Front disc brakes fail to release for 4-5 seconds after releasing brake pedal. Rear drum brakes appear OK. Problem occurs both w/power booster and w/engine off and vacuum depleted. Work to date:
1. Frt disk calipers removed and bushings lubricated. No uneven pad wear observed. 2. Using C-clamp to compress caliper piston, very little brake fluid flowed towards mastercylinder. Thought caliper piston might be hanging up so broke line from caliper to combination valve. Fluid flowed with little C-clamp pressure. Removed brake line from comb valve to mastercylinder and fluid again flowed easily suggesting problem was bad mastercylinder. Mastercylinder was replaced with new one and problem was still there. 3. Thought maybe vacuum booster shaft was hung up or return springs not functioning.and thus keeping the MC from returning fully. Backed off bolts holding mastercylinder to vac. booster two full turns and checked frt brakes. Still hanging up for 4-5 secs. There was visible play between the MC and vac, booster after 1 sec indicating the problem was not in the vac booster or brake pedal assembly.
Need any help anyone can provide - I am out of ideas. I eliminated the front brake lines due to both calipers hanging up. I understand the combination valve is bullet proof and almost never fails. Any help will be greatly appreciated.