I just completed another suspension overhaul, this time on the X5. Automotive suspensions haven't changed much in the last 40 years, but cars are lasting longer and longer. And often, when your suspension wears out, it makes the car difficult, if not unsafe to drive.
And repairing your suspension can be expensive and difficult. If you don't have the right tools, such as a spring compressor, well, you really can't take apart a MacPherson strut, at least not safely.
But what does your suspension comprise? And why does it wear out? Well, you may not believe this, but a lot of it is rubber - and what causes it to wear out is your driving style.
Most cars today use MacPherson struts up front, and then a control arm arrangement in the back with coil springs and shocks. This sort of design became popular in the 1970's, and pretty much started to dominate the market by the 1980's.
Prior to that time, most cars used a dual-control-arm setup to provide independent front suspension. Your old Chevy Caprice had this, and many sporting cars (e.g., Corvette) continue to use it today.
And like ball joints, sudden impacts with a curb or the like can egg-shape the tapered hole in the spindle, resulting in the tie rod end coming loose. The threaded nut on the tie rod end is not sufficient to hold it in place. When it separates, catastrophe can occur.
Upper Strut Bearings: I used to make these, as well as integrated spindle assemblies, for GM. The top of the strut assembly attaches to the bodywork of the car though a bearing that is set in - you guessed it - a rubber bushing. These bearings allow the strut to rotate, so the spindle can turn and your car can steer. They are remarkably thin bearings, often with steel races inserted into plastic housings. Yes, the entire weight of the front end of your car rests on a couple of plastic rings and a rubber doughnut.
Strut bearing rarely wear out, but if they do, you would notice the steering getting difficult or feeling grinding noises from the front when you steer. The rubber bushing in the strut bearing might wear out over time (crack, degrade). Many mechanics recommend replacing these when replacing the strut cartridge, but often it is not necessary.
MacPherson Strut: A MacPherson strut is a combination of spring, shock absorber, and suspension link component. By making three components into one, assembly is made easier and overall cost is less. So of course, it was invented by a Scotsman. While these are ubiquitous today in most cars, MacPherson struts do cause some camber change as the car suspension moves up and down. A dual control arm setup, like in the Fiat photo above, keeps the wheel perpendicular to the ground as it moves up and down. A MacPherson strut setup, is more like a tripod, and as the strut expands and contracts, the camber (the amount a tire leans in toward the car) changes.
To some degree, this is not a problem, as sometimes you want camber changes when the car is, for example, cornering. This can actually improve handling. And many manufacturers tweak how the strut changes camber to work this to handling advantage.
One problem with MacPherson struts is that on most cars, you can't adjust the location of the strut, and thus cannot adjust camber. In fact, on most cars today, the only thing you can adjust, in terms of a front-end alignment, is the toe-in, which is adjusted by rotating the tie rod ends in and out.
The problem with a MacPherson strut, of course, is that if the shock absorber part wears out, you have to remove the strut, disassemble the strut, and then install a new shock absorber part (which is either a cartridge, or comprises the entire strut body) and then reassemble and re-install. In a dual-control arm setup, such as the Fiat shown above, the shock absorber can be removed with a couple of bolts, and a new one installed - in a manner of minutes.
So, changing a MacPherson strut can be a pain-in-the-ass. How much of a pain-in-the-ass? This link shows how much. And while changing shocks is something a shade-tree mechanic can do in an afternoon with just a Sears socket set, rebuilding strut assemblies requires a lot more tools (such as a spring compressor) and a lot more risk.
Some backyard mechanics attempt this without the right tools, sometimes with tragic consequences. They try to take apart the strut using the weight of the car as a compression tool, and if the spring lets loose, well, it can take your head off. There is a lot of energy stored in a compressed car spring.
The good news is, the shock cartridges in MacPherson struts can outlast the car. Many last 150,000 to 200,000 miles or more. This is pretty amazing as 40years ago, a set of shocks might last only 30,000 miles, if that. Better seal technology is one reason they last longer. But again, how long they last depends a lot on how you drive. Hit the speed bumps at 50, and no, they won't last long (and your bushings will be shot as well).
The odd thing about modern cars is that in the past, shocks would wear out, but springs seemed to last forever. Today, we do hear about car springs "wearing out" - usually by sagging excessively to the point where the car has weird camber angles and handles funny. It doesn't happen often, but it can occur. If your car is taking on that "low rider" look, worn springs may be the reason why.
Rack and Pinion: Not really a suspension component, but a primary part of the steering gear, the rack and pinion unit steers the front end via those tie rod ends mentioned above. Rack and pinion units don't wear out and get loose like old recirculating ball gear or worm-gear steering "boxes" of days gone by. But they can start to leak over time, as the shaft seals wear. And usually, the only thing to do is replace them, which is expensive and time-consuming.
I replaced one rack on a car I owned, and I suspect that the reason the shaft seal started to leak was that one tire was getting old and hard, and started to vibrate when we drove. It is possible that this vibration worked on the shaft seal over time. It was not that hard a job to replace, but I am in no hurry to do it again.
Most folks never change their power steering fluid. It is hydraulic fluid (usually ATF, Dextron III or the like) and it does not "wear" out per se. However, heat does break down hydraulic fluid over time, and I notice that on my BMWs, the fluid does turn from bright red to black after 30,000 miles or so. I change the fluid at about that interval, usually by removing some fluid from the reservoir and then refilling it, making sure not to get air in the lines.
Sway Bars & Sway Bar Bushings: Independent suspensions allow each wheel to "do their own thing". A sway bar is the step back in the other direction. Essentially a giant torsion bar, it ties the two wheels of the car together so that if the car is swaying in a corner, some of this energy is transmitted to the other side, resulting in flatter cornering. Sway bars rarely wear out, but they attach to the suspension using small ball joints and are tied to the car with (wait for it) rubber bushings. Over time, if you horse the car around, these components can wear as well.
Wheel Bearings: These bear mention in that while not part of the suspension per se they a critical part of the car - they are what makes your car roll. In the olden days, repacking your front wheel bearings was something every boy learned to do in High School. Most cars had tapered Timkin roller bearings up front, and you could take apart the hub from the spindle with little more than a screwdriver and a pair of channel-lock pliers. Pay $1 for a tub of grease, and you could have the whole thing taken apart, cleaned and regreased in about an hour. If a bearing actually failed, it was a simple matter to put a new one in, and the cost was only a few dollars.
Today, only trailers have such wheel bearings. Most modern cars have integrated spindle assemblies or cartridge bearings that have to be pressed in at a machine shop. To reduce rolling resistance, most manufacturers have moved to ball bearings. They are sealed-for-life, and that life is not yours. And these bearings can be easy to damage if you attempt a "DIY" repair.
Hard cornering and overloading can damage wheel bearings over time. You will notice a "roaring" noise from the bearings when they start to fail. Usually they give you plenty of warning when they are about to let go. For most folks, the only choice is to take the car to a shop to have a new bearing pressed-in.
Tires: I saved the best for last. Tires are part of your suspension - in fact, most of it. Tires make the car - providing the handling, ride, braking, traction, and acceleration. How a car handles and feels is 90% the province of the tires. Buy crappy tires, you will have a crappy car. And yet, a lot of people try to go cheap on tires. And given the staggering cost of tires today, it is not hard to figure out why. But while shopping around on price and comparing treadwear ratings is a good idea, buying used tires or recaps is probably a bad bed for a passenger car. And I say this with firsthand experience, as dry-rotted used tires can ride like a steamroller and often be unsafe.
And how long your tires wear is a direct function of how you drive. Hard cornering, hard braking, peeling out, and the like can shorten tire life considerably. Keeping tires inflated to proper pressures is also essential, as low pressures can increase tire temperatures, causing excess wear (at best) and a blowout at speed (at worst).
Throwing $2000 to $3000 at a used car worth only $5000 or so is often not a good idea. Yet a used car needing new struts, brakes, tires, and a few other things (CV joints) can run up such a bill in a real hurry. This is why it pays to have a used car inspected before you buy it. And this is why it pays to think hard before you throw money at a used car on the premise that you are going to get into the Subaru 300,000 mile club.
And it also points out why hot-dogging your car can really wear it out. And yet most people do this on a daily basis, without thinking about it. When you slam on your brakes at a stop sign (as opposed to anticipating your stops ahead of time) you are throwing 4,000lbs of car onto some thin rubber bushings - and multiplying that weight by the rate of deceleration. This type of treatment can shorten the life of your suspension - easily in half.
It is, your choice.