Whether you are a veteran car buff or a person who rarely peeks under your car’s hood, it’s a good idea to be reminded about suspension maintenance.
At one point while driving recently on the open highway, I noticed that an older sedan traveling in front us was a perfect example of a car that needed shocks. Now how did I know that the car needed shocks and not springs?
Every time this vehicle hit a bump or irregularity on the road it would bounce over the bump and then continue to rock up and down for a few hundred feet down the road. Rather than rebound and stabilize after the road bump, the car just continued to bounce along over every bump. When a vehicle hits a bump or an irregularity on the road surface, the job of the springs in the suspension system is to lessen the impact of a bump to the body/frame and passengers.
The springs also bring the tires back in quick contact with the road surface after being bounced up in the air by a bump. The job of the shock absorbers is to dampen the springs — to help still them after they have done their job going over a bump. That is, shocks keep springs from going boing-boing-boing on down the road. So a mechanical conversation between springs and shocks would go like this: “Hey! Hey!! Wow! B-o-oing! A bump!! Zowie!” say the springs. “OK, OK, we passed that bump now — steady now, time to stabilize,” the shocks respond.
Shock Absorber Function
A shock operates using hydraulics. Basically, a shock absorber is a cylinder attached at the top end to your car’s frame — and the bottom end to an arm of the suspension. Each wheel on a vehicle has its own corresponding shock absorber. The shock cylinder has two pieces that slide up and down over each other, housing a piston (like a toilet plunger) inside.
The piston operates on a principle like the oar in a row boat. Just like you can’t “zip” an oar through the water, that piston moves up and down inside the shock cylinder resisted by a sealed-in amount of oil. When the plunger’s seal goes bad or the shock oil leaks out, that’s when the shock needs replacement. Pretty simple.
Although the sedan that I described observing on the road was certainly not comfortable for the passengers in it — in fact, as the car bobbed up and down, so did the passengers’ heads — it was also hazardous. Shocks and springs affect the safe and responsive handling of a vehicle as well as its comfort.
Shocks and Safety
The Car Care Council points out that on a rough, winding road the driver of a car with worn shocks also in danger of losing control. Weak shocks permit excessive rebound of the wheels, allowing them to become airborne. During this brief period that the tires are in the air, they lose contact with the road surface — and steering and braking control can be lost. If shocks and struts were like tires or windshield wipers, you would immediately know when they’d gone bad. But they’re not.
Shocks wear out gradually over time from normal everyday driving. That’s why you should have your shocks inspected regularly. By the way, the term “struts” that you hear (e.g., “MacPherson struts” on many new cars) means essentially the same thing as shocks.
Now, how often do you replace shocks? If your vehicle has more than 25,000 miles on it, you should be sure to have your auto technician give your shocks an inspection at your next service. However, that does not mean that shocks only last 25,000 miles.
Shocks can endure as much as 40,000 to 50,000 miles — it really depends on the kind or driving that you do. If you tow a trailer, drive a four-wheel drive vehicle over rugged terrain, or drive a ranch road daily, you’re going to get shorter shock life. In addition to continued bouncing or accumulated mileage, other signals of potential worn shocks are: roll or sway on turns; front-end dive during braking and rear-end squat during acceleration; vehicle “bottoming out” (with a thump) over larger bumps.
Though we have focused primarily on shocks to this point, the springs in your vehicle’s suspension also require periodic inspections. Since the springs are designed in variations and sizes of formed “sprung” iron, they are relatively simple. Unlike shocks, springs can sometimes last for the life of a car. However, springs can wear out earlier due to fatigue from heavy-duty use, such as towing or carrying regular heavy loads or extra passengers.
Worn springs typically exhibit their fatigue by allowing the car to sag in the front or rear, or on one side more than the other. Of course, all the vehicle’s springs can be fatigued and that will cause the car to ride lower. Each of these cases of worn springs require replacement, as the any vehicle’s sagging will adversely affect steering, alignment and — most importantly, safety. Any comments or questions?