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Its recently been cold, around 0 degrees C at night, where my bike is stored in the outside shed.

Ive replaced the pads, and bled the brakes around 6 months ago.

When taking out my bike it has 0% brake capacity initially, and the levers touch the handle bars without stopping the wheel.

After pumping them for around 5 minutes, they sharpen up to around 40%.

Then they jump between working (40%) and not (0%) randomly over the next 10-20 minutes.

What could the issue/fix be?

Should I re-bleed the brake fluid, replace the o-rings, or keep the bike indoors?

Should I be able to store my bike in a shed at low temperatures without the brakes breaking?

Thanks

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    Sounds like ice in the brake lines. (Is that zero C or zero F?)
    – Daniel R Hicks
    Jan 6, 2017 at 18:01
  • What kind of brakes are they?
    – Batman
    Jan 6, 2017 at 20:45
  • tektro hdc 300 disc brakes
    – zino
    Jan 6, 2017 at 23:32
  • I'd suggest a bleed, and if that makes it no better then a full flush and new brake fluid/oil (whichever fluid the manufacturer specifies)
    – Criggie ♦
    Jan 6, 2017 at 23:53
  • Even if there is not ice in the lines, you could have problems due to type of brake fluid that gets stiff when cold. Though the fact that the levers touch the bars when you have this problem suggests that air in the lines is at least a confounding factor.
    – Daniel R Hicks
    Jan 7, 2017 at 3:11

2 Answers 2

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I would say that you've either got air in the lines or perhaps moisture in the brake fluid. Assuming that mechanically the brakes are good. I would completely drain the brake fluid and replace it with the manufacturers spec fluid and bleed it properly.

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DOT4 oils can absorb air humidity (water) really fast. This results in brakes becoming 'spongeous' and unresponsive. If your bike remains outside in a shed all the time, the process is likely quicker. You will have to either bleed your brakes again or invest in mineral oil hydraulic disc brakes which don't have this problem.

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  • I use this oil: amazon.co.uk/Tektro-Service-Kit-Complete-x/dp/B0073D590I/… Do I need to use the manufacturer branded oil, or can I use any brand?
    – zino
    Jan 11, 2017 at 14:57
  • @zino There is not much info on the link provided. The pic does show mineral oil, which is puzzling. You shouldn't have such a problem with mineral oil. If it is indeed mineral, you must have a leak somewhere. I encourage you to check on Tektro's website with your brakes ref.
    – Standaa - Remember Monica
    Jan 11, 2017 at 15:00

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