It takes more than flipping an on/off switch to get the most from your engine retarder.

Without an engine brake, diesels don’t produce much braking compared with car engines because they lack a throttle – the biggest source of engine braking in a car. Truck diesels are also small for the weight of the vehicle, which is one reason trucks sometimes run away on steep downgrades.

Clessie Cummins, who invented the Cummins diesel, also invented the Jacobs Engine Brake, commonly known as the “Jake Brake.” The Jake Brake and its competitors use hydraulics powered by the engine’s existing valvetrain parts to convert your truck diesel into a retarder that stops almost as hard as the engine pulls under power.

The engine brake adds little to engine wear. Its biggest advantage is that it works by compressing and releasing air, eliminating the friction between dry parts of a service brake system, so it will never overheat. Having an engine brake not only will help you descend steep grades safely, it will significantly cut your maintenance costs because it will save your service brakes.

Proper operating
An on/off switch allows you to turn the engine brake off altogether or allow it to operate when the throttle and clutch pedals are fully released (your feet are off).

The brake is also controlled by a “Low/High” or Low/Medium/ High”dashboard switch with two or three positions, so you can match the power of the brake to road conditions. With a two-position switch, you get braking action on either all six cylinders or three of them, giving either full power or half power. With three positions, the switch settings engage six, four or two of the engine’s cylinders, giving full braking power, two-thirds or one-third power.