Shocks going Bad
Shock absorbers, often just called “shocks,“ are oil-filled dampers that reduce the bouncing
caused by suspension springs. In engineering terms, shocks are part of a
spring-damper system that keep the wheels in contact with the road and smoothes
out the ride by reducing spring oscillation. When a shock absorber is combined
with the spring into a single unit this assembly is termed a “strut.“
If you sliced a shock lengthways you’d see that it looks a little like a syringe. There’s a disc fitted on the end of a shaft, the other end of which mounts onto the wheel. As the wheel moves up and down, oil is forced through a small hole in the disc. When the wheel hits a bump and moves upwards, the spring compresses and oil is forced through the hole in one direction. This oil slows the upwards motion and prevents the wheel from leaving the road. In the same way, when the wheel drops down into a pothole the spring stretches out and the oil in the damper flows the other way to prevent the car from dropping down suddenly.
It’s not necessary to inspect shocks or struts on a regular basis, although there some clues that ought to prompt a check. The first is if the tires are wearing unevenly. There can be several possible causes, but worn shocks are something to check for. The second clue is excessive bouncing as the car travels down the highway. Shocks tend to wear slowly so this gradual change often goes unnoticed until the driver wonders why his headlights seem to bounce up and down when he stops.
A third clue is mileage. Most shocks and struts need replacing after 50,000 miles although many owners overlook this job. This means that if a used vehicle is being purchased it’s prudent to check what kind of condition the shocks are in.
There are two ways to check the shocks or struts. The first is to do a visual check for leaks. This usually means getting the car or truck up in the air and crawling underneath with a good flashlight to look all round. Oil running down the shocks means a seal has failed and the shocks should be replaced as quickly as possible.
The second check is to see how well the shocks are performing their job of damping the bounce of the springs. To do this, go to each corner of the car, push it down as far as possible, and then release. If the shocks are working correctly the car should bounce up quickly, slightly overshoot its “at rest“ position, and then settle. If the car overshoots, then drops and finally rises up again, that’s a sign that the springs are overpowering the damping effect of the shocks. When this happens, it’s time to have those shocks or struts replaced.
Shocks and struts should always be replaced in pairs, as changing just one will affect how the vehicle steers and brakes. Shocks can be changed by a competent do-it-yourselfer, but struts take more work and need specialized equipment to avoid injury from the springs. If in doubt, have your local repair shop do the work.
