Coil spring compressors are tools used to service certain types of automotive suspensions.
Some vehicles use components known as struts, which combine a shock absorber and spring into an integral component of the suspension system.
Springs are very strong and under significant stress, so simply removing a strut can be quite dangerous.
To accomplish this task safely and to facilitate reassembly of a strut, a coil spring compressor is generally required.
Struts have three main components, which are a housing, a cartridge, and a coil spring. The housing typically bolts to a steering knuckle and strut tower, and the cartridge fits inside. A strut plate is typically located on top of the cartridge, and a coil spring is installed between the housing and the plate. In most cases some type of bushing will also be installed between the plate and the tower. Typically a coil spring compressor is required to allow replacement of items such as cartridges and bushings.
The purpose of a coil spring compressor is to remove stress from a strut assembly so that it can be safely disassembled for service and then reassembled. This is accomplished by inserting the feet or hooks of the compressor into the spring and then tightening it with a pneumatic ratchet or hand tool. When the coil spring compressor is squeezed, its feet or hooks cause the coil springs to move closer to each other. That effectively takes the stress off the strut assembly so the plate can be unscrewed and the cartridge can be safely replaced.
Sometimes it is possible to disassemble a strut assembly without this type of tool, if the technician is careful and works very slowly, although it is generally dangerous to try.
Since the coils are very strong and under extreme pressure, they can move suddenly when the pressure is released.
If a technician is on the road when that happens, serious injury or even death can occur.
Also, at that point it would be difficult or impossible to reassemble the assembly with a new shock cartridge.
Consequently, it is generally much safer and more practical to use a coil spring compressor when performing maintenance work on strut assemblies.