•
Road speed usually decreases when the ex-
haust brake is applied during a descent. When
the vehicle is carrying a heavy load or the
grade is extremely steep, you may need to
apply the service brakes occasionally.
•
Do not expect a retarding effect similar to sud-
den hard application of the service brakes. The
exhaust brake retards the vehicle with a
smooth braking effect.
•
During a descent, the tachometer usually
shows a drop in rpm, depending on the grade
and the vehicle load.
•
Depending on the grade and vehicle load, you
may or may not feel the retarding force acting
against your body when the brake is applied.
The retarding force of the brake may not al-
ways be noticed, but it is actually preventing
the vehicle from going much faster.
Make sure the exhaust brake is turned off before
shutting down the engine.
Driving Downhill
While approaching a steep grade, make sure that the
upper half of the exhaust brake switch is pressed in,
with the amber light illuminated. The exhaust brake
comes on as soon as you remove your foot from the
accelerator pedal. While going down the grade, use
a low enough gear to safely descend with a minimum
application of the service brakes. As a general guide-
line, use the same gear as you would to ascend the
hill.
NOTICE
Do not allow the engine to exceed its governed
speed, or serious engine damage could result.
Apply the service brakes to reduce the engine rpm or
make a slower descent by using a lower gear.
Pacbrake® Exhaust Brake
The Pacbrake exhaust brake is intended as a
supplement to the service brakes and will
not
bring
the vehicle to a complete stop. The Pacbrake will
assist in the control or reduction of road speed in
conjunction with, or independent of, the service
brakes. The amount of retarding or braking force is
controlled by the driver.
Pacbrake Operation (Caterpillar)
The Pacbrake is controlled by the exhaust brake
switch and the throttle pedal. All applications are ad-
ditionally affected, controlled, or governed by engine
speed through transmission gear selection. The Alli-
son MD3060 transmission has automatic downshift-
ing when the exhaust brake is requested. See the
information on the "Allison World Transmission" later
in this chapter.
On some applications, when the Pacbrake is in use,
it may be necessary to check that the cruise control
is not set and that the throttle is in the idle position.
On some applications, the engine, transmission,
cruise control, and the Pacbrake exhaust brake may
electronically interact with each other, which auto-
matically operates their functions. Following are
some examples of the programmed options that may
be available with the cruise control in the on position:
•
The coast mode engages the Pacbrake when
the service brake is applied and disengages
when the service brake is released.
•
The latch mode engages the Pacbrake when
the service brake is applied and the Pacbrake
remains on after the service brake is released.
The Pacbrake is disengaged when another
input (depressing the throttle or clutch, engine
speed drops below 800 rpm, or the exhaust
brake switch is turned off) is supplied.
•
The manual mode does not require the cruise
control switch to be on, and operates the
Pacbrake manually at the driver’s discretion.
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
Engines
7.16
