Shocks and strut repairs are the most common auto repair fraud perpetrated against vehicle owners.
As with most other repairs, some basic knowledge will help you avoid spending money you shouldn't, and understanding struts and shocks is probably easier that you think.
To understand when struts or shocks need to be replaced, you need to know what they are and what they do. Although struts and shocks are very different in appearance, they serve the same purpose: to prevent your car from continuing to bounce up and down after the first time. If you jump up and down on the front bumper of a car with good shocks and struts and then jump off the car will immediately stop bouncing. Of on the other hand the shocks or struts are worn, the car will continue to bounce a few times after you jump off.
The more it bounces, the more the struts or shocks are worn. In fact if you took the shocks completely off of a car, it would bounce up and down five to ten times before it stopped.
Shocks and struts are needed because cars have springs that support the weight of the car. These springs help the car ride smoothly over dips and bumps, and a spring as you know, tends to bounce again and again. The shocks and struts help settle the springs down. They also prevent the car from bouncing, swerving, and swaying and they help keep all the wheels in contact with the pavement so you can maintain control in curves and on rough surfaces.
struts and shocks work? There is of course a technical answer to this question, but that is not necessary for basic understanding. The shocks and struts are filled with oil, which is forced back and forth through small openings inside the shock or strut when the car bounces up and down. Since oil tends to flow through a small opening at a slow, steady rate, this tends to make a car bounce at a slow rate, so it stops bouncing quickly. This can be loosely compared to a nozzle on a spray bottle. If you squeeze the trigger with no liquid in the bottle, it is easy to pull the trigger as fast as you please. If you spray a liquid, however, no matter how hard you pull the trigger as fast as you please. If you spray a liquid however, however, no matter how hard you pull the trigger, the fluid travels at a steady speed. This simplified explanation gives you the basic idea of how a shock works.