A wheel cyliner is a component in a drum brake system. It is located in each wheel and is usually at the top, above the shoes. Its responsibility is to exert force onto the shoes so they can contact the drum and stop the vehicle with friction. What connects these wheel cylinders to the shoes are usually small rods shaped like a birds beak. It is very similar to a master cylinder and functions in pretty much the same way, consisting of just a simple little plunger on the inside. On older vehicles these will begin to leak and hinder the performance of the brakes, but are normally inexpensive and easy to replace.