noise when slight brake pressure applied

[stoictwo]

My first post- I have a 2004 G35 coupe, non - brembo brakes. When gently applying brakes at basically any speed, there is a repetative "knocking " noise on the driver's front. It is not severe, it goes away with a little more brake pressure, it does not really make the steering wheel shake, nor does it make the brake pedal pulsate like a warped rotor. I just replaced the left lower front control arm because the bushing was bad, and this helped lessen the noise for the better. I next tried new caliper pins because it seemed like there was too much wobble when I manually rocked the caliper. This also helped lessen the noise slightly even though the "rocking" feels the same. There does not appear to be any other bad bushings or links that I can see or feel. Could the bracket be bad that the caliper pins ride in ? I want to re-state that the noise is an irritant more than a scare, and the "window" it happens in is small but happens with everyday driving.Thanks for any suggestions.

[audtatious]

have you compared left to right to see if one is more loose than another (you mentioned pins). Have you bled the front to make sure there is no air in that caliper (doubtful). Any unnecessary wear?

[stoictwo]

No, I have not compared left to right side yet, will do that this weekend. I have no reason to believe air is in system, there have been no leaks nor symptoms to lead me in that direction. Thanks for the suggestions.

[stoictwo]

follow up-- left side and right side caliper movement are the same, so pin and brackets appear okay. The outboard brake shim was bonded to the caliper so I freed it up and again have influenced/ improved the noise ever so slightly.
My next thought is that the relative "new" brake pads may have "bad" spot in them. Maybe ??

[audtatious]

If the problem started with the new brake pads then it's possible. Obviously, if the wrong pads were installed then that's a big issue

I'd remove the caliper and check the piston to see if it's straight and will move properly.

[Captain Obvious]

Could it be play in upper strut mount? Every time you touch the brakes there will be torque on that mount. (I'd also mention the lower control arm, but you already replaced it.)

Sometimes there's a bit of play between the top and bottom edges of the pad and the caliper, and the pad moves every time you go from using the brakes moving forward to using the brakes going backward. Doesn't hurt anything, but it does cause some clunking.

[stoictwo]

Update- brake pads and rotors were new 40k miles ago, replaced the pads today because it was time. problem remains- will be getting rotors machined as next step. Thanks for input on strut mount, will check.

[stoictwo]

Problem solved ! We had the rotor machined and problem is gone. I never totally suspected rotor because symptom was not typical for a out of round rotor since it never radiated up pedal or steering, and only happenned in a short "window" of pedal pressure. Guess I'm never to old to learn more! Thanks to all for input, and remember-- basics got to be right first before we complicate it.

[audtatious]

I had to replace my back brakes and rotors on the sedan because the pads went out without any noise at all. I'm pretty anal about maintenance so it was a bit embarrassing when I was told the rear rotors were eaten away where you could see the ribs through the metal.