We’ve all been to the repair shop for a routine oil change and walked out with an estimate for thousands of dollars worth of repairs. Of course, the question in all our minds when this happens is “what of this stuff really needs to be done?”.
Well, if your struts are old, chances are you’ll soon be walking out of a shop with a massive estimate wondering whether or not they even need to be done.
To answer this question, let’s start with the basics – a simple description of what struts are and what they do. Then we’ll talk about how struts wear out, and what repairing them involves.
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 (usually a coil spring) – this allows for the wheels to travel up and down on the road without causing the body of your car (and so its occupants) to bump up and down with every divet, crack, bump, or pothole in the road.
A spring on its own smooths out the impact of the road, 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 extends and contracts, trying to find its equilibrium. Think of a person taking a big jump on a trampoline – after the initial jump, it takes a couple ups and downs to come to a standstill on top of the trampoline – the principle is much the same with cars. To minimize this effect, vehicles use shock absorbers.
Shock absorbers (shocks) are just what their name claims – 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 an equilibrium), shock absorbers take the force and use most of it up themselves. The force that does make its way to the body of the vehicle, pushing it up, is absorbed by the shock absorber when the vehicle comes back down for a smooth transition to equilibrium and a normal ride without the trampoline-like oscillations.
A strut is what we usually call a spring and shock absorber combo unit.
Most smaller vehicles (sedans, station wagons, etc.) with independent suspension today use what is called a “MacPherson” strut – named after its inventor. The MacPherson Strut throws another component into the spring and shock combination unit – the swivelling 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. Struts are not often thought of as a normal replacement item – unlike your oil filter, brakes, or spark plugs, which we all know and expect to have to replace. But, like your brakes and spark plugs, they are not made to last forever. Since struts are in continual use as you drive, bearing the whole weight of your vehicle, it should not be surprising that their components wear out over time.
The shock absorber component does its work by using the force of a bumpy road to push a fluid from an internal chamber, through an orifice, and 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 all around it. These seals wear out eventually, 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 absorber can use up.
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, since it is one solid piece of metal that is tempered to be able to extend and contract many times. But, if the shock absorber component is bad, the spring is hit with much more force than it is designed to, and will wear over time to become weaker than it should.
How to tell
Springs don’t usually fail 100%, but if they’ve been subjected to excessive wear and tear (e.g. by driving on rough roads or driving with bad shocks) you may notice the vehicle sagging, or that the ride is not as crisp as it once was. In some states like New York and Pennsylvania, where rust is a common problem, springs may break, causing awful noises when turning or on bumps, steering pull, or worse, but such cases are rare. More likely you will not notice anything as your springs fail, since the changes are very gradual, and since the replacement of springs along with struts is an economical option in todays world, they will likely be replaced before they ever fail.
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. Especially if you can put the vehicle in park and the noise remains while turning the wheel, strut mounts are your number one suspect.
Failed shock absorbers can be harder to notice. With oil-filled struts, external leaks are easy to spot, especially if the leak is rapid. But if it is a very slow leak, it may never be noticed, and with gas-filled struts, external leaks are not identifiable at all. But usually struts don’t fail completely, and usually not all at once. Shock absorber wear creeps up as the internal seals lose their sealing capacity slowly. You won’t notice the difference from one day to the next, but there is probably a minute daily decline in the performance of your shock absorbers as they age.
If the failure progresses to a severe stage, drivers may notice several kinds of problems: too much “trampoline effect”, tire noise and vibration from cupping caused by excessive up/down movement, excessively harsh riding over bumps, or noise on every bump from too much suspension travel. If you car is experiencing these problems, you’ve really gone too long – most struts should be replaced before these symptoms occur.
How long do struts last?
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 included, 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, but of course they have a financial motive for it.
Usually I tell people they can expect around 70-80,000 miles out of new struts. Obviously, the worse your local roads are, the more quickly your suspension components will wear out. If you’ve gone past this timetable, it’s not the end of the world, but chances are if you get your struts replaced, you will notice a marked improvement in ride quality, handling, and even stopping distance..
What is a strut replacement anyway?
Glad you asked. Not all strut replacements are the same. Most basically, strut replacement is only a shock absorber replacement, which involves removing the strut assembly from the vehicle, compressing the spring so the mount can be removed from the top of the assembly, taking the strut cartridge (shock absorber) out, and replacing it with a new one.
But if the shock absorber component is bad, it has probably caused extra wear and tear on the other two components. That is why you will often find that shops will recommend replacing at least the mount along with the strut cartridge. In today’s world, most strut manufacturers make complete strut assemblies that come pre assembled – you get a new shock absorber, a new mount, and a new spring for a fraction of what you would pay for each individually, and you don’t have to pay for the labor for everything to be put together, just for the assembly to be installed.
If you are contemplating having your struts replaced, pay close attention to whether it is just the cartridge that is being replaced, or if the whole assembly is being replaced. At Brakes and Beyond, we use complete strut assemblies whenever possible, because it gives the most complete servicing at the most economical price.
Does it really need to be done?
As a mechanic, this is a question that I am asked all the time. While struts don’t pose the obvious safety concerns that failed brakes might, or the obvious threat of further damage that neglecting to change a timing belt on time might, they do affect both these areas, albeit in smaller ways. 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. And 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. If you can’t, don’t be scared into a repair you can’t afford, but do understand that strut replacement is a normal occurrence, and try to plan ahead for when your struts might come calling.