Bleeding brakes!

Mikerb

E*POWAH Elite World Champion
May 16, 2019
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4,328
Weymouth
A sure sign brakes need bleeding is brake rub! You know, when you get those weird little speaking sounds from the brake.
Remove the pads and it's likely 2 pistons on one side of a 4 pot calliper are extended more than the opposing pair.....and they are difficult to push back.
The reason is air in the system which has the effect of increasing the overall volume of fluid. This also makes the bite point of the brake more progressive....or some would call it spongy.
The answer is of course to bleed the brake.
The weakest design aspect of hydraulic brakes is the piston return. It only has the piston seals and pads spring cage to do that and excess volume of fluid plus air will overpower those.

Due to the vertical hose run on the front brake that air is most likely to be at the lever so a quick fix if out on the trail etc is to remove the pads and the lever bleed nipple and then push the pistons fully home. Replace the nipple and pads.
That may also work on the rear brake if the bike is tilted front wheel up and you tap the calliper and hose to encourage any air to rise to the lever. That's obviously a hack and doing a proper bleed is the true solution.
 

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