USING THE HYDRAULIC RETARDER
WARNING: 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.
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 TCM/ECU to
indicate that the brake system is activated.
NOTE: The retarder is automatically disabled and the lockup clutch is
disengaged whenever the vehicle anti-lock brake system (ABS) is active.
However, in case the ABS system malfunctions, it is recommended that
the retarder enable switch, if present, be disabled.
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 TCM/ECU. In Allison 4
th
Generation Control Systems, the TCM may also activate or limit retarder
operation in response to torque speed control or electronic retarder control
messages received on the vehicle’s J1939 Data Link. Some types of controls and
the amount of retarder application are shown in the Types of Retarder Control
table that follows.
The presence of a retarder must be “autodetected” as part of Allison 4
th
Generation Controls and the WTEC III control system.
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