Reliable contact of the wheel with the road is ensured by tires, elastic (springs, torsion bars) and damping elements of the suspension, which include shock absorbers, there are additional elements too, such as compression buffers, rubber-metal hinges.
In our article, we will discuss, as you already understood, car shock absorbers. We will try to explain simply why they are needed, how do they work, and also what a couple of tips on their selection and installation.
The functions of shock absorbers
Shock absorbers in good condition are the important elements of the vehicle’s safety. Failure of this part entails many negative consequences. The car is poorly controlled, the adhesion of the wheels to the road is deteriorated, the effectiveness of the brakes is reduced, which in turn can lead to an accident. Thus, these car suspension parts provide:
- vehicle traffic safety;
- control of the movement of the spring and suspension;
- efficient car control;
- axial braking force balance;
- prevention of early tire wear;
- monitoring of tire contact with the road surface;
- control of swinging and oscillations about the vertical axis;
- decrease in wearing of knots and units of the car.
How shock absorbers work and their basic design
Shock absorbers, as a damping element of a modern suspension, are most widely used due to a combination of work efficiency, reliability and manufacturability. To perform its function, the shock absorber must convert vibrational energy into heat. The amount of energy absorbed depends on the mass of the car, the stiffness of the spring and the vibration frequency.
The shock absorber consists of a cylinder filled with a special fluid along which the piston moves. The piston itself is connected to a rod of circular cross section, which, in turn, is attached to the car body with its upper part. Small diameter holes (valves) are made in the piston through which fluid passes. In order to increase resistance to fluid flow, they are spring-loaded.
The shock absorber is connected to the suspension arm or axle beam. The part is fastened through an elastic connection - silent block.
The principle of operation of dampers is based on the displacement of fluid by a piston through calibrated holes. In various modes, fluid is displaced through openings of different diameters. Due to this, the oscillations are absorbed both during compression and during rebound.
The types of shock absorbers
Modern shock absorbers are similar in general principle of operation, but differ in types and design features. From the whole variety of models and brands, there are two main designs that can be distinguished: monotube and twin-tube versions, which also have their own kinds, which we will discuss later.
Monotube shock absorbers are gas filled. Their design provides only one cylinder, in the lower part of which there is a chamber filled with gas under a pressure of 2-3 MPa. This chamber is separated from the liquid by a special floating piston and is designed to compensate for the volume of liquid during compression of the mechanism.
The peculiarity is that the physical barrier between the chamber with gas and oil eliminates their mixing. This allows you to place them at any angle without losing their properties. Most often, monotubes are placed upside down to reduce the unsprung mass and increase ride smoothness.
The main advantage of the monotube design is good cooling due to single walls, the heat is instantly dissipated to the body, which prevents the oil from overheating during very strong spring vibrations.
Monotube shock absorbers are considered more rigid. In practice, it means that the car heels less during high-speed cornering. But when driving on a primer with many small pits, vibration and shock will be transmitted to the body more than with twin-tube absorbers, in addition, they can't withstand blows from stones or other objects, so when the cylinder wall is bent, the piston will simply jam.
Monotube shock absorber gives almost complete freedom to choose a driving style. Careful, active, aggressive or sporty styles - in any of these
formats it will work properly and efficiently. That is why professional race car drivers install only monotubes on their cars.
Summarizing, we can say the advantages of single-tube shock absorbers are the next:
- better damping and stability;
- improved cooling compared to a two-pipe system;
- the ability to install a shock absorber in any position.
- long shock absorber length;
- low resistance to mechanical stress;
- high manufacturing costs due to the use of better seals and materials for the housing.
It is logical that they have two cylinders in their composition, placed one inside the other. The inner cylinder consists of oil and a piston connected to the suspension arm rod. The outer cylinder is a compensation tank partially filled with air. It is designed for liquid that is displaced by the stem.
Twin-tube construction provides a softer damping due to low gas pressure. This creates a feeling of greater driving comfort. With all its simplicity and cheapness, it is great fit for the usual urban driving.
The main disadvantage of this type is overheating. Double walls are a thermos for oil - it quickly heats up and slowly cools. Boiling oil occurs when driving on rough roads at high speeds. The shock absorber changes its properties, it is not able to damp vibrations and the car begins to swing. In this mode, it will not work for a long time, and dampers will require frequent replacement.
Twin-tubes cannot be installed at an angle of more than 45 degrees to the vertical, otherwise the air from the compensation chamber may enter the main one. This leads to the cessation of damping, as a result of which the part will not work. The same condition applies when transporting and storing two-tubes.
Attention! In conditions of active driving or driving on bad roads, the two-pipe view significantly loses its effectiveness: car controllability, its directional stability (entry / exit from the turn), braking properties, the likelihood of skidding on wet roads increases, etc.
As a result, when choosing twin-tubes shock absorbers, we get the following advantages:
- simple design and low manufacturing cost;
- low internal pressure (in case of leakage of a small amount of oil through the stuffing box, performance remains);
- soft damping of blows of a suspension bracket;
- better resistance to mechanical damage.
- foaming of oil after prolonged use and, as a result, reduced damping efficiency;
- insufficiently effective cooling;
- Installation, storage and transportation of the shock absorber is made only in one position.
Combined (hybrid) shocks
In an effort to combine the advantages of monotube and twin-tube shock absorbers, manufacturers began to produce combined shock absorbers. The design of such shocks is similar to the twin-tubes, but the external cylinder is not filled with air, but with a special gas under pressure up to 3 atmospheres.
The advantages of such shock absorbers include high efficiency, a simple manufacturing process and, as a result, low price. They also keep their small size and, among other things, at high temperatures, they can save their original data. In them, the formation of an emulsion does not occur. However, the combined shock absorbers adopted both the advantages and some of the disadvantages from previous types of shock absorbers.
Starting from the middle of the last century, the driver could choose the mode of operation of his suspension. Most often, the choice was between sports, comfortable and intermediate modes. Nowadays, the electronics themselves determine the state of the road surface and speed and, depending on the information received, set the optimal settings (the function of self-selection of the desired mode also has not disappeared).
The most common are such variations of adjustable shock absorbers:
- hydromechanical adaptive system with additional valve
Koni offers its own automatic suspension adjustment. Depending on the suspension oscillation frequency, the valve opens, bypassing the liquid and making the shock absorber softer. Thus, on a flat road, shock absorbers remain stiff, preventing the body from healing in corners, and when entering a broken primer, where the wheels begin to jump, the valves in the shock absorbers open, providing a smoother ride.
- regulation with electromagnetic bypass valves
Monroe offered its vision for an automatically adjustable shock absorber. The company's designers developed a system with electronically controlled bypass valves. Receiving a signal, the solenoid built into the valve changes its cross section, making the shock absorber more rigid or soft. Depending on the model, the system is either manually controlled when the driver can choose one of several modes, or works as adaptive, automatically changing the stiffness according to the readings of the sensors.
- use of a special (magnetorheological) fluid
The idea is based on the properties of a magnetorheological fluid, a colloidal solution of ferromagnetic particles in oil. Under the influence of a magnetic field, the viscosity of such a fluid changes smoothly. It is enough to place a magnet in the piston - and now the system is ready. This design has a higher speed compared to a conventional electric drive, is not afraid of accelerations, is less sensitive to heat and allows the use of complex valve systems, which improves the overall quality of the shock absorber.
Unfortunately, such a scheme also has drawbacks. Magnetorheological oil loses its properties over time and is also very expensive. But the list of advantages allowed precisely this type of shock absorbers to take their place in the fastest and most expensive cars, for example, Ferrari, Lamborghini, Range Rover, Audi, Cadillac.
At the moment, adjustable shock absorbers and active suspensions are not a big exotic for mass-produced cars. Many powerful modifications have this type of suspension as standard. Such systems are still too expensive for mass application, but no space technologies are observed in them, and their appearance in the mass segment is only a matter of time.
Sports shock absorbers
Today, auto parts stores offer sports shock absorbers from a wide range of manufacturers. There is no shortage in this product. Instead of oil, gas is pumped into them under a pressure of 28 atmospheres. They cost significantly more than standard ones. Depending on the particular manufacturer, the price difference can reach several times, however, if you mainly have to drive on suburban highways, the costs will pay off.
Sports shock absorber struts have significantly greater rigidity and shorter strokes. As a result, the suspension of the car is more elastic and energy-intensive.
The installation of such parts instead of the factory ones allows to improve handling. The car better “holds” the road and fits into corners at a higher speed, while the vehicle is much less inclined. Due to the short stroke of the rod when installing sports racks, shortened springs are also used, as a result, clearance is reduced. This factor is important to take into account, because the cross-country ability of the car will suffer from it, which means that going to the forest or to the lake on a picnic will make you to choose the road much more carefully.
Shocks with Reservoirs
Contrary to popular belief, the external reservoir on a shock of this type isn’t made to hold extra shock oil. Its purpose is to house the extra needed air space during a shocks compression cycle. Typically this is not air at all, but nitrogen. It will hold some additional fluid as needed, but this shock is designed differently from most other shocks in that the entire main shock body is completely drowned in shock oil.
All shock absorbers, regardless of the type, need some amount of dead air space to allow them to work properly. Standard shocks have dead air at the top of the valve body or utilize a twin-tube model for the needed expansion.
As mentioned previously, the external reservoir is used for storing the extra needed air space. They are typically connected to the main shock body via a reinforced flexible hose or a metal tube of sorts. The trick here is that as the shock compresses, the extra oil is forced through the connecting tube, into the reservoir body and forced against the pressurized air or nitrogen.
In theory, if the oil and the air are not allowed to mix (that’s the way the engineers designed this), the shock will dampen at a far more consistent rate regardless of the frequency of the shock compression/rebound cycles, because the oil cannot aerate. Not to mention they look cool.
The dampening provided by standard shock absorbers is provided by the valving system being located at the head of the shock piston, which determines the dampening rates. Bypass shock absorbers aren’t all that different in that aspect, but they do add to this standard method of dampening via valving. How? Bypass shock absorbers add the component of external metering valves that are completely adjustable with spanner wrench for changing the rebound and compression of the shock.
Other major aspect of bypass shocks is their oil-looping design. As the piston is compressed into the body of the absorber, the oil is pushed through the external bypass tubes and looped back underneath the head of the piston. Transversely, under rebound, the fluid does the same thing, only in reverse. This entire process is metered and dictated at an adjustable rate defined by the external, adjustable check valves. Depending upon make and model, some bypass shocks can offer multiple tubes to the shock body, typically one for rebound and one for compression. Some of which have multiple, adjustable check valves to control the metering of compression and the metering of rebound.
Adding fuel to the fire is another reason why bypass shocks are the best of all dampeners is because they’re not only velocity-sensitive like all other shock absorbers, but they are also position-sensitive as well. What does this mean? Simply put, these shocks can use a variable metering system that allows the shock to offer a much softer rebound and/or compression rate initially, and increase the dampening effect as the compression or rebound increases, similar to progressive coil springs. The really cool part? If you have the cash, all of these aspects of a bypass shock can be built to your needs and adjusted based upon the type of wheeling you do.
Let’s not confuse these air shocks with those old load-carrying air shocks that your Mullet-wearing step-brother installed on his ’72 Camaro. These shocks are a combination of a shock and a spring, allowing you to ditch your coil springs or leaf spring as well as your shock absorber and replace it with one unit. They can be identified by their large 2” or larger shafts, and look a lot like coil-over shocks without the coil springs. Generally speaking, the larger the shaft, the more load-carrying capacity this shock has.
Air shocks are cheaper than coil-over shocks (about half the cost, somewhere between $200 and $400 each), but require a link suspension to locate the axle. So, if you are considering a leaf-to-air shock (or coil-over for that matter) conversion, you will need to factor in those costs too. Currently, all air shocks are emulsion style shocks (the body is filled and charged with both oil and nitrogen in the same cylinder) and not a floating-piston style, which is ultimately a superior shock design. Cost and complexity are the big inhibitors here and the reason why they don’t exist today.
For the most part, air shocks are intended for use with light and medium weight vehicles, and you will need to consult an expert on determining what load carrying capacity air shock to run on your rig.
Keeping its basic design, shock absorbers have now become a high-tech component with electronic control, indispensable for creating various “smart” suspensions that adapt to the road surface and driving mode. In addition the variety of shock absorbers for tuning is very large. But let's not discount the old proven twin-tube shocks: as long as there is a fleet of budget cars, inexpensive "ordinary" shock absorbers will always find a use.
Signs of malfunction of shock-absorbers
During use of the car in real operating conditions, the shock absorber steadily loses the specified performance characteristics and, in the end, becomes unusable. Signs of loss of serviceability of the part are:
- loss of tightness - this implies leakage of the working fluid. Typically, a leak is a result of wear or damage to the seal or shock absorber bush. Any damage to the stem surface can result in this. Damage to the stem can be due to corrosion, as well as wear or destruction of parts such as anther or rebuff buffer.
- increased friction between the rod and the guide and between the piston and the cylinder;
- change inherent in the manufacture of characteristics, which is the most common defect. It can be due to several reasons: breakage or deformation of valve system parts, loss of the specified qualities of the working fluid, gas leakage from gas-filled structures, when working in extreme conditions - overheating, leaky fit of valves during manufacture;
- knocking, noiseness, the cause of which may be damage or failure of the valves, it can also often be the result of defects in the joints of the independent suspension or silent blocks.
- low position of the body in relation to the wheels;
- incorrect selection of the shock absorber when replacing it.
Diagnostics of shock absorbers
There is no universal way to diagnose dampers. In each case it has different approach. We want to give four main diagnostic methods:
1. Visual inspection
A simple, cheap, affordable, reliable and quick way. If you notice darkening from oil and smudges on the surface of the shock absorber, you can talk about the loss of its tightness.
If there is any doubt about the origin of spots and smudges, it is necessary to thoroughly wipe the shock absorber surface dry and repeat the inspection after a couple of days of operation.
A worn or damaged boot or bump can cause damage to the shock absorber rod. Inspection of these details is given special attention.
The shock absorber fastener elements must not be deformed or damaged by corrosion, and the silent blocks in the lower hinge must be intact, without visible signs of destruction.
Tire condition - an indicator of the state of the suspension. Uneven tread wear spots are one of the signs of shock absorber malfunction.
It is important to carefully inspect the shock absorber rod. This can be done on a device removed from the vehicle. The stem should shine with a perfect mirror surface. If this is not so, then the piston stroke is absent and the shock absorber does not perform its functions at all, and it must be replaced. If traces of clips or stains from corrosion are found on the polished part of the stem, the shock absorber must also be replaced.
2. Test for rocking the car
The method is simple - to rock the car, alternately pressing the corner (bumper or fender). If the shock absorbers are serviceable, the machine must make only one return movement, without swinging. There should be no knocks.
3. Assessment of car behavior on the go
To do this, the car is accelerated to 70-80 km / h and watch how it behaves. “Yawing” on small bumps in the road, lateral and longitudinal buildup, a decrease in the car’s reaction to the steering wheel turn, deterioration of stability - all this is evidence of problems with shock absorbers.
4. Poster diagnostics
It is carried out on special vibration and test benches. The latter is tested for damping force. Experts will examine the test results and make informed recommendations. The disadvantage of this method is the high cost and complexity.
At the stand, you can check new shock absorbers before mounting them on a car. This will save significant money if you get a cheap imitation in a bright box with the logos of a serious company. Diagnostic costs will pay off with interest.
If the shock absorber fails, it should be replaced as soon as possible, since further operation of the car is fraught with damage to other parts of the suspension, steering and brakes.
The consequences of malfunctioning of shock absorbers
As it has already become clear, shock absorbers, like any other part, are also subject to wear. Untimely replacement of these parts has far-reaching consequences. In the event of a malfunction, the length of the braking distance of the machine increases, the adhesion of the tires to the road is broken. A car whose wheel does not have reliable contact with the road cannot effectively brake, accelerate or turn - it becomes difficult to control.
The danger of the situation is also that wear often occurs without obvious signs. The driver adjusts to a gradual change in the behavior of the car, gets used to its new characteristics, but in an acute situation on the road, it unexpectedly realizes for itself that it is difficult to cope with driving.
And the thing is that the more worn out the shock absorbers of the car, the longer its wheel is in the air, and not in close interaction with the road. The consequence is an increase in braking distance, a decrease in the speed of trouble-free cornering.
In addition, the negative consequences will affect electronic security systems. Their sensors are tuned to track the behavior of wheels that roll across the surface rather than spinning in suspension. Frequent response of these systems in normal situations is an additional signal that indicates insufficient contact of the wheels with the road.
But if you are not afraid of the potential opportunity to get into an accident, you can name a number of other problems that the malfunction of shock absorbers can lead to:
- Hitting the bottom and damaging the elements. For example, when overcoming a “lying policeman” or a bump, a car on springs can jump up and, in the reverse movement, hit the bottom of an obstacle, which will lead to damage to other parts;
- A malfunction in the suspension. If you drive a car with malfunctioning or missing shock absorbers, over time there will be problems with the silent blocks, bushings, ball and other suspension elements that run the risk of failure.
In the case of a car equipped with ABS and ESP systems, the main threat is the lengthening of the braking distance. The system reduces braking power whenever the wheel loses traction. In practice, this may well lead to the fact that the car simply can not slow down before the intersection.
The setting of the electronic control unit ESP corresponds to the factory settings of the suspension. Therefore, if the shock absorbers are worn out, then the ESR reaction in a difficult road situation may be inappropriate.
We hope these reasons will be enough for you to conduct timely diagnostics of shock absorbers.
At what mileage do shock absorbers need to be changed?
The replacement period for shock absorbers largely depends on operating conditions, the condition of the remaining suspension elements, as well as tires and rims. For example, a worn spring reduces the life of dampers by more than half. And on average, the same KYB recommends changing shock absorbers every 70 thousand km, and also every 20 thousand km of mileage to undergo diagnostics. Monroe calls about the same numbers.
And also about the service life. To increase it, try not to set records on the car for transportation of excessive loads or in off-road racing. With the onset of cold weather after starting off, try at least the first 500 m to move slowly, so that the shock absorbers warm up a bit and come into operation.
How to choose the proper shock absorbers
The most important thing that affects your choice is your driving style. Let's go back to the types of shock absorbers. Oil-type shock absorbers (two-pipe) are installed on low-cost models of cars, the owners of which usually drive measuredly and calmly.
Gas-oil shock absorbers (monotube) differ from the first ones not only in their price (about 20% more expensive on average), but also in the possibility of more precise control of the car at different speeds. When driving fast, the oil filling foams heavily, making the first shock absorbers almost useless. Gas-oil shock absorbers are the best choice for price and quality. This option is good for those who like a comfortable ride on rough roads, and also do not mind "lighting up" at high speeds.
In addition, it is necessary to pay attention to the manufacturer, even the most experienced driver with vast experience and all the proper tools will not make a poor-quality product work correctly. Since it is not worth saving on shock absorbers, then not for advertising purposes, but for your further safety, we recommend choosing from the following manufacturers:
- Boge (Germany) produces gas and hydraulic shock absorbers and supplies them to automobile plants "BMW", "SAAB", "Volvo";
- **Bilstein (Germany) **produces mainly shock absorbers for sports cars;
- De Carbon (France). The company, named after the founder and author of the first gas shock absorber De Carbon, produces gas and hydraulic shock absorbers;
- Gabriel (USA) ranks second in the sale of shock absorbers in Europe as spare parts, produces hydraulic and gas shock absorbers;
- Kayaba (Japan) supplies its products to many Japanese car assembly plants, and produces shock absorbers for European cars;
- Koni (Holland) specializes in the production of expensive high-end shock absorbers. They are put on cars Porsche, Ferrari, Maserati. In the West, the company gives a lifetime warranty on its products;
- Monroe (Belgium) - a leader in the production of shock absorbers as spare parts. It produces hydraulic and gas-filled shock absorbers of low pressure. As standard, Monroe shock absorbers are installed on Volvo cars;
- Sasch (Germany) supplies shock absorbers as spare parts, as well as to car assembly plants. They are installed on production cars BMW, Audi and others.
Brands recommended by our mechanics*
Usually the technology of replacing shock absorbers does not raise questions among specialists in the field of car repair. However, it must be remembered that since dampers so significantly affect traffic safety, you cannot make mistakes when replacing them. Be sure to study all the recommendations of the automaker, because the replacement process may have things associated with the features of a particular brand of car. But basically, all the instructions and tips for dismantling and installing are universal in nature, relating to almost all brands of cars.
Manufacturers of suspension elements insist that the replacement of car shock absorbers should occur exclusively in pairs. No company will hold responsibility for your installation of only one suspension element. The reason is quite simple. If, for example, the shock absorber on the front left wheel is already quite worn out, and you put a new one on the right, then the car will become a roll. A large load will come to the newly mounted rack, and it will fail very quickly. In addition, the car will be completely unpredictable during maneuvers and sharp braking.
But back to the installation, the necessary procedure before installing new shock absorbers is to pump them. This is important to do because air can enter the interior of the part, for example, during transportation. If it is not removed, then it will affect the correct operation of the mechanism. And the presence of air will be expressed in the appearance of noise and knocks when the car is moving, and if the driver does not take operational measures, the piston system of the shock absorber will fail, which will causes additional costs.
The pumping technology is very simple, but the removal of air from classic, twin-tube shock absorbers is somehow different from the removal of air from other designs.
In the first case, it is necessary to slowly push the rod all the way into the shock absorber mounted vertically, i.e. until the working surface of the stem protrudes by 2–3 cm. After holding the stem in this position for 2–3 seconds, let it go and wait for it to come out completely. To ensure complete removal of air, you need to repeat the procedure 2-3 times.
For monotube, combined, adjustable shock absorbers, they should be turned with the stem down and the stem should be pushed without jerking until it stops. After holding the rod in its lowest position for a couple of seconds, you should turn the shock absorber without changing the position of the rod, and hold the rod for another 5-6 seconds. Then the stem extends up to its maximum position. This procedure should be carried out 2-3 times, and then you have to check the operability of the mechanism.
Any type after pumping is checked in the same way: sharp, short presses are made on the stem located in the highest position, the stem must respond to them with smooth movements up / down. After pumping, it is necessary that the shock absorber is in the stock position up to the mounting on the car.
In addition, all experts advise to pay attention to the condition of rubber anthers. If they are not present or they are damaged, then dirt can damage the piston surface in two ways, and then damage the shock absorber seals, which automatically means gas leakage or oil leakage.
Replacement must be approached comprehensively
Very often, replacement of shock absorbers does not bring the expected results, since elements such as pillows, pillow block bearings and metal rubber bushes are damaged. After all, these details have the same operational resource as the shock absorbers themselves. Therefore, when replacing it, it is better to comprehensively change the parts that work together with the shock absorbers, only then can we say with confidence that the suspension returned to its original parameters.
Well, we hope this article has been useful to you and you have learned something new. As a result, we would like to bring the following:
The shock absorber can be definitely called the most important suspension component of any car. Without it, riding would be simply unbearable due to the continuous vertical buildup of the car body. It plays the role of a kind of damper, damping the oscillation of springs or torsions. This mechanism is of great importance for your safety while riding, as they provide reliable contact of the wheels with the road.
The shock absorber itself can be conditionally divided into a cylinder and a piston. Inside the cylinder, depending on the modification, there are chambers either with oil and gas, or with oil and air. In both cases, the piston moves inside the cylinder, rising and lowering.
In the first case, the piston moves with resistance, which is created due to the flow of oil through the valves to another chamber. In the second, the piston resists the pressure exerted by the compressing chamber with gas. It turns out that due to these resistances a smooth, measured movement of the piston occurs, which as a result leads to the quenching effect.
Today, there are a large number of different types of shock absorbers, each has its own characteristics, which must be taken into account when choosing these spare parts.
It is not difficult to determine the problems associated with the operation of the shock absorber: when it hits the bumps, the car shakes noticeably, typical taps are heard. The main problem associated with the failure of this device is that this process occurs gradually, with the exception of gas-oil shock absorbers, which due to their design can fail immediately.
Worn shock absorbers can lead to an increase in stopping distance, tire wear, and poor driving performance, which in an emergency can significantly affect its outcome.
On average, the life of shock absorbers is about 70 thousand km, but you should not forget that every 20 thousand you need to do diagnostics to be sure that your suspension is working.
It is not worth saving on the purchase of these spare parts, therefore, when choosing a new set of shock absorbers, it is worth considering their manufacturer. You can completely trust the following brands: "Monroe", "Sasch", "Koni" and others that were pointed out in the article.
It is also worth considering that if you want to install shock absorbers yourself, you need to familiarize yourself with the pumping technology in detail, as this can significantly affect the safety of your movement.
- How Car Suspension Systems Work, yourmechanic
- Differences/Benefits of a Monotube & Twintube Shock Absorber, Also Info on Inverted, clubrsx
- The Best Shock Absorber Brands, ranker
- Selecting the right shock length, superiorengineering
- Shock Absorber Symptoms, Function & Solutions, mechanicbase
- The hidden danger of worn out shock absorbers, tenneco
- 6 noticeable symptoms of worn shocks, firestonecompleteautocare
- Car shock absorbers - The importance of knowing them well, sgcarmart