Controls and Operating
3-29
Transmission Retarder
This switch is used to request the transmission retarder. The retarder will
engage when the switch is pressed (refer to Section 3) and provided that
the transmission 'Stop' warning light is 'OUT', the transmission is in
'lockup', accelerator pedal is released (off gas) and the transmission oil
temperature is within operating range. Refer to Section 3 for details to dis-
engage the retarder.
The retarder is used to apply a continuous braking force to hold the truck
to a safe steady speed when descending gradients, to reduce the need
for service brake applications, thus reducing service brake wear and pre-
venting overheating. The retarder may be used any time to slow down. If
additional braking is required, apply the service brakes. The retarder is
not intended for bringing the machine to a halt, or for sudden deceleration
- the service brakes should be employed for this purpose.
Retarder Operation
Before the machine starts down the gradient, request the retarder and
release the accelerator (off gas). For maximum retardation, oil circulation
cooling and the machine downgrade speed (retarder applied), it is recom-
mended that the gear should be preselected manually. The manually pre-
selected gear should be high enough to keep the engine operating at gov-
erned speed. Generally the gear used to ascend a grade, fully laden, is
also correct for its descent. Please refer to the gradeability decal for rec-
ommended gear selection per grade specification. If the rate of descent is
too slow, the transmission should be upshifted to the next highest gear. If
the rate of descent is too fast, the service brakes should be applied and
the transmission shifted into a lower gear which will allow a safe descent
and efficient retarder operation.
Frequent use of the retarder will result in higher transmission oil tempera-
tures. Therefore, the converter oil temperature gauge should be checked
frequently. During normal operation the gauge should read between 80
o
C
and 110
o
C. However, during converter mode temperatures may reach
120
o
C, and during retarder operation the oil temperature can reach
140
o
C.
NOTICE: The transmission 'CHECK' warning light and transmission tem-
perature warning symbol on the display screen will illuminate when the
transmission oil temperature reaches 140 °C. The retarder will automati-
cally disengage when the oil temperature reaches 150 °C. The speed
must be reduced by using the service brakes so that the oil is cooled
down. Reduce downgrade travel speed to avoid the oil overheating and
possible damage to the transmission.
If the machine is approaching an overspeed condition, the transmission
upshifts automatically through the gears (to 6th) to decrease the engine
speed, whether in manual or automatic mode.
With the accelerator released (off gas) the retarder will then automatically
apply when the machine speed reaches 2150 rev/min and will disengage
at 1650rev/min. The service brakes can be applied to reduce travel speed
further.
When the retarder temperature reaches 150°C the retarder is disengaged
and a fault code will be displayed and recorded by the ECU.
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