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Tech: Z07 Brake Burnishing

 
Old 12-15-2014, 05:48 PM
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jvp
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Default Tech: Z07 Brake Burnishing

(re-posted from C6 ZR1 section as it still applies).

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?
Editor note: This part of the post has been updated on 10 April, 2017. New information from GM.
Previously, it was thought by GM that the track burnishing should be done AFTER the street burnishing, IF you intend to drive on the race track. Earlier ZR1 owners manuals called for street burnishing then track burnishing. However, this is no longer required through testing by GM. When they send their new cars to the track, they only track burnish them.

So what does that mean? Following the owners manual, drive seven or eight laps with increasing speeds and then decreasing speeds. The middle lap should be full speed or near to it. Once you've completed those laps, do a final lap or two as a cool down, using your brakes as little as possible, and then park the car for the rest of that session. That should burnish the pads properly for use on the track (and on the street!)

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.

Last edited by jvp; 04-28-2017 at 10:01 AM.
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Old 12-15-2014, 07:17 PM
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thanks for the info jvp!

i read your original post plus your follow up info and responses to replies. it was far more informative than the owners manual.

my conclusions and suggestions for new Z07 owners:

i wouldn't recommend burnishing before you reach 500 miles.

cool/cold ambient temperatures wont allow enough tire grip to allow burnishing.

its ok to wait to burnish until you drive hard on the street or run at a track (which may not be until next spring/summer).


jvp,

could you be more specific on the track burnishing procedure?

are we looking for green fade?

how long do we wait after first burnishing session to go back out on the track?

thx!
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Old 12-15-2014, 07:23 PM
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Originally Posted by 2TallTulip View Post
could you be more specific on the track burnishing procedure?
Read the manual as it's pretty well documented in there. If you assume a multi-session HPDE, figure you're going to throw the very first one away in the morning. Do 6 or 7 laps as the book mentions, then a cool-down lap, then park it for the rest of that session.

are we looking for green fade?
Nope. The green fade should be over by the time you get to the track burnishing, because you already did the street burnishing. The track burnishing is just prepping the pads for more sustained high temps.

how long do we wait after first burnishing session to go back out on the track?
My typical recipe is to just park the car for the rest of the session, and then go out for the next one.
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Old 12-19-2014, 09:36 AM
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Best thing you could do (like the book says) is find a nice road, highway that has a good 10mile stretch on a Sunday morning... follow the process. You will need every bit of that 10miles. (Did this on the ZR1). They were much better afterwards but still got more as-expected grippy after a HPDE at Road Atlanta.
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Old 12-20-2014, 10:45 AM
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Halltech was the first company to retrofit the ZR1 CC brakes on our 2008 Z06. Everyone said it couldn't be done, but it was done and imagine ZR1 brakes on a 2785 lb Z06! We used Ultraleggera wheels and the fronts required the .250" Pfadt spacer.

Now for my comment. You must find a lonely road, very lonely. Like zero cars for 10 minutes at a time.

When I did the street burnishing, at 35 times I began to feel sick from the constant stop and go. I could see a car in my RVM, about a mile back coming pretty fast, so I kept it up. Only 15 more times, right?

He caught up with me at 45 and then stayed back because smoke was coming out of the front wheel wells, which contributed to making me ever sicker. It stinks to high heaven, so beware.

Finally done, I pulled to the shoulder and waved him by. Turned around and went to brake, uh? Fade city and the pedal was moosh. Kept driving about 5 more miles and the pedal felt great, and it was back to normal.

At the track, Jimmy Painter did the track burnishing and when he got back, he said, God these brakes are worse than my Brembos! He drove the car subsequently that day, and then said, yah baby, that's what I'm talking about.

So if you are not expecting this, be prepared and find that lonely road, and get ready to puke. I almost did from the horrible smell. Great writeup JVP. Best I have seen.

Last edited by Halltech; 12-20-2014 at 10:47 AM.
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Old 12-21-2014, 12:06 PM
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It's worth noting that even the folks with the iron setup should plan on doing some sort of bedding like the street burnishing jvp describes. I know with the C7 Z51 you could count on the pads gassing badly around the 2nd or 3rd lap at speed when new if you didn't.

I tended to just throw new pads on and head out on track. I never knew exactly when but going in to a braking zone I would suddenly have very weak braking. Get through that corner, let them cool a bit, and they worked great and had much better initial bite until they wore out.
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Old 01-17-2015, 12:48 PM
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What about the high temps damaging the wheel bearings? Also some one said the heat discolored their wheels.
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Old 01-17-2015, 04:09 PM
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Originally Posted by hootowlc7 View Post
What about the high temps damaging the wheel bearings? Also some one said the heat discolored their wheels.
The bearings will be absolutely fine. I can't address the wheels, however, as they're a bit different from the ones on my ZR1.
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Old 01-22-2015, 05:51 PM
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Is it correct to assume that the street burnishing should be done with the factory installed brake fluid? No prob with that boiling off during the 50 60-0 stops?

Also, where in the world can one do this without being pulled over by the police?
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Old 01-27-2015, 08:17 AM
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I'm sorry I missed this earlier.

Originally Posted by Babaron View Post
Is it correct to assume that the street burnishing should be done with the factory installed brake fluid? No prob with that boiling off during the 50 60-0 stops?
The OEM fluid will be fine for the burnishing. Give your brake rotors some miles (1000? It should be in the manual) before you go to it, though.

Also, where in the world can one do this without being pulled over by the police?
As we discussed in the other thread: find a back-water country road and do it at 0-dark-hundred some weekend morning.
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Old 04-04-2015, 08:55 AM
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Default Liability Of Brake Burnishing

Someone responded that doing the 50 reps of Brake Burnishing caused his painted wheels to be damaged by the heat that was generated by accomplishing the Burnishing. I think you and some other members brought to everyone's attention that all of the Chevrolet instruction manuals supplied with the current C7 and past C6 cars specified only 5 reps to be performed but in fact 50 reps are required to effectively do the job correctly. What warranty legs does an owner have if they do the 50 reps and their wheels are damaged since the manuals only specify 5 reps? Is there a Chevrolet document that addresses clears up the 5 Vs 50 requirement and if so how is that document obtained?

Many Thanks!
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Old 04-04-2015, 09:05 AM
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Straight from the manual... Page 9-9

Street High Performance Brake
Burnishing Procedure (Z06 with
Z07 Performance Package)
1. From a stop, accelerate as
rapidly as possible without
activating traction control to a
speed of 100 km/h (60 mph).
2. Use enough pedal force to
completely stop the vehicle in
four to five seconds. If ABS
activates, braking is too hard.
3. Repeat Steps 1 and 2 – 50
times. This should take about
10 minutes.
4. After completing the 50 stops,
cool the brakes by driving for km
(5 mi) at 100 km/h (60 mph)

Here it is online..
http://www.chevrolet.com/content/dam...ers-manual.pdf

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Old 04-04-2015, 02:16 PM
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Originally Posted by Crazy Legs View Post
I think you and some other members brought to everyone's attention that all of the Chevrolet instruction manuals supplied with the current C7 and past C6 cars specified only 5 reps to be performed
Five stops was a misprint in, I think, the 2011 manuals and was later corrected to fifty. GM possibly misprinted five in some of the Z/28 manuals as well, but I'm not positive.

To be clear: it's FIFTY stops, not five. As Werks has pointed out: five stops won't be enough to even warm the pads up.
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Old 04-04-2015, 05:41 PM
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Originally Posted by Crazy Legs View Post
Someone responded that doing the 50 reps of Brake Burnishing caused his painted wheels to be damaged by the heat that was generated by accomplishing the Burnishing. I think you and some other members brought to everyone's attention that all of the Chevrolet instruction manuals supplied with the current C7 and past C6 cars specified only 5 reps to be performed but in fact 50 reps are required to effectively do the job correctly. What warranty legs does an owner have if they do the 50 reps and their wheels are damaged since the manuals only specify 5 reps? Is there a Chevrolet document that addresses clears up the 5 Vs 50 requirement and if so how is that document obtained?

Many Thanks!
Jon Wheelis
IIRC it was the calipers that changed color from the heat, not the wheels. I believe that since an owner is simply following the recommendations of GM, if the calipers change color, they should be exchanged under warranty.
Bish
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Old 05-03-2015, 12:40 PM
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Originally Posted by jvp View Post
(re-posted from C6 ZR1 section as it still applies).

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.
I just went through the process this AM something seemed strange when doing it because the Rt Front started smoking heavily soon in the process at around stop #25. I went ahead and finished the process with the Rt front smoking throughout. The Lft front started smoking around stop #40. Once I got home and looked at the front pads the Rt Front heated up extremely hot enough to turn the entire pad area white and melt the paint off of the metal pad backing. The left front seemed ok with just a small depth of white in the pad. I have posted pics below. I am concerned there could be something wrong with the bias in the system with more pressure going to the Rt Front. I did not have any pull to the Rt though during the process or after. From what I have read and seen pictures of post pads this doesn't seem normal.. Thoughts? Should it go back to the dealer? Is the Rt front pad still any good should it be replaced?Name:  LF pad.jpg
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Old 05-05-2015, 07:22 AM
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i had the same result this past weekend where both pads turned entirely white. i expect to hear something from my dealer today. will let you know.
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Old 05-05-2015, 09:05 AM
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Originally Posted by 2TallTulip View Post
i had the same result this past weekend where both pads turned entirely white. i expect to hear something from my dealer today. will let you know.
Mine is at the dealer also. Should know something today. I'll post what I find out also
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Old 05-05-2015, 04:32 PM
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Originally Posted by 2TallTulip View Post
i had the same result this past weekend where both pads turned entirely white. i expect to hear something from my dealer today. will let you know.
Just talked to the dealer and they told me GM Technical Assistance told them this was normal. Also told them to not even take them off and inspect them. I can't believe it. Going to run some traps on my own.
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Old 05-06-2015, 01:10 PM
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I heard the same from my dealer. We should start a new thread to find out if other cc pads look the same after burnishing.
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Old 05-06-2015, 01:38 PM
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Originally Posted by 2TallTulip View Post
I heard the same from my dealer. We should start a new thread to find out if other cc pads look the same after burnishing.
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