Question Which of the following is not a type of retarder? Answers Exhaust Engine Air Electric Explanation Retarders are mechanisms in some vehicles that help slow a vehicle and reduce the need for braking. The four basic types of retarders are exhaust, engine, hydraulic, and electric. Take a FREE Practice Test Now This questions appears in the following tests: Texas Knowledge Test Class A , Connecticut Knowledge Test Class B , Maryland Knowledge Test Class B , South Carolina Knowledge Test Class B , North Dakota Tank ,