1998 Saturn SC2 • 4 cylinder FWD • 85,000 miles

The brake pedal all of a sudden started going to the floor, checked for leaks and fluid level, no problems there. Back brakes had been completely replaced sometime last year. So I figured it was the master.I replaced it, bled it and all 4 wheels, pedal was fine, gave it back to my niece, pedal went back to the floor again. So I bled a 4 wheels again and found air at the rear, pedal came back. Gave it back and it has happened 2 more times. Found air in the rear every time. Does anyone have any ideas, maybe I got a bad master again?It has drums in the rear and no abs if that helps.
March 22, 2011.

Could be a bad new master cylinder, its probably leaking internally if there's no external leak-

Mar 22, 2011.
So are the rear wheel cylinders leaking?It's very common for the rear wheel cylinder's to leak I have replaced a lot of them. Get a small flat blade screwdriver and gently move back the dust cover to see if there is fluid behind the cover if there is replace the wheel cylinder. Did you bench bleed the master before installing it?Also do you have abs brake's?

Mar 22, 2011.