hi I have a 1979 adventure se changed booster and master cyl out now my front brakes seem to be the only ones grabbing and hard bench bleed master cyl and then bleed rear brakes first and then front its like front brakes are getting all the fluied master cyl is a two bolt was going to use old one but it would not fit new booster old master cyl was the all metal two chamber new one is metal with plastic chamber with two lids I'm not sure if this makes a diff any help would be greatly welcome

 

Sounds like your rear drums are out of adjustment, or you still have air in your rear lines. If they worked fine before the new master and booster, than it is certainly air in the lines. Sometimes they can be quite troublesome to bleed, but be patient. It will work. Start with the one furthest from the master, and work your way to the closest one. Park the truck at a slight angle to make the fluid flow easier downhill, towards your rear drums.

 

X2, lack of pressure will cause the proportioning valve to move. Make sure you have all the air out of the master cylinder/lines.