Automatic Retarder Control (ARC) modulates the retarding (braking) of the machine while the machine is travelling downgrade. The ARC allows more concentration on steering and shifting of the machine by the operator. The operator does not need to adjust the retarder control lever.

Automatic Retarder Control (ARC) is a Caterpillar automated brake system on OHT. ARC and the retarder lever function in parallel. The brakes actuate according to the system that is supplying the most brake air pressure. The retarder lever is always functional. The operator must activate the ARC with the on/off switch on the dashboard.

The ARC only functions when all of the following required conditions are present:

1. The on/off switch is in the ON position.
2. The selected transmission gear and the actual transmission gear are the same gear.
3. The engine speed is greater than the activation speed (1800 rpm for 3500 Engines and 2125 rpm for 3400 Engines).
4. The accelerator pedal is not depressed.
5. The machine is travelling downgrade or the engine speed is increasing.

(In other words, above conditions can be obtained only during traveling downgrade) 

When the ARC is active, the control valve for the ARC modulates so that the engine speed is maintained at the control speed. The control speed is set at the factory (1900 rpm for 3500 Engines and 2230 rpm for 3400 Engines).

Retarding is temporarily disabled when the accelerator pedal is depressed. Retarding is enabled again when the accelerator pedal is released.

Protection from Engine Overspeed

This function activates only when the following required conditions are present:

1. The selected transmission gear and the actual transmission gear are the same gear.
2. The engine speed is greater than the activation speed (2100 rpm for 3500 Engines and 2475 rpm for 3400 Engines).

When the function is active, the control valve for the ARC modulates so that the engine speed is maintained at the control speed. The control speed is set at the factory (2180 rpm for 3500 Engines and 2560 rpm for 3400 Engines). The control speed for this function is not adjustable.

Retarding the engine will continue until the engine speed is reduced to the shutoff speed or until the transmission is upshifted. The shutoff speed is set at the factory (2075 rpm for 3500 Engines and 2450 rpm for 3400 Engines). The shutoff speed is not adjustable.

The engine overspeed indicator will flash and a horn will sound when the engine speed reaches the activation speed of the engine overspeed function. For more information, see Systems Operation, SENR4263, "Engine Overspeed Indicator".

EPTC II upshifts the transmission by one gear above the selected gear when the engine speed reaches a critical value. The critical value is approximately 100 rpm greater than the control speed of the engine overspeed function.