86 4runner Rear Brake Problem

[JsFire757]

hey whats going on, i bought a 86 4runner yesterday. They Brake Line seemed to be leaking so we replaced the master cylinder. When bleeding the break lines the front breaks would bleed but the back brakes wouldn't. I think this is the problem, but im not quite sure what its called. I was wondering if anyone could help. This seems to be attached to the break line on the passenger side in the rear. does anyone have an idea what this is?

 

[fourwd1]

That's the Load Sensing Proportioning Valve. It adjusts rear brake power according to load.

 

[JsFire757]

Thanks bud