Question; My C7 Grand Sport front rotor are pulsing when stopping. Being that they are two piece what is the procedure for turning them?
Do they need to be disassembled and Blanchard ground? I understand that hardware has to be replaced if dis-assembled, is that correct?
Pads look great, 2017GS with 11000. miles. Appreciate some feedback. ( No I did not search this site first, sorry)

 

It sounds like you have a build up of pad material on the rotors. Find a place where you can do several high speed (60 MPH) hard stops to remove the build up.

 

This doesn't always work. Trust me. I've had my Z06 rotors smoking before with no improvement. But it definitely a good first thing to try.

 

I have a similar issue with my Z06. Asked a friend, Corvette Tech, about cutting. They would just remove rotors and cut them with hats still attached. FWIW, i was quoted $350 with me driving car to dealer..

As far as hardware, if you change rings or disassemble, new hardware is highly recommended. Might save money and hand carry rotors in..

JMO, but KNS offers a number of options for C7Z06 rotors or complete rings/hats.. They are a popular rotor source for Corvettes.

 

I recommend thoroughly cleaning the rotors and then bedding the brakes to evenly transfer brake pad material to the cleaned rotors.

 

For a long time I was of the mind you needed to cut the rotors with any pulsating. Then I saw some info here that convinced me otherwise. My new to me '15 z-51 was pulsing when I bought it at 20k miles. I scuffed up the rotors real good with my air sander, took down about .050 of the ridge that was forming, and Voila! Pulse be gone!

 

Pull the 2 piece rotors and turn them as they are assembled. No reason to remove the hats. Plus you want the rotor rings squared to the hats as they are.

 

Sand both sides of the rotor rings and rebed the brakes and see what happens.

Bill

 

Pulsing can be caused by rotor runout, as the OP is suspecting. The correct way to measure it is by setting up a dial indicator on the rotor surface, then turn the rotor by hand to read the total runout (delta of the low and high on the indicator). For vehicles, I like to use a clamp-on tool like this:

https://www.centraltools.com/6454-ti...nout-gage.html
Which I own and love.

or more reasonable:

Which is similar, but a lot cheaper than mine.

These flex arm style mounts have their drawbacks in that the flexible arm portion can sag. It has to be watched by making sure the indicator does not "creep". If one is of poor quality, it is hard to work with, but good ones can be tightened up and work well.
What I don't like about both of these examples is that they include a "dial indicator" style indicator, which are best at measuring in-line travel (great for camshaft, etc). That style of indicator will work somewhat in this application, but they are not really the correct style, as they really aren't designed for side load. I use a "test indicator" which works better on a dragging surface, such as the rotor as it passes by. This is a good example:


None of this stuff is cheap! But neither is everything else at this point.

Anyways, the general routine is to raise the car. My disclaimer here - always use jack stands, etc. (If doing the rear, then both sides need to be raised). Then, remove the wheel/tire. Put the lug nuts back on so the rotor is fixed to the hub. Tighten them slightly. Then, mount up this indicator assembly, with the indicator resting on the rotor give it a little preload (0.010" or so is good). If using a "test indicator", as I recommend, then have the tip "downstream" of the way you are rotating the rotor. Then, turn the rotor and observe runout. It should generally be less than 0.002" (said as "two" "thousandths"). The typical GM spec is that. This might not be easily obtained, even on a new car. Obviously, the greater, the worse braking pulsation.

Runout can be cured by having the rotors turned or buying new ones. In recent years, I have terrible luck with the national chain auto parts stores. My old CTS had bad pulsation and runout. But, I just couldn't get anyone to turn the rotors correctly. In the end, I bought new rotors, which also allowed an upgrade in size for that car. The new ones had little runout. Surprisingly, that didn't fix it. I could swear all of the pulsing was coming from the front of the car. Why wasn't it fixed? It turns out that the rear rotors had a lot more runout. New rear rotors and the problem was solved.

 

I'm going to give this a shot before I spend a couple grand on new brakes. Thanks, Bill.