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Brake on through

Most tractors today come equipped with an Automatic Traction Control (ATC) system and the functionality is optional on most all of today’s trucks. While active, the system monitors the drive axle sensors (4S/4M – 4 sensors/4 modulators or 6S/6M 6 sensors/6 modulators). When the outer end spins under acceleration, the system will apply that brake, moving power to the other outer ends. If the condition continues, engine torque will drop to reduce wheel spin to keep from overheating the brakes. There is also an illuminated ATC light in the dash, indicating a spinning outer end, with active ATC and a mismatch between outer end speeds.


The system either includes or has an optional switch in the dash labelled as ATC or TC. When in existence the system default is on, the switch is for override at low speeds. If the chassis comes with optional mechanical locking axles (lockers), and has the ATC switch, the system should be turned off when the locks are engaged, to eliminate a conflict. If both are engaged, brakes will be applied to the spinning drive axles and the engine will de-rate. For this reason it is imperative to have a switch that turns ATC off with locking axles. Once the chassis gets to road speeds, the ATC function will automatically reengage.


The chassis might come with a Mud and Snow switch. When engaged this feature allows a permissible amount of outer end spin during acceleration. This is designed to increase the available traction in inclement or off-road conditions. When the spin event occurs, usually the ATC light blinks on/off.


The ABS Off-Road switch desensitizes the antilock brake system. This switch is, as noted, used for improved off-road stopping. It permits a longer brake lockup period, which allows the tire to build up material (wedge) in front of the tires, so that they have to ride up over the material, which makes stopping more effective in off road conditions. This can be activated at slower speeds, usually less than 25 MPH. At speeds above the programmed threshold the feature is locked out. This function is not allowed with Automatic Traction Control, so you must make a decision about which system is most important in the customers application.

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