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Hi, I'm Marshall Brain. Have you ever had a truck pull to a stop next to you making a sound like a machine gun, or have you ever been on a long descent on a mountain road and heard that loud machine gun noise from a truck? That's a feature commonly known as a Jake brake. The basic idea behind a Jake brake is to use the engine to provide braking power. If you own a stick shift car and have ever downshifted to provide braking, you understand part of the idea. A Jake brake goes a step further.
It actually turns the engine into an air compressor to provide a great deal more braking power. A Jake brake modifies the timing on the exhaust valve so that the exhaust valve's open right at the top of the compression stroke. The energy gathered in compressing the air is released so the compression stroke provides braking power. It makes a lot of noise, but it really saves the brake pads. To learn more about this and thousands of other topics, come to howstuffworks.com.
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