Iveco Stralis AT/AD. Manual — part 229
Excessive toe-in of front wheels; excessive wear of the
outside surfaces of the tread
Rear axle out of parallel due to breakage of the leaf
spring centre pin, or springs of different lengths, or bent
springs
Overhaul the suspension
Check and adjust toe-in
Front wheels out of balance
Balance the wheels
Front tyres at different pressures
Check pressures ensuring that both are at the correct
value
Excessive difference in wear between a pair of tyres
Replace excessively worn tyre
YES
NO
YES
YES
3
NO
VEHICLE PULLS TO ONE SIDE
YES
NO
YES
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6
WHEELS AND TYRES
Base - January 2003
Figure 1
The front wheels can be balanced on the vehicle using the
electronic unit 99305037; this has the great advantage of
balancing the wheel together with the other rotating masses.
The operation must be carried out as follows :
- Raise the front of the vehicle and make sure that the wheels
rotate freely
- Position the imbalance detector (1) under the axle close
to the wheel being examined, arranging the height so that
the spin-up wheel of unit 99305037 (2) is in contact with
the tyre; position a support stand under the opposite side
of the axle and lower the hydraulic jack
Figure 2
- Connect the cable (3) of the imbalance detector to unit
99305037
- Make a reference mark on the tyre by drawing a radial
mark with chalk or using a strip of gummed paper
- Turn switch (2) to static balancing position and sensitivity
switch (4) to notch no. 5 on the graduated scale
- Turn on switch (5) for instrument light (1) and strobe
lamp switch (8).
- Turn the spin-up switch (6) of unit 99305037 to the first
speed position so as to make the wheel rotate.
Turn up the spin switch (6) to second speed and place the
balancing machine against the tyre.
While the wheel is being spun, it will be found that the
stroboscopic effect on the wheel will make the reference
mark appear stationary; the pointer of the instrument (1),
moving from the value zero, reaches a maximum value on the
scale and then returns to zero.
When the pointer has begun to fall back, withdraw the
balancing machine, turn off the spin-up switch (6) completely
and brake the motor by means of the brake lever (7). The
wheel continues to revolve due to inertia and the reference
mark made on the tyre moves; the point to which the
reference mark has moved should therefore be noted.
Read off from the instrument (1) the value shown by the
pointer, multiply it by 10, to obtain the value of the balance
weight to be fitted to the rim.
16997
WHEELS AND TYRES
7
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502511
STATIC
BALANCING
OF
THE
WHEELS
If the weight required to balance the wheel is more
than 600 to 800 grams, divide the weight in half and
position the two parts so formed with one half on the
inside and one half on the outside of the rim, making
sure that they are in the same position.
CORRECTING RESIDUAL STATIC
IMBALANCE
Figure 3
Fit the balance weight calculated in this way as shown in the
figure. If during the test, the pointer of the instrument (1,
Figure 2) remains in the green area of the box, the wheel is
balanced.
- If the weight is in the zone marked with letter A, this means
that it is too light, and in that case weight must be added
as indicated by the instrument (1, Figure 2).
- If the weight is in the bottom zone marked with letter C,
this means that it is too heavy and in that case the weight
must be reduced as shown by the measuring instrument.
- If the weight is found to be in the zones marked with letters
B or D, do not remove or add any weight but instead move
it 5 cm upwards in the direction of the arrows, see Figure 4.
16998
!
Figure 4
23885
To correct the residual imbalance, repeat the operations
already carried out above; depending to the new reading on
the instrument (1, Figure 2), refer to the diagram in Figure 4
and proceed as follows to adjust:
502510
TYRE PRESSURE
Tyre pressures must be checked with the tyres cold.
Carefullly make sure that the pressure is correct since, if it is
higher than required, a harsh ride and excessive wear of the
centre of the tread will result, while if it is lower, the load is not
distributed over the whole tread but is concentrated at either
side, causing premature wear of these areas and also damaging
the internal structure of the tyre.
Unequal pressures between tyres affects the driving stability of
the vehicle and impairs operating safety.
Abnormal wear of the tyres may appear in various areas of the
tyre treads.
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WHEELS AND TYRES
Base - January 2003
Figure 5
Schematic views to demonstrate how tyre behaviour and
performance depends on pressure.
(The value shown inside each figure indicates the tyre
pressure, whereas the performance refers to the tyre
life).
Figure 6
Figure 7
EFFICIENCY 40%
EFFICIENCY 90%
EFFICIENCY 100%
CORRECT
+ 20%
- 40%
Figure 8
It is advisable to change the tyre pair fitted to one axle when
bands - due to block wear - are visible over the entire tread
width (see dotted areas on pictures).
Tyres are provided with wear indicators (A and B) in
connection with mark TWI on PIRELLI tyres and with the
MICHELIN mark on Michelin tyres. Replacement is
compulsory when such indicators are reached.
!
WHEELS AND TYRES
9
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HOW TYRE BEHAVIOUR DEPENDS
ON PRESSURE
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