dont know if this will help you or not, but here goes.. 93 taurus. brakes were working fine when cold and starting out to work, 20 minutes later the car would heat up(?????) and the brakes would go to floor... thought it was the master cylinder???? waited to get some prices on the repair......... in the meantime i pulled the back brake drums off and found that the right rear cylinder was pushing the metal part that is suppose to push the shoe out was missig the shoe and going past it and that is why the pedal would go to the floor,,, the fluid had to go someplace and it was not leaking....., new drums and shoes on the rear and problem was solved(it was the springs that weere heating up and not pulling the shoes back to allow the cylinder the get the metal piece back in and hold the fluid force.... kits for the springs for two wheels at auto zone cost me about $5.00??? and it fixed the problem.. the metal in the springs were ruined due to the heat(long use)..... brakes are pretty easy to fix, i would not mess with the balancer valve on the brakes... the guy probably used cheap brake pads and never put the anti squeel stuff on the back of the pads and shoes when he worked on the car, thats why they are squeeling.... did he remove the slider pins that hold the calipers on and clean off the caliers and where they are attached and also the pins and put high temp. brake lubricant on the pins???? i doubt it.... if our brakes lock up when no pressure is on the pedal it could be a bad hose, sometime they fail in the hose and block off the flow of fluid....