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to slow the vehicle. When a lower speed is reached, the ECU will automatically
down-shift the transmission. Engine braking provides good speed control for going
down grades. When the vehicle is heavily loaded, or the grade is steep, it may be
desirable to preselect a lower range before reaching the grade. If engine-governed
speed is exceeded, the transmission will upshift automatically to the next range.
USING THE HYDRAULIC RETARDER
Regardless of the type of Allison retarder controls on your vehicle, the following
safety features are common to each configuration:
• The retarder can be disabled when inclement weather or slippery road
conditions are present.
• Vehicle brake lights should always be on when the retarder is applied
(periodically verify that they are working).
• Anti-lock brake systems send a signal to the transmission ECU to indicate that
the brake system is activated.
A hydraulic retarder is available on all of the models covered in this manual. The
retarder is activated and controlled in various ways. The control depends upon the
vehicle type and particular duty cycle. Both manual and automatic controls are
available. Automatic controls are applied by the ECU. Some types of controls and
the amount of retarder application are shown in Table 1 on Page 20.
WARNINGS: DO NOT USE THE RETARDER DURING
INCLEMENT WEATHER OR WHEN ROAD SURFACES ARE
SLIPPERY. De-energize the retarder at the master control switch.
To help avoid injury or property damage caused by loss of vehicle
control, be ready to apply vehicle brakes or other retarding device if
the transmission retarder does not apply. If a retarder is present but is
not detected by “autodetect”, the retarder will not function. Be sure to
check for proper retarder function periodically. Whenever the retarder
does not apply, seek service help immediately.
On vehicles which have the primary retarder control based upon
closed throttle position, brake pedal position, or brake apply pressure,
always manually disable the retarder controls during inclement
weather or slippery road conditions.
NOTE: The retarder is automatically disabled (and the lockup clutch is
disengaged) whenever the vehicle ABS (anti-lock brake system) is
active. However, in case the ABS system malfunctions, it is
recommended that the retarder enable switch, if present, be disabled.
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