Springs and Dampers

Diyers can make vast improvements to their cars' safety, by replacing worn springs and dampers in good time. Rob Marshall details how you can do it at home, with confidence.

You can make vast improvements to your car’s safety by replacing worn components. We show you how to do this at home.

Considering the critical influences that they have over secure handling, road-holding and braking, it is somewhat surprising that the MOT Test is not more rigorous with assessing the conditions of springs and, especially, dampers. Unless there is a problem with their mountings, physical breakages, or severe leaks, they will pass scrutiny. This leads many owners into a false sense of security, because springs and dampers wear-out gradually. Therefore, it is possible for your suspension to pass the annual inspection, when they are way past their best. To put it into perspective, worn (but not leaking) shock-absorbers can increase your stopping distance at 50mph by as many as six metres extra.

SPRINGS What goes wrong?

Although it may not be obvious, coil springs and shock-absorbers turn motion energy into heat. Springs support the car’s weight and work in conjunction with the other components, including tyres, to maintain contact with the road. As they age, springs can sag and corrode, reducing the vehicle’s ride-height and prejudicing its handling and braking capabilities. Should your garage have problems establishing correct wheel alignment and you notice irregular tyre wear, the springs could be the problem, although physical breakage is the most obvious issue.

According to KYB, one of the world’s leading suppliers of springs and dampers to both car factories and the quality independent aftermarket – and our technical partner for this feature – there have been significant increases in the number of speed bumps, potholes and cracks on UK roads, which puts significant extra stress on springs. Seasonal factors also come into play, which may explain why the demand for coil springs increases considerably as conditions become cooler. If any stones, or debris, have chipped away the spring’s protective paint, the metal becomes more vulnerable to corrosion, especially when salty road grit, or fluids, are spread on the roads. Vehicle manufacturers’ drive to shed weight to meet fuel efficiency and emissions targets adds a new problem. Coil springs have suffered from weight reductions, with different shapes, sizes and reduced wire dimensions being used – all of which contribute to the breakage risks.

A typical DIYER cannot repair coil springs. Attempts to make modifications and repairs can weaken their structures and make them seriously

unsafe. Therefore, the best advice we can offer is to replace worn/broken springs with original manufacturer

(OE) replacements. Another issue is misdiagnosis, because many Diyers blame worn suspension on the springs alone, without considering the dampers.

Even so, you can perform preventative maintenance to increase damper life at service time. Inspect the condition of any flexible gaiters, or covers, that protect the shiny piston rod from the elements and check that any bushes are intact. Shine a torch into the suspension turret to check the spring condition. Driving habits affect damper life, too. KYB advises that you should not drive at high-speed through puddles, or standing water, because the pressure can force moisture and dirt into the suspension components, where the resultant abrasion and corrosion courts premature failure. Additionally, an enthusiastic driving style that features harsher acceleration, braking and more erratic steering inputs will make the dampers work harder and run hotter. Consider also that certain modifications can influence damper life. Lower profile tyres than those fitted as standard create more work for the dampers because, as the height of the sidewall reduces, so too does the tyre’s

compliance, leaving the dampers to absorb extra forces that would have been catered for otherwise by tyre flex.

DAMPERS What goes wrong?

We prefer to refer to shock-absorbers as ‘dampers’, as it describes their technical purpose more accurately. Without some means of dampening the forces introduced into a coil spring, the spring would oscillate uncontrollably, reducing tyre to road contact. Dampers do this by forcing hydraulic oil through an array of internal valves. Damping characteristics are exploited in the development process, by engineering the number/ sizes of these valves. A problem with this is that the oil’s viscosity becomes thinner as it warms, making it easier to flow through the valves, which reduces damping effectiveness. This is the reason why many higher performance models feature gas dampers, where the hydraulic oil has pressurised nitrogen added. The gas is not only very effective at dissipating heat, therefore keeping the oil cooler, but it also prevents external air from entering and mixing with the oil that can result in small bubbles forming, further reducing damping efficacy.

While all dampers (including nitrogen pressurised types) contain hydraulic oil, a seal at the top of the damper prevents it from leaking out, which would render the damper useless. Damage, including

corrosion, to the polished piston rod will tear the delicate seal, hastening its demise. While an MOT tester may permit very slight weeping (or ‘misting’), you should replace the damper regardless.

Even if you do not encounter leaks, dampers do not last forever, because their effectiveness reduces gradually. As modern suspension has become very hard, conducting the simple ‘bounce’ test to evaluate damper effectiveness is almost impossible, due to the lack of available movement. For our younger readers, this is when you would ‘bounce’ each corner of the car to note that the suspension rebounded once, before settling after you stepped back.

Many garages have also ditched ‘wobble plates’, where you would drive onto a vibrating surface, which would assess the dampers’ reactions, to calculate a percentage efficiency rating.

So, how often should you change your dampers, when wear is almost impossible to assess by sight alone? KYB recommends a 50,000 miles interval. It reasons that, by the time the car has covered this mileage, hydraulic fluid would have passed through the valves over 75 million times. The resultant gradual deterioration means that more fluid can pass through than intended

and this is what causes the damping efficiency to reduce. As the valves are made from thin metal, KYB provides the analogy of bending a wire coat hanger several times; the metal becomes weakened and, eventually, it will snap.

Fitting considerations

Popularised in the UK by Ford of Britain, from the 1950s, most modern cars feature a common Macpherson strut design, especially on the front suspension, which combines the damper and spring into a single assembly. When replacing the damper and its associated parts on this design, you need to strip the unit off the car, by compressing the coil spring and removing all of the various parts. We must emphasise that the force behind the coil spring alone is considerable and sudden release of a compressed spring can cause severe damage and injuries. This Facebook video demonstrates this point quite conclusively: (https://bit. ly/3dljbfg). The strut must not be dismantled, until you have compressed

the coil spring further to release the pressure on the top and bottom mounts. Use a decent-quality spring compressor and respect the forces involved. Do not drop the spring under compression with its tool for example.

Never replace one spring, or a single damper alone; change them in axle sets. Having a new damper on one side of the car only can introduce a 25% imbalance

in damping qualities, resulting in unsafe vehicle dynamics, even though it might still pass an MOT Test. If you replaced one damper and not an axle pair, KYB’S research shows that stopping distances could increase by up to two metres. Further advice, regarding the ancillary parts and fixings, follow in this Macpherson strut replacement procedure.

Macpherson strut suspension dictates that you remove the combined spring and damper and strip them off the car. It is a viable DIY job, providing that you are obsessive about safety.

 Where applicable, should damper bushes be damaged, or worn, consider the age of the damper internals. It is possible that a better move would be to replace both axle set dampers, instead of renewing just the bush.

 Failure of the top piston seal causes hydraulic oil to leak out, which is an MOT Test failure. The damper can neither be serviced, nor topped-up. However, even non-leaking dampers can be dangerously ineffective.

Bump-stops tend to act as spring assisters, by slowing-down the rate of compression, once the spring reaches a certain height. This springassister is almost half the length of the spring. Spring assisters wear over time. What is obvious here is that the central hole on the part pictured right, has worn into an oval shape; what is not obvious is debris inside, which would be transferred onto the new damper’s piston rod had it been refitted.

This replacement spring (pictured right) would have fitted the car but has more coils and is taller than the original. It is suspected that the replacement spring is for ‘comfort’ versions of this model, rather than the slightly lowered ‘sports’ configuration that was fitted to this example originally.

Like damper specs, different examples of the same model can possess several different spring specifications. The car-maker tends to identify them by painted markings. Even quality aftermarket springs don't normally have these markings, so compare the number of coils, spring diameter and height dimensions.

Broken springs pose an obvious safety hazard – some designs can even pierce the tyre. This is an obvious MOT failure and the spring will need to be replaced, along with the item on the opposite side.