What was the very first Sentai Live Action Series?
 

does anyone know?

And the answer is the GORANGERS back in 1975. Though the first Mecha(Megazord) didn't appear until a few years later in a series called Jaq, or something like that I beleive.
The original Ranger suits looked like monster rejects from Finster's monstermatic, lol. Check out their pic at PowerRangersCentral.com
go tot he photo galleries and then to sentai and it'll give ya pics of every sentai from 1975 up to GOGOV (Lightspeed Rescue)