I did a disc brake conversion on my 70 El Camino.Everything is new including the brake lines from inline tube,I tried bleeding the brakes today but I can't fluid to the rear brakes.It seemed it started to flow then stopped.I have fluid at the front.I used a vacuum pump and the old fashion way but can't get anything.Is there some kind of reset on the proportioning valve,this is the one I have.Is the reset under the black rubber cover.I'm wore out, any help on this would be much appreciated