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M2 Technical Topics > Track / Autocross / Dragstrip > Brake upgrade suggestions needed!

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      08-26-2020, 01:13 PM   #23
eeyang92
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Quote:
Originally Posted by Megator View Post
Look up "knock back" or "pad nock back". If the feeling corelates to having just done a high G corner then this is likely what is happening.

I notice it on my brakes from time to time.

https://nasaspeed.news/tech/brakes/p...o-do-about-it/
I've heard about that - but could it really cause the difference between feeling squishy in the middle of the pedal vs. very firm at the top of the pedal? My guess would be if it were pad knockback it would feel equally squishy at the top too?

Also, now I've remembered - driving to the track, my pedal generally goes 1/3-1/2 of the way down, and isn't super firm. But occasionally on the track, it will get maximum firm at the top of the pedal, generally right after I've gone wide-open throttle, as if the brake booster went on overdrive. Then it goes away until maybe 10-20 corners later. Extremely odd feeling.

Last edited by eeyang92; 08-26-2020 at 01:26 PM..
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      08-26-2020, 04:42 PM   #24
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Speaking of upgrades, anyone know where to get the larger brake fluid reservoir from the M2 race car? Would that be the same part for the M2/M2C?

It at least requires cutting a small circle in the hood bracing since it’s taller.
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      08-26-2020, 04:44 PM   #25
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Quote:
Originally Posted by eeyang92 View Post
I've heard about that - but could it really cause the difference between feeling squishy in the middle of the pedal vs. very firm at the top of the pedal? My guess would be if it were pad knockback it would feel equally squishy at the top too?

Also, now I've remembered - driving to the track, my pedal generally goes 1/3-1/2 of the way down, and isn't super firm. But occasionally on the track, it will get maximum firm at the top of the pedal, generally right after I've gone wide-open throttle, as if the brake booster went on overdrive. Then it goes away until maybe 10-20 corners later. Extremely odd feeling.
Well with this info maybe not. Its hard to diagnose at a distance could be your pad drops back to a happy temp after a long straight and then slowly heat back up beyond its limit.

I do find the brakes a bit varriable in general but drove around the issue.
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      09-04-2020, 12:00 AM   #26
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Originally Posted by eeyang92 View Post
Regarding the pedal feel - do you get inconsistent pedal feel? I usually get the normal progression of the pedal becoming spongey after a few laps, but everyone once in a while the pedal will be a maximum firm and the bite point will be 1cm from the top (whereas usually it's halfway to the floor), and then the turn after that it will go back to be it's usually spongey self.

I can't really figure this one out, so usually I test the brakes just a bit before I really stomp on them.
I have felt this same thing in my OG M2. A few weekends ago I did a track day at Hockenheim in M2CS with CCB and felt the same. I asked one of the BMW instructors and he said it was likely related to the throttle to brake transition (how fast and how hard you transition). Certain circumstances can boost brake pressure for safety panic type situations. If this is the case, the difference in pedal feel combined with any kind of fluid fade is frustrating especially when trying to be consistent with rev matching and not know where the brake pedal will be.
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      09-04-2020, 02:24 AM   #27
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Interesting discussion. I have not noticed a super firm pedal like you’re describing. Panic brake assist might be the answer here. The ABS/ESP pump can trigger to add extra volume to the brakes to aid in panic braking situation and helps to get to locking pressures quicker.

I tend to get on the brakes slower at first, then push hard about a half a second after I applied the brakes. I like to let the weight transfer before really getting on the pedal. Habit from my Mustang days. I think this style avoids the ABS unit recognizing a panic brake apply and I don’t get the assist. Would explain why I get consistently squishy pedal after a few laps.

Last edited by 5.M0NSTER; 09-04-2020 at 02:35 AM..
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      09-04-2020, 03:22 AM   #28
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Quote:
Originally Posted by KHAP13 View Post
I have felt this same thing in my OG M2. A few weekends ago I did a track day at Hockenheim in M2CS with CCB and felt the same. I asked one of the BMW instructors and he said it was likely related to the throttle to brake transition (how fast and how hard you transition). Certain circumstances can boost brake pressure for safety panic type situations. If this is the case, the difference in pedal feel combined with any kind of fluid fade is frustrating especially when trying to be consistent with rev matching and not know where the brake pedal will be.
Super interesting! I will have to test that out next time at the track to see if I experience that. Yeah, honestly it's sort of frustrating. I wonder if there's a way to set it to one mode or the other - I'm guessing it doesn't activate all the time because it probably puts a lot of stress on the brake booster.

Quote:
Originally Posted by 5.M0NSTER View Post
Interesting discussion. I have not noticed a super firm pedal like youíre describing. Panic brake assist might be the answer here. The ABS/ESP pump can trigger to add extra volume to the brakes to aid in panic braking situation and helps to get to locking pressures quicker.

I tend to get on the brakes slower at first, then push hard about a half a second after I applied the brakes. I like to let the weight transfer before really getting on the pedal. Habit from my Mustang days. I think this style avoids the ABS unit recognizing a panic brake apply and I donít get the assist. Would explain why I get consistently squishy pedal after a few laps.
I usually transition fairly smoothly as well. Now that it is mentioned, I did notice this mostly happened after a high speed straight - I find at high speeds I can transition from throttle to brake much faster without upsetting the car, perhaps that could be the culprit.
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      09-05-2020, 04:49 AM   #29
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The steps I've gone through on my OG 16.

PFC08 without extra cooling - gets a bit softer after a handful of laps. How many depends a lot on the track. Higher pad wear rate.

PFC08 with GT3 brake cooling scoop directed at the disk with a bit of the brake shield removed - the pedal gets slightly soft on the worst tracks only. Actually no trouble with the disc's being cooled the wrong way.

PFC08 with scoop, hose and brake shield with hose connector aimed at disc center - No problems, good margins, good wear rate. No need for upgrades for brake performance, only for other pedal feel.
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