I have a 00 xj..i put new brake system all the way around, calipers, pads rotors, the whole nine yards front and rear..other than replacing lines..i have changed the master cylinder, checked the booster, and still...no brakes...when trying to bleed them...i'm getting fluid from the front, but nothing out of the rear...it does have abs as well, I'm thinking it is the ?fluid modulator?, right underneath the M.C. the lines go into it, and then into the pump...has anyone ran into this issue before????

 

before i dug into that id take the rear rubber line off from the steel line coming from the M/cyl and see if anything comes thru then when hitting the brakes.
if it does your rubber line has collapsed internally not allowing fluid thru it. If still no fluid time to dig into the abs valve.