What Are Struts?
Struts are the main component of a modern independent suspension system … they are what “suspend” the body and frame of your vehicle above the wheels. All the weight of your vehicle rests on your struts, which transfer the weight, via several other components, to the wheels. Struts have at least two components: a spring and a shock absorber – and many have a third: the swivel mount.
The weight of your vehicle is “suspended” above the wheels by use of a spring … permitting the wheels to travel up and down on the road without causing the body of your car -- and its occupants -- to bump up and down with every uneven spot in the road.
By itself, a spring smooths out the road impact, but on its own it would cause the body of the vehicle to move up and down several times after each bump as the spring expands and contracts. To minimize this effect, vehicles use shock absorbers.
The Shock Absorber
Shock absorbers, or shocks, are just what the name suggests: they absorb the shock of an uneven road before it reaches the body of the vehicle. Instead of all the force of a bump being transmitted to the body/frame of the vehicle via the spring -- then causing continued oscillations as your vehicle tries to reach equilibrium -- shock absorbers take the force.
A strut is usually a spring and shock absorber combination.
Most smaller vehicles with independent suspension use what is called a “Macpherson” strut – named after its inventor. The Macpherson Strut adds another component into the spring and shock combination unit – the swiveling mount. These strut mounts, where the strut connects to the body of the vehicle, have to be strong enough to bear the weight of the vehicle, but also able to swivel when the wheels turn.
What Makes Struts Go Bad?
Wear and Tear
Struts need to be replaced if any of the three components wear out. Like brakes and spark plugs, struts do not last forever. Because struts are in continual use during a drive, bearing the whole weight of your vehicle, it should not be surprising that strut components wear out over time.
The shock absorber component does its work by using the force of a bumpy road to push fluid from an internal chamber, through an orifice, into another chamber. It does this as its internal piston is travelling up and down, and so it requires seals to keep the fluid where it is supposed to be while parts are moving around it. These seals eventually wear out, either by leaking fluid externally, or by leaking internally, allowing too much fluid to pass too easily from one chamber to another, and so reducing the amount of force the shock can absorb.
The mount component uses a bearing to carry the weight of the vehicle while allowing the wheels to turn. It also uses molded rubber between the strut and the vehicle to further dampen vibrations. If the bearing wears out or the rubber gets old and cracks or tears, the mount will need to be replaced.
The spring should be the longest lasting of the three components, because it is one solid piece of metal that is tempered to be able to extend and contract many times. However, if the shock absorber component is bad, the spring is hit with much more force than it is designed to take, and it will wear out more quickly than it should.
When To Replace Shocks Or Struts
Springs don’t usually fail completely, but if they’ve been subjected to excessive wear and tear you may notice the vehicle sagging, or that the ride is not as crisp as it once was.
Failed mounts are the easiest to recognize of the three because they usually make the most noise. Failed mounts often cause a popping or clicking noise while you’re turning the steering wheel, because the bearing inside is bad.
Failed shock absorbers can be harder to notice. With oil-filled struts, external leaks are easy to spot, especially if the leak is rapid. A failed air strut is fairly easy to recognize: you’ll see a corner of your air suspension slammed to the ground.
So when should struts be replaced? Relying on your senses as a driver to tell when struts are bad can be deceitful – since strut failure is usually very gradual you may never notice it at all. But certainly if you are experiencing any of the symptoms listed above, your struts are due for replacement. Having your struts inspected regularly, including a test drive by a technician, can be helpful to monitor the performance of your struts.
There is no mileage interval that covers all shocks on all makes and models in all road conditions. Most vehicle manufacturers don’t specify an interval when they recommend strut replacement. Some strut manufacturers recommend an interval of only 50,000 miles. A rule of thumb is to expect approximately 70-80,000 miles out of new struts. Obviously, the worse your local roads are, the more quickly your suspension components will wear out.
Does It Really Need To Be Done?
Bad struts mean poor handling – a definite safety concern – and bad struts mean more wear and tear on all suspension parts, and much of the steering system as well. Of course, there is the obvious comfort factor: new struts just make for a more pleasant drive, allowing you to enjoy your vehicle the way it was designed to operate.
The bottom line for the budget conscious is that struts are more than a cosmetic or even comfort concern. They are not usually a high-priority safety item like brakes, but they are an important part of the way your vehicle operates, and neglecting them can cause more wear and tear on the rest of your car. So if you can, stick to the 70-80,000 mile timetable for strut replacement.