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20th Annual Technical Forum: Shocks And Struts


9/6/2012

 

Q: Are mechanical shocks and struts going away?

A. Ordinary hydraulic shocks and struts on many late-model vehicles have been replaced with electronic adjustable dampers that are capable of varying suspension stiffness and ride quality to match changing driving conditions. Some use adjustable valving while others contain a special magnetic fluid that changes viscosity when an electric current passes through it. Such innovations in ride control provide the best of both worlds: a smooth comfortable ride and outstanding handling and control when it is required.

Some late-model vehicles also have automatic leveling systems that use air shocks or air springs to control ride height. Ride height sensors detect load changes so the suspension control system can add or vent air pressure as needed to maintain the desired ride height.

But conventional shocks and struts are not going to disappear any time soon. Many new cars, SUVs and light trucks continue to use these tried and proven ride control parts as a less expensive alternative to the complicated and expensive electronic suspensions that are found on many luxury and performance cars and SUVs.

Q. Do shocks and struts affect driving safety?
A. Yes. Though shocks and struts affect ride quality and comfort, they also can affect handling, stability, driving safety and the operation of the Antilock Brake System (ABS) and Electronic Stability Control (ESC). Stability control systems are calibrated to the handling characteristics of a vehicle’s suspension. If the shocks or struts are weak, or the springs are weak or sagging, ESC may not function with the same degree of effectiveness as it normally would.

On ABS-equipped vehicles, worn rear shocks can allow wheel bounce when braking hard on rough roads. If the tires lose momentary contact with the road, it can trigger the ABS system unnecessarily. Many motorists are often unaware of the effects worn shocks and struts can have on braking, handling, traction, tire wear and driving safety. Shocks and struts typically deteriorate gradually over time as the miles add up, so many motorists may not notice how their vehicle’s ride control capabilities have declined since it was new. For this reason, replacing conventional shocks and struts every 50,000 miles may be recommended to restore like-new ride control, handling and driving safety.

Q. How can you tell if the shocks or struts need to be replaced?
A. Symptoms that typically indicate a need for new shocks or struts include suspension bottoming after hitting a bump, excessive nose dive when braking, excessive body lean or sway when cornering, a bouncy or undulating ride, wheel shudder or shimmy after hitting a bump, and cupped tire wear. Fluid leaks are another clue that the piston seals are leaking. Sooner or later the loss of fluid will diminish the shocks or strut’s ability to control the motions of the suspension.

Gas leaks are harder to see, but if a piston is leaking fluid chances are it has probably lost its gas charge, too. This will significantly reduce the shocks ability to resist fade when it is working hard. A bounce test is still a valid means of identifying weak dampers. Rock the suspension several times up and down, then release it. If the dampers don’t stop the motion within one bounce, the shocks are weak and should be replaced to restore like-new ride control.















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