mzllodr

The brakes on my 1980 280ZX have become very difficult to stop my car. Pedal is hard and all, but car won't stop quickly. Took it to my Nissan dealer, he says the brake fluid was black. He flushed the system, checked that the power system is working and O.K., the discs are O.K, checked that the calipers are all working, (pistons going in and out) but he says only one caliper is really working well and O.k., (will slide that tire, but he says the other 3 corners seem weak). He doesn't know what is wrong, he says maybe the master cylinder, the proportioning valve, bad brake hoses or ???? I checked the system diagrams and I don't see any proportioning valve, looks like the master cylinder does that job. Am I right ?? I'm ready to replace the 4 brake hoses and the master cylinder, all 4 wheel brake pads, anything else I should consider ?? Appreciate your help, I can also be reached at mzllodr@iowatelecom.net Thanks **** Brees