freightliner BUSINESS CLASS M2 Driver Manual page 87

Engines
The amount of braking power the engine will develop
is related to the speed (rpm) of the engine. The
higher the engine rpm, the greater the retarding
power.
Certain conditions may require that the transmission
be downshifted in order to generate adequate rpm
for the amount of retarding power required. Pacbrake
exhaust brakes are designed and approved for safe
use at 300 rpm above the engine's maximum gov-
erned rpm. Refer to individual engine manufacturer's
specifications.
The Pacbrake will function best if it is used all of the
time. However, if the vehicle is used inconsistently or
seasonally, it may be necessary to perform a preven-
tive maintenance procedure.
1. With the engine shut down, use any oil-free or
nonpetroleum-based high-heat lubricant, and
spray or coat a sufficient amount on the restricter
valve shaft and the attaching locations at each
end of the actuation cylinder. See
A
A
03/06/2000
A. Lubrication Point
Fig. 7.20, Pacbrake Exhaust Brake and Air Cylinder
2. With your hands or a pair of pliers, motion the
valve several times to distribute the lubricant
down the shaft and the attaching locations.
NOTE: Starting the engine and idling for short
periods of time is not recommended. During a
cold engine start-up, enough moisture is devel-
oped within the engine and the exhaust system
to create a corrosion hazard that could affect
the future operation of the Pacbrake. The brake
housing may trap water in the valve shaft bore
causing corrosion in an improperly functioning
7.17
or nonfunctioning brake. If it is necessary to pe-
riodically start the engine, it is recommended
that normal operating temperatures be attained
before shutting down the engine.
Allison World Transmission
Pacbrake exhaust brakes used with the Allison World
Transmission MD series, are interfaced with the
transmission electronic control module (ECM). An
exhaust-brake-enabled transmission ECM will usually
provide converter lockup in gears two through six.
Effective exhaust braking begins when the transmis-
sion automatically downshifts into fifth gear (62 mph
or less). Once on, the Pacbrake exhaust brake will
control road speed and/or slow the vehicle suffi-
ciently that the transmission will automatically down-
shift, if necessary, to Allison's preselect mode.
The preselect mode is normally assigned to second
gear; however, the transmission can be repro-
grammed by an Allison Transmission Distributor to
Fig. 7.20.
third or fourth gear, should the operator desire. If ad-
ditional retarding power is required before the auto-
A
matic downshifting occurs, you can select a lower
transmission gear on the Allison shift selector.
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