A vehicle automatic transmission including a torque converter having a lock up clutch. A lock up control circuit is provided and has a memory including a first lock up control line for controlling the engagement and release of the lock up clutch when the torque converter turbine speed is close to the pump impeller speed, and a second lock up control line which is drawn along a line wherein the engine output torque is substantially zero so that the lock up clutch is released at a given engine load when the turbine speed is decreased beyond the first lock up control line, or when the turbine speed is increased beyond the second lock up control line.