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Hot weather and hydraulic brakes!!
NB: Originally posted elsewhere on the Global Riders Network and appears via syndication.
Made the mistake of leaving my bike out in the sun (40c here) for awhile. Came to get on it and the front brake was really dragging and unridable. Worked out the heat had either expanded the oil in the system, and/or other parts of the system. Put it in the shade and once it cooled down everything was normal.
Moral: dont park bike in direct sun when its hot.
FWIW.
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Very interesting.. What brakes do you have because i no with dot fluid (avid and most brands) if you boil it you severally decrease braking performance. I no shimano use mineral oil so i'm not sure about that.
At least in cars it works like that but i shouldn't see why it would be different on bicycle hydraulic disk brakes.
Jono.
I had this the other year after changing the fluid in my Hope M4s. I had overfilled the system & there was nowhere for the fluid to go.
By simply loosening each nipple & pulling the lever in a bit thereby letting a wee bit of fluid out all was fine from then on.
Systems with hardly any reservoir at all like Avid's may be different.
Dot oil won't expand unless stupid hot. But air bubbles do. More likely they have air in them and need a good bleed.
Brakes are Avid XX - should have stated that :/
Don't think there is air in them as they are very solid (not spongy) with lots of feel - but maybe a brake bleed is worthwhile.
I wasn't sure how far op had ridden on binded brakes. On a 40˚c day i don't think it would take too much riding to cook the fluid??
I one thing i do really love about the avid's are the bleeding system.. its great - makes bleeding the brakes a 10min affair and you can get all the air out of the fluid before its introduced to the system.
Its funny, i used to have elixir 5's and every ride something else was wrong never got a good ride out of them but now i've got elixir cr's (not by choice i might add) and love them, never had an issue.
Jono.
The mineral oil shimano uses boils at 230 odd degree C with little expansion. One of its main advantages is that it doesn't absorb water like dot fluid does.
While overall it's claimed as an advantage one of the draw backs is if you do get moisture in the system it sits in little pockets.
A small bubble of water in a black hose in direct sun in 40* heat could easily boil and the resulting pocket if steam cause you issue. It wouldn't have to be much.
Liquid water if basically incompressible so you wouldn't feel the spunginess associated with air in system.
I'd go with the bleed
I know that a mate that raced the croc trophy had to remove his AVID XX brakes as they are known to absorb mositure at high temps thru the brake lines. His brakes in Cairns were dragging. They were changed under warranty as it is a known issue.
Avid uses DOT oil which is a different kettle of fish.
DOT oil does absorb water and will absorb it from atmosphere in the reservoir. Never heard of anyone claiming it did so through the lines before, seems unlikely, but I really don't know.
Used Cotic Tony's suggestion and let a little fluid out of the system - and all is good. Deliberately left the bike out in the sun - and no dragging brake - temp was around 40c - again!