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 tyres, steering knuckles, brake assemblies, and the suspension members connecting these to the rest of the vehicle.
On a vehicle with a solid front or rear axle, both of these will be unsprung weight. While the tyres 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 £70 to £100 an hour as a labour rate:
- 1995 Ford F-150 with a 4.9-liter engine
The labour time to replace the front shocks is 0.8 of an hour. A pair of factory front shocks costs about £105 and a pair of non-OEM shocks costs about £40. The total cost of replacing shocks would be about £160 using OEM parts or about £100 using aftermarket parts.
The labour time to replace the rear shocks is 0.7 of an hour. A new pair of factory rear shocks costs about £95, and a new pair of aftermarket shocks would cost around £40. The total cost to complete the job would be about £145 using factory parts or about £90 using aftermarket parts.
- 2006 Jeep Grand Cherokee with a 5.7-liter engine
The labour time to replace the front struts is 2 hours. A pair of factory struts costs about £175 and a pair of non-OEM struts costs about £120. The total cost to complete the job would be about £315 using factory parts or about £260 using aftermarket parts. The cost of alignment would be additional.
The labour time to replace the rear shocks is 0.5 of an hour. Factory shocks cost about £60, and aftermarket shocks cost about £70. The total cost to complete the job would be about £95 using factory parts or about £105 using aftermarket parts.
- 2005 Toyota Camry with a 3-liter engine
The labour time to replace the front struts is 2.4 hours. A pair of factory front struts cost about £300, and a pair of non-OEM struts cost about £85. The total cost to complete the job would be about £470 using factory parts and about £250 using aftermarket parts.
The labour time to replace the rear struts is 2.3 hours. A pair of factory rear struts also cost about £300, and a pair of non-factory struts cost about £90. The total cost to complete the job would be about £460 using OE parts and about £250 using aftermarket parts. The cost of alignment would be additional.
- 2003 Volkswagen Golf with a 2.0-liter engine
The labour time for replacing the front struts is 4.5 hours. A pair of factory front struts costs about £245, and a pair of aftermarket struts costs about £135. The total cost to complete the job would be about £560 using factory parts, and about £450 using aftermarket parts. The cost of alignment would be additional.
The labour time to replace the rear shocks is 0.7 of an hour. A pair of factory rear shocks costs about £185, and non-OEM rear shocks cost about £70. The total cost to complete the job would be about £235 using OEM components, and about £120 using aftermarket parts.
In the case of strut replacements, there is also an aftermarket option to replace 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 labour costs.
One drawback of cheaper options is that good factory components (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 practises.
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, preventing 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, excessive amounts of road force 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.
For a long time, there was a recommendation that shocks and struts needed to be replaced about every 50,000 miles. This was always more of 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 the 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,” which is 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 tyres.
These eventually cause cupping in the tread pattern (a specific type of tread wear) which causes more vibrations. Other things such as tyre balance or simple lack of tyre rotations can also cause that kind of wear, but shocks and struts are the prime suspects.
Noise going over bumps is also a common symptom. Shocks and struts use pressurised 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 go unnoticed.
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.
The main time it may come up is when a vehicle is checked for alignment or tyre 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.
However, after a strut is replaced, 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 specialise in tyres, suspension, and alignment work.
In many markets, strut replacement is a common and competitively priced job that is often done at a set labour charge that is lower than book time. Many shops will also match competitors’ pricing for the job, so calling around for estimates is worthwhile.
Sometimes, the best choice can be a shop that specialises in the job, has well-experienced suspension mechanics, and has good familiarity with the various brands available and their suitability for specific vehicles.