Long time member here, but lost access email to my old account. These are my 2 cents after owning 2 G37S (2008 and 2010) coupe autos and the current one with 230K miles on it.

For most of the time I have run Centric PosiQuiet (ceramic) pads all around. While using stock OEM and PosiQuiet pads I had for years always had issues with shudder build up. Through my extensive research over the years and extensive shade tree mechanic experience, these are the conclusions I have confirmed. Centric has great white papers on this.

1. Rotors do not warp unless you are tracking your car.
2. Cementite build up forms when deposits are not cleared off the rotor via a harder compound than your used pad.
3. If you do not check run out of your rotors and place on hub with the least amount of run out, you will develop shudders with this car. Use to be the same thing on my Z32 TT.

My guess is that whoever put your brakes on did not check run out of the rotors. IMO the PosiQuiet are the best pads for aggressive street driving along with quietness.

 

I could have followed up as promised a bit earlier, but wanted to put a bit more miles on my installedCentric coated blanks and Akebono ASP pads. But with that said, after 2500 road miles and two track days with about 3 hours total of moderately to very hard braking on track, I can report that this combo has performed pretty much perfectly, with no shuddering present and brake feel overall that I have found to be spot on to this day. I did experience a moderate amount of fade on the track near the end of my last session, but I was really pushing hard, and it was perfectly manageable in that regard. That was about 1000 miles ago. I can also report extremely negligible brake dusting.

I also need to say that in spite of what seems to be a general consensus here, as voiced by many members over the years, that "rotors do not warp", that the shudder or pulsing that is so very common with our cars is caused by irregular buildup of pad deposits, or poorly heat treated factory rotors or whatever only is simply not true, or at least not in every case, because my stock rotors WERE DEFINITELY WARPED, as I stood by as they were being turned. No cracks, but most definitely warped. Now I bought this car with 50K miles on it, and when I did there was no pulsing present whatsoever, but after 17K miles of moderate to occasional hard street use and one track day roughly in the middle of that 17K miles added on, my pulsing issue became quite severe, and several "Italian brake repair" attempts frankly only made it worse, also contrary to many posts here over the years. Sorry folks, but that's just the truth. Of course I can't say at this stage how long this combo will last before any potential shudder problems, but so far so good.

 

So I'm part of this group now. I bought a set of Centric rotors that I replaced my original ones with. I rarely replace both rotors and pads and have had great results. This time since my ceramic pads were still in good condition I decided to re use them.
Note: When I first got my car 16k miles ago I decided to cut the rotors, EVERY SINGLE ROTOR WAS WARPED. Had them all turned and off I went. For my pads the ones that came with the car were still meaty enough so 10 minutes of flat sanding with some rough grit had me set for 16k miles after I decided to just abuse the brakes themselves.

This time after the rotor change I repeated the sanding technique and have developed the shudder within 100miles. The only thing I can think of is I did not use a rough grit like the first time.
Hugh though your approach makes sense, the brake rotor turning machine invention is over 100yrs old and still works. I think this happens in the center pocket of the pad over abuse and mainly on Automatic cars since most will be idling on gear with the brakes applied.
Meaning if you go through an overheat event then come to a stop while in gear you will warp/cook that area.

 

My guess is they weren't perfect prior to putting on and and were worse with build up. I've personally never seen a warped rotor other than from tracking a car, but I have seen new rotors that could be turned and seemed warped.

 

Did you confirm your hub runout was in spec? Did you do the same for the rotors?

 

I did not, but now that you mention I did wire wheel the rust on the hub. Possibly changing the clearance, had not thought about that.

 

I had shudder/judder/pulsing on my 2015 q40. It mainly happened when i braked hard but no problems when gently. I tooked at the calipers and they looked dirty and caked up with what looked like mud so i took the wheels off sprayed everything down with brake parts cleaner now brakes like a champ

 

You'd likely start to hear wheel bearing noise if your hub was out of spec unless it took a big hit or hard acute impact. My guess is the hub was not placed to optimize runout in spec. Just because the rotor is in spec for run out in one position on the hub doesn't mean it's always the best. All 5 positions of rotor to hub placement should be checked for run out.