Shocks and Struts- What they do. When to change them. How to buy them.

Shocks and struts do far more than give you a comfortable ride. They affect your car's stopping distance and ultimately your safety. They also play a significant role in tire wear and steering control. Yet they are the most overlooked maintenance item in car repair today. Why? Because they're expensive to replace and most drivers aren't aware of their importance in safety and steering control.

What shocks do

We've all seen cartoons with characters on Pogo sticks. Now imagine your car with a Pogo stick at each wheel. You drive down the road and your tires hit bumps or potholes. At each bump, the spring compresses and then rebounds, sending the corner of your car soaring upwards. Launching that kind of weight upwards literally lifts the tire off the pavement, as well as shaking the fillings right out of your teeth. Worse than the initial rebound however, are the follow-up rebounds. Because as soon as the car reaches the peak of its first rebound, it begins its descent back onto the spring, compressing it a second time. This cycle of spring compression and rebound continues until the energy of the bump is dissipated. This is known as spring oscillation.

So the first job of a shock is to dampen or eliminate spring oscillation. Constructed just like a doctor's syringe, shock absorbers incorporate a plunger, a cylinder, and a non-compressible liquid. The bottom of the shock absorber contains the fluid filled cylinder and is attached to the lower control arm of your car, forcing it to take the first hit from the bump. The top end of the shock absorber is the plunger and is attached to the body of your car. As the plunger gets pushed in, it forces fluid out of the cylinder through a small valve, limiting the rate of compression of the spring. When the spring begins its rebound, the plunger sucks the fluid back into the cylinder. The valve in the shock allows the fluid to flow out of the cylinder faster than it can get sucked back in. That's how a shock absorber works to control spring oscillation, or rebound

Over thousands of miles, the seals around the piston and the valve itself begin to wear. Worn piston seals allow fluid to bypass the small opening in the valve. Instead, the fluid actually flows around the piston, provides far less resistance to spring compression. A worn valve allows too much spring compression and allows spring rebound to occur too quickly. The result? Spring oscillations.

The bottom line is that it's the shock's job to eliminate tire and car bounce and keep your tires firmly in contact with the pavement. A tire that's bouncing can't stop your car quickly. Even on flat pavement, an aggressive stop tends to lift the tire and cause bounce. Worn shocks increase that tendency. In fact, a University of Cologne study has shown that a single worn shock can increase your stopping distance by as much as 4 feet! That can mean the difference between life and death. A worn shock also affects steering control simply because the tire spends less time in contact with the road. Ever drive down a bumpy road and feel like your car wants to change lanes? That's the symptom of a worn shock.

What the heck is a strut?

The easy answer is that a strut is a fancy name for a shock absorber. But it's not quite that simple. Car makers use struts as part of the structure of your car. They support the entire wheel assembly of your car. You can drive without a shock absorber. You cannot drive without a strut. Because they are part of the support structure, they are built sturdier. A strut piston is usually more than twice the diameter of a shock piston. The strut housing is sturdier as well because it supports the spring. That's why struts are usually 25-50% more expensive than shocks.

When to change them?

It's difficult to give a hard and fast answer to this question because it all depends on your particular driving conditions. If you drive on country dirt roads, your shocks/struts will wear out faster than continuous highway driving. Shock/strut manufacturers recommend replacement at 50,000 miles. However, most shocks/struts are still going strong at that low mileage. 80,000 miles is a more realistic benchmark. On the extreme end, few shocks/struts make it beyond 100,000 miles, no matter what your driving conditions. But rather than rely on a mileage benchmark, I suggest you and your auto mechanic rely on your car's actual handling.

Here's what you'll notice in terms of handling if your shocks/struts are worn:

1)Your car will nose dive at stops.

2)On bumpy roads, you'll have to fight the steering wheel to keep the car in its own lane.

3)Your tires begin to show a "cupping" pattern-almost as if someone was "scooping" little pockets of rubber from your tire.

4)A less comfortable ride. Dips in the road seem more noticeable. Bumps seem to "rattle" your car more.

Here are the physical signs of shock/strut wear:

1)Visible signs of oil leakage between the chrome piston and the body of the shock/strut.

2)Cracked or disintegrated rubber bushings where the shock/strut attaches to the vehicle.

3)Advanced rusting on the shock/strut cylinder, or pitting on the chrome piston.

How to Buy Shocks/Struts

There are three main manufacturers of shocks/struts—Monroe, Gabriel, and KYB. The latest trend in shock/strut design is a "road sensing" construction. Road sensing shocks/struts "adapt" to individual road conditions. One road sensing design incorporates a "smart valve" that responds to road conditions by opening or closing the orifice size. Another design incorporates grooves in the piston, allowing fluid to bypass piston at the beginning of the stroke but closing off the bypass at the end of the stroke.

Private label versus name brand

In addition to the regular and road sensing designs, two of the three manufacturers offer additional designs for private label to the aftermarket. For example, if you take your car to a nationwide automotive repair chain, chances are they purchase their shocks/struts in bulk from one of these two major manufacturers. In some cases, these private labeled products are ECONOMY versions of the manufacturer's branded line of shock/struts. They may carry the same lifetime guarantee as the name brand version, but they are not built with the same materials or to the same specs as the premium name brand parts. They will not last as long. Since the guarantee does not cover the labor for a warranty replacement, those shocks/struts may ultimately cost you far more than the original difference in price between private label and name brand. If you plan to keep your car for a long time, it's wise to invest in a name brand shock/strut, rather than a private label brand.

What else to look for?

1) Strut Mounts-All struts are bolted into a strut mount which then fastens to the body of the vehicle. Strut mounts usually incorporate a rubber cushioning material and the upper bearing. Both the strut mount and the bearing begin to deteriorate at around 80,000 miles. Make sure your repair shop examines the condition of the strut mount and upper bearing before installing the new strut. If they suggest a new strut mount or bearing, you should follow their advice. However, aside from the additional cost of the strut mount or bearing, there should be no additional labor to replace the mount. You've already paid to remove the strut from the mount.

2) Stabilizer Links-Some car manufacturers attach the stabilizer links to the strut assembly. If your car has that design and you have worn stabilizer links, this is the time to replace them. The technician has already removed one end of the link to get the strut out. The charge to remove the other end should be minimal.

3) Alignment-Proper alignment is critical to steering and tire wear. However, some repair shops offer strut/shock packages that either don't include an alignment, or claim that you don't need one because of their procedures. Those shops use an inexpensive tool that allows them to return your alignment to "close" to where it was before the strut installation. However, those tools only measure camber (the inward or outward tilt of the tire) and they are not as accurate as a real alignment. Once you've invested hundreds of dollars in new struts, it's not a cost effective decision to skip the alignment.

Can you do this job yourself?

Technically yes. But in reality, compressing the strut spring is dangerous business. If you really want to change your own struts, here's the safest way to do it.

1) Buy an alignment tool-Purchase a set of Tool Aid #61800 bubble gauges, or a set of Thexton #447 alignment gauges. Attach the alignment tool to the rotor and center the bubble. Then, noting the locations of the attaching bolts, remove the entire strut assembly.

2) Take the strut assembly to an auto parts store that has a machine shop or one that offers strut service. If you can't find one, talk to a repair shop and ask how much they charge to compress the assembly for you. The going rate is somewhere around $15 each.

3) Reinstall the new strut/spring assembly into the vehicle and re-attach the alignment gauges to the rotor. Move the strut/steering knuckle in or out until you re-center the bubble.

Strut/Shock Tips

Front struts/shocks wear faster than rear struts/shocks.

Always replace struts/shocks in pairs on either the front or rear.

The old bounce test for shocks (get the car rocking and makes sure it doesn't rebound more than 1 times) doesn't apply to struts. If an auto shop tries to sell you struts based solely on this test, find another shop.

New struts/shocks cannot compensate for worn springs. If your car "bottoms out" on large bumps, ask the shop to check your vehicle's "ride height" before doing a strut replacement. If your car needs new springs, have it done at the same time as strut replacement. The labor is already paid for at that point.

Monroe now offers complete strut packages that include the strut, a new spring, and a new strut mount. If you're planning on replacing these parts, ask the shop if this might be a less expensive option than buying all the parts separately. It might save you some labor costs.

If your vehicle is equipped with air shocks, you do NOT have to buy replacements from the dealer. Try these vendors: www.suncoreindustries.com, www.strutmasters.com, www.shockwarehouse.com, or www.rockauto.com.

© 2007, Rick Muscoplat

Read More......