785G Off-Highway Truck Caterpillar

The retarder will not apply full braking capacity.

Manual Retarder Control (Lever)

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Aggressive application of retarder capacity in slippery conditions may cause loss of operator control and/or power train damage. Apply the retarder gradually in slippery conditions. Serious injury or death may occur if the retarder is applied too aggressively in slippery conditions.

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Manual Retarder Control (Lever) (1) - The manual retarder control (lever) is used to manually regulate the machine speed when you travel down a grade. Move the lever rearward in order to apply more retarding force and slow the machine. Move the lever forward in order 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) (If Equipped)

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When the proper gear is selected during Automatic Retarder Control (ARC) operation, machine speed and engine speed will be automatically regulated. When the transmission shifts to the selected gear and the engine rpm increases to 1900 rpm, the ARC will apply the retarder in order to maintain the engine speed at 1900 ± 50 rpm. Use the manual retarder control lever in order to apply additional retarding during operation of the ARC.

Automatic Retarder Control (ARC) Switch (2) - Push the top half of The ARC on/off switch in order to select the ON position for the ARC. Push the bottom half of the switch in order to select the OFF position for the ARC.

The ARC on/off switch should remain in the ON position during all normal operation. When you place the switch in the OFF position, the ARC will not control the engine speed during normal operation. However, the ARC will override the switch if the engine speed is too high. See the Operation and Maintenance Manual, "Changing Direction and Speed" in order to learn more about the engine overspeed protection.

Machine Speed Control (MSC) (If Equipped)

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When the proper gear is selected during Automatic Retarder Control (ARC) operation, machine speed and engine speed will be automatically regulated. When the transmission shifts to the selected gear and the engine rpm increases to 1900 rpm, the ARC will apply the retarder in order to maintain the engine speed at 1900 ± 50 rpm. Use the manual retarder control lever in order to apply additional retarding during operation of the ARC.

Machine Speed Control (MSC) Switch (2A) - Push the top half of The ARC on/off switch in order to select the ON position for the ARC. Push the bottom half of the switch in order to select the OFF position for the ARC.

The ARC on/off switch should remain in the ON position during all normal operation. When you place the switch in the OFF position, the ARC will not control the engine speed during normal operation. However, the ARC will override the switch if the engine speed is too high. See the Operation and Maintenance Manual, "Changing Direction and Speed" in order to learn more about the engine overspeed protection.

Retarding Information and Conditions

The maximum operating weight of a loaded 785D Off-Highway Truck is 250000 kg (550000 lb).

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785D film for retarding guidelines

Selected Gear - This column represents the gear that is selected on the transmission control before descending down a grade.

Percent Grade - This column represents the percent of grade. The "X" value above the column represents the distance of the grade.

Approximate Retarding Speed - This column represents the approximate machine speed that will be held by the ARC on a given grade and a given gear.

The film that shows the retarding capabilities for your machine's configuration is located on the inside of the cab. Refer to Operation and Maintenance Manual, "Additional Messages" for more information. 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, the condition of the cooling system, tire size and altitude.

Engine speed that is relative to ground speed will vary due to differences in tire size and types.

Travel at a constant machine speed. Do not speed up immediately before you retard the machine. Do not try to do all the retarding at the bottom of a hill. Keep retarding steady and keep the machine speed under control. The ground speed must be slow enough for the conditions and at a rate that will not cause the brakes to overheat. Slow down the machine for better brake cooling. Do not travel at high ground speeds and do not stop in a short distance.

Selection of the proper gear is essential for effective operation of the retarder system. Refer to the film for retarding guidelines in order to select the proper gear.

When the film for retarding guidelines 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.

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Put the shift control lever (3) in the P position 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, "Operator Controls".

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Frequently observe brake oil temperature gauge (4). 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 in order to slow the machine speed. For additional cooling, park the machine in a safe location and 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 (5) will illuminate when the automatic retarder control is engaged. Indicator (5) will illuminate when retarding is applied with the manual retarder control.

Never coast down a grade in neutral. Always keep the transmission in gear.

Note: The power train ECM will prevent shifting from a forward gear to NEUTRAL at ground speeds that are greater than 8 km/h (5 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 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 in order to reduce the ground speed. Avoid repeated engaging and disengaging of the retarder control lever. Adjust the retarder control lever in order 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.

Maintain the engine speed under 1950 rpm.

Note: If the engine speed reaches 2150 rpm, the Automatic Retarder Control (ARC) will automatically begin to apply the brake. If the engine speed reaches 2300 rpm, the transmission will upshift to the next higher gear. If the transmission is in the highest gear and the engine speed reaches 2300 rpm, the torque converter will shift into TORQUE CONVERTER DRIVE in order to protect the power train from engine overspeed.