Egg on face

[lutronjim]

Not long ago I posted about front disk hanging in my 70 C10. I installed a rebuilt booster and problem went away.

Until 3 weeks ago when it reappeared. I jacked up the from wheels so I could check without driving. Stood on the brake as hard as I could and sure enough I couldn't turn front wheels. Since both fronts locked I assumed it was something before calipers. I was planning to loosen line fittings to see if I could free brakes.

At a whim, I popped the proportioning value and the brakes freed. Stood on brakes and locked them again. Popped value and they didn't unlock. Popped it harder and they unlocked. Ran out of time and left it for the night.

Over breakfast I was wondering if the shock could have propagated to the master cylinder via the connecting lines. Decided to lock em up again and pop master cylinder.

Well try as I might, I couldn't make fronts lock this morning.

The problem went away with the booster for better part of a year - booster probably had nothing to do with temp fix. Might have jarred something during install.

Anyone hear of a valve doing this? Thanks