2004 ISUZU TF SERIES piston

5A-8 BRAKE CONTROL SYSTEM

Normal Braking
During normal (non anti-lock) braking, the solenoid
valve has current flow. The dump valve is closed and
the isolation valve is opened due to spring force.
Brake fluid travels through the center of the isolation
valve (normally open) around the dump valve (normally
closed) then to the brake pistons.
C05L300012

5A-10 BRAKE CONTROL SYSTEM

Pressure Reduction
Once the brake pressure is isolated, it must be reduced
to allow the wheels to unlock. This is accomplished by
dumping a portion of the brake fluid pressure into a
buffer chamber.
The microprocessor activates the normally closed dump
valve to open, allowing fluid from the wheels to be
dumped into the buffer chamber. This is done with very
short activation pulses opening and closing the dump valve passageway. Brake pressure is reduced at the
wheel and allows the wheel to begin rotating again. The
fluid from the brake piston is stored in the buffer
chamber against spring pressure and a portion of this
fluid also primes the pump.
The dump valves are operated independently to control
the deceleration of the wheel.
C05L300014

BRAKE CONTROL SYSTEM 5A-11

Brake Release
At the end of the anti-lock stop, when the brake pedal is
released, the pump will remain running for a short time
to help drain any fluid from the buffer chamber. As this
fluid returns into the system, the spring forces the piston back to its original position.
The isolation valve opens and fluid may return to the
master cylinder. Conventional braking is then resumed.
C05L300015

BRAKES 5C-9
MAIN DATA AND SPECIFICATIONS
FRONT DISC BRAKE mm(in.) 4

2 4

4, 4

2 HIGH RIDE
Caliper type Pin slide
Disc outside diameter 256(10.079) 280 (11.023)
Disc thickness 26(1.024) 27 (1.063)
Piston diameter 42.8 (1.685)

2 45.5 (1.79)
Adjustment method Self-adjusting
REAR DRUM BRAKE mm(in.) 4

2 4

4
Type Leading and Trailing
Drum inside diameter 254(10.008) 295 (11.614)
Brake lining dimension 244

50

5 283

45

5
(Length
Width
Thickness) (9.57
1.97
0.20) (11.14
1.77
0.20)
Adjustment method Self-adjusting
WHEEL CYLINDER mm(in.)
Inside diameter : rear 25.4 (1.000) 23.8 (0.937)
MASTER CYLINDER mm(in.)
Type Split
Bore diameter 25.4 (1.000)
Piston stroke (Primary + Secondary) 21.8 + 12 (0.86 + 0.47)
VACUUM SERVO mm(in.) 6VE1/C24NE 4JA1-T/4JA1-TC/4JH1-TC
Diaphragm diameter 205(8.077) + 230(9.055) 180(7.087) + 205(8.077)
4JA1-T
Power cylinder stroke 35 (1.378)
PEDAL RATIO 3.7
BALANCE EBD (with ABS)
Type Load sensing proportioning valve (without ABS)
Blend valve (without ABS)

BRAKES 5C-19

SERVICING
BLEND PROPORTIONING VALVE (IF SO EQUIPPED)





Structure and Operation






Structure

Side
a shows P-valve ; side b shows bypass valve.
Bypass valve seals the routes
4 and 5 using the seal 2at
the piston
1 end.
In addition, spring
3 presses against the piston 1, and in
order to seal out the route
4 and route 5 sufficiently, spring
3 presses seal 2 against cylinder end surface.
The left figure is a characteristic curve diagram.

5C-20 BRAKES







Operation

The operation of the P-valve by the master cylinde
r
pressure is unchanged up to the brake points
A and B.
If master cylinder fluid pressure penetrates into the second
break point
B, the fluid pressure pressing against the seal
2, (which isolated route 4 and route 5), passing the route
4of the master cylinder side, overcomes the operating
force of the spring
3 + fluid pressure affecting the seal 2of
the wheel cylinder, and presses the piston
1to the right
side, resulting in the opening of the routes
4 and 5, and
canceling of the P-valve operation.
Then, because the master cylinder fluid pressure and the
wheel cylinder fluid pressure, up to the point
C, operate on
the identical surface of the seal
2, both have identical
ascending ratio.
However, because of the operation of spring
3 in the wheel
cylinder side, wheel cylinder fluid pressure operate to
preserve the balance against the master cylinder fluid
pressure on the lower level with the difference in pressure
resulting from this spring.
03260002-2


Valve Maintenance
In the case of fluid leak or other abnormalities, faulty valve
should be replaced.
The valve is set up at the engine room.
Note:
The blend proportioning valve is not repairable and must
be replaced as a complete assembly.

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