Rick's Free Auto Repair Advice

Signs of worn shocks or struts

Signs of worn shocks or struts

When to replace shocks and struts

The simple answer is 80,000 to 100,000 miles. Period. If you think yours will last longer, you’re kidding yourself. In fact, most shocks and struts are seriously compromised by the time they rack up 100,000 miles. However, since they wear slowly, driver’s rarely notice.

What happens as shocks and struts wear

• Your stopping distance increases
• You lose steering control.
• You decrease vehicle stability in turns and maneuvers.
• You accelerate the wear on your tires and suspension component

Shocks and struts dampen spring oscillations after hitting a bump. When they wear, they lose their dampening ability, so the tire spends more time bouncing and less time in conatct with the road.

How a worn strut or shock increases stopping distance and decreases stability

When you stop hard, the vehicle weight transfer to the front tires which loads the front suspension, causing the springs to compress. But how much the springs compress is directly related to the condition of the shock or strut. A worn shock or strut allows for more spring compression. Yet, when a spring compresses and transfers body weight to the tires, the contact patch area of the tire decreases, so you have less rubber in contact with the road.

Meanwhile, as the weight shifts towards the front, the rear lifts up, taking more weight off the rear tires, again giving you less traction on the rear tires and forcing a more pronounced nose dive on the front tires. All of which increases stopping distance and decreases stability.

The combination of weight transfer and the smaller contact patch causes oversteer or understeer which compromises vehicle stability.

What wears out in shocks and struts

Most people think that a fluid leak is the only sign of a worn strut. Wrong. By the time you see fluid leaking from the top seal, that shock or strut has been under performing for a long time.

95% of all Shocks and struts contain about twelve spring steel discs in the valve assembly. Six of the discs control the compression rate and the other six control the rebound rate. On average roads, each shock or strut will complete about 75,000,000 compression/rebound cycles. That causes metal spring steel disc metal fatigue which reduces valve effectiveness. If you drive on poor roads with more than average potholes or you drive on dirt or gravel roads, your shocks and struts will wear even faster.

How much do struts costs? See this post

Shocks and struts increase traction and control by dampening spring oscillations

As you can see in the image shown here, the bottom portion otest car strutsf the strut is attached to the steering knuckle and the top portion is attached to the body of the vehicle. When you hit a bump, the bottom portion quickly compresses against the coil spring and into a fluid filled chamber.  When it reaches the peak of upward travel, the strut restricts the decompression by slowing down fluid flow inside the strut.

What is a strut?

The easy answer is that a strut is a fancy name

Image of fully loaded strut assembly showing new strut, new coil spring, new strut mount and new strut bellows

Fully loaded strut assembly

for a shock absorber. But it’s not quite that simple. Carmakers 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 a strut is actually part of the support structure. 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.

Here’s how to tell if your struts are worn

Your car nose dives at stops.

• On bumpy roads, you’ll have to fight the steering wheel to keep the car in its own lane.
• Your tires begin to show a “cupping” pattern-almost as if someone was “scooping” little pockets of rubber from your tire.cupped tire, worn shock, worn strut, underinflated tire
• You’ll notice 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 leaking strutchrome 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.

Most people think you can bounce on a strut and determine it’s condition by counting how many times it rebounds. That’s NOT a legitimate test. Many totally worn struts will pass that test. See this post to learn how to test a strut.

How to Buy Shocks and 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.

Should you buy a name brand shock or strut?

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 chain repair shop, chances are they’ll install a private labeled shock or strut. Those shocks and struts are made by the big three manufacturers, but they’re usually not the same quality. Chains buy economy units in large qualities to get the lowest price, but they charge you the premium price. They won’t last as long. Since the shop’s guarantee doesn’t 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 should you replace when replacing shocks and struts?

1) Strut Mounts-All struts are bolted into a

strut mount

Strut mount

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 stabilizer bar end linksattach 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 replace shocks and struts 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.

Or, buy a complete strut assembly that comes with a new coil spring and strut mount. See this post for more information on strut assemblies

Other 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, KYB and Gabriel now offer 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.

© 2012 Rick Muscoplat




Posted on by Rick Muscoplat

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