
Conduct air bleeding from the wheels in the above order. I
f
no brake fluid comes out, it suggests that air is mixed in the
master cylinder. In this case, bleed air from the maste
r
cylinder. In this case, bleed air from the master cylinder in
accordance with steps 6 through 16, and then bleed ai
r
from the caliper or wheel cylinder.

RTW35CSH000501

18. Place the proper size box end wrench over the bleeder
screw.
19. Cover the bleeder screw with a transparent tube, and
submerge the free end of the transparent tube in a
transparent container containing brake fluid.

5042

20. Pump the brake pedal slowly three (3) times (once/sec),
then hold it depressed.
21. Loosen the bleeder screw until fluid flows through the tube.
22. Retighten the bleeder screw.
23. Release the brake pedal slowly.
24. Repeat steps 21 through 24 until the air is completel
y
removed.
It may be necessary to repeat the bleeding procedure 10 o
r
more times for front wheels and 15 or more times for rear
wheels.
25. Go to the next wheel in the sequence after each wheel is
bled.
Be sure to monitor reservoir fluid level.
26. Depress the brake pedal to check if you feel “sponginess"
after the air has been removed from all wheel cylinders and
calipers.
If the pedal feels “spongy", the entire bleeding procedure
must be repeated.

5C-28 BRAKES


27. 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 “MAX" level as necessary.
28. Attach the reservoir cap.
29. Stop the engine.




05007-1


BRAKE LINE (HOSES AND PIPES)

Inspect all hoses and pipes for wear, bending, chafing,
cracks, dents, or any other damage.
Make necessary correction or parts replacement if these
abnormal conditions are found through inspection.

All hoses, pipes and joints can be damaged easily.
Do not allow the hose to become excessively twisted and
bent when working with then, and pay special attention to all
the brake lines not to damage them when repairing o
r
replacing other parts (axle, suspension, etc).

Inspection for leakage should be performed by depressing
the brake pedal fully.
If leakage is apparent at the circumference of joints,
retighten or replace these parts.
This procedure must be performed whenever brake lines
are installed.

After disconnecting the hoses and pipes, cap or tape the
openings to prevent entry of foreign material.