discs siezing when hot
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discs siezing when hot
Postby davehirst » Sun Apr 22, 2018 2:38 pm
Is this possibly to much fluid.
The brakes are new, replacing avids where we were having a similar problem.
It is the wifes bike and she is heavy on the brakes.
thanks
dave
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Re: discs siezing when hot
Postby 10speedsemiracer » Sun Apr 22, 2018 2:55 pm
Generally a slightly harder pad compound is recommended for sustained heavy usage however the trade-off is less initial bite when cold.
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Re: discs siezing when hot
Postby davehirst » Sun Apr 22, 2018 5:52 pm
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Re: discs siezing when hot
Postby Duck! » Sun Apr 22, 2018 10:21 pm
The lower-spec Shimano brakes don't have a metal pad option, so really you should be looking at altering technique and letting the brakes breathe between corners.
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Re: discs siezing when hot
Postby Defy The Odds » Sun Apr 29, 2018 11:33 pm
The only other thing I could say is firstly try changing the pads to something more high performance and suitable. However as mentioned earlier the trade off is cold weather braking.
If this doesn't work bleed the brakes with Dot 5 or Dot 4 fluid of a reputable brand
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Re: discs siezing when hot
Postby Trevtassie » Mon Apr 30, 2018 8:33 am
Don't using DOT 4 or 5 fluid on Shimano brakes, they take mineral oil as Duck mentioned, different stuff.... you need the genuine oil.Defy The Odds wrote:
If this doesn't work bleed the brakes with Dot 5 or Dot 4 fluid of a reputable brand
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Re: discs siezing when hot
Postby Defy The Odds » Mon Apr 30, 2018 9:04 am
These fluids have a higher boiling point which can create brake fade
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Re: discs siezing when hot
Postby MichaelB » Mon Apr 30, 2018 10:42 am
Oils CANNOT be mixed and/or used in different systems - the seals will fail.Defy The Odds wrote:Not sure of Shimano but I have seen recommendations for dot 4 or 5 on SRAM mountain bikes.
These fluids have a higher boiling point which can create brake fade
Even at 95kg + bike, I've never even gotten close to boiling my fluid even down European passes with steep descents. IMHO, the boiling point of the fluid is a not issue.
Pad fade due to high temps/poor braking is a more common occurrence
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Re: discs siezing when hot
Postby Calvin27 » Mon Apr 30, 2018 11:13 am
Please don't tell the dude to put DOT in a shimano brake system if you are unsure!Defy The Odds wrote:Not sure of Shimano but I have seen recommendations for dot 4 or 5 on SRAM mountain bikes.
These fluids have a higher boiling point which can create brake fade
You can buy finned pads for a little bit more cooling - they come in organic and metal.
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Re: discs siezing when hot
Postby eeksll » Mon Apr 30, 2018 12:24 pm
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Re: discs siezing when hot
Postby MichaelB » Mon Apr 30, 2018 2:17 pm
If anything, that will lead to a spongy lever and poor braking, rather than seizing on.eeksll wrote:no one else has said it, so I am probably wrong here, wouldn't this symptom be caused by having a bit of air in the caliper?
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Re: discs siezing when hot
Postby Duck! » Mon Apr 30, 2018 6:58 pm
DO NOT EVER UNDER ANY CIRCUMSTANCES USE DOT FLUID IN A MINERAL OIL BRAKE SYSTEM!!!!! Sure-fire way to destroy the seals, leaving you with no brakes at all.Trevtassie wrote:Don't using DOT 4 or 5 fluid on Shimano brakes, they take mineral oil as Duck mentioned, different stuff.... you need the genuine oil.Defy The Odds wrote:
If this doesn't work bleed the brakes with Dot 5 or Dot 4 fluid of a reputable brand
Absolutely not DOT 5. SRAM specify DOT 5.1. DOT 3, 4 & 5.1 are all the same chemical base, so are interchangeable. DOT 5 is quite different, and must only be used in brake systems designed for it. As far as I'm aware, no bike brakes use DOT 5.Defy The Odds wrote:Not sure of Shimano but I have seen recommendations for dot 4 or 5 on SRAM mountain bikes.
Actually not necessarily the case. Not all mineral oils are formulated equally. Shimano's oil has a higher boiling point than DOT5.1, and because it does not absorb moisture, maintains consistent performance. DOT fluids absorb water, which lowers the boiling point and degrades performance. Additionally, brake fade is not caused by boiling fluid; that's vapour lock and pressure loss. Brake fade is the loss of friction resulting from overheated and glazed pads.These fluids have a higher boiling point which can create brake fade
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Re: discs siezing when hot
Postby Duck! » Mon Apr 30, 2018 7:01 pm
Not for those brakes. Metal compound & cooling fins are only options on higher-spec models.Calvin27 wrote: You can buy finned pads for a little bit more cooling - they come in organic and metal.
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Re: discs siezing when hot
Postby Duck! » Mon Apr 30, 2018 7:11 pm
Air is compressible, so would indeed cause a spongy feel and poor brake performance. If there was sufficient volume of air in the system to expand that much, the brakes would be in all probability not even be functional. Additionally, if any air was inside the system and trying to expand, it would tend to push the fluid up the line & back into the reservoir, where there is only atmospheric pressure acting against the expansion bladder. Path of least resistance & all that.MichaelB wrote:If anything, that will lead to a spongy lever and poor braking, rather than seizing on.eeksll wrote:no one else has said it, so I am probably wrong here, wouldn't this symptom be caused by having a bit of air in the caliper?
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Re: discs siezing when hot
Postby eeksll » Mon Apr 30, 2018 7:25 pm
thanks for the clarification.Duck! wrote:Air is compressible, so would indeed cause a spongy feel and poor brake performance. If there was sufficient volume of air in the system to expand that much, the brakes would be in all probability not even be functional. Additionally, if any air was inside the system and trying to expand, it would tend to push the fluid up the line & back into the reservoir, where there is only atmospheric pressure acting against the expansion bladder. Path of least resistance & all that.MichaelB wrote:If anything, that will lead to a spongy lever and poor braking, rather than seizing on.eeksll wrote:no one else has said it, so I am probably wrong here, wouldn't this symptom be caused by having a bit of air in the caliper?
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Re: discs siezing when hot
Postby Trevtassie » Wed May 02, 2018 8:26 am
Water used to get into brake systems on cars through condensation because they weren't sealed at the master cylinder , if it wasn't absorbed into the fluid it would travel down the brake lines to the lowest point, the brakes, where it could boil or corrode brake mechanisms. So the idea was brake fluid, although prone to absorb moisture, if changed regularly (which you should do every few years, or more often in the tropics) was a better bet than non hygroscopic fluids. It's not such a big issue nowdays because systems are much better sealed. Shimano use non hygroscopic mineral oil because like modern cars, their brake systems are sealed, water can't get in, and because there are advantages to mineral oil, like a long shelf life after being opened and the fact it doesn't eat paint like most brake fluids. There is some interesting reading here about the various brake fluids: http://www.stoptech.com/technical-suppo ... rake-fluid
In terms of your modern car, it's still worthwhile changing your brake fluid every 5 years or so at a minimum. Your average mechanic will look at you like you are a weirdo if you insist, but basically your brake internals will outlast the rest of your car if you do this.
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