no fluid to rear sounds like the check valve in the proportioning valve is stuck in one direction. This can happen if you have one side or the other open and you push down on the pedal hard. Is you valve the one with the electric switch to tell you if the brakes are bad? when the valve moves it lites up the brake light if it is hooked up. Sometimes they will not come back to center and have to be replaced. Loosen the lines to the valve and check for fluid. Retighten the lines then loosen the outbound lines from the valve and check for fluid when depressing the pedal.
