91 Dynasty brake problems

[pontiacfreak_81]

Hello all, I have a 91 Dynasty that blew the master cylinder or so i thought.. First my front brakes started dragging, shortly thereafter i lost brakes altogether. I assumed the master cylinder was no good so i replaced it, bled the brakes twice but i still get no pressure behind them. when the car is off and i pump the brakes the pressure is there but once running the pedal just sinks to the floor, also the brake light has not gone off since they first seized up on me... so im kind of at a loss, (only an amateur mechanic here) anyone have any ideas??

[rhandwor]

It sounds like the vacuum booster is going bad. Loosen one bleed line at a time on the master cylinder. Make sure you are getting pressure at this point.
Did you you use the two hoses and bleed the master cylinder before you tried to bleed the brakes. If you have no pressure remove the master cylinder put it in a vise use the two rummer hoses and push in with a steel rod until the master cylinder is bleed.
Use a block of wood and have somebody press on the brakes engine running and you putting some pressure on the block of wood. If you don't get any pressure the brake vacuum booster is bad. You would require as much pressure as bench bleeding the master cylinder would take.
If this is bad use a couple of straight edges and measure the length. The rebuilt should be the same length. This is the rod which pushes on the master cylinder.
Remember anti locks may need a scanner to cycle the valves.