I did an axle swap yesterday and had to move the blazer half way through. having just finshed installing the rear 12 bolt, every thing hooked back up except the braked lines. I moved the blazer and the brake light in the dash came on. I finished the front and got everything connected and went to bleed the brakes ,but only the front brakes would bleed the rear don't seem to let any fluid out???? someone told me the proportioning valve where the wire hooks up is where the truoble is. any ideas?