So I was driving the other day, slow rate (say 20mph) -- when I applied the brakes, not very hard, but with enough force to bring me to firm stop, the brake pedal seemed to lose a considerable amount of pressure for a split second. It was so fast and so random that I thought nothing of it...sparked my curiosity a little bit, but not alarms.

Then, just a couple of days ago, it happened again. I don't know if it had anything to do with it, but it was when I was entering the parking lot of my work, I applied the brakes at almost the exact same time that the tires hit the entrance of the driveway (uneven surface) -- the time previous was also on an uneven pavement surface.

I'm thinking it is something to do with the anti-lock break controller, and the timing of the brake applications. Maybe a possible compensation of some sort by the computer? I'm not ABS expert (or an expert on anything for that matter) so I was seeing if anyone else has had the same thing happen or not...and if they did, did you have it looked at? Anything come up as wrong?

 

Sounds like your ABS is working.
When your ABS starts working you will feel a pulsation in the pedal.
The ABS lets you stop as quick as you can - quicker than you pumping your brakes,your wheels still spin - without locking them up, but you stop
in a straight line.
Sometimes on rough surfaces you may notice this more if the wheels lose a little traction of the surface of the road.
Some vehicles have more pulsations than others.
You may want to check your brake fluid to be sure its up to the proper level,
and if there is any doubt bring it to a brake expert to confirm they are working 100%.

 

I know the function, workings and benefits of ABS...it was more than the pulsing of the brakes. The only time I have felt that hard of a pulse was when I was trying to stop my moms intrepid to keep from hitting a deer...

...but like you said, the uneven road surface is what I chalked it up to as well...just throwin it out there to see if anyone had any experiences to the contrary.

 

My only problem with the ABS theory, is that you dont feel a pressure drop. The pedal stiffens and pulsates as the pump works, more like a vibration with a matching loud noise. Pedal drop, that is occasional, in my expierience, is most likely a master cylinder issue. When the seals on the piston shaft begin to wear, it can cause pedal drop during a quick hard brake or when sitting stopped with your foot on the brake and the pedal slowly drops. Let it run, hold the brake pedal while stationary, and see if it starts to drop further than it was at first. If so, you may have a master cylinder issue. Also, keep in mind that your brake booster is vacuum operated, vacuum is greater at idle. So, if you hit the brakes, and the engine slows directly after, you may be feeling the increase in vacuum, causing a stronger action from the booster.