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Clark's M2 brakes. One of the pistons wasn't moving properly. Had a play and managed to free it up to some extent but think I might have advanced it too far as now the lever is all spongy and the brake doesn't work properly.
Is a bleed likely to fix this, or have I likely damaged the seals in the caliper?
Bear in mind that hydraulic brakes do not work by the piston sliding in the seals; they work by the rubber seal distorting into a parallelogram shape then returning to its original shape to retract the piston, which is an extremely tight fit. As the pad wears the piston will creep slowly through the seal to take up wear but it's very gradual.
Might be that you've got a little air in the system, so a bleed is quite likely to fix it. If you bled it and it doesn't solve the issue, then its something else, which may be a damaged piston seal or distorted lever diaphragm
If a seal was damaged, hydraulic fluid would be bursting out and the lever bottoming.
The lever feel was fine before I started fiddling with it. Now there's little pressure in the system. Will try a bleed though.
How close are the pads to the rotor? Some brakes have quite a gap, about 0.5mm or more, between pad and rotor so as to avoid rubbing and if you squeeze the brake really hard you can force a piston to move in a seal, taking up that gap and causing the brake to bind. The brake will feel lifeless as pumping won't be deforming those seals.