While most drivers have heard of ‘shocks’ (short for ‘shock absorbers’, also called ‘dampers’), few realise what they do or just how safety critical they are. Like all moving parts on a car, shock absorbers become worn over time and need replacing but to the uninitiated it’s not always obvious when they should be replaced. How long shock absorbers last depends on a huge number of variables such as the make/model of car, the mileage driven, the type of road surfaces driven on and the quality of the shocks that are fitted but as a broad generalization 4-5 years seems to be about the average. With that in mind, a typical car might go through 3 or 4 sets of shocks in its lifetime, so it’s reasonable to expect that you’ll have to replace some at some point. Here’s our guide to identifying issues with your shocks and what to watch out for when the time comes to replace them.
First up: what are shocks?
Put simply, the shock absorbers control unwanted movement of the car body by controlling the movement of the wheels. The springs themselves absorb bumps and changes in the road surfaces, but the shocks then control/dampen the movement of the wheels after that. Without them the cars wheels will bounce up and down uncontrollably every time you go over a bump, which is not only uncomfortable, but also dangerous, as it would result in the tyres losing touch with the ground.
In effect, it’s the job of the shocks to keep the tyres in uniform contact with the road. The way they do this varies from car to car, but the principle is the same. In sportier models, for example, the damping is ‘firmer’, which may feel a little less comfortable, but it means that car body movements are more rigidly controlled than they would be in a more comfort-oriented set-up. Most modern cars use telescopic shocks that feature a piston and valve arrangement within an oil-filled tube. These are called hydraulic dampers and as the wheel rises, it shortens the shock. The oil within is forced through small holes in the piston, which slows and controls the movement of the wheel as the spring oscillates. Some more sophisticated shocks have an additional gas chamber within this arrangement to further control and ‘soften out’ the movement. There are also many different types of adaptive or electronically controlled damping systems, in which the firmness of the damping can be altered on the move to suit the road surface or the driver’s preference, but the vast majority of cars make do with fixed shocks.
How to tell if your shocks need replacing.
When shock absorbers wear, they become less effective at controlling the movement of the wheel, ie the damping becomes less and less. However, as the effectiveness of shocks slowly degrades it’s not always easy for the average motorist to realise they could do with replacing. You can visually inspect them within the wheelarches for signs of leakage of their oil (in which case they should be replaced immediately – this is also an instant NCT/MOT fail), but worn shocks don’t always obviously leak externally so don’t rely on that method. Another thing to watch for is scalloped dips in the tyre edges. This is called cupping, and though it can be caused by damage or wear to other suspension components, it is most common with worn shocks.
That’s about it for visual inspection. Next you need to be aware of unusual noises in the suspension, especially over a rapid sequence of bumps. If you hear a rapid, dull thumping sound it’s a good indication that the shock itself is worn (the noise is the sound of the tyre whacking up and down on the road, not the actual shock itself) Other noises to listen out for are knocks and rattles which could indicate shock bushes or other suspension bushes probably need replacement. Worn dampers can also be identified by longer braking distances, more nose dive under braking, poor cornering or the nose of the car more noticeably raising under acceleration, but all of those things are difficult to assess unless you’re acutely aware of your car’s dynamic abilities and how they have changed. Saying that, if you think that the car isn’t as good to drive, or as secure on the road as it used to be, then it’s worth popping along to a good mechanic to have the shocks tested.
A quick and dirty DIY test you can try yourself is to simply push down hard on the wing of the car, let go quickly and see if it bounces. A fully working damper will compress, rebound and immediately settle. A damper that has completely failed is likely bounce a couple of times before it settles again. This is more difficult to ascertain with modern McPherson strut suspension designs but is still worth a go.
Replacing your shocks.
While replacing shocks is not the most difficult maintenance job on a car, we’d recommend that it’s left to the experts unless you’re a dab hand with the spanners and you have tools such as spring compressors to hand. (That said we will have a DIY video guide to replacing them in the coming months). Whether you’re doing the job yourself or getting a professional to do it for you, insist on replacing the shocks in pairs, across either the rear or the front of a car. This ensures consistent levels of damping across the axle. (An imbalance in damping performance left-to-right greater than 30% will result in an NCT/MOT fail).
When fitting them, be aware that some shocks are specifically designed for just one side of the car. When ordering new shocks you should be aware that there could be different types that will physically fit your car. For example a Mk5 Volkswagen Golf, like our project car came as a standard hatchback with standard shocks, there was a GTi version with firmer sports shocks and a commercial version with heavy duty shocks all of which look virtually identical and will all fit but will all offer very different handling characteristics so it’s important to look closely all the technical details when buying new shock absorbers. We would also recommend that you never, ever fit second-hand shocks.
Although you can drive a car on worn shocks, it’s not something you should scrimp on, as they are integral to everything the car does, especially braking and turning. On badly worn shocks, braking distances can increase; a car could ‘skip’ across the road mid-corner over bumps; or it may react in an unexpected manner during an emergency manoeuvre, so at the first sign of an issue, get them replaced.