When I got my 85 745 Turbodiesel @ 170K, it had a bad case of the saggin wagon blues. Or so I thought. New springs and shocks only brought the back up 1/4". I wasn't too dissapointed since it took under two hours to do the swap. GO Volvo! Engineers earned their money. I got the parts at my local Pick n Pull for about $25, and the receipts were still in the car. Still, the car was definitelly nose up. High beams were good mostly for inspecting the trees. for a few weeks, i parked next to a 700 or 900 every chance I got, and found my front bumper 2" higher than average. I posted here and got a few responses indicating the front springs can and do somehow lengthen and soften with age.
I was doing some work at my friends body shop, and couldn't resist the big shiny torch in the corner. I set up a floor jack under each rocker panel about where I thought ride height should be. As I set up my safety gear, my friend stopped me, and said 'you gotta try this' a windex bottle marked 'heat disipating spray'. He put a few squirts on a plastic bag, it went on like aloe vera burn gel, maybe a little thinner. Much to my amazement, he lit up the oxyacetylene torch, cranked it up, and played it across the clear plastic grocery bag for about 6 seconds several times with no harm done! Astonished, i sprayed a good coat on the rubberized strut boots, and scraped the undercoat off the bottom coil of my springs. Moving the torch back and forth to evenly heat half the bottom coil to a gentle glow, I watched the car settle slowly onto the jack, and stopped the heat.
Repeated the process on the other side. Today, a few weeks have passed, I went nose to nose with another 740, and my height is a perfect match! Ride stiffness is maybe a tiny bit stiffer, but that may be wishful thinking on my part. So my springs wore out, and I restored them to near original condition...Impossible as far as my metalurgical knowledge.
Any dealer or suspension company pro will tell you never to do this(what do they make if you do?). Most old hot rodders wil tell you they have done it many times. Normaly heating a spring upsets the original geometry of the suspension, but I have not, as I only lowered to stock height. I must disclaim any responsibility for others who use this note as justification for their actions. You should not modify your suspension in any way unless you have a good understanding of what you are doing. Failure can have injurious or even fatal consequenses. Having said that, in 25 minutes with about a dollar worth of gas, I acheived results that would have cost me hundreds at the shop. The time will come when I find some nice fresh or aftermarket struts at the wreckers, and I will install those with some brand new ball joints.