Suspension spring compressors are tools used to take a spring off a strut or generally out of the suspension components that hold it in place. It is a famously dangerous procedure, as the compressed spring is under a lot of pressure, and can cause immense damage (to humans, life forms, or objects) if the spring slips from the tool.
A typical spring compressor clamps on to the outside of the spring and squeezes down on the spring, making it shorter and come loose from components above and/or below it. While compressed, the components that would otherwise be holding the spring together can be disassembled.
Exteme care should be taken to not shock the spring while it is compressed. Knocking the spring compressor off the spring can cause the spring to shoot off with tremendous force, leading to serious injury or death. Make sure you read the instructions that come with your tool, because the proper way to use the tool will differ based on the design.
How to Remove Springs Safely with a Coil Spring Compressor by ECS Tuning
A video produced by ECS Tuning showing how to safely use a particular spring compressor. The video mentions tightening both sides equally; this is important because one being too tight compared to the other may encourage the loose one to suddenly slide towards the tight one, potentially causing serious injury and/or property damage.
How Much Energy is in a Spring?
It's good to visualize how much energy is in a spring to understand how dangerous they are when compressed. Since a typical four-wheeled vehicle has a spring for each wheel, at a standstill, each spring is holding up about 25% of the weight of the vehicle. Since a vehicle isn't typically perfectly balanced at all four wheels, that number isn't precise, but there's more to it. Each spring typically gets put in a suspension assembly in such a way that suspension forces will have leverage on the spring, so springs are not just holding up their portion of the vehicle's weight, but doing so at a disadvantaged state (so they have to be able to withstand more weight). In further addition, vehicles move, and can experience a lot of unbalanced forces when accelerating, braking, and cornering. When taking a sharp corner with heavy braking, the front spring on the outside of the turn has to hold a significant portion of the vehicle's weight, ideally without bottoming out. In order to compress a spring enough to remove it, it may have to be compressed to the same level as when it is holding up a large portion of the car. Even worse, when this is happening on a vehicle, the car also has a shock absorber to help dampen the spring's movement, while someone removing the spring from a strut won't have the aid of that dampener on their side if a mistake is made.