freightliner M2 Plus 2023 Manual page 148

Brake Systems
When the exhaust brake switch is on, an amber LED
illuminates inside the switch. When the panel lights
are on, the EXHST BRK legend is backlit in green.
Mercedes-Benz Exhaust Brake
An exhaust brake is an optional auxiliary braking
system that assists but does not replace the service
brake system. The exhaust brake can be used alone
or together with the constant-throttle valves for steep
or long grades. The exhaust brake switch located on
the control panel, in combination with the accelerator
and clutch pedals, allows the driver to make
maximum use of the exhaust brake in off-highway
and mountain driving as well as in traffic or high-
speed highway driving.
When only the exhaust brake is installed, a two-
position switch on the dash controls the engine
braking system. The exhaust brake is only active
when the engine speed is between 1100 and 2700
rpm. Depressing the accelerator or clutch pedal
deactivates the exhaust brake. The ABS system,
when active, also deactivates 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
butterfly valve, which restricts the flow of exhaust
gases and retards the engine. This retarding action is
carried 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
primary braking system during vehicle operation.
Operating Characteristics
WARNING
Do not use the exhaust brake when driving on
slippery or low-traction road surfaces. Failure to
follow this precaution could result in a loss of
vehicle control and possible personal injury or
property damage.
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
exhaust brake on until the engine has reached
normal operating temperatures.
When you remove your feet from both the
accelerator and clutch pedals and the upper half of
11.5
the exhaust brake switch is pressed in with the
amber light illuminated, the exhaust brake is applied.
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 normal.
•
Engine temperature should remain in the
normal operating range.
•
Road speed usually decreases when the
exhaust 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
sudden 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
always 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
guideline, 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.