Name the two kinds of retarders.

• A. Mechanical and hydraulic
• B. Pneumatic and mechanical
• C. Magnetic and chemical
• D. Electric and hydraulic

Answer: (D)

Retarders provide braking without using the regular service brakes, helping slow a heavy vehicle especially on long or steep grades and reducing brake wear. The two kinds you’ll encounter are electric retarders and hydraulic retarders. Electric retarders slow the vehicle by turning kinetic energy into electricity with a generator or motor, and that electricity is dissipated as heat in resistors or managed by the vehicle’s electrical system. Hydraulic retarders slow through a fluid-filled turbine or similar device in a hydraulic circuit, converting kinetic energy into heat in the fluid, with cooling needed to keep the system from overheating. These are the two main types used in trucks for supplemental braking, whereas other descriptors like mechanical, pneumatic, magnetic, or chemical aren’t standard retarders in this context.