Thursday, April 15, 2021 Detailed Auto Topics
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Shock absorbers and McPherson struts are often recommended for replacement. The reasons sometime have more to do with profit margins in the shop than actual need of the client.

Why shock absorbers and McPherson struts?

Vehicles today are very complex. Diagnosing problems requires highly skilled and well-equipped personnel. Unfortunately, many shops have failed to keep up. The needed repairs on vehicles are often over their heads.

Selling shock absorbers and McPherson struts requires very little training. Replacing these components is easy and requires little specialized equipment. This makes the sale of shock absorbers and McPherson struts profitable as an add-on sale. A set of struts or shock absorbers will handsomely increase the bottom line.

Who is Shockulla

Shockulla tells everyone they need shocks and struts

Shops that recommend parts, just to make a profit, are a small part of auto repair trade. An example is "Shockulla," a person in business just to sell things. Selling shock absorbers and struts is easy and profitable. This is why Shockulla pushes them.

Manufacturers of replacement parts also profit from selling these components. Advertising misleads a great many folks into needlessly replacing shock absorbers and McPherson struts. Unfortunately, the original shocks and struts they replace are often better than the replacements being installed.

Original shock absorbers and replacements

Vehicle makers use high quality shock absorbers and McPherson struts on their vehicles. Original parts often last more than 100,000 miles. The products "Shockulla" sells are usually selected to optimize the profit margin, rather than the client's vehicle.

Many times a high quality original part is removed and replaced with a much lower quality aftermarket shock absorber or McPherson strut.

What is the difference in shock absorbers and McPherson struts?

The differences in a shock absorber and a McPherson strut are subtle. Shocks merely dampen motion while a strut also acts as a suspension component. For this reason struts are generally heavier in design and may be more expensive than a shock absorber. Over the years, they have both evolved and today the two words are used interchangeably. The picture below shows a strut on the left and on the right is a typical shock absorber.

The difference in a shock and a strut

Some signs that shock absorbers are worn out

Worn out struts and shocks cause excessive bounceWorn out struts and shock absorbers cause a vehicle to bounce excessively. The purpose of a shock absorber or McPherson strut is roughly the same. They design these parts to dampen movement of the suspension, in both directions. 

When the suspension moves down, we refer to it as jounce. When it bounces back up, we call it rebound. Shocks and struts that wear out no longer control jounce and rebound. Excessive bouncing may cause a loss of vehicle control.

Parts of a shock absorber

Shocks and struts use hydraulic force, to control movement. Though there are many designs, basically there is a tube filled with oil. Some also have pressurized gas to keep the oil under pressure. This is referred to as a gas shock and offers some performance advantages.

Parts of a hydraulic shock absorber

The lower end of the shock or strut is attached to the suspension. The upper end is usually anchored to the frame or body through a shaft. This shaft is attached to a piston, which contains valves and is the heart of the shock absorber.

How shock absorbers work

Jounce and rebound are controlled by valves in the shock absorber

When the suspension jounces, the piston moves down in the tube. This forces the hydraulic oil through the jounce-valve. The smaller the valve, the more the shock resists jounce. On a rebound, the piston moves up and fluid is forced through the rebound-valve.

Vehicle makers use many combinations of valves to allow different jounce and rebound rates.  Various valve-rates control ride and handling. More complex designs may use multiple valves, that actuate at different rates.

When do shock and struts need replacement?

When the oil leaks out of the shock or strut, replacement is necessary. Many folks are misled by this. Slight oil near the top of a shock or strut is normal.  This does NOT indicate a need for replacement, unless there are other symptoms. When the entire unit is wet or when oil is dripping, replacement is indicated.

slight leakage does not indicate a bad shock, without other symptoms

shock absorber actually leaking

Shocks and struts can also physically break and require replacement. This is more common in aftermarket replacements than in original equipment parts. The aftermarket shock below, had less than 20,000 miles when the lower mount broke.  Needlessly installing aftermarket shocks may be an invitation to future problems. 

Broken aftermarket shock absorber 

Excessive bouncing when driving is also an indication of worn struts and shocks. The driver is perhaps the best judge of changes in handling. Also be aware that struts and shocks wear out gradually. A slow degradation in handling might be harder to detect, than a sudden change.

When there are no symptoms and shocks or struts are recommended, a second opinion is in order

 Neither shocks, nor struts will make a vehicle lean. Leaning will normally be a spring or chassis problem.

 Neither shocks, nor struts cause a vibration when driving at speed. Vibrations are caused by tires that are not round or out of balance rotating components.

 Tire chopping is rarely caused by worn shocks or struts. Chopped tires result from bad wheel alignment or out of round tires in most cases. Ironically, out of round tires will wear in a chopped fashion and can ruin struts and shocks.

Don't let Shockulla sell you something that is not even as good as what you already have.  If you feel you have a ride or handling concern, have a trusted professional diagnose the actual problem. You may save even more than you realize.

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