So driving my 73 Century a couple months back I got stranded with no forward or reverse. It's a 200-4r built up by yours truly with a 2200 stall converter. The trans had worked fine for a year or two. Regular street driving with a few burnouts...no racing. It developed a slippy feel. Barely noticeable. Only very occasionally after a hard pull. So I ignored it to make it go away. Fast forward to the breakdown. I took the car out cold and got a good hard acceleration on it at which point it slipped like crazy. Eased down the road and it got worse fast until I lost forward and reverse. Sitting on the road in D. The engine would rev like I was in neutral but I could lightly hear something sounded like splines slipping or like that. Or loose gears meshing. Shut it off dragged it home left it 2 months. Finally dropped the trans figuring I broke something hard inside. Full disassembly reveals no damage. Clutches, steels, hard parts all good. Air tests fine. Pump is good. Fluid is pristine. I need to look at the valve body still but I imagine that will be fine. The only thing I can imagine is a bad torque converter. Losing both forward and reverse at the same time. Trans internals good. Wtf? I have not had a converter failure before. Is this a failure mode? Anyone have this happen?