Road spring failure?

ou can normally see some rust on the outer edge of the crack, but only after it's snapped.

T i m put finger to keyboard:

There would have been a warning sign on the Corsa - the Vauxhall badge :-)

I've had several Vauxhalls and the rear springs did seem to be prone to shortening themselves. They sat in a tray that collected water and contributed to corrosion. The tapered end used to go. My local garage commented that it was common on Vauxhalls, though I'm talking about mid '90s vintage here.

Once a crack is visible it isn't long to failure. One large civil aero engine has a 50 flight on wing borescope inspection interval for the HP turbine disc. (That's at a cost of about one lost revenue earning flight per month.)

The only way to see a crack before it's visible is to remove the part. Strip the surface coating or clean the rust off. Then do a non-destructive test (NDT), Take your pick from - x-ray, ultrasonic, eddy current, magnetic-particle (MPI), liquid (dye) penetrant (FPI). Then reapply the surface coating and refit.

Even when you know within 5mm where to look for the crack (that's where all the others have been found) due to dirt and surface corrosion there may be no visible cracks even during off wing inspection of the part in an overhaul shop but after a full 15 hour tank and water jet cleaning NDT finds cracks that are of visible size.

Chose carefully. The aero industry do a lot of crack testing. The lowest cost inspection, dye pen can't be sure of finding cracks smaller than

0.03" rad (60thou, 1.5mm surface crack). The service overhaul and inspection interval of the part is calculated based on that crack being in the part when it goes back into service such that it won't grow to failure between inspections. The life of a part may be 15,000 flights but the inspection interval is only 3,000 flights. Some other parts may only have a life of 1,500 flights, so the part gets inspected every 2nd shop visit.

If crack testing was done for cars as part of the annual service on all parts that could fail by fatigue it would cost more than the car is worth. Internals of F1 engines are NDT tested during rebuilds, over £100,000 a rebuild - currently every other race, maybe 5-6 hours running. All high stress metal chassis parts like hubs and suspension cranks will be tested too. Composite parts will be tested for de-lamination.

I doubt you would see any crack before failure.

Ive always changed springs and dampers in pairs for handling sitting issues. Partially on advice from the usuals on here and from the expirence of changing one and using the car for a couple of days before getting around to doing the other and seeing the car sitting visibly higher on one corner.

I never used to understand why loaded coil springs running at normal temperatures "settle" as they get older. There should be a good margin between working stress and yield. Leaf springs wear, so that makes sense, and exhaust valve springs on air cooled motorbikes run hot, so they might be in the creep regime. Then I asked a metallurgist. In a real spring there are microcracks and defects where the stress level is close to yield. Over time, lots of little bits of local plastic deformation add up to a shorter spring. So yes, change in pairs (except perhaps for an obvious defect in a low mileage vehicle).

Thanks very much to those who have replied (so far) and all the detailed explanations re what *is* (rather than might be) going on behind the scenes.

One thing I was already pretty sure about was that the MOT nor any std high street garage could possibly predict (just by looking) the pending and potentially catastrophic failure of nearly any such component, certainly without fairly specialised equipment.

Along similar lines ... this morning I replaced the exhaust section between the manifold and the main exhaust on my SIL's old Fiesta and while I was there I replaced *both* wishbones because they looked a similar age / condition, they were cheap, I was under there already and *one side* was showing signs of wear and tear (rubber bushes de-bonding).

After today's efforts I'll probably recommend he changes *both* disks and *all* pads soonish.

The bit I can't quite yet fathom (re my nephew and his Dad) was it isn't like one side hadn't already failed, the second spring job was out of reach financially or that we were doing anything than looking after their best interests. I think it was my (82 year old) Mum refusing a lift from him 'because' that finally persuaded him to get it done. ;-)

Cheers, and thanks again, T i m

Complete and utter waste of money IME. If it was a damper, yes, sure, change them in pairs. Springs? I've changed plenty, never changed them in pairs, never had a problem. It's generally the N/S ones I end up changing, and I believe this is because they are subject to more abuse/ road s**te/kerbing/potholes etc. I've never had an O/S one fail. I've just had to replace most of the N/S suspension on the Berlingo (apart from the spring, that was done last year) because it was worn out. The O/ S is absolutely fine, no cracked bushes, no damage to anything.

The "change springs in pairs" thing is a myth perpetuated by garages to part you from your money because "it's dangerous and will cause handling imbalances". Bollocks. Like I said, dampers, yes, it will, but not springs.

Whilst I follow most of the spirit of your post unfortunately it doesn't seem to tie in with the FACT that BOTH the rear springs went on the Corsa within a month of each other (and after 10+ years and

160K+ miles (that we know of, if they were the original springs etc).

I do go along with the n/s/(f) getting the most work most, not only from drains and kerbs but roundabouts etc.

I'll make no comment on the issue of handling (no vehicle I have is that sensitive).

But changing road springs (brake calipers / cylinders, tyres, struts) in pairs seems no different to me than replacing the (more than low mileage) cam belt whist doing the thermostat or the half worn clutch friction plate when doing the thrust release bearing (or visa versa).

And none of this because that's what the garage says because in this case it wasn't them that choose to have it done. ;-)

Cheers, T i m

& a quick look at ride height says that both springs sag fairly evenly over time.

As I've seen all too often.

When we built the kitcar (Rickman Ranger) we used a 1978 MkII Escort (20 years ago) and used the springs that came on it always seemed to ride a bit lower (than expected) on the front. A few years later a spring broke I so bought a new 'stock' pair (for a 1978 4Dr 1300 Sal) and was surprised to see how much higher it rode. However, it was till a bit low (from measuring the maximum and minimum movement range so had some 'Stock (spring rate and length) +1"s' made and they helped even more.

Then, getting ready to swap the 1300 Kent for the 2L Pinto (from my Sierra) I put some springs in as supplied by the RROC and 'heavy duty' dampers while I was there (again, as recommended). The Pinto upgrade was abandoned (insurance costs + other matters) so I changed the springs back but left the dampers (strut inserts). This means the ride is still 'stiff' and something I need to resolve before I can enjoy it (for what it is) again.

For what is still basically a MkII Ford Escort, the full M+S tyres allowed it to go where even some 'softroaders' (with road tyres) feared to tread (excuse the pun, ... or were not mad enough to attempt more like). ;-)

Whilst the Escort suspension was hardly true (or even) 4x4 spec, the softness of the std saloon springing under what was a heavier chassis / body combo meant all 4 wheels generally all played their part (rather than cocking a wheel over the bumps etc).

Cheers, T i m

I had a coil spring replaced on my MK2 Mondeo.

Within 12 months the other side broke.

On Thu, 22 Aug 2013 19:18:21 +0100, Gordon H wrote: [...]

Broken front springs on those is a very common fault however.

Chris

Yes, that's something I already gleaned from this group. :)