Brakes functioning in the rain....

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...
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It probably just feathers the brakes very slightly, presumably using the ABS in some way. I've never actually looked at how it worked but my dad's '96 Mercedes had it, I think.
 
Regardless of whether a car has such a feature, I can sympathise with the fact that his cars previously haven't had an astronomical drop off in braking performance when it's raining, I've certainly never had issues with brakes failing to bite first time.
 
Wouldn't grooved discs aid in clearing the water. Cant say i have ever noticed it on my commute where i can go ages without touching the brakes.
 
By contrast my M5 with standard steel discs stops like a dream in both dry and wet and makes a wicked whirring noise as the drilled discs really get pummelled by the pads.
 
Type_R said:
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!
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Yeah because a modern double decker doesn't need to be safe at all... However, my point was that this occurs and is scary in a bus, not that his car was working properly, maybe my english was hard for you to understand?

The BMW brake drying function works from the windscreen rain sensor, it is merely gently applying the brakes to clear the water off the discs which is what I stated you should do.
 
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Is it a failure of the DSC unit? M135i cars seem to have an issue that lets water get into the braking system, after which corrosion affects the DSC unit and the auto brake drying feature. If this has failed, the brakes could be too wet/cold to function initially?

My colleague had a failure recently on his car and the DSC was grabbing too hard when the wipers were switched on. BMW Cheltenham tested the brake fluid and found >4% water content!
 
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.
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Never had an issue with braking in heavy rain be it in a 44t artic, my 735i (doubt the e38 had this brake drying functionality) or for example my sisters M4.
 
Dr Who said:
Yeah because a modern double decker doesn't need to be safe at all... However, my point was that this occurs and is scary in a bus, not that his car was working properly, maybe my english was hard for you to understand?

The BMW brake drying function works from the windscreen rain sensor, it is merely gently applying the brakes to clear the water off the discs which is what I stated you should do.
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I am a BMW driver...so obviously I have no grasp of the English language (notice spelled with a capital E) :)
 
Lopéz said:
So if it was first introduced on the 2006 Passat a 1999 Golf didn't have it....
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I stand corrected...but my point is even in that car...which I drove for 60k I never got the feeling in torrential rain that the brakes wouldn't slow me down on first application.

theone8181 said:
Im guessing a 1999 golf may of had drum brakes at least on the rear?
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I am sure it had discs and pads all round as I had them changed during its lifetime.
Alex_6n2 said:
Is it a failure of the DSC unit? M135i cars seem to have an issue that lets water get into the braking system, after which corrosion affects the DSC unit and the auto brake drying feature. If this has failed, the brakes could be too wet/cold to function initially?

My colleague had a failure recently on his car and the DSC was grabbing too hard when the wipers were switched on. BMW Cheltenham tested the brake fluid and found >4% water content!
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Just did a diagnostic fault check to make sure...Carly reports all clear and functioning normally :) Brake fluid was changed in Aug 2017.
 
Type_R said:
I stand corrected...but my point is even in that car...which I drove for 60k I never got the feeling in torrential rain that the brakes wouldn't slow me down on first application.



I am sure it had discs and pads all round as I had them changed during its lifetime.


Just did a diagnostic fault check to make sure...Carly reports all clear and functioning normally :) Brake fluid was changed in Aug 2017.
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would have probably been 2/3s the weight of a modern car tho.
 
My Chrysler 300 had RBS { Rain Brake Support }, but any car I've driven in the last few years has been unaffected by
torrential rain or puddles [ which we get a lot of in Scotland ] even after a jet wash the discs dry out just by driving along, the pads
should be a few thou from the disc ideally.
 
The closest I ever experienced to that is on my old 125 motorbike, turns out it was cheap brake pads in the front. My Leon Cupra however never fails to stop on a sixpence.
 
All these wiping mechanism seem very flimsy if they just rely on having the wipers on (golf) or rain on the windscreen detector (bm),
in either standing water or slush it may not be working ?

Nonetheless how often have you had an emergency stop in the wet, usually have much more margin (town driving, albeit lower speed, worst scenario?)
with progressive application of the brakes and feathering to determine adhesion (which would wipe them), usually have some 100's ms to play with.
 
Regardless as if the car has brake drying there should be no problem unless you go through standing water slow enough to get water on the discs. That is why you used to see "Try your brakes" signs after floods as that is the only time it will be an issue, any other time the centrifugal force stops water build up. In the OP's case it does actually sound like the pads are being forced back away from the disc causing them having to move more to make contact with the disc.
 
That is too obscure for me ... use of a capital E is meant to ironically illustrate a mastery of the English language ? or there is some missing capitalization in the earlier reply ?
 
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