A fundamental component for vehicle safety
A FAULTY HEADLIGHT? TRY
THE SHOCK ABSORBERS
All the negative effects caused by worn shock
absorbers on other parts of the car
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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 safety.
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 inevitable.
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 linkwork.
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.
Tenneco Automotive Europe
Tel. +32 2 706 9147
Fax +32 2706 9199