General Information
Warning: To avoid injury from loss of vehicle control, do not activate the engine brake system under the following conditions:
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on wet or slippery pavement, unless the vehicle is equipped with antilock braking system (ABS) and you have had prior experience driving under these conditions;
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when driving without a trailer or pulling an empty trailer;
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if the tractor drive wheels begin to lock, or there is fishtail motion after the engine brake is activated.
Each engine manufacturer uses a specific engine brake for their engine. Regardless of the manufacturer, the engine brake is operated with the principles outlined in this chapter. Refer to the engine manufacturer's operation manual for details of their particular engine brake product.
Whenever vehicle braking is required on good road conditions, the engine brake may be used in conjunction with the service brakes. There is no time limit for operation of the engine brake. However, an engine brake does not provide the precise control available from the service brakes, and is not a substitute for a service braking system.
Warning: Usage of the engine brake as the primary braking system can cause unpredictable stopping distances, that could result in personal injury or property damage. Service brakes are the primary vehicle braking system.
There are two switches that control the engine brake.
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The dash mounted ON/OFF switch (ENG BRK), is used to turn the engine brake ON and OFF. See Fig..
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The HI/MED/LO (in some cases HI/LO) engine brake level switch on the dash, controls the amount of engine braking.
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Engine Brake ON/OFF
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Engine Brake Intensity Switch
Fig. 1, Engine Brake Switches
Since the engine brake is most effective at rated engine speed, gear selection is very important. Gearing down the vehicle, within the limits of the rated engine speed, makes the engine brake more effective. Recommended engine braking speed is above 1800 rpm and below the rated speed.
Warning: The engine brake must be disengaged when shifting gears using the clutch pedal. If the engine brake is engaged when the transmission is in neutral, the braking power of the engine brake can stall the engine, which could result in loss of vehicle control, possibly causing personal injury and property damage.
Notice: Do not allow the engine to exceed 2500 rpm. Serious engine damage could result.
"Control speed" is the speed at which the engine brake performs 100 percent of the required downhill braking, resulting in a constant speed of descent. The control speed varies, depending on vehicle weight and the downhill grade.
For faster descent, select a higher gear than that used for control speed. Service brakes must then be used intermittently to prevent engine overspeed and to maintain desired vehicle speed.
A driver may descend slower than control speed by selecting a lower gear, being careful not to overspeed the engine. Occasional deactivation of the engine brake may be necessary to maintain the designated road speed under these conditions.
Below a set engine temperature when the engine is cold, the brake may be disabled depending on the brake type.