brakes freezing in v. cold weather? - Subaru Forester Owners Forum
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post #1 of 19 (permalink) Old 02-19-2008, 08:54 PM Thread Starter
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brakes freezing in v. cold weather?

Hmm... no other threads in this forum... hope someone reads this!

I just made a long road trip in my Forrie, from Philadelphia to Montana via Minnesota and Wisconsin. We stopped overnight outside Madison, and when we got on the road the next day, the brakes were very stiff. I.e., when I pressed on the brake pedal, there was a lot of resistance and very little braking. After a lot of pressing, they came back, but throughout that day, usually after long periods of driving on the highway when we didn't use the brakes (and were slowing down to pull into a rest station or something), that stiffness came back and I really had to jam on the pedal to get them to work.

The temperature that day was -7 F, -30 with wind chill. So I'm thinking that something in the brake line was freezing up during those long periods of disuse, and we haven't experienced it since driving through those temps. Does that sound plausible? If so, is there any way to prevent it? If that doesn't sound like the answer, what else might it be?
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post #2 of 19 (permalink) Old 02-19-2008, 09:51 PM
 
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I don't have input into your braking problems other than guessing so I'll leave that to denizens of areas with more severe weather than California.

But if your not seeing threads then you need to change your user settings. Hit the User CP at the top off the forum page, then on the control panel list on the side of the page hit Edit Option, then scroll down to "Default Thread Age Cut Off" and check whatever time limit you want, up to show all.

There are 22 pages of threads in the Brakes subforum.


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post #3 of 19 (permalink) Old 02-19-2008, 10:54 PM
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Question

Could that be the moisture freeze at those low temperature? How long ago did you replace brake fluid?

…what to do with the time that is given to us…
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post #4 of 19 (permalink) Old 02-20-2008, 03:10 AM
 
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There is a check-valve inline between the brake booster and intake manifold.

If there is moisture in that check-valve (which is fairly likely, as moisture is common in the intake manifold), it could freeze causing the check-valve to stick closed.

If the valve is frozen closed, you lose vacuum assist on the brakes, and effectively have "manual brakes" like back in the day.

Also, at that cold of temperature brake pads are WAY below their range of optimal efficiency, so it will require greater pressure to achieve equal pad/rotor friction, which translates to a VERY stiff pedal until the pads warm up.

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post #5 of 19 (permalink) Old 02-20-2008, 07:16 AM
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It sounds like your brake fluid has gotten contaminated with water and is freezing. Bleeding the brakes periodically will fix and prevent this.
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post #6 of 19 (permalink) Old 02-20-2008, 07:19 AM
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I occaisionally had similar problems with my previous vehicle (a F@#d pu) and it was apparently caused by frost sticking to the rotors. After a few years of being exposed to winter road salt, the rotors would develop some mild pitting and the roughened surface allowed some frost to stick to them. It melts off once the brakes heat up from the first use and they would work normally after that. Always needed new rotors before passing the next annual safety inspection too.

I would recommend a brake job.

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post #7 of 19 (permalink) Old 02-20-2008, 07:20 AM
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Happened to me as well, up in the mountains. Was about time to change my brake fluid anyway. Did that, no more problems!

Dash: '03 XS MT
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post #8 of 19 (permalink) Old 02-20-2008, 08:35 AM
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Happens to me all the time, usually goes away after a minute or two and only happens when it is cold, like below 5 degrees or so.
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post #9 of 19 (permalink) Old 02-20-2008, 09:46 AM
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I'll say its moisture in the lines. Its plenty cold here all winter (-10 is not rare) and this never happens to me. Brake fluid does absorb moisture so this may be an idicator its time to change your fluid.
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post #10 of 19 (permalink) Old 02-20-2008, 10:11 AM
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^^

Good to know I am basically at 30k so I think its due for new fluid anyways.

Thanks!
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post #11 of 19 (permalink) Old 02-20-2008, 10:11 AM
 
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If you have absorbed enough water to cause brake fluid to freeze, you have bigger problems than no brakes.

Brake fluid absorbs approximately 3% by volume over the course of it's usable life. So in 1000mL, only 30mL of water will be absorbed (evenly, you can't see the water in brake fluid). "Dry" brake fluid has a freezing point of around -59C (-75F). Fully saturated, it will not be significantly raised.

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post #12 of 19 (permalink) Old 02-20-2008, 10:32 AM
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I thought you were going to ask about this after going through the car wash! Always fun going through the car wash when it's like -20 out and trying to come to a stop right outside the wash and almost sliding through the stop signs. It does sound like you need to change your brake fluid if you haven't done that recently.

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post #13 of 19 (permalink) Old 02-20-2008, 03:20 PM
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Quote:
Originally Posted by sjwelna View Post
I thought you were going to ask about this after going through the car wash! Always fun going through the car wash when it's like -20 out and trying to come to a stop right outside the wash and almost sliding through the stop signs. It does sound like you need to change your brake fluid if you haven't done that recently.

-Steve
How does water get into the brake fluid while in a car wash?

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post #14 of 19 (permalink) Old 02-20-2008, 07:35 PM
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Originally Posted by missinaibi View Post
How does water get into the brake fluid while in a car wash?
It doesn't unless you've left the top off the master cylinder and driven through the car wash with the hood open. That wasn't what he was suggesting anyway, if you read it again.

As BAC5.2 has observed this, is unlikely to be your brake fluid: if it has absorbed enough water to freeze, then it's going to boil and cause complete loss of brakes very, very readily.

I'd check what BAC5.2 suggested earlier, and if the car has non-standard pads, they might not be working too well at these low temperatures, especially if some cheap ones have got put in there at some point. Your brake booster (aka servo) might be failing too.

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post #15 of 19 (permalink) Old 02-20-2008, 07:51 PM
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Originally Posted by Graham View Post
It doesn't unless you've left the top off the master cylinder and driven through the car wash with the hood open. That wasn't what he was suggesting anyway, if you read it again.

As BAC5.2 has observed this, is unlikely to be your brake fluid: if it has absorbed enough water to freeze, then it's going to boil and cause complete loss of brakes very, very readily.

I'd check what BAC5.2 suggested earlier, and if the car has non-standard pads, they might not be working too well at these low temperatures, especially if some cheap ones have got put in there at some point. Your brake booster (aka servo) might be failing too.
Good points. The way the OP described it does sound like symptoms of a brake booster failure.
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