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Hello all,

Thanks for the help.
So I was riding in the mountains today. About halfway down (was on the rears kinda hard) my rear brake pedal stopped working. I can push it all the way down and it eventually does a little bit of something but not much. Feels mushy and definitely not building pressure. Don’t see any leaks, reservoir looks good. Where to look next? Master cylinder? Take it to shop?
 

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You may have just boiled the fluid and now it's Airbound. Check the fluid level, I'm guessing it's low. Add some more and bleed the brakes and see if that helps.

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I would just drain out the old brake fluid
And start with fresh fluid rebeed the rear brakes...


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Hello all,

Thanks for the help.
So I was riding in the mountains today. About halfway down (was on the rears kinda hard) my rear brake pedal stopped working. I can push it all the way down and it eventually does a little bit of something but not much. Feels mushy and definitely not building pressure. Don’t see any leaks, reservoir looks good. Where to look next? Master cylinder? Take it to shop?
Update: went back out and it’s building up pressure just fine.
Based on the above, the brake fluid compound broke down and reached boiling point temperature.
Perhaps because of age and or contamination or possibly the removal of the rear aluminum finned rotor cover that acts as a heat sink.

I would suggest replacing the Brake Fluid with a premium quality DOT 4 or DOT 5.1 compound that has a higher boiling point.
Both these compounds are glycol-based brake fluids and are compatible with each other.
  • DOT 5 which is silicone-based should never be mixed with glycol-based DOT fluids.
 

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If braking hard and often like always down the mountain, using such higher boiling point fluids might be good idea.
 
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