brake oppurtunity 90 tc

I was driving my new 90 model towncar yesterday while it was raining and after a 30 mile cruise i felt a roughness in the brakes when i was coming to a gentle stop and at the same time i felt the pedal force back against my foot, it done it again a few moments latter, so i put the car in reverse and stroked the pedal while backing up a few times,and i did not have the problem resurface until again later in the day. when it done it again, I tested the brakes stopping power at 40 mph and no surge in the pedal, and it stopped fine, but I felt the surge and roughness each time when applying brakes at a slow speed while coasting to a stop.
I have put about 500 miles on it since i got it and only had this problem show up when it is raining. rotors are smooth and pads show a lot of life left any suggestions? :uhoh: :banghead:

Sounds like abs brakes are coming on which will give you that roughness and the pedal will force back up against your foot. You say it only happens in the rain, that's a good time for abs to kick in.
perhaps one wheel is starting to skid, if so, the abs will come on right away.