Has anyone run into "intermittent" brake system problems on 1990 (or thereabouts) C1500 SWB 350 5.7?
Very hard to push pedal half the time, then brakes seem kinda spongy and a bit grabby other times. I have systematically replaced most parts of the system and bled the lines countless times. 2 parts that I haven't changed are the Combination valve and Iso/Dump
Valve (for the ABS?). Can't be sure if they have problems or not.
Anyone have similar issues around this year model?
Anyone know how to test the combination valve and/or Isolation/Dump valve?
Manual says to hold open the Comb valve while bleeding, does anyone know why?
Man, I'm lost at this point and any help would really be appreciated?

PS: I'm new here and already love the site! Great job all!!!

Got 179000 on her and she still runs great (just doesn't stop too well at the moment...)