I bought a pair of Clarks m2 Hydraulic disc brakes, pre-bled, and installed them on my bike. The rear brake worked great, good stopping power, but the front feels more like the mechanical disc brake that I replaced. Lever is hard and the stopping power is not nearly as good. I bought a bleed kit after being told the brake may not have been pre-bled properly. Went through the procedure (first time I have bled a brake) and now the brake works even worse than before. The lever is firm but the stopping power is lousy. I noticed when removing the bleed screw from the caliper that the screw was very tight and the o-ring fell off when pulling the screw out. Perhaps the seal is not good, allowing air to enter the system? Any help would be appreciated.
If the lever is hard but there is no stopping power, two things it could be (there may be more of course):
Brake fluid was spilled on the brake pads/rotor when bleeding. This is pretty easy to do if you dont take the pads out when bleeding. If you bled them again yourself for the first time you may have done this again (which could be why they are now worse). Check the brake pads and rotor to see if the have fluid on them. If so it is easiest to clean the rotor and get new brake pads. (This happened to me last week) some people clean the brake pads in an oven but that seems tedious.
Brake pads need to be broken in before they work very well. My guess is that your front brakes could have used thise before you bled them. Easiest way is to get up to high speed and lightly hold the brake for a while the press if hard until you stop. If you have a long hill nearby you could do this there. Or just on the street in front of your house.
And If the o ring near on you bleed screw is busted you should replace that
I have 3 things for you to think about.
- 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) thoroughly.
Half-lever the brake with pads out (carefully) whilst checking all pistons are moving equally. 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"
Hopefully as the simpler fix to opening up the caliper body, you can lever 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 lever a piston out 9 - 12 mm but again - be careful. Set a, DIY 'block' in place so you don't have to worry, just lever out until it gets to your block.
Seeing as the lever is firm, it could be that something is obstructing the movement of the lever. For example perhaps the lever-pivot joint, which is where you can adjust the lever reach with a 2mm Allen key. It may be that it has worn, or got something stuck in it or beyond it maybe the metal arm is bent. It may be that the adjustment screw has something wrong with it?
Lastly, it could just be that your pads & rotor setup is wrong or/and damaged. Cheaper rotors only take, 'resin' brake pads (aka organic, not semi/metallic ) it should hopefully be written on the rotor, 'resin only' yet not all the cheap ones do. Oddly enough, they don't seem to tell you when they are also suitable for metallic.
Take your pads out and look if they have a, 'sheen' to them? (if so, replace or fine sandpaper them (180 grit) and wipe with isopropyl alcohol. Do the same for the rotor pad braking area (is rotor bent too?) I would even scuff the rotor with fine sandpaper as it will help to bed-in your brakes. Remember brakes can take a while to, 'marry' perfectly together, say, 6 or more hours of XC riding.