Note: The optional engine brake provides engine compression braking automatically. The engine brake will only function when the switch for ARC is in the ON position. For more information on the engine brake, refer your machine Operation and Maintenance Manual, "Operator Controls".
Reference
Operation and Maintenance Manual, "Retarding"
Systems Operation, "Automatic Retarder Control (ARC)"
Manual Retarder Control (Lever)
| NOTICE |
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Do not use the retarder control as a parking brake or to stop the machine. |
| NOTICE |
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When you quickly apply the entire retarder capacity on a slippery road, the wheels can lock and the transmission can downshift. This can cause serious damage to the power train. Gradually apply the retarder control on slippery roads in order to prevent the wheels from locking and the transmission from downshifting. |
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| Illustration 1 | g01242261 |
| Manual Retarder Control (Lever) (1) - The manual retarder control (lever) is used to regulate the machine speed when you travel down a grade. Move the lever rearward to apply more retarding force and slow the machine. Move the lever forward to reduce retarding force and allow the machine speed to increase. When the lever is in the full forward position, the manual retarder is off. |
Automatic Retarder Control (ARC)
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| Illustration 2 | g02174275 |
| Automatic Retarder Control (ARC) (2) - Push the top half of the switch to select the ON position for the ARC system. This action allows the machine to maintain a constant downhill speed. Push the bottom half of the switch to select the OFF position for the ARC system. |
When the proper gear is selected during ARC operation, vehicle speed and engine speed will be automatically regulated. If necessary, use the manual retarder control to apply more retarding force during the operation of ARC.
The ARC should remain in the ON position during normal operation. When you place switch (2) in the OFF position, the ARC will not control engine speed during normal operation. However, if the engine speed becomes too high, the ARC will perform engine overspeed protection.
Engine Overspeed Protection
This machine is equipped with automatic engine overspeed protection. If the engine speed reaches 2475 rpm, the ARC system will automatically engage, regardless of the position of the ARC switch. To prevent further engine overspeed, the transmission will upshift one gear if the following conditions are met:
- Engine speed reaches an unsafe engine speed.
For the engine overspeed rpm of your machine, refer your machine Changing Direction and Speed, "Operator Controls". - Transmission is in the same actual gear as the selected gear on the transmission control.
Retarding Guidelines (Film)
| NOTICE |
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Retarding performance charts provide an indication of the energy absorption capability of a given truck powertrain on a specified continuous, and less than 610 m (2000 ft) decline. Retarding performance charts serve to indicate the correct transmission gear selection and ground speed that should be used on a given grade to avoid situations which may result in machine overspeed and damage to the machine. Retarding performance charts do not give an indication of the ability of the truck to stop or the ability of the truck to remain stationary on the grades that are listed on the chart. |
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| Illustration 3 | g01260983 |
773G film for retarding guidelines | |
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| Illustration 4 | g01260990 |
775G film for retarding guidelines | |
The film for retarding guidelines is located inside the cab.
| Maximum Operating Weight - The maximum operating weight of a loaded Off-Highway Truck |
| Transmission Gear for the Downgrade - The selected gear for downhill travel |
| Downhill Slope Percentage - The percentage value of the slope for downhill travel |
| Distance of the Downgrade - The distance of the slope for downhill travel |
The retarding capabilities that are listed on this film are based on an ambient temperature of 32 °C (90 °F).
The actual retarding capabilities for each gear will vary depending on the following conditions:
- Outside temperatures
- Rolling resistance
- Load
- Cooling system condition
- Tire size
- Altitude
Retarding Information and Operation
Selection of the proper gear is essential for effective operation of the retarder system. Refer to the film for retarding guidelines to select the proper gear.
Select the proper gear on the transmission control before you start down the grade. The actual gear should also match the selected gear before you start down the grade. For more information on the transmission control, refer to Operation and Maintenance Manual, SEBU8561, "Operator Controls".
When the film does not address the current conditions, use the following rule: The desired gear on a downgrade is the gear that is required to go up the grade when the machine is loaded.
The ground speed must be slow enough for the conditions and at a rate that will not cause the brakes to overheat. Braking should be steady. Slow down the machine for better brake cooling. Do not travel at high ground speeds and do not stop in a short distance.
Note: Engine speed must be at least 1700 rpm to circulate sufficient brake oil through the oil cooler. This oil will keep the disc brakes cool.
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| Illustration 5 | g01449286 |
Frequently observe brake oil temperature gauge (3) . If the needle enters the red range on the gauge, the capacity of the brake oil cooler has been exceeded. Reduce the load on the machine to slow the machine speed. For additional cooling, park the machine in a convenient location. Put the transmission in PARK. Run the engine at high idle.
Note: If the brake oil temperature is high after going down the grade, select a lower gear when you travel down the grade again.
Indicator light (4) will illuminate when the ARC is engaged or retarding is manually applied with the retarder control lever.
Never coast down a grade in neutral. Always keep the transmission in gear. The chassis ECM will prevent shifting from a forward gear to NEUTRAL at ground speeds that are greater than 8 km/h (5 mph). Also, the Chassis Electronic Control System will prevent shifting from a forward gear to REVERSE gear at ground speeds that are greater than 5 km/h (3 mph).
Attempting to prevent upshifting on a downgrade that is long or steep by retarding can be unsuccessful. The transmission control should be in the desired gear before you start the downgrade. The actual gear should match the selected gear before you start the downgrade. If you rely on retarding, engine speed may reach the upshift point. The lower engine speed reduces brake cooling oil flow. This reduction in oil flow can cause overheating of the brakes.
When the service brake or the retarder is applied, the transmission upshift point is raised to a higher rpm than a normal shift point.
If you experience undesired shifting, move the transmission control to the proper gear.
If the machine builds up excessive speed during retarding, the engine can overspeed. Use the manual retarder lever to reduce the ground speed. Avoid repeated engaging and disengaging of the retarder control lever. Adjust the retarder control lever to maintain a proper rpm and a constant speed. If skidding is experienced, ease off the retarder control lever.
If additional braking is still needed, depress the service brake. Maintain a constant vehicle speed. Do not speed up and brake. Do not try to do all of the braking at the bottom of the hill. Keep braking steady and keep ground speed under control.