freightliner BUSINESS CLASS M2 Driver Manual page 86

the amber light is not illuminated. Do not turn the ex-
haust brake on until the engine has reached normal
operating temperatures.
When you remove your feet from both the accelera-
tor and clutch pedals and the upper half of the ex-
haust brake switch is pressed in with the amber light
illuminated, the exhaust brake is applied. The follow-
ing conditions should exist if the brake is operating
properly:
•
A slight change in the sound of the engine may
be noticed when the exhaust brake is applied.
•
Exhaust smoke should appear normal.
•
Engine temperature should remain in the nor-
mal operating range.
•
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.
Engines
7.16