dash controls the engine braking system. Like the
engine brake, the constant throttles are deactivated
when the accelerator or clutch pedal is depressed.
The ABS system, when active, also deactivates
constant-throttle braking.
Exhaust Braking System—CAT,
Cummins, DDE S60, M-B
General Information
An exhaust brake is an optional auxiliary braking sys-
tem 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 maxi-
mum 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 brak-
ing system. The exhaust brake is only active when
the engine speed is between 900 and 2700 rpm. De-
pressing 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 exhaust brake switch is in
the on position, 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 ap-
plications.
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 ex-
haust brake switch is in the off position. Do not turn
the exhaust brake on until the engine has reached
normal operating temperatures.
Driving Downhill
While approaching a steep grade, make sure that the
exhaust brake switch is in the on position. The ex-
haust 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.
CAUTION
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.
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.
Exhaust Brake Operating Characteristics
When you remove your feet from both the accelera-
tor and clutch pedals and the exhaust brake switch is
in the on position, the exhaust brake is applied. The
following conditions should exist if the brake is oper-
ating 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
Engines and Clutches
7.22
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