[2PUTT]

Noticed that the big brakes on the M2C require the pedal to be pumped a few times to engage after an extended exposure to water during driving or after the car was washed...

Took about 3-4 pumps for me to stop last night after a wash. Almost went through a red light.

(pic for attention)

[bri1042]

I haven't had any extreme reactions to the brakes getting wet. There's always SOME reduction in braking with wet disc brakes, but I've had cars that were more sensitive than this one. I did own a car with all drum brakes once...even in light rain the thing didn't want to stop at all, so perhaps I'm just still using that as a comparison almost 30 years later.

[Bumpinjeep]

After i wash my car, i'm always wary of stopping for the first time because when these brakes get clean, it takes a good pump to stop em. It's not bad as long as you remember to stop the car in a parking lot or something and then youre back on the road.

[Frank K]

When you use your wipers, the car assumes it's raining and will periodically engage the brakes to keep the rotors dry.

[nearwater4me]

Originally Posted by Frank K

When you use your wipers, the car assumes it's raining and will periodically engage the brakes to keep the rotors dry.

I’m aware of this brake ‘wiper’ function on BMWs.
Wasn’t sure it was on M cars as well.

[chris719]

I am surprised you had this happen with drilled rotors also. I've had this happen with certain pad / rotor combos on some cars, but not on drilled or slotted or OEM pads. Might be that the larger surface area of the 2NH brakes makes it more likely to happen.

[somberlaine]

i don't think i ever observed this behavior.

My biggest issue with the breaks since I got the car back in June is the break squeaking. I am at 5k miles and it is still happening unpredictably. I am tempted to take it to the dealership but i am afraid i won't be able to reproduce the problem.

[johnung]

Originally Posted by chris719

I am surprised you had this happen with drilled rotors also. I've had this happen with certain pad / rotor combos on some cars, but not on drilled or slotted or OEM pads. Might be that the larger surface area of the 2NH brakes makes it more likely to happen.

I'm not sure what year/brakes exactly are being discussed but if you mean 370mm front 4-piston Brembo (S2NHA) vs 340mm front 4-piston Brembos (P337A), the swept area of the brakes are identical since they use identical size and identical part numbers for brake pads. The calipers are identical except for a casting stretched by 15mm to fit over 30mm larger rotors. That extra rotor area doesn't increase pad swept area in this case.

Actual fully cross-drilled (not dimpled) brake rotors provide the best performance in rain because they give any water between the pad and rotor surfaces somewhere else to go. If you are having to pump brakes to get them to work under wet conditions (and they work fine otherwise including cold temperatures) with drilled rotors, I would suspect the pad compound is the issue.

Also remember that braking under wet conditions is also a function of tire compound, tire pressure, tread design and tread condition. Is it possible that you are focusing on brakes when it's your tires that may be suspect under wet conditions?

I've got 370mm drilled rotors front, 345mm drilled rotors rear, Hawk 5.0 pads and 245/40-18 Michelin Pilot Sport 4S tires. I honestly can't tell if the road conditions are completely dry or pouring rain, the handling and braking performance of these components working together as a system seem identical under varying conditions.

Hope this helps!

[Vulpe]

Originally Posted by johnung

I'm not sure what year/brakes exactly are being discussed but if you mean 370mm front 4-piston Brembo (S2NHA) vs 340mm front 4-piston Brembos (P337A), the swept area of the brakes are identical since they use identical size and identical part numbers for brake pads. The calipers are identical except for a casting stretched by 15mm to fit over 30mm larger rotors. That extra rotor area doesn't increase pad swept area in this case.

Actual fully cross-drilled (not dimpled) brake rotors provide the best performance in rain because they give any water between the pad and rotor surfaces somewhere else to go. If you are having to pump brakes to get them to work under wet conditions (and they work fine otherwise including cold temperatures) with drilled rotors, I would suspect the pad compound is the issue.

Also remember that braking under wet conditions is also a function of tire compound, tire pressure, tread design and tread condition. Is it possible that you are focusing on brakes when it's your tires that may be suspect under wet conditions?

I've got 370mm drilled rotors front, 345mm drilled rotors rear, Hawk 5.0 pads and 245/40-18 Michelin Pilot Sport 4S tires. I honestly can't tell if the road conditions are completely dry or pouring rain, the handling and braking performance of these components working together as a system seem identical under varying conditions.

Hope this helps!

Do you know what forum you're on? I came from the 3/4 series ones so I know what you're talking about but the M2s have either 380 or 400mm front rotors and absolutely do not use the same pads.

[johnung]

Originally Posted by Vulpe

Do you know what forum you're on? I came from the 3/4 series ones so I know what you're talking about but the M2s have either 380 or 400mm front rotors and absolutely do not use the same pads.

Thanks for your comment. I do know what forum it is, hence what I said in my first paragraph. Wasn't sure if order code that I recognized meant same thing in M2. However other generic statements I made about drilled rotors, pad compounds and tires are valid. Thought it might help so that's why I posted.

[chris719]

Originally Posted by johnung

Thanks for your comment. I do know what forum it is, hence what I said in my first paragraph. Wasn't sure if order code that I recognized meant same thing in M2. However other generic statements I made about drilled rotors, pad compounds and tires are valid. Thought it might help so that's why I posted.

2NH is the exact option code for the M2C brakes. They are 6 piston front, nothing related to the 3 series brakes.

[grl.racr]

I experience this a little on my OG M2, and a LOT on the GT4 - almost feels like I have no brakes right after I leave the car wash lol

[Vulpe]

Originally Posted by johnung

Thanks for your comment. I do know what forum it is, hence what I said in my first paragraph. Wasn't sure if order code that I recognized meant same thing in M2. However other generic statements I made about drilled rotors, pad compounds and tires are valid. Thought it might help so that's why I posted.

I hope I didn't come off as insulting, I didn't mean it that way if it did. When I read your post I had to check if I was in the M2 section myself because I got confused.

[johnung]

Originally Posted by Vulpe

I hope I didn't come off as insulting, I didn't mean it that way if it did. When I read your post I had to check if I was in the M2 section myself because I got confused.

No problem at all. HaHa, but if you really feel bad my wife and I can come spend the winter with you in Hawaii. Also we'll need use of the M2!