Transmission retarders slow a vehicle by which mechanism?

• A. Use mechanical friction at wheels
• B. Use electric motors
• C. Use hydraulic braking
• D. Use fluid friction to slow a vehicle, while service brakes use mechanical friction

Answer: (D)

Transmission retarders slow a vehicle by creating resistance through the transmission fluid itself. They use the hydraulic system inside the transmission to generate drag on rotating components, converting the vehicle’s kinetic energy into heat in the transmission fluid. This slows the vehicle without using the wheel brakes. The service brakes, in contrast, apply mechanical friction at the wheels to slow or stop the vehicle. The other mechanisms described—using electric motors or hydraulic brakes at the wheels—do not describe how a transmission retarder operates. So, slowing by fluid friction inside the transmission is the correct concept.