Vibration when hitting brakes

[slimco]

I have a 99 Pontiac grand am, 4 cyclinder engine with anti-lock breaks.

I have noticed a vibration or shaking when I hit my breaks. The vibration seems to happen when I am at about 30 mph to 40 mph. When I am below 30 mph the vibration/shaking goes away.

I have had new tires put on the front since with an alignment. I have also had the brakes changed and are about 4 months or so old. I just had a friend last night look at the brakes and he says they are good. I don't know what else could be causing the vibration/shaking.

[Knifeblade]

1] Out of balance tires

2] Warped rotors

3] Sticking caliper piston

4] A worn suspension, or loose , suspension part, such as a ball joint or tie rod end.

Myself, I'd start with the rotors, my G/F's GA did same thing, it turned out the rotors were west, we replaced them, they not too bad, around $15 each, and the shaking went away. I can't say that's the prob. you have, but it seems to be to me.