I just fitted a new set of Clarks M2 hydraulic disc brakes.

I aligned the calliper to make sure the rotor doesn't rub the pads when the wheel is spinning.

I then pressed the brake lever, when letting go the pads stay pushed against the rotor.

I took out the pads, pushed in the pistons with a flathead and tried all above again.

Pressed lever again and same result.

Any ideas?

Many thanks.

  • 1
    Did you bleed the brakes after installation? Sounds like you don’t have enough fluid in the system.
    – MaplePanda
    Aug 18, 2020 at 17:39
  • Maplepanda - I didn't bleed the system - do I need to add more fluid (mineral oil)
    – ak94
    Aug 18, 2020 at 17:43
  • 1
    Did you have to trim the brake line? Most brakes come factory bled, so if you didn’t disconnect the line, it should work fine. If you DID trim the line, you will need to bleed it.
    – MaplePanda
    Aug 18, 2020 at 19:52
  • I didn't trim the brake line - it is literally out of the box
    – ak94
    Aug 20, 2020 at 11:25
  • You should probably just ask for a warranty then.
    – MaplePanda
    Aug 20, 2020 at 18:39

1 Answer 1


Sorry to hear this.

As I've see it so many times and quite a few YouTube tutorials (although a blessing to have) miss this step out (yes, GMBN have missed it too) it's VITAL to the bleeding process.

BEFORE pushing the pistons in, they need to be cleaned (isopropyl alcohol) throughly.

If, you pushed your pistons into the caliper body, without a proper clean, then you have just pushed gunk into the caliper body through to the hydraulic fluid and onto the inside of the piston seals. Thus reducing their ability to freely move in and out, aka, "sticky pistons"

Hopfuly as the simpler fix to opening up the caliper body, you can leaver out one piston at a time (while holding the other/s back) but not too far that it pops out. Clean it well then push back in. Repeat a few times or until fully clean before moving onto the next one. You can usually leaver a piston out 9 - 12 mm but again - be careful. Set a, DIY 'block' in place so you don't have to worry, just leaver out until it gets to your block.

Good luck!

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