Car suspension failure

Coil spring failure is a growing problem

AA patrols have reported a big increase in the number of broken coil springs

AA patrols have reported a big increase in the number of broken coil springs

Collapsing suspension due to coil spring failure seems to be a growing problem - caused by a combination of recent harsh winter conditions and weight-saving designs.

AA patrols have reported a big increase in the number of broken coil springs – in the year to February 2011 we saw more than 21,000 breakdowns related to spring failure. The number of broken springs in January 2011 was 25% higher than in January 2010.  Figures from 2012 (the graph below shows, 2010, 2011, and 2012) show no signs of the problem going away.

There are myths suggesting that the problem is caused by 'cheaper metal', speed humps or over-loading but the simple fact is that springs are lighter, thinner and don't cope as well with salt and rust.

Collateral damage

On older cars with fairly small diameter and narrow wheels, the damage was usually confined to the spring itself when one broke.

Modern cars are fitted with much bigger/wider wheels for better looks and handling but the penalty is that the tyre sidewall is much closer to the spring. If a spring breaks, tyre damage is much more likely.

Reducing weight

Reducing vehicle weight is one way of cutting fuel consumption and CO2 emissions.

An obvious example of this is the trend towards smaller spare wheels or runflat tyres instead of a full size spare but car manufacturers are challenging the design of every component in search of weight reduction.

Mechanical components are being re-specified so they will still do the job but may have less spare capacity. This has included specifying lighter, more highly stressed springs.

Suspension springs - reported breakdowns (AA)

Suspension springs - reported breakdowns (AA)

Spring coatings

A plastic coating is applied to coil springs when they are made to reduce the risk of corrosion. Over time, contact between coils as the spring is repeatedly compressed in service can cause damage to this coating.

Corrosion

Most often coil spring failure seems to be caused by corrosion, accelerated by salt applied to the roads in winter.

The corrosion exposes the micro structure of the material to the atmosphere and makes it susceptible to a process known as hydrogen embrittlement.

We've checked with other motoring clubs across Europe too. Italy, Portugal and Spain have seen no change in the number of coil spring failures but the German club, ADAC has reported the same increase in spring breakage experienced in this country. Roads aren't salted in winter in southern European countries.

Hydrogen embrittlement

Electrolytic action between the salt solution, formed by road salting, and the iron in the spring generates free hydrogen atoms which enter the steel and can cause microscopic cracking. Cracks propagate and combine, ultimately leading to failure of the spring.

Spring catchers

Some car manufacturers fit 'spring catchers' to try to minimise the damage caused by spring failure. These won't always work because the amount of energy trapped in the spring makes it almost impossible to predict the way they will break.

Fitting spring catchers also adds an appreciable amount to the cost of assembly.

Prevention

During winter and early spring, a regular clean underneath the car with a hose or pressure washer might help extend spring life.

(26 October 2012)