[jessemthompson]

What you have circled is the proportioning valve. There is a button under the black cap on one end of your prop valve. Use a clamp to depress & hold. Slowly push brake pedal to the floor or as close as you can get the pedal to the floor pushing firmly onthe pedal, and release. Remove clamp from prop. valve. It should be centered again. That should give you fluid to the rear brakes.