Ok, what you are feeling is the ABS kicking on.
If you are stopping fast, and are in a situation where the wheels should be locking up, then this is normal.
If it is happeing all the time, then you either had a bad wheel sensor or bad encoder wheel (the part that turns on the hub when the wheel turns that the sensor reads). I beleive, but am not certain that on OBD II (On board Diagnostics 2) cars (1996 & up) that a scanner can read the ABS system and locate the suspect wheel.
ALSO, when applying the brake in a situation where the ABS kicks on and for good reason (ICE, SNOW, RAIN, Panic stop) DO NOT pump the brakes, keep your foot on and apply steady presure until you stop. The ABS system is 'pumping' for you and can only do so when your foot keeps steady pressure on the brake pedal.
2005 Dodge Magnum R/T-Can you say...HEMI?
1999 Bonneville SSEi-Going Fast...With Class!
1989 WS6/L98 Trans Am-Got Torque?
1999 Grand Prix GT-Wife'* Widetrack
1995 Camaro Z28-Project Bitch