Paccar PX 8 Operator's Manual - page 44
Operating Instructions
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Y53-1030A 12/09
PACCAR
WARNING! Do not use an engine brake when
driving bobtail or with an unloaded trailer. There
may not be enough weight on the rear axle to
provide traction. This could cause a lose of con-
trol and jackknife resulting in an injury accident.
Make sure the engine brake is switched OFF
when bobtailing or with an unloaded trailer.
Control speed is the speed at which the forces
pushing a vehicle down a grade are equal to the forces
holding it back.
CAUTION: Never exceed governed engine speed
because engine damage can occur. Operating
engine beyond the governed speed causes addi-
tional strain on valve train and internal engine
components. Operate the engine within gov-
erned engine speed.
NOTE: Once you have determined what the safe
speed is for your vehicle, operate the engine brakes
with the transmission in the lowest gear that will not
cause the engine speed to exceed the rated engine
speed. The optimum braking power of the engine
brakes is reached at rated engine speed. Correct
gear selection, therefore, is critical.
The two-position selector switch can be used to vary braking
power as road conditions change.