Corvette C6 ZR1 and Z07 Brake Pad Burnishing
Why do I have to burnish the brake pads in my new ZR1 or Z07-equipped Z06?
The pad material that’s riveted to the pad backing is made by pouring a slurry of muck into a mold and letting it set. That slurry of muck includes a bonding agent, or glue of sorts. That agent needs to be there, but it will cause a problem if the pads get overly hot.
When a non-burnished pad gets hot (I don’t know the exact temp), the bonding agent will begin to out-gas and boil off. What happens with that gas is that it forms a barrier between the pad and the rotor. An air cushion of sorts. And an air pocket pressing against a spinning rotor is not as effective at stopping the car as a pad pressing against it.
The driver experiencing this will note that the pedal will get somewhat soft and resist slightly when they try to slow the car down. Simply pressing the pedal harder will force the air pocket to evacuate, and the pad will then come into contact with the rotor.
This unsettling feeling is called green fade. It feels like the pad is fading, but it isn’t. The car will stop, but it takes a harder pedal press to make that happen.
Thus the burnishing procedure. The stops in question need to be done sans ABS, ie threshold braking the car, so that a constant pressure is kept on the pad during the stop. This is to help build up the heat in the pad. The goal here is to bake off the top layer of bonding agent from the pad so that an air pocket forming becomes impossible or highly unlikely.
GM has determined that, on average, it takes 50 60-0 stops in 10 minutes’ time to get the pads hot enough for that. Basically what you’re looking for is the pad to start fading bad during the procedure. That generally happens around stop 40 or so, when braking distances feel like they’re increasing dramatically. Once this point has hit, the gasses are beginning to boil off. A few more stops after that point and the brakes will feel like they’re grabbing before you even touch the pedal. At that point: you’re done. Drive the car for a while at legal speeds to cool the pads.
Why not bake ALL of the bonding agent out? Well, if you do that, the entire pad will fall apart. That’s not a good idea, right? Instead, the pad will continue to slowly boil off the rest of the bonding agent over time as you wear the pad down. You’ll never notice it happening though.
How do I know I’ve done it right?
As described in the owner’s manual, once you’ve correctly burnished the pads, you’ll see a white outline around the edge of the pad, right where it meets the rotor. It’ll look something like this:
What’s the track burnishing procedure for?
The street burnishing procedure is to prevent green fade, as described above. Your owners manual also describes a track burnishing procedure, which has you perform a series of 7 or 8 laps at your local road course, and then park the car after a cool-down lap. The first few laps should be done at increasing speed, and the last few should be done at slower and slower speeds.
Why do this? To further season the pads for high-temp use. The street burnishing preps the pads, and is enough for cars that are only driven on the street. But those that see continued high temps (ie, high speeds) at the track will need to perform this procedure after they perform the street one.
But I never drive my car really fast. Do I need to do the burnishing?
There’s a lot of miss-information out there that the street burnishing procedure only needs to be performed if you’re going to race or track your car. That statement needs to clarified carefully, to: if ALL you do is drive your car on the street and highways at legal speeds and NEVER intend to carve canyons, drive quickly up or down a mountain road, or perform high-speed runs (legal or otherwise), then you don’t need to perform the burnishing. However, if there’s even a remote possibility that you will do any of those things, it’d behoove you to at least perform the street burnishing.
Failing to do that with pads that get heated up will likely result in green fade, and a very uncomfortable driver.