02 Explorer Sport, 2wd v6
While driving home from having my Front pads and rotors replaced I noticed that while braking my pedal would sink further than normal and my brakes would lose their grip forcing me to depress harder to stop. It happens maybe once out every 8 stops, and is more likely to happen when going from about 10 mph back down to a complete stop at the last couple feet of stopping.
I took it back to the shop and the mechanic looked for air by bleeding something under the mc reservoir. They did this twice without finding air. They then tried the same for the rear and found that a little air was released even though they didn't touch the rear brakes. The problem persisted.
He started to think my booster was going bad due to the fact that when the steering wheel was turned the engine would lose idle power like it was going to die. But then he changed his mind when he disconnected the ABS module, test drove it, and the problem stopped.
Could this solely be caused by a failing Abs system? Another forum recommended checking the ABS wheel speed sensors, I could only find the Front two, they looked intact, but dirty so I wiped them cleaned. No fix.
I should note that I haven't properly flushed the brake fluid in over six years, and wonder if this could be caused by air in the brake line/water/old fluid as well.
Anyone have any experience with this issue?

 

I would start with a complete brake fluid flush first. That stuff has been in there for awhile and has a lot of heat cycles on it. Its not that hard to do! Then go from there. When you had brakes replaced where the pad evenly worn. Inside and outside worn down the same. Driver side same as passenger side. Just asking to make sure that you dont have a caliper sticking. Usually a sponge brake pedal has to do with air in the line or water moister in the the line. Flush it out starting with the the line farthest from the brake resivior and go from there. Hope this helps.

 

What your describing could be a bad MC. Usually the sinking pedal is a constant and pumping the pedal builds up enough pressure to bring back proper braking. I would start by doing a complete flush of the brake system, this means until the fluid coming out is clear. If you have a vacuum pump and self bleeder kit this is very easy, highly recommended. Next I would see when your pedal sinks if pumping it brings back proper pedal pressure, then look at replacing your master.

 

Thanks for the responses.
As my ABS is disconnected, the breaks do not sink at all, but what I am noticing is a sort of slight grinding noise coming from up front (driverside I think) at the end of a stop.
Ridinred, the wear of my brakes WAS uneven at the time of replacement. Specifically, the driver side, inside-half was metal on metal while the other three had a bit more wear left. Sticky caliper?
I will flush the brake lines at my next opportunity I get.

 

I would think that you may need a new caliper also. I cant remember if these are rebuildable or not.

 

rock auto is usually pretty good on prices if you dont mind ordering online.

 

RockAuto Parts Catalog

 

So after much sweat and tears I found the true cause of my problem.. and by accident. It wasn't the master cylinder, booster, calipers, or a failing Module.
It turns out the new rotor that was put on had a slightly warped ABS Exciter Disc built in to it. Therefor, As the wheel would turn, the ABS speed sensor would lose some 'signal' from the disc, and if the timing was right, confuse the ABS system and cause it to randomly kick in during low speed stops. So, I exchanged the rotor at Autozone (did I mention the brand was Duralast?), inspected its quality before I installed and the issue finally resolved.

I appreciate all the help from everybody. Who would have thought of examining the inside of the rotor?!