Read the following information in order to become familiar with the compression brake controls that are in the vehicle.
The compression brake controls may vary slightly depending on the design of the vehicle cab. The basic operation of the compression brake does not change if the switches are in a different location.
ON/OFF Switch - This switch activates the system for the compression brake.
Progressive Braking Switch - This switch allows various settings for different conditions.
LOW Setting - This switch position will activate the braking function on two cylinders. This setting will provide approximately one-third of the total available braking horsepower. This setting is typically used on flat roads when light loads are hauled.
MED Setting - This switch position will activate the braking function on four cylinders. This setting will provide approximately two-thirds of the total available braking horsepower. This setting is typically used when the LOW setting is not adequate in order to provide the desired braking horsepower.
HIGH Setting - This switch position will activate the braking function on all six cylinders. This setting will provide full braking horsepower. This setting is typically used on downhill grades or the setting is used when heavy loads are involved. Use this setting only when there is good traction.
In addition to the switch controls that were previously discussed, other switches are available. A control switch exists for the compression brake that is activated by the position of the clutch pedal. There is also a switch that is activated by the position of the accelerator pedal.
The function of the compression brake operates in much the same manner regardless of a manual transmission or an automatic transmission. However, some vehicles are equipped with autoshift transmissions. In this situation, the compression brake may actuate in order to help the transmission make an upshift. This feature is controlled automatically through the transmission control module. This automatic control can happen even if the compression brake switch is in the OFF position.
Additional system controls may temporarily interrupt the operation of the compression brake. These parameters vary by OEM, but the parameters may occur under the following conditions.
- Engine speed is below 1000 rpm.
- The vehicle slows to a preset speed.
- This may occur when the torque converter shifts out of lockup in vehicles with automatic transmissions. This is usually between 10 to 25 mph.
The information that is shown in the Operation and Maintenance Manual, "Auxiliary Engine Brakes" must be read and understood before proceeding to the following information.
- Before descending a long grade or a steep grade, test the compression brake in order to ensure proper operation.
- Never exceed a safe control speed.
- Do not use the compression brake when the vehicle is "bobtailed".
- Do not use the compression brake when an empty trailer is pulled on wet pavement or slippery pavement. This is particularly important if the vehicle has a single drive axle.
- Do not shift gears without using the clutch when the compression brake is turned on. Do not make a double clutch when the compression brake is activated. Power train damage may occur.