Very vague movie description???

...ya know, I just recently saw a film, which has a similar subplot, which you describe; it was on a double-feature 'grindhouse' DVD, coupled with a vicious female motorcycle movie, called "The Hellcats"; anyways, despite the deceptive movie title (...and the equally deceptive attached trailer), I propose that might be looking for the 1971 prison break film, "Chain Gang Women"...