I bought a used 2004 G35 about a year ago. The brakes were shot when I bought it. First day I had it I took it to shop and had new rotors,calipers and pads installed. During install they found that bolt in right front caliper bracket was seized and they had hard time getting it out. I had severe pedel feedback, pedel almost to floor to stop and would shake the fillings out of my teeth. I am now at 12,000 miles since this work and am now having same issues. I have 20" non staggered after market wheels.

 

I am having issues as well..For the last week..been hearing a noise under hood.. brake pads were shot...Peddle will go further then normal, but not to floor.(grinding noise) Today Replaced pads with hawk PC, turned rotors, and replaced brake fluid...(flushed old) Still no bite when applying brakes,and peddle gets soft with grinding noise. Anybody no what the problem is? ABS? No warning lights etc..

 

I wonder if it is the 20" wheels and spacers causing the issue ? I also wonder if I have a suspension issue I don't know about since it was bought used and I have no idea what this car has been through in it's life.

 

Try changing out your brake hoses. I've had similar issues to what you guys are describing and I've been doing a complete overhaul of the brake hoses, swapping out a couple of seized calipers, bleeding the lines and what not.