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Discussion Starter · #1 ·
Hello, My brakes are kind of acting like they have air in them. Brake lever engages very early, not much stopping power - even when i squeeze hard. Is this because the cold weather or probably need to bleed them? It is really cold here. Any advice here would be appreciated.

Mike
 

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Discussion Starter · #3 ·
pelts79 said:
Yup, it's the cold. I have xt's and they act the same way in the cold.
Thanks. That will save me some time trying to bleed them when they don't even need it.
 

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If yours uses mineral oil like mine do, then yeah, it's the cold. We took a trip to Lake Tahoe and the calipers engaged very early, lost some stopping power, and make more noise than usual. My buddy's bike with DOT fluid was not affected.

-J
 

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While it never is a bad a idea to do maintenance such as bleeding, the symptoms of having air in a hydraulic sytem are the opposite of a tight, hard lever.

Air compresses, unlike fluid, so the symptoms of air in a sytem would be a soft, mushy lever that squeezes easily and goes all the way to the bar.

I agree that the cause of your recent issue is the cold. Maybe the master cylinder is contracting, causing the piston to not want to slide easily.
 

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I am by NO means an expert on hydro's. In fact, I run BB7's on both my bikes. But, FWIW, I just read an article about this. Supposed to be very low temps before the oils are affected. DOT at a lower temp than mineral oil but I think it was something like 0 degrees (maybe lower?) before mineral oil really starts to have issues.
However, the one issue with Shimanos/mineral oil systems is that it absorbs water over time. If you have not bled the brakes in a while it might be good to do so as fresh oil should have less H2O and thus be less effected by the cold temps. This is also why DOT systems are affected at lower tmeps than mineral oil systems.

This article was in Mountain Bike Magazine I think.
 

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Discussion Starter · #10 ·
You might be right about that. It has been about 6 months since I have installed these and I haven't messed with them since that. I Think I am going to buy some new rotors/pads and I will do a good overhaul on them then. Thanks for all the replies on this.

Mike
 

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This is a known issue with Shimano's, they were even worse when they first came out. I had to have mine warranted and the rear replaced. It expanded so much, oil leaked out and I'm guessing did other damage. They made some changes but I still have some issues on brand new brakes, just not as severe so far. I'd postpone the overhaul, it's the cold.
 

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Still do a bleed. I reread the article and mineral oil is not supposed to be affected until 0 degrees unless there is a lot of water in the system. DOT is good to about -25 F before issues start.
 

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mnigro said:
Still do a bleed. I reread the article and mineral oil is not supposed to be affected until 0 degrees unless there is a lot of water in the system. DOT is good to about -25 F before issues start.
"Supposed" to being the key word here. I have experienced first hand the symptoms described here with new mineral oil when the temp was in the upper 20f degee range.
 

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pelts79 said:
"Supposed" to being the key word here. I have experienced first hand the symptoms described here with new mineral oil when the temp was in the upper 20f degee range.
This, along with all the other fuss, headache, PITA maintenance etc. is why I run BB7's. With good housing and set up correctly they are hard to beat. And the price...damn.
 

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mnigro said:
I am by NO means an expert on hydro's. In fact, I run BB7's on both my bikes. But, FWIW, I just read an article about this. Supposed to be very low temps before the oils are affected. DOT at a lower temp than mineral oil but I think it was something like 0 degrees (maybe lower?) before mineral oil really starts to have issues.
However, the one issue with Shimanos/mineral oil systems is that it absorbs water over time. If you have not bled the brakes in a while it might be good to do so as fresh oil should have less H2O and thus be less effected by the cold temps. This is also why DOT systems are affected at lower tmeps than mineral oil systems.

This article was in Mountain Bike Magazine I think.
Actually it's DOT fluid that's hygroscopic not mineral oil...
 

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Do not listen to anyone who has "read an article". This is the root of so many problems it makes my head hurt. Where to begin ...

Mineral oil does not absorb water. Mineral oil congeals well above the quoted zero degree threshold quoted. Worn pads do not make the caliper engage early, it does the opposite. Bent rotors also have no effect on early caliper engagement.

Listen to the three guys who have the same brakes and experience the same phenomenon. It's the cold ambient temperatures.

Also, read this page, section I-B.

-J
 

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AH HA! I just figured it out. I have current XT and XTR brakes. When riding in sub 20 degree weather I get serious "pump up". First squeeze of the lever results in normal travel. Quick, subsequent squeezes get shorter and shorter till the lever moves very little. Lay off the brakes for a minute and the first pull feels normal again (is this what you're getting?).

It's caused by the slave cylinders being sluggish to retract! NOTHING to do with the oil.

This could be because the o-rings around them get sticky in the cold or something like that but the result is when you let off the lever they don't retract instantly. Now, on the next quick pull the pads are already close to the rotor and you've got very little lever travel (the open system allowed oil from the reservoir to enter the system when you let off the lever to make up for the pistons' non return, like if your pads suddenly wore a few mm).

What I can't figure out is how the pads are able to get back to their original position and push the extra oil back into the reservoir. But they do every time, so long as the lever isn't pulled for 10 seconds or so.

Next ride when I feel the brakes "pump up" I'll quicky jump off and eyeball the pads to see if they're closer to the rotor than normal.
 
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