Hi my bike has nissin brake calipers. The pads have 12,000 miles on and are still have plenty of life left in them (not down to the indicator yet).

Now the rear brake always feels spongy, rubbish and pointless, it doesn't really grip all that well in the warm dry weather(I can still move the bike with full rear brake applied).

Now then today it was raining pretty good and the rear brake felt the best it has done in a long time. The sponginess was gone, instant grip and effective like a brand new bike.

What could cause this situation?any ideas?


1 Answer 1


That sounds an awful lot like the rear brakes need bleeding, and the fluid replaced.

Air (or steam) in the brake lines stops the brakes from engaging properly, and causes them to feel spongy and lack power.

This happens because gases (air or steam) are compressible, and liquids aren't. Hydraulic systems rely on the incompressiblity of liquids to transmit and amplify force.

Bleeding the brakes is quite straightforward and cheap. Just need some new fluid, something to catch the old fluid in, and some patience.

You don't say which model bike or brake you've got, so I can't give detailed instructions for bleeding. But the basic process is to use the pedal as a pump to force out the old fluid and any air trapped in the lines.

  • How does this change with the weather? With the brake system being a closed system. I understand how to bleed the brakes and have some new fluid to use. I just need some hose tight enough for the bleed nipple. Thanks for your response.
    – DamoC
    Jul 22, 2018 at 9:02
  • +1 flush and replace the fluid. If youve overheated the brakes you may have boiled the fluid. Start there. Why they work better in the wet is a mystery. Maybe they had a build-up of dust which has been washed off? Jul 22, 2018 at 9:31
  • @DamoC Weather won't cause the fluid to boil, it's much too cold for that until it would literally roast you. I'm not totally sure how it would affect air trapped in the lines, since the lines and cylinders will shrink a little with the cold. I recommend it as a likely first step because changing the fluid is cheap, easy, and will eliminate bad fluid/air ect as a problem. It also needs to be done regularly anyway. It's also a very common problem, so good odds that it fixes the issue
    – Leliel
    Jul 23, 2018 at 6:32
  • Hmm odd. I shall change the fluid and see if it makes a difference. To be fair the fluid is 2 and half years old.
    – DamoC
    Jul 23, 2018 at 16:21
  • 1
    @DamoC at which point it's about a year older than should be changed :P
    – Leliel
    Jul 24, 2018 at 0:55

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