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Monthly Archives: November 2015

  • All About Car Struts, Springs, Shock Absorbers & Mounts


    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 Spring

    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.

    The Mount

    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.

  • What Are Load Leveling Shocks

    Load-leveler suspensions maintain an optimum ride height when heavy cargo is loaded into the rear of a vehicle or when towing and hauling a trailer. In either case, the additional weight causes sagging suspension: the rear end sags and the front raises up … causing problems with handling, braking, and stability.

    There are two main types of load leveling shocks. One is a hydro-pneumatic system that automatically pumps more fluid into the rear shock absorbers to maintain the right ride height, while still absorbing bumps. This is one of the best shocks for towing.

    The other is an air-spring suspension -- sometimes at all four corners -- that automatically pumps air into “air bags” to raise the vehicle and compensate for a heavy payload or trailer. You can buy self-leveling rear shocks and air suspension products as aftermarket items. If you have to carry heavy loads and/or tow a heavy trailer, a load-leveling suspension can make your life easier and driving safer.

  • Struts vs Shocks and How to Test

    Modern vehicles benefit from many technological and engineering innovations designed to make them safer and more reliable. In addition, most modern cars, trucks, and SUVs provide drivers with an extremely smooth and comfortable ride, especially when compared to the rough ride common with early motor vehicles. The smooth ride is caused in large part by two key components: shock absorbers and struts.

    Shocks and struts, including air shocks, have several key functions, including maintaining contact between the tires and the road, preventing the car from leaning and swaying during turns, and absorbing the impact of a speed bump or pothole. However, while both shocks and struts are key to vehicle safety and comfort, they are two distinct parts.

    The difference between shocks and struts is described in the following sections outlining the functionality of both parts, the features distinguishing them from one another, and signs indicating they should be replaced.

    What Is A Shock Absorber?

    The shock absorber is the first line of defense against cracked pavement, rocky dirt roads, and other uneven surfaces. Contrary to popular opinion, shocks do not actually support the weight of the vehicle, but they slow down and reduce road vibrations of the road by a process known as dampening. In essence, a shock absorber is similar to an oil pump located between the frame of the car and the wheels. The key components of the shock absorber are piston, coil, and hydraulic fluid. When a car’s wheel dips, the shock initiates a compression cycle, and a piston exerts pressure on hydraulic fluid in the upper chamber of the device. The fluid serves to slow the coil as it relaxes back into place, helping prevent what the driver might describe as a bumpy ride.

    What Is A Strut?

    A strut integrates numerous suspension parts, including a shock absorber, into one assembly. These parts include the coil spring, the spring seats, the strut bearing, and the steering knuckle. Essentially, struts are advanced shock absorbers that have a couple additional functions. For example, the coil spring can support the weight of the vehicle and adjust to road irregularities like bumps, hills and valleys. In this regard, the strut functions as a standard shock absorber. However, the strut also serves as an integral part of the suspension system as well. The strut is mounted directly to the vehicle on one end, and on the other end it is attached to the vehicle’s suspension. Specifically, the struts connect the upper bearing to the lower ball joint so that the entire assembly can pivot when the vehicle is turned in any dir ection.

    Shocks Vs. Struts

    While shocks absorb impact, struts function to support and control the vehicle in motion. These two parts differ not only in terms of their specific functions but also their location in the vehicle. Most cars feature struts on the front and shock absorbers at the rear. Because struts are more complex, they are more expensive. Drivers should have their shocks and struts checked every 25,000 miles. Most factory recommendations advise a replacement after 60,000 miles.

    How Shocks and Struts Affect Safety

    The Royal Automotive Club (RAC) tested the effect on stopping distance at 50 mph and 70 mph, with automobiles fitted with rear shocks that were at 100 percent and 50 percent efficiency. The results were significant: a vehicle traveling at 50 mph stops an average of 12.3 feet shorter with new shocks. The benefit is comparable when the car travels at increased speeds. A vehicle traveling at 70 mph stops 22.6 feet shorter than a car with only 50 percent left in the shocks. The results of this particular test are clear: newer shocks mean safer vehicles. Therefore, drivers should pay attention to the signs of worn shocks and struts and have their car, truck, or SUV maintained regularly.

    How To Tell If Shocks or Struts Need Replacement

    There are many different indicators of worn shocks and struts, and all of them relate to the handling and braking of the vehicle in motion. Drivers should pay close attention to these factors, as worn shocks and struts are both a nuisance and a potential safety hazard. In terms of the feel of the car, vehicles that provide an excessively bouncy or stiff ride probably suffer from inadequate shock and strut support. Also, if the car has trouble taking tight corners and sways during turns, the suspension component of the strut may be worn down significantly. When applying the brakes, if the car bounces back and forth instead of coming to a quick stop, the shocks may be damaged. Another telltale sign of spent shocks is if the vehicle’s nose-dives down toward the ground once the car comes to a complete stop. In addition to these indicators, drivers can inspect their tires for visible signs of wear and tear. Specifically, if the tires have uneven wear patterns or flat spots on the surface, the problem is often related to worn shocks.

    How To Test for Worn Shocks

    While auto professionals have sophisticated equipment to test shocks and struts, drivers can apply the bounce test to a stationary vehicle in their garage or driveway to test the amount of life left in these parts. To perform a bounce test, push down on the rear fender of the vehicle and rock the vehicle up and down several times, and then release pressure. If the vehicle makes just one more bounce on its own before settling down, the shocks are in proper working condition. However, if the vehicle bounces several times before coming to a complete stop, the shocks or struts may need to be replaced.

    One additional factor to pay attention to is the sound of the vehicle while it is bouncing up and down. If there is a knocking or tapping sound, it probably means that there is a loose piston or worn piston shaft bushing.

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