Ceramic Pad Brake Delay.. In the Rain... When it's Cold

[kayger12]

I'm wondering if it's maybe that the ceramics cool down faster, whereas the semi-metallics hold the heat longer. I'm thinking the heat possibly evaporates the water from the pad surface longer?

Again, this problem appears completely temperature dependent. I can drive in a driving downpour for an hour when it's warm out and the braking action is immediate. It's only when it's wet AND cold out that it occurs.

Also, same roads/same conditions-- I never had it happen with my 325i with semi-metallics.

[ryankokesh]

I wonder if slotted rotors wouldn't fix this? I have slotted/drilled and have never noticed this with the ceramic pads.

[zj96sc]

Does/did the 325i have brake cooling ducts?

If it was a temperature issue, you'd notice it the first time you tried to apply your brakes cold too. So...do you?

Pretty simple test either way. After a good 20-30 minutes of no brakes in the rain, give the pedal two quick taps, and then lay on. Good brakes = water, delay = temp.

EBC kind of hints at it, i will see if i can find my original sources from a few years ago.

If brakes become wet it can have a negative impact on their performance, tapping and testing your brakes can help the rotors and pads to dry out.

more edits:

here's a thread based on similar "symptoms." Like I said, these discussions are common for E36M guys, basically anything with cooling ducts.

http://forums.bimmerforums.com/forum...ht=rain+brakes

http://www.e90post.com/forums/showthread.php?t=409511

apparently new BMWs are equipped with a brake drying function, basically quick pulse on the brakes timed with the wipers to clear water off.

apparently also exacerbated by more open wheel styles....5 spokes, etc.

[zj96sc]

seems to be a pretty fair amount of material out there all indicating the water is the problem:

http://editorial.autos.msn.com/artic...umentid=435355

For example, Mercedes began using electronic brakes a few years ago. They can automatically sense when the road is wet and imperceptibly apply the brakes just enough to keep the brake discs dry. This way, brake performance, which can be weakened by moist discs and pads, remains consistent no matter the kind of weather the car is in. BMW added this feature, which it calls Brake Drying, to its 2006 BMW 3-Series. It's standard equipment.

apparently brake drying with 3ers hit the e9x.

[Hornung418]

Quick recap: When it's wet, proper procedure is to tap the breaks twice before needing to actually use them. What do you do for an emergency stop?

[kayger12]

Does/did the 325i have brake cooling ducts?

If it was a temperature issue, you'd notice it the first time you tried to apply your brakes cold too. So...do you?

Pretty simple test either way. After a good 20-30 minutes of no brakes in the rain, give the pedal two quick taps, and then lay on. Good brakes = water, delay = temp.

EBC kind of hints at it, i will see if i can find my original sources from a few years ago.



more edits:

here's a thread based on similar "symptoms." Like I said, these discussions are common for E36M guys, basically anything with cooling ducts.

http://forums.bimmerforums.com/forum...ht=rain+brakes

http://www.e90post.com/forums/showthread.php?t=409511

apparently new BMWs are equipped with a brake drying function, basically quick pulse on the brakes timed with the wipers to clear water off.

apparently also exacerbated by more open wheel styles....5 spokes, etc.

Good info. Thanks. Not sure if my 325 had ducts. It had the sport package and 17" wheels, so maybe?

It's definitely partially a temperature issue (OAT, anyway), because when it's pouring out yet warm it never happens. Only when it's cold and wet as described in the threads you found. So water combined with cold temps is the trigger.

Looks like something I have to live with and just preemptively manage when the trigger conditions exist.

Does anyone else in a cold-climate area experience this? And if so (or not) what pads/rotors are you running?

[zj96sc]

Quick recap: When it's wet, proper procedure is to tap the breaks twice before needing to actually use them. What do you do for an emergency stop?

Its not a bad habit to form to occasionally do a 'confidence tap' on the brakes anyway. If you're cruising in pouring rain (and honestly even in clear weather) just make it a habit to put some pressure on every couple miles - should help mitigate any delay in a panic stop situation.

[M0nk3y]

I had this happen on my E46 325xi w/OEM brakes...Happened twice to me as well.

One at 35mph, one at 70mph on a exit. Both times I thought I was going through another car. Scariest feeling I've had.

[Mtnman]

Keith,
I have Ceramics. I have noticed something similar, but never been able to identify the issue. By that i mean sometimes, rarely, my brakes feel different than normal, like it takes longer to stop. I thought (and still may be the case) this was just in my head. After reading this thread, I will pay more specific attention to these details. Of course, we just got through 3 cold rainy days, but there will be more this winter. Ill post after I have something worthy of reading.

[kayger12]

Keith,
I have Ceramics. I have noticed something similar, but never been able to identify the issue. After reading this thread, I will pay more specific attention to these details. Of course, we just got through 3 cold rainy days, but there will be more this winter. Ill post after I have something worthy of reading.

Thanks, brother.