The role of shock absorbers and struts is fairly simple. On any vehicle, there is both “sprung weight” and “unsprung weight”.
Unsprung weight is the weight of the tires, steering knuckles, brake assemblies, and the suspension members connecting these to the rest of the vehicle.
On a vehicle with solid front or rear axles, both of these will be unsprung weight. While the tires absorb some vibrations, the shocks and struts absorb the rest and prevent bouncing, vibration, and harmonic resonances from developing from road forces.
Costs of Shock and Strut Replacement
Presented below are some estimates on the shock and strut replacement cost for some common vehicles using $100 an hour as a labor rate:
- 1995 Ford F-150 with a 4.9-liter engine
The labor time to replace front shocks is 0.8 of an hour. A pair of factory front shocks costs about $122 and a pair of Gabriel shocks costs about $48. The total cost to replace shocks would be about $202 using OE parts, or about $128 using aftermarket parts.
The labor time to replace the rear shocks is 0.7 of an hour. A pair of factory rear shocks costs about $112, and a new shocks price (a pair of Gabriel rear shocks) would be about $48. The total cost to complete the job would be about $182 using OE parts, or about $118 using aftermarket parts.
- 2006 Jeep Grand Cherokee with a 5.7-liter engine
The labor time to replace the front struts is 2 hours. A pair of factory struts costs about $206, and a pair of KYB struts costs about $142. The total cost to complete the job would be about $406 using factory parts, or about $342 using aftermarket parts. The cost of alignment would be additional.
The labor time to replace the rear shocks is 0.5 of an hour. Factory shocks cost about $72, and KYB shocks cost about $86. The total cost to complete the job would be about $122 using factory parts, or about $136 using aftermarket parts.
- 2005 Toyota Camry with a 3-liter engine
The labor time to replace the front struts is 2.4 hours. A pair of factory front struts costs about $346, and a pair of Monroe struts costs about $100. The total cost to complete the job would be about $586 using factory parts, and about $330 using aftermarket parts.
The labor time to replace the rear struts is 2.3 hours. A pair of factory rear struts also costs about $346, and a pair of Monroe struts costs about $106. The total cost to complete the job would be about $576 using OE parts, and about $336 using aftermarket parts. The cost of alignment would be additional.
- 2003 Volkswagen Golf with a 2.0-liter engine
The labor time for replacing the front struts is 4.5 hours. A pair of factory front struts costs about $284, and a pair of Sachs struts costs about $158. The total cost to complete the job would be about $734 using factory parts, and about $608 using aftermarket parts. The cost of alignment would be additional.
The labor time to replace the rear shocks is 0.7 of an hour. A pair of factory rear shocks costs about $216, and Sachs rear shocks cost about $78. The total cost to complete the job would be about $286 using OE parts, and about $148 using aftermarket parts.
In the case of strut replacements, there is also a common aftermarket option of replacing the entire strut, spring, and bearing plate assembly. Usually, this will be about double the price of a strut insert, but as the strut doesn’t need to be disassembled, there are some savings in labor costs.
One drawback of cheaper options is that good OE parts (most notably, the spring ) are replaced with sometimes less well-built parts. As with many things, going with an established brand and taking the parts warranty into consideration are good practices.
Shock and Strut Replacement
Sprung weight is the whole of a vehicle that is supported by the springs. Driving down the road in whatever conditions, the springs absorb the road forces and the shocks and struts dampen and control those forces and prevent them from excessively affecting the sprung weight.
Without shocks and struts, the sprung weight would bounce and sway pretty freely. If the shocks or struts are too stiff, then, excessive amounts of road forces are transmitted into the chassis.
A lot of engineering goes into providing for a smooth ride and optimum handling in a variety of conditions, which depends, to a great extent, on the dampening rates of the shocks and struts.
There was, for a long time, a recommendation that shocks and struts needed to be replaced about every 50,000 miles. This was always more an industry recommendation than a vehicle manufacturer’s recommendation. In any case, it’s much less common to hear nowadays and much less applicable to modern vehicles.
Shocks and struts should be inspected on about the same schedule as other wear items, but it’s common for them to last for quite a long time. Lifespan depends on original build quality and driving conditions.
Sometimes, shocks and struts do begin to fail at around the 50,000-mile mark or not long after. However, it’s also not uncommon to see vehicles with 200,000 miles on them and still running the original shocks or struts without any symptoms of failure.
Shocks and struts are almost always replaced in pairs in order to maintain balanced handling conditions on each axle. Shock absorbers don’t affect the alignment, but in most cases, a vehicle that has had struts replaced will need to be realigned.
The Difference Between a Shock and a Strut
A shock absorber bolts to the suspension on one end and the chassis or frame on the other – connecting sprung weight and unsprung weight. It is a vital part, but also an independent part. If a vehicle’s suspension uses shocks, they can be removed and the vehicle can still be driven (though it will be bouncy and unsafe at speed).
A strut is more complicated. In addition to dampening suspension movements, it holds the spring assembly and establishes ride height.
A strut usually sets the angle of the knuckle at its lower attaching point and often anchors the upper anti-sway bar end. If used on the front of a vehicle, the strut also has the upper pivot point of the steering mechanism built in as a bearing in the upper strut plate.
A strut is integral to the vehicle’s suspension. The part of the strut assembly that typically wears and is replaced is the “strut insert”; the body of the strut that houses the dampening mechanism.
Signs of Shock and Strut Problems
As the shocks and struts are designed to dampen vibration and provide a smooth ride, one of the main signs of wear is a rough ride or vibration problems. If normal unsprung weight vibrations aren’t dampened, they can allow harmonic vibrations to develop in the tires.
These eventually cause cupping in the tread pattern (a specific type of tread wear) which causes more vibrations. Other things such as tire balance or simple lack of tire rotations can also cause that kind of wear, but shocks and struts are a prime suspect.
Noise going over bumps is also a common symptom. Shocks and struts use a pressurized oil in the internal cylinder that the shock piston moves through.
If oil pressure is lost, then, you can get cavitation as the piston works. That’s the generation of air bubbles in rapidly moving turbulent fluid which makes a sound like a thunking noise when heard from the driver’s seat.
Sometimes pressure loss can be seen as external leaks; oil escaping around the seals where the steel piston rod enters the shock or strut body is a sign. Other times, there are no external leaks and the process of elimination is applied.
If a suspension has a noise going over bumps but every other suspension part checks out ok, then, usually, it is an internal issue in a shock or strut.
Another common issue is the slow deterioration of ride quality. On a car that a person drives regularly, it’s very common for this to be so gradual as to be not noticed.
If a car bounces a little more than it should, dives or shudders on stops more than it should, or corners a little rougher than it should, sometimes, the driver is not aware.
Probably, the main time it may come up is when a vehicle is checked for alignment or tire wear issues when a mechanic is likely to check the front end and give the vehicle a decent test drive.
Replacing shocks or struts is not always mechanically necessary. But it can significantly improve the ride and handling of a vehicle.
Where to Have Shocks and Struts Replaced
Replacing shock absorbers is relatively simple work, and replacing struts is something most automotive shops are capable of. Aside from ordinary shop tools, a spring compressor is the main tool needed.
After a strut is replaced, however, an alignment is needed. It’s best to have all the work done by the same shop, so choosing a shop that can do alignments is a good idea.
All the estimates above are priced at book time which is the norm at dealerships and most full-service shops. There are, however, many shops that specialize in tires, suspension, and alignment work.
In many markets, strut replacement is a common and competitively priced job which is often done at a set labor charge that is lower than book time. Many shops will also match competitor’s pricing for the job, so calling around for estimates is worthwhile.
Sometimes, the best choice can be a shop that specializes in the job, has well-experienced suspension mechanics, and has a good familiarity with the various brands available and their suitability for specific vehicles.