Why does my 94 Taurus' brake pedal push back at me...?

It's done this for a while.


I replaced the rear caliper with new pads and all..and the brakes are spongy..but I'm guess it's because theirs air in the line since the old caliper had a leak, which leaked quite a bit of fluid.


But..sometimes..prolly half the time that I use the brakes..I hear a humming sound..and they push back at me. The pedal gets higher and harder .. thats what she said.. and I come to an abrupt stop.


There is anti-lock brakes, but no error codes at all.


Is something wrong with the Anti-lock system?


Thanks.|||you may have ABS problems.|||No, something is wrong with your vacuum booster. It is the disc looking thing behind the master cylinder, and it sounds like it is intermittently failing internally by not relieving the assist. Try this one time - leave your key off and pump the brakes. Does it feel the same? The reason your pedal gets higher with the car off is because the vacuum booster is working properly, but has not vacuum applied. Another alternative is that you have insufficient vacuum at the booster. You can check vacuum at the large rubber hose connecting to the front of the booster with then engine on. It is unlikely that you have insufficient vacuum without an engine problem, though.|||amatera is right, it must be the master cylinder, no vaccum is created, your brakes should work even if the ABS fails..just that a sudden brake might lock the wheels.