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      05-22-2020, 11:47 AM   #1
raceyBMW
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Brake advice from the track nerds

Took my E92 M3 for an open lapping day last weekend and had brakes that were acting very strange. Hoping to get advice from you all.

Essentially, brakes would feel great for about one lap and then stopping power would go way down, such that I had to really really stand on the pedal to get it to stop. The really strange thing however was that the pedal didn't feel soft, it almost felt as if I lost brake boost power. If it were soft, then I would have at least known that I had air in the lines.

Can this type of brake feel occur from glazing my pads? See photos below of the rotors. I did swap out from street pads (also PFC) to the race pads at home the morning of the lapping day and didn't get a proper bedding before I got to the track. Will be pulling pads this weekend.

Brake setup
Front: PFC V3 DD rotors, PFC08 pads, SS lines, brass caliper slide bushings

Rear: Stock rotors, Carbotech XP8 pads, SS lines, brass caliper slide bushings.

Here is what my rotors looked like after the day was done (cross-drilled are the rears)


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      05-22-2020, 11:52 AM   #2
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That's a pad problem. Looks like they didn't want to bed. I had this problem when I had a nice layer of one race pad compound. I went out with another race pad thinking I could do the old one lap bed-in and it didn't go well. The pads just never took to the rotors.
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      05-22-2020, 12:05 PM   #3
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Your setup should work perfectly.

The best practice is to put your track pads on at home, then drive to the track which will remove the old pad material. After the weekend drive home on the track pads again and the rotors will be ready for the street pads again

If you drive the track pads on the street in your current situation they will clean the rotors from all that junk
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      05-22-2020, 12:12 PM   #4
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Quote:
Originally Posted by SYT_Shadow View Post
Your setup should work perfectly.

The best practice is to put your track pads on at home, then drive to the track which will remove the old pad material. After the weekend drive home on the track pads again and the rotors will be ready for the street pads again

If you drive the track pads on the street in your current situation they will clean the rotors from all that junk
That is exactly what I did, swapped to track pads at home, drove to track (1hr30 away). Just seems like they never bedded. They feel fine driving around town now, but like I said above, they also felt fine for about 1 lap at the track as well.

I am just hoping it is not something else related to the booster/master cyl. that I won't find out about until I am out on the track again...pretty annoying problem to find out there.
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      05-22-2020, 12:16 PM   #5
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Quote:
Originally Posted by roastbeef View Post
That's a pad problem. Looks like they didn't want to bed. I had this problem when I had a nice layer of one race pad compound. I went out with another race pad thinking I could do the old one lap bed-in and it didn't go well. The pads just never took to the rotors.
That's what I was suspecting as well after seeing the rotors. Any way to come back from this without new pads? Will sanding/honing rotors and scuffing the pads be enough?

I was hoping sticking with PFC street and race would be compatible enough, but evidently not.
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      05-22-2020, 12:20 PM   #6
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Quote:
Originally Posted by raceyBMW View Post
That is exactly what I did, swapped to track pads at home, drove to track (1hr30 away). Just seems like they never bedded. They feel fine driving around town now, but like I said above, they also felt fine for about 1 lap at the track as well.

I am just hoping it is not something else related to the booster/master cyl. that I won't find out about until I am out on the track again...pretty annoying problem to find out there.
Something is clearly wrong. Master cyl issues are exceedingly rare. They didn't bed properly

Who did you buy the rotors from? If you got them from Bimmerworld call them, ask for Phil and tell him about this issue. Or just email him at phil@bimmerworld with the pics

Pfc doesn't usually take any bedding at all. I've run through more than 20 sets of pads over the years, never bedded a single one in, never ran into the ice pedal you're struggling with. So the problem is solvable!
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      05-22-2020, 12:21 PM   #7
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Quote:
Originally Posted by raceyBMW View Post
That's what I was suspecting as well after seeing the rotors. Any way to come back from this without new pads? Will sanding/honing rotors and scuffing the pads be enough?

I was hoping sticking with PFC street and race would be compatible enough, but evidently not.
Just street driving with the track pads should be enough to clean them
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      05-22-2020, 12:57 PM   #8
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Try a Flex-Hone tool like this. You just put it on the end of a drill and it will clean the rotor surface. Dave Zeckhausen recommended it to me long ago.

https://www.amazon.com/Brush-Researc...rd_i=256184011
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      05-22-2020, 06:25 PM   #9
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I use to run pfc08. No need to bed the pads in. I switch between stock and track pads frequently Weird.
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      05-22-2020, 06:53 PM   #10
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I also had a weird brake pedal pressure that exhibited itself under hard braking at track. Took me over a year.to troubleshoot, including changing nearly every damn component of the braking system.

Turned out my ABS/DSC pump was leaking at the deal that joined the mechatronic portion to the hydraulic portion. It only happened under extreme pedal pressure and when the fluid was very hot (ie track conditions). On the street it was fine. So if you can't solve the problem any other way, take a look at the ABS pump and see if it's leaking fluid.
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      05-24-2020, 02:15 PM   #11
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Are you sure it wasn't your tires falling off? Heat cycled, overheated or otherwise crappy tires will result in a loss of braking power and cause ABS to come on.

Which feels like...helplessness.
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      05-24-2020, 09:32 PM   #12
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Quote:
Originally Posted by Redd View Post
I also had a weird brake pedal pressure that exhibited itself under hard braking at track. Took me over a year.to troubleshoot, including changing nearly every damn component of the braking system.

Turned out my ABS/DSC pump was leaking at the deal that joined the mechatronic portion to the hydraulic portion. It only happened under extreme pedal pressure and when the fluid was very hot (ie track conditions). On the street it was fine. So if you can't solve the problem any other way, take a look at the ABS pump and see if it's leaking fluid.
Thanks for this. This sounds like it could be my issue potentially. Bought a flex hone to use on the rotors to give that at try and see if it comes back next track day. I have used this setup before a couple times at the track with no issues, so I just have a hard time believing its a material problem.

What all did you have to replace to fix your issue?
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      05-25-2020, 01:32 AM   #13
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Quote:
Originally Posted by raceyBMW View Post
What all did you have to replace to fix your issue?
Replaced the entire ABS/DSC pump module with a low mileage used one I got off eBay. No issues since.

You can easily check the ABS/DSC pump. Just remove the plastic cover around the brake fluid canister and the ABS pump shd be under that. It's the silver and black module with a few black hard pipes going into it. Check for signs of weeping or wetness. Mine was so bad the black paint had started to bubble from brake fluid damage.

I have a thread here somewhere on this. Let me try and find it.

https://www.m3post.com/forums/showthread.php?t=1477226
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      05-25-2020, 03:56 AM   #14
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Quote:
Originally Posted by raceyBMW View Post
That's what I was suspecting as well after seeing the rotors. Any way to come back from this without new pads? Will sanding/honing rotors and scuffing the pads be enough?

I was hoping sticking with PFC street and race would be compatible enough, but evidently not.
i'll expand a little bit. i could have had a combination of problems that i didn't realize at the time. i had a track day at willow springs, no really big braking zones, just a few places you tap to get down to the appropriate speed. there is only one place where you threshold brake for about 1.5 seconds. i took a set of race pads down to about a 1-2 millimeters (cobalt friction xr1 - they didn't chunk apart!), but i could feel through the pedal they weren't right. swapped pads to my backup ferodo ds2500's, good to go for the rest of the day.

fast forward to my next track day at laguna seca (three hard brake zones, no long straights to cool brakes), i had a set of endless me20's that i wanted to try. i didn't realize this at the time, but those pads like to be bedded in a certain way, and i already had a nice layer of another compound on the rotors. i was experiencing what i perceived to be brake fade, problem is, these brakes don't fade. i had a soft pedal that would get better with one pump. it wasn't knock back, it happened at every corner and i have anti-knockback springs. i had to lengthen my braking zone, and when i did get that second press, i had ok torque, but not much bite.
so i came up with two theories-
(1) i cooked the srf my previous track day at big willow and just didn't realize it when i took the pads down way too low and they held up (putting a lot of heat into the caliper).
(2) the me20 pads are a different compound and i learned they like a specific bed-in procedure.

i haven't used the me20 pads again to test this theory, mainly because i'm tired of experimenting with endless (no pun intended) amounts of available race pads and i'm just going to proceed with the cobalt xr1's that i love, but the original post reminded me of this experience.
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      05-26-2020, 06:06 PM   #15
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Quote:
Originally Posted by Redd View Post
Replaced the entire ABS/DSC pump module with a low mileage used one I got off eBay. No issues since.

You can easily check the ABS/DSC pump. Just remove the plastic cover around the brake fluid canister and the ABS pump shd be under that. It's the silver and black module with a few black hard pipes going into it. Check for signs of weeping or wetness. Mine was so bad the black paint had started to bubble from brake fluid damage.

I have a thread here somewhere on this. Let me try and find it.

https://www.m3post.com/forums/showthread.php?t=1477226
Thanks for this, much appreciated!! I will hunt it down this weekend and see if I have the same seepage. Did you DIY the ABS unit at home? If so, did you take your car to BMW to cycle bleed the ABS afterwards?
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      05-26-2020, 07:39 PM   #16
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No I got everything done at a specialist mechanic. But yes I did cycle bleed the ABS. The best way to ensure all the fluid gets removed along with any air bubbles is to use the diagnostics computer to cycle/bleed the system. The 2nd option is to use a pressure bleeder.

Another thing to check - Recently I noticed a leak between the master cylinder and brake booster. There was signs of wetness and fluid stains on the black part of the brake booster body. This was a cheap fix, I just replaced the rubber O-ring between the MC and booster.

I've spent a ton of time/money troubleshooting brake issues on this car. Lol

Last edited by Redd; 05-26-2020 at 07:50 PM..
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