A retarder is a secondary braking system installed on heavy trucks and buses to slow the driveline without using the primary friction brakes. It operates using hydraulic fluid drag or electromagnetic induction to generate resistance against the driveshaft or transmission. This system absorbs massive amounts of kinetic energy, preventing the service brakes from overheating and failing during long downhill descents.
Hit the retarder before we crest this grade so we don't cook the drums on the way down.
Drivers must turn off driveline retarders on wet or icy roads, as the sudden drag on the drive axles can easily induce a dangerous skid.
Also heard as
- driveline retarder
Do not mix it up with
- Engine braking: Engine braking uses internal engine compression and valve timing to slow the vehicle, while a retarder applies hydraulic or magnetic resistance directly to the driveline.
Related terms
Brake fade
The loss of stopping power caused by excessive heat buildup in the braking system.
Engine braking
A deceleration technique that slows a vehicle by letting the drivetrain drag against the engine's internal resistance.
Heavy vehicle
A large commercial truck or bus designed to carry extreme loads or numerous passengers.