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Alfa Romeo Wipers
OK so as always I was having trouble finding something to write about in this edition of the
magazine and usually I have a wander round the workshop and see what is going on or what
cars are in the workshop, however, today I am not feeling at all inspired! Over the last twenty
years I think I have covered just about everything, so today I have randomly opened one of
my reference books and I have decided that the page it opens at will be this edition's topic
so..
Windscreen wipers is the topic I have to write 1500 words on and hopefully keep you
engaged! Well this might not surprise you, but there is a whole load of legislation covering
windscreen wipers and it starts with; the wipers must sweep a certain percentage of the area
of the windscreen; then they have to be able to operate between -40 and +80 degrees
centigrade; they have to be corrosion resistant against acids, bases, salts and ozone; they
have to be able to work under a significant snow load; they have to not be a hazard to
pedestrians in case of accidents and work when the car is traveling at high speeds and lastly
they have to work silently. When you look at that list you think that it’s all obvious stuff,
however I was driving a Sprint Speciale recently and the wipers quite simply didn’t work. They
came off the screen at speed and that was even with the Bertone fitted little perspex screen
in front of them to help solve the problem. So in many ways these regulations have proved
effective in making things work properly over the years.
A windscreen wiper will generally work at around 40 cycles per minute on slow speed
and around 60 cycles per minute on its high speed operation, this is set down in the
regulations and the difference between the two speeds has to be at least 15 wiping cycles per
minute. This is a difficult problem as the torque required to make the wipers sweep the screen
can vary greatly, fairly obviously a wet screen has very little friction while a screen covered in
snow has huge amounts of friction and to deal with these variations of torque required the
manufacturers now use a high speed electric motor geared down through a worm drive. This
is a gear system with a screw-like "worm" engaging a toothed "worm wheel," ideal for high
gear reduction, transmitting power at 90-degree angles, and creating self-locking
mechanisms where the wheel can't turn the worm. They offer large torque multiplication in a
compact space.
The motion of the motor is then transferred to the wiper arm by a linkage and there are
two types of drive: a “conventional” drive where the motor rotates in a single direction and
reversing drives, where the motor changes direction completely on the reverse stroke of the
blades. Alfa Romeo uses conventional drives and varies the speed of the motor by using a
third carbon brush, this third brush is at an angle to the other two brushes and results in a pull
out of the motor characteristic thus reducing the speed. The motors also have a system in
them to ensure that they park in the correct position. As the drive on the motor output and the
position of the wipers are the same, the park sensor is fitted on the motor output. This is
usually in the form of a disk of conducting material with a section that is insulated that
corresponds with the position you want the wipers to park in. When you switch the wipers off
the disk continues to conduct power to the motor until the insulated section is reached where
the power is then cut to the motor and the motor then stops in the correct position. On more
modern cars they tend to include a relay to reduce the amount of power that is transmitted
through the motor output which increases the life of the wiper motor drive.
The motion of the wiper motor needs to be transmitted to the wiper arm or arms and
this is done by a linkage, this converts the rotary motion of the wiper motor to an oscillating
motion that is required for the wiper arm. The linkage can be connected directly to the body of
the car but Alfa Romeo tend to use a sub assembly consisting of a number of tubes that
ensures that all the forces exerted by the wipers are confined to the sub assembly. This
reduces the stresses that are put through the body panels, meaning that lighter gauge panels
can be used and it also reduces the time required for fitment during the cars assembly
process. Other systems that can be used are motor reversing where the motor simply
reverses at the end of each stroke, this reduces the amount of space required for the wiper
mechanism as the motor does not have to complete a whole circle, it merely oscillates over a
very small portion of the circle meaning the linkage may only cover a quarter of whole circle,
halving the space required. There is also the possibility of using two motors with a linkage
from each or even using a single direct drive motor with no linkage. The design of the linkage
is also important as it is best from the drivers point of view to have the wiper arm travel at an
even speed across the windscreen and not decelerate significantly at each end of the stroke.
The wiper arms transfer the motion of the wiper linkage to the wiper blade. The arm is usually
bolted to the wiper linkage by a nut and the die cast aluminum end of the arm fits over a taper
that allows the possibility of very fine adjustments of where the blade sits on the windscreen.
The arm itself will usually be made of sheet steel although in some applications like the rear
wiper they may be made of plastic.
Wiper blades are the most important component of the whole system, there are
generally two types used on Alfa’s. Conventional blades with a number of arches which are
used to maintain even pressure over the entire length of the blade and flat “aero” blades.
Conventional blades are perforated to reduce the aerodynamic lift on them at speed and
sometimes wind deflectors are integrated into the blades to help with this. Flat blades are the
more modern trend in wiper blades and they are constructed so that two pre shaped spring
strips are incorporated within the blade causing the blade to form a curve when lifted off the
windscreen, this curve helps to create an even pressure along the whole length of the blade.
This type of blade also tends to have a much simpler attachment to the wiper arm, usually
consisting of a simple pin and hole. The overall height of the wiper system is significantly
reduced which reduces the likelihood of injury to pedestrians in case of an accident.
The rubber part of the blade is the final piece of the jigsaw, this is the part that actually
clears the windscreen. The blade itself has two edges, one clears the screen on the way up
and the blade then flips over and the other edge of the blade cleans the screen on the way
back. The contact area between the blade and the screen is between 0.01 of a millimeter and
0.015 of a millimeter. When moving across the screen the blade must be able to cope with a
coefficient of friction of between 0.6 to 0.1 on a wet screen to 0.8 to 2.5 on a dry screen. The
blade will often consist of two materials, a synthetic rubber hardened abrasion resistant edge
which merges into an extra soft spine which ensures the wiper blade has optimum reversing
characteristics.
So what goes wrong with Alfa Romeo's wiper systems?
On 159’s the plastic housing comes loose where the bearing at the end is
inserted into the metal tube of the linkage and this leaves a triangle in front of the drivers
vision that doesn’t clear.
On 147’s and GT’s again the plastic housing breaks where it changes from a steel tube
to the plastic insert the plastic snaps off, the wiper then behaves erratically.
On all models the nut that secures the arm to the linkage comes loose and the
mechanism rotates but doesn’t drive the arm.
On 916 series cars the park stops working when the conductive disk in the motor
assembly gets covered in grease and this needs to be taken to pieces and cleaned, then it
will work again.
Stelvio’s and Guilia’s can get the hebie gebies after the battery has been disconnected
and quite simply wont turn off.
Mito’s and Giulietta’s tend to suffer with rear wipers stopping when the wiring loom
between the tailgate and the body fails.
On 147’s the rear wiper has a tendency to seize up where it goes through the screen
due to the ingress of dirt.
On all models if the blade judders when traveling in one direction on the screen the
angle of attack is incorrect, this can be cured by simply twisting the wiper arm so it is parallel
to the screen.
Well there you go, who thought you could write 1572 words on windscreen wipers!
Related Links: 147 front wiper motor and linkage removal. | MiTo front wiper motor with linkage replacement | How to change the wiper blades on a Brera or Alfa 159