DD15 Operator Guide – Descending a Long, Steep Grade

Descending a Long, Steep Grade

An explanation of “control speed” may be helpful in understanding how to use the engine brake system while descending a grade. Control Speed
is the constant speed at which the forces pushing the vehicle forward on a grade are equal to the forces holding it back, without using the vehicle service brakes. In other words, this is the speed the vehicle will maintain without using the service brakes or fueling.
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Use the following guidelines when descending a long, steep grade:‪

1. Before beginning the descent, determine if your engine brake system is operating properly by lifting your foot briefly off the accelerator pedal. You should feel the system activate.
   

   BRAKE FADE ‪
   To avoid injury, do not over apply the vehicle service brakes when descending a long, steep grade. Excessive use of the vehicle brakes will cause them to heat up, reducing their stopping ability. This condition, referred to as “brake fade”, may result in loss of braking, which could lead to personal injury or vehicle/property damage or both.‪

2. Ensure the progressive braking switch is in the appropriate power position.
   

   PERSONAL INJURY ‪
   Failure to keep the vehicle within safe control speed limits while descending a grade may result in loss of vehicle control, which could cause personal injury.‪

   NOTICE:
   Failure to keep the vehicle within safe control speed limits while descending a grade may result in vehicle or property damage or both.‪

3. Do not exceed the safe control speed
   of your vehicle. Example: You could descend a 6% grade, under control only at 10 mph (16 kph) without an engine brake, but at 25 mph (40 kph) with an engine brake. You could not descend that same hill at 50 mph (80 kph) and still expect to remain under control. Get to know how much slowing power your engine brake can provide. So get to know your engine brake system before
   climbing hills and do not exceed a safe control speed.
4. Check your progressive braking switch often for proper position, since road conditions can change quickly. Never skip a step when operating the progressive braking switch.
   Always go from OFF to LOW and then to a higher position when on slippery roads.