Been searching for hours--proportioning valve? MC? Help!

[K5thatShmobs]

When bleeding the brakes I'm getting very poor pressure to the rear brakeline... the fronts have more, but when bleeding the rears, fluid barely dribbles out. Pedal pressure feels firm when the engines off, but as soon as you start it, the pedal gets firm only an inch or two from the floor. Could this be the proportioning valve? Master cylinder? I have to get this truck done by this wednesday! Thanks all...

 

[MJF]

What all did you change? Did you do an axle swap, lift, extended brake lines? I'm trying to figure out what could have caused the lack of pressure.

One tip someone gave me was to "burp" the prop valve. The two lines on the top are the inlets. Loosen them half a turn or so & that will let the air out & gravity will force more fluid down so no air will get in. It didn't work for me, but I may have more problems.

 

[Grim-Reaper]

Maybe THIS would help /forums/images/graemlins/thumb.gif