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Hydraulic retarders are available on some models of the AT 500, MT 600, and HT 700
Series transmissions. The AT 500 retarder and the MT 643R input retarder are located
between the torque converter and the transmission gearing. The MT 600 output
retarder is installed on the rear of the transmission in place of the output housing. The
HT 700 retarder is installed between the torque converter and the transmission
gearing. The function of the retarder is to provide auxiliary retardation.
The AT 500 Series retarder is available on models without lockup or PTO provision.
The MT 643R retarder is available on models with lockup but without PTO provision.
The retarder is an integral part of the transmission which slows the vehicle by
applying a hydraulic braking force. Retardation and cooling are greatest at high input
(engine) speeds. Maintain high input speed by preselecting a lower range. The
external retarder controls (OEM-furnished) consist of a master switch and typical
options shown in Table 1. External retarder controls apply the retarder at the
50 percent or at the 100 percent level. External controls are also required to
automatically turn off the retarder in first range or when the vehicle anti-lock brake
system is activated. External controls also provide a signal to the modulator control.
The signal causes downshifts to occur at a higher speed when the retarder is operating
than would normally occur during closed throttle operation.
The MT 600 Series output retarder is mounted on the rear of the transmission as an
integral part of the transmission and provides your vehicle with an auxiliary
retardation system to slow the vehicle. The unit combines hydraulic and friction clutch
retardation capabilities. In many applications, the retarder is applied in conjunction
with the service brakes.
Table 1. Typical AT/MT Input Retarder Controls
Type Description Amount Of Application
Manual Manual 3-Position Switch 0%, 50%, Or 100%
Automatic 12V or 24V Signal When Closed Throttle Is Sensed 50% Or 100%
12V or 24V Signal When Brake Pedal Is Applied 50% Or 100%
Combination Manual 2-Position Switch and Closed Throttle
Sensor
50% From One Device,
100% From The Second
Device
Manual 2-Position Switch And Brake Pedal Apply 50% From Switch,
100% From Brake Pedal
Closed Throttle Sensor Plus Brake Apply Sensor 50% From Closed Throttle,
100% When Brake Applied
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