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C6 Corvette ZR1 & Z06General info about GM’s Corvette Supercar, LS9 Corvette Technical Info, Performance Upgrades, Suspension Setup for Street or Track
Why do I have to burnish the brake pads in my new ZR1 or Z07-equipped Z06?
Pad Burnishing
The pad material that's attached 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 owners 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.
jas
Last edited by jvp; 04-28-2017 at 09:02 AM.
Reason: fixed technical inaccuracies.
Excellent post and explaination. Your description is very accurate.
When I did mine, I used 2nd gear from 1500 rpm to 6000 and after only 40 stops it was complete and happened very quickly, less than 5 minutes.
The reason it took less time and less repetitions as the car got up to 90 mph before braking. The energyy need to stop a 90 mph vehicle is 225% that of stopping a 60 mph vehicle as the kenetic energy is a squared function of speed.
The reason the owners manual says 1st gear and up to 60 mph is because the lawyers will not let them print anything that telsl owners to do anyhtng illegal like exceed the speed limit.
The reason it took less time and less repetitions as the car got up to 90 mph before braking. The energyy need to stop a 90 mph vehicle is 225% that of stopping a 60 mph vehicle as the kenetic energy is a squared function of speed.
Well, if I'd known that it would've been a whole lot more fun completing the process.
Good post JVP. I did a video on bed-in/burnishing a while back. My procedure was for iron discs and their associated pads. The concept remains the same though. Hopefully my video provides some further insight into the why's and how's of properly preparing brake pads and discs. Regardless of whether you have iron or carbon ceramic's, you'll still get similar benefits.
As GaryZR1 says, the speed will have a dramatic impact on how many stops it takes, as high speed/high energy stops introduce much more heat into the system. Most people (including me) always recommend 60mph because 1) it won't get you thrown in jail if you're doing it on the street, and 2) the amount of heat generated in any given stop is limited because of that speed. Once you've done this process a number of times, it becomes easy to feel when you've accomplished what you're trying to do.
One more note on the subject of burnishing...pro race teams view this procedure as being extremely important. Our company burnishes thousands of brake discs per year for pro racers. It is an important part of getting the most out of your brakes.
Our company burnishes thousands of brake discs per year for pro racers. It is an important part of getting the most out of your brakes.
Hopefully you're not burnishing the discs, but rather bedding the pad material into the iron ones. You don't burnish discs, you burnish the pads. Right? ;-)
Bedding is done to the rotors, burnishing is done to the pads. And in the case of the carbon ceramic rotors, bedding them will be very, very, VERY bad and expensive. You never want material transfer from the pads to the rotors with CCs. If you get that, you've destroyed the rotor.
I had this exchange shortly after purchasing our 2010:
From: XXXXX@aol.com To:lynn.yyyyy@gm.com
Date: 07/27/2010 08:30 AM
Subject: Customer Vehicle Assistance
Name: Dick
Email: XXXXX@aol.com
Message:WE just purchased a new 2010 ZR1 and just passed 500 miles. We see in the OM that we need to "BURNISH the BRAKES" via the 50 repetions of 0-60-0.Question.....this car wil only be used for cruising on the US hiways .. (realizing many owner never read the OM and our dealers do not bring this up during the purchase) IS there any and if SO, What are the adverse consequenses of not doing the Burnishing proceedure?
From: lynn.yyyyy@gm.com
To: XXXXXX@aol.com
Sent: 7/27/2010 7:38:10 A.M. Central Standard Time
Subj: Re: Customer Vehicle Assistance
Hello Mr. XXXXX,
It is suggested for owners who will be using their ZR1s as performance vehicles on the race track. If you are just using your ZR1 for "cruising on the US highways," there will be no need and no adverse consequences for not burnishing the brakes.
Why do I have to burnish the brake pads in my new ZR1 or Z07-equipped Z06?
GM has determined that, on average, it takes 50 60-0 stops in 10 minutes' time to get the pads hot enough for that.
My 2011 manual says FIVE (5) hard stops in sequence, NOT fifty (50). 50 full hard stops seems like an awful lot!
My 2011 manual says FIVE (5) hard stops in sequence, NOT fifty (50). 50 full hard stops seems like an awful lot!
The 2011 manual has a misprint. It's 50. If you read through the entirety of the procedure in your manual, you'll see the number 50 show up later. GM's printers goofed a bit with that one.
Excellent post and explaination. Your description is very accurate.
When I did mine, I used 2nd gear from 1500 rpm to 6000 and after only 40 stops it was complete and happened very quickly, less than 5 minutes.
The reason it took less time and less repetitions as the car got up to 90 mph before braking. The energyy need to stop a 90 mph vehicle is 225% that of stopping a 60 mph vehicle as the kenetic energy is a squared function of speed.
The reason the owners manual says 1st gear and up to 60 mph is because the lawyers will not let them print anything that telsl owners to do anyhtng illegal like exceed the speed limit.
I just burnished my second set of pads and the 2nd gear option 80-20 mph is WAY quicker and more effective. I did mine on a 70 mph interstate....no ticket worries
I just changed my rear pads. I am planing to track the car in three weeks. I recon I have another track weekend on my fronts. Do you recommend barnish the rears before the track day, or not to worry about it till I do the fronts.
How does one knows he/she has successfully burnished the brakes correctly? I did it tonight, got smoke, got brake fade, just lost count of how many I did. Is there a physical indication on the pads outer edges? (mine have turned white).
Did mine today. Have white on TOP of front pad, which would be trailing edge of pad given tire rotation. Doesn't look like photo as it isn't a tiny clean line, but more of an accumulation of ash on top of pad. I have not experienced the immediate response at top of peddle. It does feel less wooden, if that makes sense. I may attempt to replicate the track procedures on the road as I have a good section of road that would allow for this. If I replicate track conditions shouldn't I get less or no fade? After cool down I did a 60-0 test in sport mode. It was 100' or less no doubt.
Wow. Ok, I have "some" white, but nothing like that. They were pouring smoke, and I admit to being a little weirded out by the abuse. Did your pedal feel change during the procedure as is described in the sticky?
I will take mine out and retry. I guess my concern is how far do I take it once the breaks are smoking hot? I want to do it right, but not hurt anything on the car either.
10-06-2011, 05:43 PM
******* Brake Burnishing*******
