Introduced in 1990. The A518’s torque converter definitely does not lock up. My 90 D150 is my daily and even though it does not lock up this transmission has saved me a bunch on gas. Old school non locking TC transmissions are 90-92 I believe. When I sourced a A518 for my duster it was from a van at the junk yard. The identifier I used was the 3 wire connector. I chose the a518 transmission because what I’ve read is that you can run a 727 converter in the non locking converter a518. I wanted this option to run a loose converter 3500 stall. This is all of course if I ever get around to finishing my project.