As Charlie says springs do fail and these days it's quite a common event. Edinburgh still has quite a number of, pretty rough, cobbled streets and thousands of speed bumps. It's not at all unusual to see, from time to time, a piece of broken coil spring lying in the gutter! A few years ago, before he suffered ill health and closed down his business, I was talking to my friend (who owned an independent motor factors). I had recently suffered broken springs on two of the family vehicles and I was complimenting him on how quickly he had been able to supply the new ones. "Just come through and look at this" said he, leading me through into the warehousing area. There was shelf after shelf after shelf of road springs! "A few years back I would have only stocked a few of the worst offenders on the shelf. Now the demand is so great I have to carry all these"! His opinion was that speed bumps were a big part of the problem as demand increased sharply after their introduction. I tend to agree with him as I can't really think of any other road feature which causes such a large deflection of the springs and I think it's this large degree of deflection (and to some degree the shock of the potholes too) which breaks them. I myself, try always to slow to such a degree that minimal deflection of the suspension takes place whilst traversing one of these evil features. I think I used to cause annoyance to some by going so slowly but now there are so many 20mph zones in Edinburgh that this seems to not be a problem any more! (Whilst I was initially very frustrated by these 20 zones I find I quite like them now but do wonder what it's doing to my gearbox driving around in 2nd and 3rd gear all the time.)
The comments made by Eklipze and P.B. are also very relevant. Changing springs in "axle" pairs is very good practice and, as Eklipze says, If only the one was renewed last year it's a pretty good bet the other one has now gone. P.B's point about the anti roll bar drop links is also a good one. Like ball joints and track rod ends they can make a devil of a racket. If you jack up just one side of the vehicle although steering ball joint and track rod end free play can be easily felt you won't detect any in a drop link as the anti roll bar will be putting it under tension/compression. You need both front wheels off the ground and even then there is sometimes enough disparity between resting position side to side to still tension the links and so mask the play. A couple of months ago I spent a couple of days, on and off, trying to find a "clunk" in my daughter in law's Honda Jazz. Eventually (due to the noise it was making. I am a retired mechanic so have heard many noises) I convinced myself it was the O/S/F anti roll bar drop link although with it still bolted to the vehicle I could detect no play! As soon as I had it off the vehicle it was obvious that the lower joint had failed. It's rubber was still intact but there was very very little grease in it and you could merrily rattle the ball end around!
