Modern torque converters use electro hydraulic control with the lock-up clutch. The hydraulic circuit which locks/unlocks the torque converter clutch is managed utilizing hydraulic valves. The valves are actuated specifically or indirectly by solenoids. M (highest performance stage): On this stage the torque converter hits its maximum effectiveness as torque https://torqueconverterclutch60357.rimmablog.com/33131168/torque-converter-clutch-for-dummies