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Suspension Systems- Shock absorbers

A shock absorber damper


The purpose of a shock absorber

Shock absorbers are also known as dampers, they are devices that offer resistance to suspension movements.

They are necessary to dampen out the vetical oscillations or bounce of the suspension and car body after the springs have been deflected by road surface irregularities. With out damping, a car will bounce, pitch and roll uncontrolably which in turn affects the safety of a vehicle - comfort and economy (excess stress and wear on other components).

The Function And Basic Principles Of A Shock Absorber

The upper end of the piston rod is attached to the car body and the piston is attached to its lower end, inside the pressure tube. As the piston moves up and down (extension and compression movement) there is an advantage of oil (damping fluid) between the two operating chambers.

During the compression stroke, when the piston is pushed down in to the working cylinder, oil flows from below the piston to the above piston, the oil flow is regulated by valves.

At the same time the oil flows through the base plate valve from the working cylinder to the reservoir. During the extension (upwards) stroke, oil flows, in the opposite direction from above the piston, through the piston valve, to below the piston as well as from the oil reservoir through the base plate valve in to the working cylinder.

Inside A Basic Shock Absorber


Gas Charged Shock Absorbers

Gas shock absorbers are damped by either hydraulically or by gas pressure.

Hydraulic oil contains 10% air, and rapid changes in direction result in pressure differentials that release it. This forms lots of little bubbles, which are of course compressible, they confuse the passage of fluid through the valves, causing jerky movement and a loss of damping action but gas charging changes that.

The reservoir of fluid is kept under pressure by a locked-in amount of nitrogen. This keeps the bubbles from forming no matter how violently the pistons moving (hence why they maintain their damping efficiency, especially under load)

There are other advantages too, the charge accelerates the shock absorbers response and it provides a short booster-spring effect increasing resistance near the end of piston travel on hard compression.

  • You can upgrade from hydraulic to gas
  • gas must be replaced with gas
  • never downgrade from gas to hydraulic



What Is Inside A Shock Absorber

The Effects Of Worn Shock Absobers.

The most common effects of tyre wear are;


This is where the wheels have lost contact with the road and the vehicle rolls, excessively on corners; the vehicle is difficult to control and therefor dangerous.


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The tyre wear is accentuated due to irregular contact with the road.

Cupping and feathering are clear signs of defective shock absorbers.

Cupping, (patchy wear also known as flat spots) can accrue on both front and rear tyres as a result of poor adhesion to the road surface, when travelling over bumps and also during braking.

Feathering only indicates worn shock absorbers when seen on the rear tyres and is caused by loss of grip when cornering.

Feathering to the front tyres IS NOT associated with worn shock absorbers and is often caused by incorrect toe-in and toe-out adjustment (wheel alignment also known as tracking).

Understanding Steering



A vehicle with defective shock absorbers moving at a constant speed on a 6mm film of water may start to skid at a speed 10% lower than an identical vehicle with new shock absorbers.

Steering loss

When over taking large vehicles, especially on motorways, the sudden side wind, coupled with weak shock absorbers, can create an EXTREMELY DANGEROUS situation.

Headlamp Dazzle

Headlamp alignment is impaired, causing dazzle and therefor danger to oncoming traffic, as well as being a nuisance to the vehicle,


Increased stopping Distance

It is no good having good tyres and brakes and tyres if the wheels are off the road and unable to brake the vehicle adding perhaps 10-15 feet to the stopping distance.

Body Stress

Steering, suspension linkages and body parts are subjected to excessive stresses and vibrations, with subsequent inconvenient roadside breakdowns, early fatigue and failure.


The all-familiar risk of towing a caravan or trailer can be considerably increased if the vehicle shock absorbers are defective.

Difficulties often arise simply because, a caravan or trailer fundamentally changes the way the vehicle reacts, particularly when cornering and braking.

In these cases defected shocks can seriously affect the handling characteristics, especially steering and brakes.

Remember; under normal conditions, shocks wear out slowly. So slowly in fact, that deterioration on a vehicle handling, performance and comfort can go unnoticed.

Quite simply, the driver will compensate their driving style to suit the handling characteristics. According to the shock absorber manufacturers, shock absorbers can lose their efficiently and advise replacement from 24-30,000 miles, otherwise should be examined at 12,000 miles or twice a year.

How to check a shock absorber

there is quite a simple test for checking a cars suspension , as pictured below just give one firm push down on the corner of the vehicle. you should get 1 full bonce plus a 1/2 any more than this could in fact indicate that the shock absorber is worn and due for replacement.

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