62 Falcon with 69 Mustang drive line (250cubic inch 6 cylinder & C-4 trans). Before engine swap from 170 cubic inch 6 cylinder all worked well. After engine swap when drive is selected RPM will drop to show trans engaged but will not move vehicle. Only change with swap was stock torque converter replaced. What is wrong?
If all worked well before the engine swap and the only thing replaced was the torque converter see if the new converter cross referances with the old stock number for the C4 transmission. The input shaft and or the splines on the front pump may not match. You could try the old converter to see if it is at fault.