A Jake brake is an engine brake, also known as a compression brake, that is used to slow down a large vehicle. It is most often associated with semi-trailer trucks, or "big rigs." The Jacob’s Company is credited with perfecting and marketing it, the name is a nickname that developed over time. The nickname became common for most types of engine brakes, much to the consternation of the Jacob’s Company, since these brakes often get bad publicity for being too noisy.
Diesel engines have greater compression than typical gasoline powered engines, and that compression is used by the Jake brake to help slow the engine. It works by altering the operation of exhaust valves and the function of the pistons as they cycle up and down. The compressed air is then released by opening the exhaust valves as the compression reaches its highest point. This creates an explosive effect, which creates a draw on the engine’s power, slowing it down.
The explosive effect can also create a good deal of noise, although the Jacob’s Company believes that with its brake, the noise is caused not by the engine brake itself but by irregular modifications or ineffective maintenance of the exhaust system. Some people also believe that truck drivers just enjoy making noise as they cruise through town in order to draw attention to themselves. While this may actually happen at times, truckers most often use the compression brake in order to slow the engine especially on steep hills or downgrades.
Regular brakes can often become too hot when trying to stop the momentum of an 80,000-pound (36,363-kg) truck and trailer moving downhill, and the Jake brake is a valuable tool in helping to slow a truck. Still, many areas have implemented ordinances disallowing the use of this device due to the loud thumping or sputtering sound it can make as it slows the engine.
Not only is this an issue of contention for truckers because of safety concerns, but it is also an issue for the Jacob’s Company. The company is not happy that its trade name is being used generically on many local ordinance signs. They hope to have such signs removed and replaced.
Some trucking companies and owner operators contest the compression brake bans. The noise can be compared to that of a lawnmower and only lasts a few seconds, but it may make the difference in a truck driver being able to slow his truck efficiently. Using the Jake brake can also help lower costs, since the regular brakes will last longer, so the battle continues. In some areas, there has been compromise and the device can be used during certain hours, usually during the day.