Hi all. I have a 1985 GMC C7000, and the rear brakes are not fully disengaging. They are front and rear disc brakes. I have read a few threads going about this issue, but none I could find had both disc brakes. Both rear calipers have been replaced, all new lines, new fluid. What we've whittled it down to is that the master cylinder is bad and or wrong. The thought is that it's for the models that came with drums in the rear because those MCs came with a different size orifice. I'm hoping someone has a little more experience with this area before I go buying an MC and it ending up being the wrong one.
Were Either ALL Drum or ALL Disc, no Halfway systems out there. Have own Two. Have someone apply brakes, then release, break open a rear bleeder, if Sprays is holding pressure, if dribbles is Normal. Slide Bars are HORRIBLE for locking in place, Pistons or Bores on some remans are crap and will seize in bores so cannot expect 'Has recent Remans and is good'. Is also Rubber Lines from MC to Frame, these can Blister as bad as wheel lines, is also a Rubber line Frame to axle that should also be new or could be issue.
BTW, was also a Line Mechanic when these were new and NO Better than occur now. Calipers were Crap, Lines were Crap ALL From Day One when the Disc Craze began. If pressure is releasing Remove the tires, and remove the calipers from the rotors. Place a C-Clamp on the pistons LIGHTLY with a Old Pad in between, loosen Bleeder, start screwing tension on Clamp, if takes more than finger pressure buy REPLACEMENTS, and on these ALWAYS replace in Pairs, RR or FR.
I'll have to give that a try next week. There were several websites where there were claims that the fronts were disc and the rears were drum, along with MCs that were being sold for such, so from that I couldn't find any that were specified for all disc is all.
So more info for on this, ALL the hoses have been replaced with new stainless braided. 6 sets of rear calipers and the same result with all. rears bleed out poorly compared to the front
Start with That Thought, Back up ONE connection at a time opening them up until flow resolves or end up at the MC
good stuff dm I have one acting stupid also