What the he**

[SillyOldDufferModerator @sillyoldduffer]

Depends what's meant by 'common'! I've never broken a spring nor do I know anyone who's ever broken a spring. But like Clive I've seen bits in the gutter and once heard one break as a car traversed a roundabout.

As there are about 31,000,000 cars on the road in the UK, that's 124,000,000 springs available for breaking. This American website gives the probability of a suspension spring breaking as 1 in 1000 per year. My maths is awful and ignores mileage and other factors, but I reckon that means the average individual has a 20% chance of suffering a spring break in 50 years of motoring. Not exactly 'common' but frequent enough to be noticeable.

While it's tempting to blame value engineering, recycled steel, speed bumps, bad roads, weak shock absorbers and curved compression etc, the chief cause is RUST. The pits caused by rusting act as stress concentrators. Being a spring the metal is hard which encourages fatigue cracking anywhere stress is concentrated. As springs are also brittle it doesn't take much for a crack to propagate catastrophically. More likely to break on a speed hump than a flat road, but as happened to Roger, damaged springs can fail whilst parked up. Cold weather increases the risk too. Sharp corners and steel going brittle in cold weather caused at least 7 Liberty ships to break in half during WW2. The Schenectady was in harbour when she broke with a bang.

Suspension springs are exposed to the weather and – in the UK – to salt on the roads. It seems suspension springs are more likely to break than valve springs even though the latter are thrashed hard and hot: I think that's because corrosion is far less likely inside a well-protected oily engine.

Dave

[Mike PooleParticipant @mikepoole82104]

My wife had a Renault 18 that went through a few rear springs and this was when the roads were free of potholes and the car was not driven aggressively, 3 springs in 197,000miles my sons VW Polo broke one spring and both bearings on the front strut swivels, different style of driving though he thinks the throttle is a switch.

Mike

[Nick Clarke 3Participant @nickclarke3]

Posted by SillyOldDuffer on 24/09/2019 13:13:34:

Sharp corners and steel going brittle in cold weather caused at least 7 Liberty ships to break in half during WW2. The Schenectady was in harbour when she broke with a bang.

I haven't seen that picture for nearly 50 years! My materials lecturer at University, Dr Moon used it to show, not the cause of the crack, but rather how cracks can propagate further in a welded structure than a riveted one built out of individual plates.

[RMAParticipant @rma]

Posted by SillyOldDuffer on 24/09/2019 13:13:34:

Depends what's meant by 'common'! I've never broken a spring nor do I know anyone who's ever broken a spring. But like Clive I've seen bits in the gutter and once heard one break as a car traversed a roundabout.

As there are about 31,000,000 cars on the road in the UK, that's 124,000,000 springs available for breaking. This American website gives the probability of a suspension spring breaking as 1 in 1000 per year. My maths is awful and ignores mileage and other factors, but I reckon that means the average individual has a 20% chance of suffering a spring break in 50 years of motoring. Not exactly 'common' but frequent enough to be noticeable.

While it's tempting to blame value engineering, recycled steel, speed bumps, bad roads, weak shock absorbers and curved compression etc, the chief cause is RUST. The pits caused by rusting act as stress concentrators. Being a spring the metal is hard which encourages fatigue cracking anywhere stress is concentrated. As springs are also brittle it doesn't take much for a crack to propagate catastrophically. More likely to break on a speed hump than a flat road, but as happened to Roger, damaged springs can fail whilst parked up. Cold weather increases the risk too. Sharp corners and steel going brittle in cold weather caused at least 7 Liberty ships to break in half during WW2. The Schenectady was in harbour when she broke with a bang.

Suspension springs are exposed to the weather and – in the UK – to salt on the roads. It seems suspension springs are more likely to break than valve springs even though the latter are thrashed hard and hot: I think that's because corrosion is far less likely inside a well-protected oily engine.

Dave

Sorry you're wrong. Rust isn't the problem, my own spring looked brand new, as did my son's which failed two weeks later. The one's I see in my local MOT garage are somewhat dirty but in the main totally rust free!

I think the problem is value engineering, and the worsening road surfaces accelerate breakages.

[Michael GilliganParticipant @michaelgilligan61133]

For what it’s worth in this discussion … [i.e. not much]

I bought my little BMW, six months old, as an ‘Approved Used Car’ in 2004

… it handled beautifully.

At the first service, I was informed that both rear springs were broken [and probably had been since before I purchased it].

They fitted new springs, of course … but in the following 95K miles the handling [‘though still very satisfactory] has never been quite as good.

One missing coil = Lowered and Stiffened

MichaelG.

[J HancockParticipant @jhancock95746]

What I find hard to understand is 'why ' suspension springs ?

Compare their failure rate with those on the engine valves and I'm sure you will see my point .

I have NEVER had a valve spring break on any car, and traveled 230,000miles in the same Probe that

regularly broke suspension springs.

[Roger ClarkParticipant @rogerclark]

Valve springs = regular travel and load, road springs = variable travel and load plus shock,

[martin perman 1Participant @martinperman1]

I should be up for some breakages after typing this, in 48 years of driving I've had twenty private and company vehicles from a hillman imp to a Vauxhall Vivaro and have never had one broken spring.

Martin P

[Andrew TinsleyParticipant @andrewtinsley63637]

I have had an exhaust valve spring break on my type 2 VW Camper (air cooled engine).I only noticed it when I did the regular tappet check. There was absolutely no difference in performance!

Andrew.

[Mark RandParticipant @markrand96270]

Most valve springs are pairs. I think the reasoning is that it cuts down resonances due to having two different springs and the slight friction between them.

[SillyOldDufferModerator @sillyoldduffer]

Posted by RMA on 24/09/2019 13:57:21:

Posted by SillyOldDuffer on 24/09/2019 13:13:34:.

…

While it's tempting to blame value engineering, recycled steel, speed bumps, bad roads, weak shock absorbers and curved compression etc, the chief cause is RUST. The pits caused by rusting act as stress concentrators. …

Dave

Sorry you're wrong. Rust isn't the problem, my own spring looked brand new, as did my son's which failed two weeks later. The one's I see in my local MOT garage are somewhat dirty but in the main totally rust free!

I think the problem is value engineering, and the worsening road surfaces accelerate breakages.

Who wrong me! Never happened before. I ask for 30 other offences to be taken into consideration.

But I said rust was the chief cause of failure, not the only reason. Manufacturing and other defects are always possible.

Here's a similar example where an entire strut failed on a Boeing 737. In 2014 EI-STD landed normally at East Midlands Airport but the landing gear collapsed when the pilot applied the brake.

The account of the accident on the ASN website says: 'The origin of the failure was an area of intense, but very localised heating, which damaged the chrome protection and changed the metallurgy; ie the formation of martensite within the steel substrate. This resulted in a surface corrosion pit, which, along with the metallurgical change, led to stress corrosion cracking, fatigue propagation and the eventual failure of the inner cylinder under normal loading.' It appears that an unidentified person heated a small part of the strut for reasons unknown, and cracked the chrome plating and altered the structure of the steel underneath. Although the damage was invisible the crack grew big enough enough to write-off the aircraft. Nothing poor quality about the broken part, the cause seems to have been dodgy maintenance.

Dave

[Howard LewisParticipant @howardlewis46836]

For may years, (30s on in road vehicles. Aero engines do not encounter much salt! ) Valve Springs have lived in an oily environment. Ends are scragged so that they sit "square". Some valve springs are wound with a variable pitch, in an attempt to make them aperiodic.

Road springs are exposed to road salt, and more sudden shock loading (Valve Spring loads and accelerations can be calculated well before before production starts ) as well as corrosion. Rust pits can be the stress raisers that originate fatigue failure. Plus, not all springs are installed with either scragged ends, or seats sloped to match the spring ends.

Howard

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