1998 Pontiac Bonneville car shakes when braking

I had the same problem after putting new rotors and pads on and I found out that even new rotors can be warped. If you checked your alignment, and calipers to make sure that isn't the problem then see if your pads are wearing evenly. If they are then your rotors could be warped. Also make sure you have your lugs at 100 ft. lbs.