Some manufacturers call for ATF in their power steering systems while others call for dedicated power steering fluid. Best to go with whatever the manufacturer recommends, or a synthetic version thereof. Fords, AFAIK, call for ATF, so M1 ATF would be a good choice in them. OTOH, GMs call for PS fluid. I have an 88 Camaro with 150k on the clock, so I run a 50/50 mix of Valvoline Maxlife and Valvoline Synpower PS fluids in my PS system. Works fine.