A spring compressor is a device used to remove coil springs from an automobile. Comprised of two threaded rods and four hook-like apparatus, the spring compressor is placed on the spring's coils and tightened. As the adjustment nuts on the spring compressor are tightened, the hooks are drawn together, thereby compressing the spring. These compressors are also used in the process of removing strut-type suspension systems. Failure to use a compressor when removing a coil spring can result in injury and even death.
A coil spring is under constant pressure when installed in an automotive suspension system. This pressure is known as stored energy. When a coil spring is removed without the aid of a spring compressor, the stored energy can cause the spring to fly out of the spring pocket at great speed. This can result in serious injury — including death — for anyone near the automobile. The use of a spring compressor allows a mechanic to compress the powerful spring and remove it from the spring pocket without fear of releasing the stored energy from the coil.
While some compressors utilize a one-piece design, the vast majority use a two-piece design that allows the user to fine tune the amount of compression used on each side of the spring. For added safety, most spring compressor manufacturers recommend using a safety chain on each spring being removed. By passing a chain through the spring's coils and securing it to the vehicle's chassis, any spring that might come loose will be contained from flying across the garage. Most automotive supply stores include a compressor in the loaner tool catalog to eliminate unneeded injuries from ill-equipped mechanics. For this reason, there really is no reason for anyone to attempt the removal of a coil spring or strut without the aid of a compressor.
There are several styles of compressor available to mechanics, from two-piece, rod-type compressors to a clam-style and free-standing type. There are also wall-mounted models of spring compressor that offer the utmost in strength and ease of use for mechanics who perform a lot of strut work. The ease of use of the two-piece rod type of compressor makes this the most popular type of spring compressor found in the home mechanic's tool chest. The two-piece design is made to be used with hand wrenches in order to prevent damage to the puller, however, many clam-type compressors are designed to be used with an impact wrench or air tool to speed the removal process.