Brakes functioning in the rain....

Type_R · 17 Dec 2017 at 21:31

I have a strange query which I was hoping you knowledgeable lot might be able to help me with please.

So the current F8x series of cars (BMW M3/4) have a very strange problem with braking in the rain. There are multiple threads in various M3 forums talking about 'lack of bite' or just plain 'no braking effect' when the car has been driving on the motorway in the rain. Both CCB owners and steel brake owners are complaining alike.

I must admit I have had a Golf, Golf GTi, E92 M3 and now the F80 M3 and apart from this car have never experienced anything like it.

Your driving along in the rain generally at motorway speeds and you hit the brakes, literally nothing happen for 1-2s - there is no bite at all. If you continue to press on the pedal and increase pressure on it, the car will start to slow down, but the braking effect is probably 25% of normal. If you let go of the brakes and depress the pedal again, you get about 50% of braking power back.

Am I right in thinking that relatively modern cars automatically clear the water off brake pads automatically at regular intervals? Is there a reason why you would choose not to implement this in your flagship 400+bhp model?

The words 'pad-knockback' are being suggested as reasons for this...although I'm not buying it.

mushtafa · 17 Dec 2017 at 22:07

Sounds like poor friction material. Is it only in the wet, or also in the cold?

Type_R · 17 Dec 2017 at 22:12

mushtafa said:
Sounds like poor friction material. Is it only in the wet, or also in the cold?

Just in the wet. Doesn’t it seem strange that it affects both CCBs and steel brakes though?

Regy53 · 17 Dec 2017 at 22:29

It wouldn’t make any sense as they are two different sets of brakes

I have a m5 wth Ccb the the initial bit is just unbelievable fantastic however a ccb trade of on some vehicles is poor first bite

What pads are you running it doesn’t sound right for sure, pumping the pedal with pad knockback will do as you say ( initial bite poor but better on second application) but I highly doubt it’s the case

Also there’s so few people with Ccb i wouldn’t pay much attention to that side

TripleT · 17 Dec 2017 at 22:39

I get this on my motorbike, makes it err interesting!

Did it on old pads and on brand new pads.

Type_R · 17 Dec 2017 at 22:49

Regy53 said:
It wouldn’t make any sense as they are two different sets of brakes

I have a m5 wth Ccb the the initial bit is just unbelievable fantastic however a ccb trade of on some vehicles is poor first bite

What pads are you running it doesn’t sound right for sure, pumping the pedal with pad knockback will do as you say ( initial bite poor but better on second application) but I highly doubt it’s the case

Also there’s so few people with Ccb i wouldn’t pay much attention to that side

Well this is the thing, everyone running the standard brake pads is complaining of the same thing. It isn’t exclusive to my car...it seems to affect every F8x out there to some degree!

CaptainRAVE · 17 Dec 2017 at 22:51

I can't relate, my amg brakes detect the moisture and lightly touch the disc in order to dry it. I am surprised that modern tech would allow such a problem in this day and age.

delta0 · 18 Dec 2017 at 06:56

BMWs have air ducts that direct air from the front of the car to the brake discs. These channels are quite straight and won’t filter out water so in the rain so you will get a lot of water going through them as well.

theone8181 · 18 Dec 2017 at 07:37

Have you been reading m3cutters as well? delta0's response seems to make sense, but you think there would be a kink in it to try and reduce rain going through.

Type_R · 18 Dec 2017 at 10:44

delta0 said:
BMWs have air ducts that direct air from the front of the car to the brake discs. These channels are quite straight and won’t filter out water so in the rain so you will get a lot of water going through them as well.

This does seem to make the most sense

but don't most cars have some kind of auto-dry feature?

Dr Who · 18 Dec 2017 at 14:03

Discs/Pads get wet in heavy rain, you should gently apply the brakes every so often to clear the water (and other detritus). If you think it is exciting in an M3 try it in a 12 tonne double decker.

Treat your brakes in heavy rain like you are constantly driving through fords and test them regularly.

Type_R · 18 Dec 2017 at 15:54

Dr Who said:
Discs/Pads get wet in heavy rain, you should gently apply the brakes every so often to clear the water (and other detritus). If you think it is exciting in an M3 try it in a 12 tonne double decker.

Treat your brakes in heavy rain like you are constantly driving through fords and test them regularly.

Which is all good and well but with all due respect a M3 is not a double decker...it is a modern performance car...which should have the latest (I use the word loosely) safety features built in!

acemastr · 18 Dec 2017 at 17:29

My truck is the opposite, the rust build up when raining makes them super touchy on bite, it's lovely.

Sounds like pad material

snapdragon69 · 18 Dec 2017 at 17:56

Type_R said:
Am I right in thinking that relatively modern cars automatically clear the water off brake pads automatically at regular intervals? Is there a reason why you would choose not to implement this in your flagship 400+bhp model?

My 11 year old Audi A8 does this when rain is sensed and speed is over a certain value - it has Bosch ABS/ESP version 5.7. It is not perceptible to the driver, I have read it in the documentation.

Lopéz · 18 Dec 2017 at 18:54

Type_R said:
This does seem to make the most sense but don't most cars have some kind of auto-dry feature?

I'm happy to be corrected, but I'd be surprised if "most" cars have this feature.

Type_R · 18 Dec 2017 at 19:14

Lopéz said:
I'm happy to be corrected, but I'd be surprised if "most" cars have this feature.

If my 1999 Golf 1.6 had it, I am pretty sure most cars have it

Jonnycoupe · 18 Dec 2017 at 19:15

Most other cars have to use lane 1 and lane 2 hence occasional braking to prevent this problem. Seems extended periods of warp drive in lane 3 result in this!?

Lopéz · 18 Dec 2017 at 20:25

Type_R said:
If my 1999 Golf 1.6 had it, I am pretty sure most cars have it

Your 1999 Golf had auto drying brakes? How did they work? I've had a Mk4 in bits, as far as I remember it's got completely conventional braking system...

Type_R · 18 Dec 2017 at 21:09

Lopéz said:
Your 1999 Golf had auto drying brakes? How did they work? I've had a Mk4 in bits, as far as I remember it's got completely conventional braking system...

I have no idea but let me tell you in torrential rain I never had a feeling that there was any difference in brake bite compared to when dry!

jpaul · 18 Dec 2017 at 21:12

it was worth a quick google lol hopefully it is actually more robust than this

Brake Disc Wiper- a great feature on your VW!

First introduced in the 2006 Volkswagen Passat and by model year 2009 installed on all vehicle with stability control (ESP or ESC), brake disc wipers are a little known safety feature on Volkswagen vehicles. As a vehicle drives in the rain a film of water builds up on the brake rotor. When the brake pads are applied to the brake disc the film of water must first be removed before braking can take place, resulting in longer and slower braking response. Here’s how Volkswagen vehicles correct this concern:
-The driver activates the wipers
-The windshield wiper switch position is broadcast across the vehicle’s computer networks (The vehicle has detected a rain driving situation)
-The ABS (Anti Lock Braking) control module receives this signal and begins to monitor how often the brakes are applied
-If the module has not detected a brake application for a 5 minute period brake disc wiping is initiated
-The ABS module applies slight braking pressure for 15 wheel revolutions to wipe to disc clean of any accumulated water film
-The ABS repeats this cycle as long as the wipers are on without the driver ever being aware of this process