1995 Acura Integra ABS

My brakes intermittently act as if there is air in the lines causing the pedal to gradually go to the floor. Pumping the brakes will not change the brake pedal position. A visual inspection of the brake components showed no signs of fluid leaks, but a pumping sound would briefly come from the the ABS system. The ABS light was on steady. The system was bled at all wheels and now the ABS light only comes on as it should during initial start-up and then remains off, but my original intermittent problem still exists - any ideas?

Could be a faulty seal in the master cylinder.

I’m with Tardis on this. I suspect the MC.

If air in the system were the cause, you’d be able to firm up the pedal by pumping the brakes. The air would compress as you pumped. The brake pedal position would not stay the same.

An internal leak past the piston seal in the MC would not show visually. The fluid leaks past the seal but stays within the master cylinder chambers. It doesn’t leak to the outside world for viewing.

Beyond that, how quickly you apply the brakes can affect how the pedal feels. If you’re applying the brakes quickly, the fluid may not be able to pass through the leak at a rate sufficient to be felt, but of you apply them more gradually the fluid could pass by the seal and the pedal sink. This would be a normal symptom for a leaky MC piston seal.