Tech Tip: What Really Wears Out Inside Shocks and Struts – UnderhoodService

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Tech Tip: What Really Wears Out Inside Shocks and Struts

When shocks and struts wear out there are almost no visual clues. When a unit is leaking, it is a sign of failure and not wear. Next to performing an autopsy or throwing the unit on a dynamometer, there is no conclusive way to determine if the internal components are worn to a point where it could compromise vehicle stability. Even the "knee on the bumper" test can give false results due to how some units handle low frequency movements.

Andrew Markel
By Andrew Markel

3_01_2009/86804PistonSeal_00000041859.jpg” border=”0″ ” align=”right” alt=”one area of wear is the seal between the piston and bore. the seal must prevent fluid from flowing between the two surfaces without creating excessive amounts of friction. if the seal allows to much fluid to pass, it will influence how the valves in the piston and base perform. if the fluid becomes contaminated, it can cause wear to the bore and piston. according to some shock and strut suppliers, wear on these surfaces does not happen until the unit has become significantly degraded. “/>when a stone hits the chrome shaft of a shock or strut, it will first cause a pit or scratch. this might cause damage to the seal, which might cause a loss of fluid. if the the damaged area starts to corrode, it could cause the shaft to lose even more chrome. the seal at the top of the body is the barrier between the harsh environment outside and the fluid and gas within the unit. the seal can not be effective if the surface of the shaft is pitted or damaged. poor sealing surfaces can cause the unit to leak. if the pitting or lost chrome plating is large enough, it can damage the seal, this can lead to water and debris getting into the unit and damaging the valves and piston seal. to protect the seal, it is essential to replace the boots, dust covers and jounce bumpers. if any of these items are missing, it could cause the premature failure of the new unit. Here is where most of the wear occurs in a shock or strut. These small discs of metal are mounted on the shaft and are held in place with either a nut or a nut and spring. As the piston moves, the discs deflect and fluid moves between the two chambers. Even under normal conditions on a smooth road, shocks stroke on average 1,750 times for every mile traveled. The action causes a “shearing” action on the fluid that is not unlike what motor oil is subjected to when it is between engine bearings. This action can break down the base oil and additive package. The wear on the fluid can change the viscosity of the fluid and make the unit unable to dampen suspension movement. The discs and springs in the valves can also suffer from metal fatigue due to the constant movement of the suspension and the passing of the fluid.

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