- Cross-reference: photo was sent via satellite and is available at:
- Is one of your car headlights not working? When
you change the bulb it is also a good idea to check the efficiency of
the shock absorbers, because they could be the cause of the fault!
This is one of the unsettling facts that emerged from tests set up by
Tenneco Automotive, a world-leading manufacturer of Monroe(r) brand
shock absorbers. Tenneco commissioned an independent association of
car testers to check which and how many of a car's components are
seriously affected when the efficiency of shock absorbers is reduced.
For years Tenneco Automotive has been campaigning to heighten
awareness, among car repairers and drivers, of the importance of
shock absorbers, components that are far too often overlooked. In
terms of active safety, they are crucial not only for road holding,
but also in emergency stops, as their role is to ensure that the
tyres maintain contact with the road surface, even on bumpy ground.
Still today, many drivers are convinced that shock absorbers should
only be changed when they are damaged by external elements, or when
they show signs of leakage. The wear of the shock absorber is in fact
a gradual process, often almost imperceptible to the driver, who
becomes used to his car's movement and is unlikely to realise that
there is a problem.
But every small movement of the car corresponds to an action, of
the internal mechanism of the shock absorbers, which leads to
continuous and progressive wear and tear. It has been calculated that
for 18,000/20,000 km driven by a driver each year, the shock
absorbers go through on average 10 million cycles each! It is
therefore easy to imagine the extent of the stress to which all the
mechanical parts directly affected by the motion of the shock
absorbers are subjected and the severe damage that is sustained by
other vital parts - damage that will reduce their life and can even
result in them breaking. However, there are many drivers who take
their cars for repair, and focusing on the damage to the tyres, the
braking and the steering system or the powertrain, they fail to
eliminate the factor responsible for the problem. In fact, at
relatively little cost, a considerable amount of damage, and thus
extra expense, could be avoided: i.e., simply by replacing the shock
absorbers. More important still, this simple investment would also
help to ensure that the vehicle maintains a high level of active
The research carried out on behalf of Tenneco Automotive on a
selected group of auto repair shops therefore gave surprising
results. Below we illustrate these in detail.
BRAKES Tyres and shock absorbers are vital to a vehicle's
road-holding capacity. For a brake to be fully effective, three
fundamental elements must be coordinated: tyres, brakes and shock
absorbers. If just one of these components is faulty, stopping the
car in any conditions can become a problem and, depending on the
speed, be very dangerous.
The braking system normally consists of a disk, a caliper (to
accommodate the brake pistons) and pads. During braking, the pistons
act progressively on the brake pads bringing them into contact with
the disk surface. Worn shocks and struts can allow excessive vehicle
weight to transfer from the rear to the front whilst braking. This
transfer will severely decrease the braking efficiency of the rear
axle. Moreover, that reduces the tyres ability to grip the road,
increasing the braking distance and decreasing safety. This effect
will also increase the wear on the front brake disc and pads.
It also must be noted that during the life of a well maintained
car, the calipers rarely have to be replaced and, even in the most
unfortunate circumstances, not usually more than once. When the shock
absorbers are faulty, on the other hand, the probability of having to
replace the calipers increases. Indeed, it is almost always
ABS AND ESP Even ABS, the anti-lock braking system, and ESP,
the electronic stability programme, are not exempt as the car's
wheels have to be constantly be in contact with the road for these
systems to function. When they are not, the brakes become unreliable
and the ABS and ESP do not function as they were intended. It has
been demonstrated that just one worn shock absorber can upset the
system control unit.
The steering components must always be perfectly tuned and
registered in line with standards indicated by the manufacturer. In
certain conditions, however, a driver will notice vehicle
instability, and often put it down to a tyre being low, even if he
later finds the pressure to be normal. It is also worth remembering
that the vehicle oversteering or understeering will become
increasingly evident as the shock absorbers gradually lose their
original characteristics. For this reason, regular checks are
essential for driving safety.
Steering boxes on vehicles that are used mainly on uneven road
surfaces must be changed at least once in their lifetime When this
is done, the shock absorbers are normally found to be worn out, or at
least, no longer in good condition. This is because excessive
vibrations that are produced by inefficient shock absorbers are
passed onto the internal organs of the steering box through the
People often mistakenly believe that suspensions and shock
absorbers are the same thing. The suspension is, rather, the group of
elements that make up the system whose role is to dampen the effect
of bumps between the wheels and the body: springs, anti-roll bars,
swinging bars, struts, flexible bushings, silent-block mountings and
balljoints are essential to the vehicle's road-holding function and
to the long life of the shock absorbers themselves.
With worn out shocks or struts on the front axle, the tyres are
allowed to leave the ground whenever the driver encounters a bump or
hole in the road. This action will increase the wear on other
components, such as the steering arm joints, power steering
couplings, control arm bushes and wheel bearings. To the consumer it
is false economy not to replace the damping units once they show
signs of wear!
Adherence is the most important characteristic demanded of tyres,
but to ensure a good level of safety, it is also essential that a
number of functions are oriented in order to achieve the highest
level of reliability and the least probability of error. For
example, fitting four excellent quality tyres to the car without
taking into consideration the bad state of the shock absorbers is, in
the end, a pointless operation as not only will the road hold be
compromised and braking inefficient, but the wear and tear of the new
tread will be more irregular and premature. For optimum performance,
shock absorbers should always be replaced in pairs. A vehicles
ability to steer, brake, and accelerate depends on the adhesion or
friction between the tyre and the road. Worn shocks and struts can
allow excessive vehicle weight to transfer from side to side and from
front to rear.
Braking by not fitting a pair of shock absorbers or struts to the
front of the vehicle, you upset the balance of the braking ability
across the front axle. In some cases, there could be a possibility of
the vehicle 'pulling' to the side where the new damping unit has been
fitted. In fact, with worn shock absorbers, you could decrease the
life of your tyres by up to 20%.
POWERTRAIN PARTS These mechanical components are particularly
delicate (and expensive, too), and shocks caused by irregular contact
of the tyres with the road contribute considerably to the premature
wearing, due to inefficient shock absorbers, of the gearbox, clutch,
transmission shaft, joints and differential gear.
When the car is driven with worn shock absorbers on an uneven or
paved stretch of road, even the bodywork is subject to a real
"bombardment" of shocks and counter shocks: noisy doors, vibrating
bonnet and boot doors and rattling dashboards are all overt signs of
a situation that is harmful to the vehicle, irritating to both driver
and passengers and certainly threatening to safety.
The abnormal swinging motions that are produced while driving with
worn shock absorbers not only undermine the efficiency of the
headlight bulbs, which must be replaced more frequently, but also
affect the stability of the light beams. As a consequence, the driver
is forced to drive under conditions of limited visibility, and will
dazzle and thus distract oncoming drivers.
"Inefficient shock absorbers generate a whole range of problems
and are responsible for damage to other parts of the vehicle" remarks
Mr Jean-Pierre Dolait, Vice President of Tenneco Automotive Europe's
Aftermarket Sales and Marketing division. He goes on, "This, in
itself, should induce more regular checks to be carried out on these
components, which are far too often overlooked. Our advice is to have
an expert mechanic carry out regular shock absorber efficiency checks
at least every 20,000 km. It is also crucial to realise that the car
of the future will have an increasingly high number of electronic
features using extremely sophisticated systems which will require the
perfect functioning of the car's other mechanical components in order
to guarantee maximum safety and the utmost comfort."
Headquartered in Lake Forest, Illinois, USA, Tenneco Automotive is
one of the world's largest producers of ride control and exhaust
systems and products under the Monroe(r) and Walker(r) brand names.
With 23,000 employees and a turnover of US$ 3.5 billion, the company
has over 100 facilities in 22 countries in North and South America,
Europe, Africa, Australia and the Far East.
ots Originaltext: Tenneco Automotive Europe
Tenneco Automotive Europe
Tel. +32 2 706 9147
Fax +32 2706 9199