S-10 Brakes '93

[newpiper]

'93 S-10 Blazer 4.3 CPI Vortec with Kelsey-Hayes ABS. Three times in the last two weeks I've stepped on the brakes only to find they are ROCK-HARD...and no brakes! (Thrilling. Trust me.) Twice I was able to stand on them (thank you for holding, seat bolts) and they finally broke free. With it came a lot of wandering from side to side as though one side grabbed and then the other. One other time I was able to pump them five or six times (who can keep track at a time like that) and they broke free somewhat...at least enough to stop the truck. All three times, the next time I applied the brakes they were normal. I don't see anything wrong in the calipers (excessive rust, misalignment, etc.) and the ABS motor did not run in any of the events (as far as I could hear and feel.) Is there some failure mode in the ABS that might cause this? (BTW, 277,800 miles.)

[old_master]

Check the vacuum line from the intake manifold to the power brake booster. Make sure it has vacuum while the engine is running. Make sure the connections are tight and no leaks. The fitting that goes into the booster has a check valve in it, make sure it operates smoothly. It should allow vacuum to flow in one direction. The power booster diaphragm may have a leak, in which case the only fix for that is replacement. Hope this helps.