It could be something as simple as pad material buildup on the rotor, especially if the pads weren't bedded in when new.
Fair warning: This post contains a lot of detailed information on brakes and I know some of my fellow nerds like
@xBlitzkriegx,
@SkylineDreamz and
@Avedis53 will most likely enjoy it.
Dollars to donuts it's this. I had that done on my G37S (dealer machine rotors) due to pad material build up on the sport rotors. It kept happening and I live in Texas where the summertime road surfaces are as hot as 160°F on asphalt and breaking over 80mph just throws that much more kinetic energy into them and they can only dissipate heat so fast when the ambient road surfaces are that hot and you can get pad material buildup on the rotor. It builds up unevenly on the rotor surface and gives the feeling of brake judder or steering wheel shake.
I got fed up with continuing to have to do that and bought a bad ass two-piece rotor kit from Racing Brake. The iron they use for the rotors is extremely hard. I ran track pads on the G37 and while they were noise in drive-throughs, I never had brake pad material building up on the rotors. They are the BEST brakes I've ever had on a car. I did some tests braking from 80mph and they barely blinked and it was like they said, "Is that all you've got dude?" Once the brakes on my Q wear out, I'll be installing the Racing Brake rotors I bought for my G37S.
Heat control is affected by mass when it comes to rotors. High mass rotors resist heat up but cycle poorly (i.e., they resist getting hot for a time but cool and dissipate heat much more slowly) and lower mass rotors will heat more quickly and cool faster. If the rotor isn't bigger, you have the same "work" being done and when you have the same work, spread over the same swept area and mass, you have the same heat. Bigger brakes with a good pad require less time to do the same work, and it's spread over a larger area, and therefore create less heat density in the rotor. With a lower mass rotor, the heat will dissipate faster and when you have a very hard and tough iron rotor and a tougher pad, they withstand the heat that does build up MUCH better and you'll get zero deposition of pad material on the rotor. If you get any, the pad will scrap it off.
If you really want to nerd out on gray cast iron brake rotor metallurgy, check out these two links:
However a G3000 rake rotor formula contains a higher percentage of carbon to give added strength and sound damping qualities.
ricksfreeautorepairadvice.com
They were overkill sure, but they saved my ass on more than one occasion with moron DFW drivers doing stupid stuff. I paid a bit over $2k for the whole kit, front and rear rotors, pads and stainless steel brake lines. The Racing Brake kit is about $400 more than Z1's kit and it comes with braided stainless steel lines. I would be curious as to what grade of iron that Z1's rotors are constructed with. They don't mention it on their site. I get nothing from recommending RacingBrake. They were indestructible. I even did a few 100-0 braking sessions and could not get them to fade in summer heat. They are badass and require very little brake pedal input because the coefficient of friction is so high. I would even go as far to say that when you lean into the brake pedal even just a little bit, the braking torque force is violent, but violent in a way that instills extreme confidence in any situation. They will stop on a dime and give you .09 cents change. But most times, they only require the weight of your foot, even in crazy DFW traffic.
I initially ran their ET500 street pads but became dissatisfied with them because they ended up having the same issues with pad material build up. After those wore out, I switched to their XT-970 / XT-960 pads front / rear and I was exceptionally happy with them. I ran them in temperatures as cold as 8°F with zero issues. They are just f'ing badass and worth the money if you are an enthusiast driver.
INFINITI - RacingBrake.com
racingbrake.com
