freightliner S2 Operator's Manual page 91

switch is on, an amber light emitting diode (LED) illu-
minates inside the switch. When the panel lights are
on, the EXHST BRK legend is backlit in green.
11/28/2001
Fig. 13.3, Exhaust Brake Switch
The exhaust brake is only active when engine speed
is between 1100 and 2700 rpm. Depressing the ac-
celerator or clutch pedal deactivates the exhaust
brake. The ABS system, when active, also deacti-
vates the exhaust brake.
The exhaust brake is a butterfly valve mounted in the
exhaust pipe. When the driver's foot is not on the
accelerator pedal and the upper half of the exhaust
brake switch is pressed in, with the amber light on
the switch illuminated, an air cylinder shuts the but-
terfly valve, which restricts the flow of exhaust gases
and retards the engine. This retarding action is car-
ried through the engine and drivetrain, slowing the
vehicle and reducing the need for frequent service
brake applications.
Exhaust brakes are not intended for use as the pri-
mary braking system during vehicle operation.
Starting the Engine
Before starting the engine, make sure that the lower
half of the exhaust brake switch is pressed in and
the amber light is not illuminated. Do not turn the ex-
haust brake on until the engine has reached normal
operating temperatures.
Operating Characteristics
WARNING
Do not use the exhaust brake when driving on
slippery or low-traction road surfaces. Failure to
Hydraulic and Air Brake Systems
follow this precaution could result in a loss of
vehicle control and possible personal injury or
property damage.
When you remove your feet from both the accelera-
tor and clutch pedal (if so equipped), and the upper
half of the exhaust brake switch is pressed in with
the amber LED illuminated, the exhaust brake is ap-
plied. The following 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 as normal.
•
Engine temperature should remain in the nor-
mal operating range.
f610589
•
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, the driver 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.
Driving Downhill
While approaching a steep grade, make sure that the
upper half of the exhaust brake switch is pressed in,
with the amber LED 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.
13.6