Simplicity Legacy XL Manuel D'utilisation page 14

Automatic Controlled Traction
Automatic Controlled Traction (ACT) applies a preset
amount of torque to both rear wheels even if one starts
slipping (a transmission without ACT will lose traction
completely if one rear wheel starts slipping). This preset
torque is just enough to provide additional traction, and still
allow the wheels to turn at different speeds in a tight turn
without damaging the lawn.
Under certain circumstances the ACT system limit can be
exceeded, and one of the rear wheels may slip (for instance
if trying to turn up a hill while accelerating). This is normal.
If you start to lose traction, do not speed up. Instead,
slow to a stop, straighten the steering wheel, and slowly
accelerate. Stopping the tractor allows the transmission to
regain more traction.
14