I have started a collection of fragments of coil springs that I find on the roadside during my walks. They are becoming more and more common, and I have visions of a car driving past quickly and throwing one at someone's windscreen.
I can't remember ever seeing them until recently, and drove for many years in Africa where the the main roads have far more potholes, and much worse. Can one of the BR experts tell me whether the cause has anything to do with the modern rigid tyres (45 profile and below) and non-flexible alloy rims passing too much shock to the springs ? The older tyres were so much more compliant and cushioned the spring from the worst of the shock.
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The usual bad thing that happens with small, dense bits of steel shrapnel is that the front wheel kicks it up into the rear tyre at high speed, killing the tyre.
Happened to me in France in my Renault with a bolt which ended stuck through the middle of the tread of the back tyre. The garage man removed the bolt and plugged the tyre, a Pirelli P6, with a rubber mushroom from the inside, but advised me (quite unnecessarily) to leave that wheel on the back... It quite all right afterwards.
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>>Can one of the BR experts tell me whether the cause has anything to do with the modern rigid tyres
HJ talks about springs not being pigtailed being the cause - but, despite his frequent repetition of this in print, I don't think he's right. There are plenty of people with Vauxhalls with broken pig tailled springs.
On a spring I replaced recently, I had a close look at the fresh fracture surface, and I found a few small areas of corrosion, suggesting that corrosion has a part to play.
Most of the fractures I have seen are in an area of the spring where the protective covering had failed. This is also the area where the spring contacts the sculpted spring base.
The contact area actually does fulfill a rather clever engineering function which helps the cars handling. As the spring compresses in bump, more of the pigtailed end coils touch down against the spring cup. This makes the compressed spring have fewer active coils, and makes it become stiffer. This is usually considered to be a good thing by suspension designers - a rising rate spring allows good ride, and stiffens in bump, providing a good response.
This repetitive making and losing of contact between this portion of the spring and the spring cup is very hard on the protective coating. I suspect that during processing, before the application of the final plastic coating springs would have been coated with materials now strongly discouraged in the EU like Cadmium, or hexavalent chromate. Perhaps these coatings aren't as restricted in Asia?
So, the springs could be made without this contact/rising rate effect, and while they are working, they wouldn't perform as well. I expect there will an entirely predictable backroom split between those who would be happy to sacrifice performance for reliability, and those who wouldn't.
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I would agree NC
I would also agree that HJ is barking up the wrong tree
Springs i do invariably break where the coating has been breached and i too am sure its corrossion that starts the process
I also feel that the materials used arent as good as im convinced all springs are made outside the eu and the materials arent as good as of a few years ago
i did another spring this week on a car strangely a front one whereas on this type of model its usually always rears
Progressive springs also sounds a good reason for breakage too, seeing as one particular part of the spring will do most of the work
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The remains of both my recent spring breakages are almost exactly one turn of the spring.
They are straight cut springs and from the paint codes, original 1990 Mazda ones.
So if is the comparatively sharp edge causing localised high stresses, or the sharp edge removing any coating - or any combination of the two, I leave it to the metallurgists.
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I have been hearing tales broken coil springs from several sources and if I was investigating I would be concentrating on the quality of the springs themselves.
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The plastic coating often makes matters worse.Once breached it can trap water,or salty water in winter,at one particular point.It is probably best to remove any loose pieces.
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Surely the quality must be poor if they need coating to prevent corrosion?
I've said this before I know, but I've had old cars with 40 year old springs suffering from nothing other than mild sagging. They had surface rust, but I've never had a broken spring.
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>>Surely the quality must be poor if they need coating to prevent corrosion?
Possibly, but, not necessarily. As I mentioned in my post above, there are processes for the surface treatment of metals which were routine 40 years ago which are now all but banned.
I would be happier if more were done to contain the broken spring fragments - the breaking of the coil spring is generally just a nuisance, with many drivers not noticing, as evidenced by the number found during servicing and MOT. The loose fragments, and sharp spring end are, however, quite dangerous.
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My last Astra (M reg Mk3 5 door saloon) ate rear springs in the latter years of its motoring life - no matter what make they were. From those sold in cheapo car mart places to the genuine Vauxhall and even on to the more expensive makes.
My current Astra 53 plate Mk4 estate - seems to be fairing a lot better though with to date not having a single spring or shock absorber needing replacing.
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What strikes me as odd is the way that they often break while the car is parked - I've seen it suggested that this is due to temperature changes.
You'd think an extra sudden jolt would finish off a weakened spring, long before temperature changes etc affected it.
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Yes, funny thing stress, in humans as well as cars.
Hatchback rear windows are another example, several stories of them shattering overnight.
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>>What strikes me as odd is the way that they often break while the car is parked.
>>Hatchback rear windows are another example, several stories of them shattering overnight.
The common factor is not just the stress, but that the failure is by the relatively slow growth of small cracks.
Among other growth mechanisms, there are stress cycle related crack growth, and pure time based crack growth under constant stress.
While the crack is very small, the amount of growth per stress cycle or, per unit time at constant stress is also small.
As the crack nears the size where it becomes critical (by which I mean that the crack is large that the remaining material carrying load fails suddenly), the amount of growth per stress cycle, or per unit time at constant stress accelerates.
As cars, mainly, are parked for much greater proprtion of time than they are being used, it is not surprising that failures occur in large numbers to parked cars. Changing temperature will give a small stress cycle, and hence some crack growth on top of that caused by the simple action of time under stress, but, I wouldn't ascribe the failure to be caused by temperature.
A difference between the cases of the coil spring and the stressed hatchback window is in the critical crack size - in the spring, it's a few mm, while in the glass it will, typically, be less than 100 microns.
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It does seem ironic that manufacturers continue to trumpet their great 'breakthroughs' in car technology, whilst seemingly unable to manufacture a durable coil spring :-)
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I have to agree old sock.
I once.spent a fortune on a 10 month old car (sold on after 6 months), to find within 1 month, that 3 of the 4 doors leaked water. (plastic seals behind the doors trim not stuck properly)
and water coming in via the high level brake light after leaking through the rear wash wipe water nozel. also had the adjuster for the drivers seat fall of over night,,,
when i went to the main dealer to buy another one, they said they'd sold one of those that very morning to the local police station who also had one fail over night...
so in short, the car had airbags, abs, cd player, fancy alarm that would shut the windows etc etc...but would leak worse than a 10year old pug205 (been there)
paul.
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just done a ka front spring :-)
nice start to a monday morning
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BB - 'tis the right season for it, I suppose :-)
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Can one of the BR experts tell me whether the cause has anything to do with the modernrigid tyres (45 profile and below) and non-flexible alloy rims passing too much shock to the springs ? The older tyres were so much more compliant and cushioned the spring from the worst of the shock.
No I dont think this is the reason at all.
There is evidence to suggest that it is a combination of chep quality springs and the abundance of speed bumps.
We had a newish Merc C220 spring break recently, and not only were we told that this is quite common on this model, looking at the broken spring, you ddin't really have to be a metallurgist to see that the spring had broken due to a flaw in the steel.
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I think the roads in the UK are far more punishing than they used to be, this is made worse by the artificial narrowing of lanes or roads and concrete cushions which cause vehicles to travel in rigid single file instead of being staggered. Not only does this rut and wear the road quicker, but makes many road hazards unavoidable.
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>>you ddin't really have to be a metallurgist to see that the spring had broken due to a flaw in the steel.
How did you come to that conclusion?
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a flaw in the steel.
How did you come to that conclusion?
Well, the fracture won't have occurred at a point where the spring has the elasticity and internal consistency it is supposed to have, will it? Unless it is a freak extra strong spring and that is the weakest point of course...
I'm only teasing NC.
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>>I'm only teasing NC.
Thanks Lud!
I asked because for a true material flaw to be responsible, it would have to have been very small - or else the crack would have grown to failure very quickly indeed. The critical crack size for these highly loaded parts is quite small.
I have found, in the cases where I've been able to see the fracture surface soon enough after failure, that the small area of corrosion where the crack has propagated from is only a millimetre or two across, and the remainder of the fracture surface is quite fresh; indicating rapid crack propagation.
As an aside, yesterday, in my work, I was considering some fracture faces to try to find the root cause of the failure. The similarity was that the fracture face was helical, indicating torsion was the predominant driving stress. The difference was that I was looking at pictures from an electron microscope of a failed optical fibre, which was only 100 microns in diameter!, with some of the fracture surface details like the initiation and river marks being in the sub-micron range.
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phone pictures so quality poor but this is the ka spring i changed yesterday
2 things
no 1 it has broken where the plastic coating has been breached
no 2 you can see rust and clean metal in the break
i6.photobucket.com/albums/y246/smartiesx3/08-05-09...g
i6.photobucket.com/albums/y246/smartiesx3/08-05-09...g
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Bell Boy,
Did the broken spring really come off Scooby's Mystery Machine?
;¬)
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Would you say that fracture had a helical quality NC? Big rust area too, suggesting a deep crack...
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It's difficult to say Lud, I can't really make it out.
There does look to be a large amount of rust, but, perhaps I'm not interpreting the picture properly. If there is a lot of rust on the fracture surface, it's indicating the crack has been growing for a long time, and has covered a significant area of the section before final breakage - usually, this is interpreted as being in a low stress area, perhaps closer to the end of the spring than usual - on a fully working coil, this would be most unusual.
One of the other confusing things is that you have to see the fracture surface very soon, ideally, within a few hours after fracture, unless special protective steps are taken to prevent further corrosion. Failing that, the surfaces need to be specially cleaned and prepared to allow the fracture to be properly assessed. When a part fails inside an oily gearbox, it's usually well protected by the oil, and there isn't the same rush.
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"The usual bad thing that happens with small, dense bits of steel shrapnel is that the front wheel kicks it up into the rear tyre at high speed, killing the tyre."
Lud....
I saw an exhibit at a motor show. The exhibit was a section of steel wheel where a pair of industial tailoring scissors had been picked up in a similar way and gone through both the tyre and the rim.
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>>you ddin't really have to be a metallurgist to see that the spring had broken due to a flaw in the steel. How did you come to that conclusion?
Because someone I know who IS an engineer/metallurgist looked at it, and immediately commented on the flaws/slag that was visible across the broken segment. I, who am not a metalurgist could also see this easily.
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immediately commented on the flaws/slag that was visible across the broken segment.
That's interesting - it's unusual to see such an obvious flaw in a part like this.
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N.C.
Just picked up, by hand, the follwing at the edge of the approach road leading onto the A34 at Handforth Dean, all within a meter.
One spring fragment, half coil, 9mm dia, 55mm pitch circle diameter, looks like a torsion fracture, 20 mm long, 1.5mm step and then chiselled to a sharp edge. I thought, "I'd better get that before someone else does to their detriment".
One 100mm nail, rusty
One 45mm woodscrew, very rusty
One knife blade (Rambo style) 110mm by 28mm with 95mm tang
Then SWMBO was getting nervous so I stopped collecting.
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>>then chiselled to a sharp edge
It's quite unfortunate that these spring failures will almost always leave such a sharp edged fracture - especially as the failure occurs so near the tyres.
>>One knife blade (Rambo style) 110mm by 28mm with 95mm tang
Eek!
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Oh, I forgot to include...
One tubular bracket, shaped as though for the attachment for a rubber exhaust hanger piece. The bracket is made from bright steel tube, 11mm o/a, 270mm developed length and having two bright steel welds at one end that have obviously been attached to an unsuitable metal body member. Or, the base metal has not been cleaned.
That would have made a mess of somebody's car. The road verge hasn't been swept for a least a year that I know.
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