marks on discs after high speed run

[jaylazy2020]

Do these marks look strange? I found a great stretch of unrestricted autobahn from Stuttgart to Munich so gave my (new to me) 2NH brakes a test.

They were fine, no droning like standard set up but they didn’t give me that re assuring bite when a golf pulled out in front of me at 280!

Anyway I noticed all the discs had these marks.

[M3SQRD]

Originally Posted by jaylazy2020

Do these marks look strange? I found a great stretch of unrestricted autobahn from Stuttgart to Munich so gave my (new to me) 2NH brakes a test.

They were fine, no droning like standard set up but they didn’t give me that re assuring bite when a golf pulled out in front of me at 280!

Anyway I noticed all the discs had these marks.

No pics attached

[jaylazy2020]

Originally Posted by M3SQRD

No pics attached

Uploaded now. Thanks

[M3SQRD]

First, did you properly bed the pads and rotors after the install?

Second, had you been running for miles without having touched the brake pedal before having to hit the brakes hard to avoid hitting the VW?

Third, using stock or oem pads?

From the pics it looks like very uneven pad transfer due to not bedding them or hitting them hard while cold or potentially a combo of the two. Go out and try rebedding them. Drive around normally for 15 minutes with low-medium braking to get the rotors up to a reasonable temp then try 8-10 hard stops from 70-30 mph in quick succession without engaging ABS. Once this is done try and drive for 20-30 min on the highway without having to use the brakes or use them as little as possible. If this doesn’t clean things up, remove the pads from the calipers and sand off the glazing that’s formed on the pads, and then repeat the bedding procedure.

[jaylazy2020]

Originally Posted by M3SQRD

First, did you properly bed the pads and rotors after the install?

Second, had you been running for miles without having touched the brake pedal before having to hit the brakes hard to avoid hitting the VW?

Third, using stock or oem pads?

From the pics it looks like very uneven pad transfer due to not bedding them or hitting them hard while cold or potentially a combo of the two. Go out and try rebedding them. Drive around normally for 15 minutes with low-medium braking to get the rotors up to a reasonable temp then try 8-10 hard stops from 70-30 mph in quick succession without engaging ABS. Once this is done try and drive for 20-30 min on the highway without having to use the brakes or use them as little as possible. If this doesn’t clean things up, remove the pads from the calipers and sand off the glazing that’s formed on the pads, and then repeat the bedding procedure.

Many thanks for the guide.

I bought the discs and calipers second hand but they had only done 10k km and are very fresh.

It’s completely stock 400mm fronts and 380 rears wit oem pads and upgraded to steel lines with Castrol SRF fluid.

I drove slowly from Munich to Stuttgart as it was snowing

They I drove short local journeys and all was fine.

Today it was cold but dry and sunny.

So perhaps the when I did the first big big stop from 283 they discs had cooled down?

I didn’t stand on the brakes as I always like to modulate the brakes have a little bit in reserve.

They didn’t grumble like the old standard set up with DS2500.

I’ll try the process you describe.

Should I aim to get the pads back to looking like the picture below?

[M3SQRD]

The rotor in the last pic (couldn’t clearly see rotor with wheel installed) looks decent. One last thing, do not apply the handbrake with hot rotors, for example after bedding the brakes, after a track session, or driving aggressively in the mountains with heavy brake use. If you do then you’ll see an outline of the brake pad on the rotor surface. This is what typically causes brake vibrations.

[jaylazy2020]

Originally Posted by M3SQRD

The rotors in the last pic looks decent. One last thing, do not apply the handbrake with hit rotors still really hit after, for example bedding the brakes, going to track, or driving in the mountains with heavy brake use. If you do then you’ll see an outline of the brake pad o n the rotor durfave

Thanks. I’ll keep that in mind. Hopefully once I crack 306km/h 190mph I’ll retire !

[M3SQRD]

Originally Posted by jaylazy2020

Thanks. I’ll keep that in mind. Hopefully once I crack 306km/h 190mph I’ll retire !

Are there a limited number of pad compounds/brands available for the BMW Gold calipers? PFC 01, 03, 05 and 11 are my favorite pad compounds. Hawk DTC are ok but find them lacking in initial feel and modulation. I’ve heard great things about Cobalt pads but have used them. Carbotech was my go to pad for ~12 years and one huge advantage is they’ll make custom shaped pads and thickness quickly. I’m positive CT offers pads for the Gold calipers - I’d recommend the 1521 for street and XP12 (or XP20 which requires grippy race tires).

[NSX2M4]

Not sure if they look strange or not. However, buying brakes second hand is like buying used tires. Don't risk it.

[jaylazy2020]

Short 15 km trip to airport this morning and marks on discs are a little bit less. Hopefully they will clean up.

There is no vibration and they are smooth from high speed

[M3SQRD]

Originally Posted by jaylazy2020

Short 15 km trip to airport this morning and marks on discs are a little bit less. Hopefully they will clean up.

There is no vibration and they are smooth from high speed

The rotors and pads are fine. You just need to rebed the brakes - remove uneven pad deposits and transfer a uniform layer of pad material. Brakes work by adherent friction which is when the pad transfer layer is what gets worn away while braking. When brakes are cold and/or no transfer layer then it’s called abrasive friction which is when the pad machines away the rotor surface to generate brake force.

[M3SQRD]

Originally Posted by NSX2M4

Not sure if they look strange or not. However, buying brakes second hand is like buying used tires. Don't risk it.

I disagree. I have sold and bought used kits over the years and also know quite a few people who have done the same. With enough pictures of various details and rotor thickness measurements then the level of risk is the same as buying any other used part. If you really want to play it safe then buy a piston replacement kit and remove&replace seals and pistons (and dust seals if street setup) before installing the kit.

[jaylazy2020]

Originally Posted by M3SQRD

I disagree. I have sold and bought used kits over the years and also know quite a few people who have done the same. With enough pictures of various details and rotor thickness measurements then the level of risk is the same as buying any other used part. If you really want to play it safe then buy a piston replacement kit and remove&replace seals and pistons (and dust seals if street setup) before installing the kit.

Good to know. From that add that I bought them from you can see they had little wear from new.
They were bought new from Bmw and the company that fired them and took them off his M4 fitted them for me.

[robbo mcs]

Originally Posted by jaylazy2020

Good to know. From that add that I bought them from you can see they had little wear from new.
They were bought new from Bmw and the company that fired them and took them off his M4 fitted them for me.

1) They are pad deposits. Rebed the brakes as advised, they should wear off

2) That is not the optimum way to measure disc residual thickness. Measuring with a flat caliper like that can overestimate the thickness, as it will measure the thickest part across the face, usually at the extreme outside. You need a proper brake disc gauge, that has caliper ends that can measure the thickness anywhere across the disc, like these
https://www.ozwidetools.com.au/digit...measuring-tool

[hC1001]

You are fine. Thats just pad transfer. After driving the car normal for a bit, it will clean it up and go back to normal...

Since you dont have any vibration under braking, you are good. Dont worry.

[jaylazy2020]

Originally Posted by hC1001

You are fine. Thats just pad transfer. After driving the car normal for a bit, it will clean it up and go back to normal...

Since you dont have any vibration under braking, you are good. Dont worry.

Thanks.

They are way smoother than the standard set up but to be fair to the blue caliper set up it had 90k km on it.

Ferodo ds2500 pads seemed to cause a terrible drone from high speed.

I’ve read that this can be down to cross drilling and maybe slotted are better?

Girodisc 400mm fronts are €1600 a pair!

[jfritz27]

Originally Posted by robbo mcs

1) They are pad deposits. Rebed the brakes as advised, they should wear off

2) That is not the optimum way to measure disc residual thickness. Measuring with a flat caliper like that can overestimate the thickness, as it will measure the thickest part across the face, usually at the extreme outside. You need a proper brake disc gauge, that has caliper ends that can measure the thickness anywhere across the disc, like these
https://www.ozwidetools.com.au/digit...measuring-tool

Cheaper caliper option (for those in US):
https://www.amazon.com/Anytime-Tools...s%2C103&sr=8-3

[SilleM3]

Originally Posted by jaylazy2020

Thanks.

They are way smoother than the standard set up but to be fair to the blue caliper set up it had 90k km on it.

Ferodo ds2500 pads seemed to cause a terrible drone from high speed.

I’ve read that this can be down to cross drilling and maybe slotted are better?

Girodisc 400mm fronts are €1600 a pair!

Like the guys said it's just a transfer layer of the pad. You over heated them a little bit. I have the same n2h brakes. I bought mine brand new from bmw and the same thing happens In the canyon and at the track or bedding them in.

First picture is after I bed the brake pads in. HAWK HPS 5.0

when I use track pads that doesn't happen. It's the pad material. No biggie.

1st picture upside down 😱

[NSX2M4]

Originally Posted by M3SQRD

I disagree. I have sold and bought used kits over the years and also know quite a few people who have done the same. With enough pictures of various details and rotor thickness measurements then the level of risk is the same as buying any other used part. If you really want to play it safe then buy a piston replacement kit and remove&replace seals and pistons (and dust seals if street setup) before installing the kit.

Well, I'm glad you are one of the lucky ones. Being that you sell used brakes, this response is no surprise. It's a consumable part, like tires it's all how the product is used per owner. I'm merely starting that brakes and tires in a used products forum is a seriously high risk buy.

[jaylazy2020]

I just drove a 991.2 Gt3 touring.

Amazing car and prob not as fast as my stage 2 F82 but amazing letting it rev out! The power is so linear! The sound!

But the most impressive part was the bite from the brakes!

150kph and a stab of the brakes really stops the car to the point where your chest is thrown forward.

I’ve read that CCCb versus steel only offer much less fade and know Porsche have always had amazing brakes but I was shocked at how good they were.

Could it all be down to the pad? For that intial bite and them ability to modulate?

[M3SQRD]

Originally Posted by jaylazy2020

I just drove a 991.2 Gt3 touring.

Amazing car and prob not as fast as my stage 2 F82 but amazing letting it rev out! The power is so linear! The sound!

But the most impressive part was the bite from the brakes!

150kph and a stab of the brakes really stops the car to the point where your chest is thrown forward.

I’ve read that CCCb versus steel only offer much less fade and know Porsche have always had amazing brakes but I was shocked at how good they were.

Could it all be down to the pad? For that intial bite and them ability to modulate?

Braking distance is dominated by tire grip. Pad initial bite can make it feel like you’re stopping much faster and in a shorter distance. CCB and brake kits, with the same tires, will have similar braking distance to stop except it can be done over and over again without fading. Stock system will fade after only a couple-few threshold stops. I prefer a brake pad with a decent initial bite but great modulation/control.

[jaylazy2020]

Originally Posted by M3SQRD

Braking distance is dominated by tire grip. Pad initial bite can make it feel like you’re stopping much faster and in a shorter distance. CCB and brake kits, with the same tires, will have similar braking distance to stop except it can be done over and over again without fading. Stock system will fade after only a couple-few threshold stops. I prefer a brake pad with a decent initial bite but great modulation/control.

I get what your saying but that intial bite and grab on the 991 is so much better than my 2NH set up.

I’m not pushing the grip levels on a bone dry motorway at 150kmph.

It just feels like the pads are grabbing the discs so well on the 991

Whereas on my F82 is doesn’t have that immediate feeling when I hit the brakes

I’d love to drive a F82 or even G82 with carbon brakes to see how they compare to the 991