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so, I've been through a lot of fiddling with my brake levers, giving them a small clean out and bleed, but I've noticed now that when i keep my bike inside (on heated floor) the brake levers go stiff, and the pads pinch the rotors... I've had friends saying the piston swells up in the lever or 'too much fluid', but when i leave it outside, the brakes go back to perfect, perhaps the fluid, is there such thing as cheap fluid that expands perhaps? Shimano saint if it helps.

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  • This appears similar to the gen 1 Guide issue where the levers would seize when left in the sun. The fix was to pour cold water on them. It was a seal on or around the lever piston that caused the issue. SRAM warrantied a lot of them so I'm not sure if a fix was found. Can you get your's replaced under warranty?
    – DWGKNZ
    Commented Dec 9, 2021 at 19:27
  • Mineral oil does expand when heated, but only marginally. Have you tried to remove a small amount of fluid while the levers are sticking and does it make a difference? Even just removing the reservoir plug while the brake is warm and sticking may allow enough oil to escape.
    – DWGKNZ
    Commented Dec 9, 2021 at 19:29
  • Because it's not a known fault with Saints, it could easily be too much oil.
    – DWGKNZ
    Commented Dec 9, 2021 at 19:33
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    @mattnz not if it's heat at the levers (or indeed anywhere away from the calipers). The path the heat would have to take is just too long and narrow
    – Chris H
    Commented Dec 9, 2021 at 21:39
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    ...You also heat a tiny amount of fluid in the caliper body and bottom of the hose compared to the whole length of hose+master cylinder+reservoir so you'd need to consider the same ratio in temperature change as in heated volumes. If the volume heated by braking is 5x less than by warming the bike, the same pressure change will be caused by 5x higher temperature: 0°C ambient, 20°C room temp, and 100°C caliper temp are reasonable values (in this hemisphere where it's currently winter) and 5x is IMO a reasonable guess for the volume ratio
    – Chris H
    Commented Dec 10, 2021 at 9:50

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