On Slippery Road Surfaces - Mack Granite GU Series Operator's Handbook Manual

In any gear selection higher than sixth gear (in this example), it would be
necessary to occasionally apply the service brakes to maintain a safe vehicle
speed and to avoid overspeeding the engine.
DANGER
As with any vehicle, regular and excessive application of the service brakes
during a downhill descent can lead to a brake lining overheat condition, resulting
in a very dangerous loss of service brake retarding capability.
Note: The previous figures apply only to this hypothetical example. Specific vehicle
control speeds and engine speeds for a given descent are dependent upon the actual
vehicle and engine configurations, the gross weight of the vehicle, and the percent
grade of the road.

On Slippery Road Surfaces

As with many aspects of operating a heavy-duty vehicle, special care should
be taken when using the MACK PowerLeash™ Engine Brake on slippery road
surfaces. The potential for unpredictable loss of vehicle traction is a serious
concern; in some situations the engine should not be used at all.
As always, approach untested driving conditions with caution. Avoid use of the
MACK PowerLeash™ Engine Brake in these situations until you have gained
some experience under normal driving conditions.
As a rule, make sure that the vehicle is demonstrating good tractability with the
engine brake off before checking for tractability with the engine brake enabled.
Then, provided traffic conditions are safe for "testing" tractability, switch the
MACK PowerLeash™ Engine Brake to the LOW position. If the vehicle shows
any signs of loss of control (ABS activation or vehicle swerving, for example),
immediately switch the engine brake back to the OFF position.
OPERATION 157