Is there a simple home test? How do you test the leafs, coils and shocks? Do you have to replace the shocks more often than the springs?
Director of Ironman 4×4 Mic van Zyl explains
A vehicle’s suspension system does not have an infinite life span. Wear may be gradually with replacement needed at some stage. Shocks can fail suddenly and springs can break. Here are some things to look out for:
Leaking Shocks and broken Shock mounts are easy to spot. A Shock that has had an internal failure is harder to spot and will have to be removed from the vehicle for diagnoses. Flat spots on your tyres are often a sign of worn Shocks. The worn Shock is unable to control the up and down movement of the wheel / axle and the tyre is allowed to bounce up and down. This bouncing and skidding on the road causes the flat spots. This uncontrolled movement also transfers into the cabin and your vehicle may progressively develop a rougher ride.
The most telling sign that your shocks are worn may unfortunately manifest itself when you least expect it. Cornering at too high a speed or performing an emergency swerve in a vehicle with worn shocks may cause the vehicle to break traction and start to spin, roll over or perform some similar uncontrollable action.
An increase in vehicle sway, nose diving under braking or squatting down in the rear under hard acceleration could also indicate worn shocks. The old method of bouncing the vehicle by hand at each corner to test the Shocks often works on passenger vehicles but is harder to perform on your Hilux 4×4 with 2 inch suspension lift.
The only truly accurate way of testing a suspected worn Shock is to remove it from the vehicle, run it on a Shock Dyno and compare the graphs to the original specs. This is costly, time consuming and it is very difficult to locate a shock dyno, never mind the original specs.
It is important to note that worn shocks do not affect the ride height of the vehicle (more about this in a later article).
A broken or worn spring should be pretty obvious from the fact that the vehicle will lean down on the corner or axle of the affected spring/s. A worn or broken spring can no longer support the weight of the vehicle and its load resulting in the sag.
There is certainly no specific life span for shocks or springs and it is entirely dependent on how hard they work. A vehicle that only drives on smooth road ways could have its shocks last the lifetime of the vehicle whereas that identical vehicle that lives on a farm will not be so lucky. As for the springs, provided they are manufactured correctly and the vehicle is never overloaded for any extended period of time, they should easily last the lifetime of the vehicle.