Iveco EuroCargo (12 to 26 t). Manual — part 163

77848

The two steering limiting valves A and B are housed in the rack
piston (8) end.

They are composed of a valve body (4) inside which valve
intervention adjustment bush (3) is placed, with a forced
coupling, such valve in turn operating as small piston (2) seat.
Small pistons (2) are kept in their closing position on bushes
(3) by counter-spring (5). Valves A and B are kept closed till
small pistons (2) stems are taken in contact by the rack piston
displacement:

- with adjustment screw (1) if the displacement is towards

the left;

- with cover (9) if the displacement is towards the right.

Consequently, the pressurised oil present in the affected
chamber will pass through the valve A or B opening in the
opposite chamber and from there it will be discharged into the
tank.

When the hydraulic limiting valve is open, the hydraulic
servoassistance is highly reduced, and consequently it will be
necessary to exert a higher force on the steering wheel in
order to continue to steer till it stops.

1. Steering hydraulic limiting screw - A and B steering limiting valve - 2. Small piston - 3. Bush - 4. Valve body - 5. Spring -

6. Thrust sleeve - 7. Spacer pin - 8. Rack piston - 9. Cover - X. Left cylinder chamber - Y. Right cylinder chamber.

!

The figure shows the left steering condition.

Figure 22

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The adjustment is carried out after having assembled the
hydraulic power steering on the vehicle, with unloaded vehicle
and lifted front wheels. Moreover both right steering and left
steering must be performed operating as follows.

60924

60925

Make sure that the gearbox is idle.
Start the engine up and keep it at a rotation speed that is
≤ 1500 revs/min.
Rotate the steering wheel along a direction, applying thereto
a 34 Nm torque till the stop screw (2) assembled on the stub
axle (3) is taken in contact with front axle (1).
In this way bush (4, Figure 18) will go back with respect to
valve body (5, Figure 18) of affected steering limiting valve.
The position that bush (4, Figure 18) will get will make the
hydraulic pressure discharged inside the affected chamber
before screw (2, Figure 18) comes in contact with front axle
(1), safeguarding hydraulic system components.
Repeat the same procedure steering to the opposite side.

Automatic adjustment setting of hydraulic
steering limitation for TRW TAS 55 hydraulic
power steering

!

In case of an hydraulic power steering detached from
the vehicle, the outlet shaft rotation must not exceed
29

° (equal to 1.3 revolutions of the inlet shaft (1))

with respect to center drive position marked by
references (2).

Automatic adjustment check

The automatic adjustment check is carried out with full-loaded
vehicle moving and at low speed, both in right and in left
steerings, operating as follows.
Rotate the steering wheel along a direction till the absence of
hydraulic interlock is detected.
From this condition verify that the steering wheel rotation to
reach the steering stop (screw (2) in contact with front axle
(3)) is included between 60

° and 120°.

Repeat the same procedure by steering along the opposite
direction.
When detecting different values, operate as described in the
following chapter ”Manual hydraulic drops adjustment”.

!

For disconnecting and reconnecting the TRW TAS 55
hydraulic power steering, comply with the procedure
disclosed for ZF 8095 - ZF 8098 hydraulic power
steering.

Figure 23

541430

HYDRAULIC POWER STEERING
DISCONNECTION AND
RECONNECTION (TRW TAS 55)

Figure 24

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60926

Arrange under the hydraulic power steering (1) next to screw
(2) a vessel to collect the possible oil outflow, unscrew screw
(2) itself and screw screw (3) equipped with spare part
completed with nut (4).

Make sure that gearbox is idle.
Start the engine up and keep it at a rotation speed that is
≤1500 revs/min.
Rotate the steering wheel by applying thereto a torque that
is

≤ 34 Nm; leftwards for left-drive vehicles or vice versa for

right-drive vehicles, till the steering stop is reached and keep
it under such position.
Stop the engine.
Loosen nut (4) and screw, using a dynamometric wrench,
screw (3) till a torque increase by 1.1

÷ 2 Nm is detected.

!

Screw (3) must be screwed till distance B is 0 mm.

For left-drive vehicles, steer the wheels rightwards by applying
to the steering wheel a torque that is

≤ 54 Nm (vice versa for

right-hand drive), till stop screw (2, Figure 24) is taken in
contact with front axle (1, Figure 24).
Take wheel in straight running conditions verifying that
references (2, Figure 23) showing the drive center coincide.
Unscrew screw (3) so that distance B is 20-22 mm and lock
nut (4) at the required torque.
Top-up the tank till the provided oil level is reached.

Under the above condition, unscrew screw (3) by 2.5
revolutions and lock nut (4) at the required torque.
Carry out the automatic adjustment check as described in the
related chapter.

!

When screwing screw (3) keep nut (4) unmoving.

Hydraulic drops adjustment

Lift the vehicle from its front side, arrange the steering wheels
under straight running conditions and verify that references (2,
Figure 23) showing the drive center coincide.

!

The vehicle must be unloaded.

Figure 25

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78681

Carry out the air drain from hydraulic power steering circuit
proceeding as follows:

- fill with required oil (TUTELA GI/A) the circuit tank;

- rotate the engine with the starter and top-up the oil

continuously in order to avoid that the pump sucks air.
Top-up the oil till its level does not go below the upper
rod mark;

- start the engine up and rotate it at minimum speed

checking that the oil level does not go below the upper
rod sign;

- rotate the steering wheel many times from stop to stop

so that air cannot go out of the hydraulic power steering
cylinder till no air bubbles are noted incoming into the
tank;

- accelerate the engine at its maximum, stop it and check

that the oil level in the tank does not rise more than 1

÷

3 cm.

Hydraulic power steering oil level restoration

The oil level check must be carried out with moving engine
verifying that the level corresponds to the ”MAX” indication
included on the tank side.

Under off engine conditions, the level, due to the backup of
oil contained in the upper tank part, will be able to exceed the
”MAX” indication by two millimeters.

501430

MEASURE OF DRIVE CASE
CLEARANCES DETECTED ON
STEERING WHEEL

Check that there are no mechanical clearances in the related
connecting tie-rods.
Lock the left wheel under straight running position with
suitable shims on coupling bar; lift the front axle.

Arrange on the windscreen, through a suction cup, a fixed
index (2) and the millimeter sector (1) on the steering wheel.
Arrange the pair of manometers 99374393 (3) from 0 to 10
and from 0 to 160 bar, mutually connected by means of a
short-circuit valve.

MAXIMUM PRESSURE CHECK IN
HYDRAULIC POWER STEERING SYSTEM

With the pair of manometers 99374393 already previously
connected and the wheel on drive side locked with suitable
shims, start the engine up at its minimum speed, steer along
one direction with an effort of 10

÷ 20 kg on the steering

wheel and measure the pressure on the manometer from 0
to 160 bar.
Carry out the same operation by steering along the opposite
direction; if the detected values are different from the required
ones, search for their cause.

Connect the piping of the pair of manometers on the hydraulic
power steering oil delivery piping fitting.
Possibly restore the oil level.
Start the engine up at its minimum speed and read on the
manometer from 0 to 10 bar the pressure value at that time.
Slowly rotate the steering wheel leftwards till the
previously-read pressure value is increased by 1 bar, keep the
steering wheel unmoving and mark on the millimeter scale
99374398 the reached value in mm.

Rotate the steering wheel rightwards till a 1 bar pressure
increase is again obtained; read what the scale 99374398 is
marking, sum the two left steering plus right steering values:
the sum must not exceed 40 mm.
Lower the front axle.

!

The maximum pressure value can be detected by the
ZF or TRW plate applied onto the drive case.

Figure 26

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AIR DRAIN FROM HYDRAULIC
POWER STEERING CIRCUIT