Terex TA35 Operation, Safety, Maintenance Manual Download

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3-17

Retarder

This switch is used to request the
transmission retarder on TA35
machines. The retarder is engaged
when the bottom of the switch is
pressed and provided that the
transmission 'Stop' warning light is
OUT and the transmission is in
'lockup'. To disengage retarder, press
the top of the switch. On TA40
machines, the retarder switch is
incorporated in the brake pedal. The
first 7° of pedal travel engages the
retarder, provided that the
transmission 'Stop' warning light is
OUT and the transmission is in
'lockup'. Further depression of pedal
applies service brakes. To disengage
retarder, release brake pedal.

The retarder is used to apply a
continuous braking force to hold the

truck to a safe steady speed when descending grades, to reduce the need for
service brake applications, thus reducing service brake wear and preventing
overheating. The retarder may be used anytime to slow down. If additional braking
is required apply the service brakes. The retarder is not meant 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 grade, release accelerator, slow the machine
with the service brakes, select the required gear, and apply the retarder. For maximum
retardation, oil circulation and cooling, the machine downgrade speed (retarder
applied) in the gear selected should be high enough to keep the engine operating
at governed speed. Generally the gear used to ascend a grade is also correct for its
descent. 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 temperatures.
Therefore, the oil temperature gauge should be checked frequently. During normal
operation the gauge should read in the green zone. However, during retarder
operation the gauge can read in the yellow zone.

Provided the vehicle is not in an overspeed condition, the transmission 'Stop' warning
light will illuminate when the transmission oil temperature reaches 140° C (284° F).
The retarder will automatically disengage when the oil temperature reaches 150° C
(302° F). 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.

The transmission will automatically upshift through the gears (to 6th) to prevent the
engine overspeeding, the service brakes should be applied to reduce travel speed.

With the accelerator released, the retarder will automatically engage when the engine
speed reaches 2 100 rev/min and it will disengage at 1 950 rev/min to prevent engine
overspeeding.

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