The brakes on my MH are very poor and seem to be getting worse. I have replaced the fluid (purged) and have no improvement. I seems as though the rear brakes are not effective or have less effect. The front brakes squeal loudly if I stop in traffic several times without a chance to cool off. Could I have a defective master cylinder that would cause the rear brakes to act this way? On first press of the brake I have 1/2 peddle, on one pump I get more peddle and in all cases the peddle dose not drop with continued pressure. I could not come to a panic stop if I had to. Also, could a defective vacuum booster cause this problem?