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Discussion Starter #1
I bought my new M3GT in October and have been driving it in light snow as of late. I have noticed that the brakes REALLY grab for a moment when pressing them after going through deeper snow. Is the snow/ice getting int he way of my front brakes? Is there a safe way to "clear" them while in motion? Or are my calipers sticking? The pedal thumps a few times and sticks a little and then clears up... But so far as I can recall, this ONLY happens when there is deep snow or heavy freezing slushy ice...
 

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It is moisture on the rotors. happens on every car I have ever driven in once a large amount of moisture or snow gets on the rotors. Happens to if you let your car sit out for awhile in high humidity/rain the first time you hit the brakes...in that case it is rust brushing off your rotors.
-Matt

PS yes it is safe so long as you are expecting it. Some vehicles like a few Mercedes models detect rain/snow and will actually lightly apply the brake pads during driving to keep them cleaned of moisture. I am sure this adds up to a lot of additional brake pad wear though (and decreased fuel economy)...even if the pressure is very slight.
 

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Discussion Starter #3
Let me be a little more clear. ::grin:: Last night the temperature was -15F where I am. This morning, there was no issues with the front brakes.

This happens after I've driven through slush or snow - and I've never felt this with any of my previous cars. Then again, msot of my previous cars didn't have disk brakes in the front either...

The pedal actually thumps as I press down on it- as if the rotor suddenly was warped beyond all imagination... but it clears up in a few seconds. But during this, the brakes really grab..

Still - it is just moisture?
 

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Discussion Starter #5
I guess I can't make myself too clear today :) Forgive me.. :) It is an UNEVEN THUMP - not like a rythmic pulse that I would expect ABS would be giving me the feel of. I will try to reproduce the feeling by driving through some snow as soon as it warms up a little bit..
 

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Discussion Starter #6
Okay - I have found the constant. When I start the car on hard-packed snow and ease it forward a little and use the brake, this is when I get the uneven feel of the brakes and a bit of a noise. When I brake at 5 miles an hour, the front brakes lock - no ABS action there. When I get to clear pavement, the issue dissapears.
I tried pumping the brakes before rolling the car an inch with no change. I stopped after 10 minutes of driving and parked it in some hard-pack snow, and restarted after about 10 minutes. Same condition with the brakes.
Any idea whats going on with my front brakes? Are they supposed to do this?
 

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so is it just ice on the rotors?

Once the rotors heat up after initial use, then the ice should melt and the brakes should function like normal.

Perhaps try driving while lightly depressing the brakes. This is what you're supposed to do per "DMV" if you hit a puddle of water that wets your rotars.
 

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Discussion Starter #8
Tonight, like last night my car is on hard-pack snow in the parking lot. I'll start it up as I did last night, put it in first and slowly drive forward. Then I will lightly put my foot on the brake, gradually increasing pressure. Last night, I got feedback on the pedal, and with a grinding noise my front brakes locked at 5mph or less. I hit reverse, then forward again with the same results. Driving out of the parking lot on to clear pavement I would brake again the same way - no feedback, no locking.
It feels like it is locking and sliding on the packed snow, although I didn't hang my head out the window to verify. I'll try to tonight - even stop the car and examine the tracks to see if they do indeed lock if at all possible. This is a 2007 GT that I bought in October so this is my first winter with this car. I'm familiar with "drying" the brakes on my motorcycle after running in the rain and understand the deal... I just can't see what the deal is with this...
 

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I got my car stuck last weekend I have covers on my steelies that got ice and snow on them driving did not melt the ice off. In my case it was making the car vibrate BUT it also was in my brakes so I was not stopping right. I went to the car wash and the hot water cleaned it out. Maybe try going through the car wash...
 

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Discussion Starter #10
Okay - I think I have it narrowed down to some problem in the ABS. It's been in the single digits and below here for the past week. It seems I ONLY get this pedal feedback and grinding sound when I am on slippery hardpack snow or ICE. When starting on dry pavement and slowly pressing the break, I get no grind, no feedback. But if I go to ICE, or hardpack where the tires will slide (and what I thought would trigger the ABS) I get this grinding sound and the feedback in the pedal while breaking. This happens in either forward OR reverse.

ABS SHOULD apply braking rapidly and controlled, but I am not getting that at all on slipery surfaces... So - Has anybody had issues with ABS failing and is this what it sounds and feels like?
 
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