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Need help adjusting my mech disk brakes

803 Views 8 Replies 4 Participants Last post by  Bikinfoolferlife
06 Piranha, came with those cheap mech disk brakes, I like them and they have served me well.

Some squeak I could never fix when doing heavy braking though.

I just started doing off road riding recently (yay finally found some trails) so this is the first time I really had to clean my bike. When cleaning it and inspecting it I noticed my rear wheel cant spin freely its rubbing the piston inside the rear disk brake. Not enough to really feel it or make sound but its definitely rubbing and I can see the rotor has wear on it from it but I cant for the life of me see how to move it.

It looks like the actual rotor or the brake mech needs to be move, not just the piston needing adjusted as its almost all the way inside its casing.

Also are there not supposed to be 2 moving pistons one from each side? On both front & back I can only see one piston moving when I activate the brake levers.

If you have advise please let me know, other than that I need to take some pictures of it when I get off work and post back. I think that will help greatly in showing the problem.
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Only 1 piston should move.
I presume that you have Hayes MX-2's as those are listed as what came standard on the 06 Piranha.
Have a look at the Installation/Set-Up Manual for the MX-2's:
If it's rubbing intermittently you might just have a slightly warped rotor that needs some truing, or is it rubbing for the full rotation of the disc? Truing is easily accomplished using the caliper as guide and gently bending the rotor with a clean small adjustable wrench (or you can buy a specific tool like Park's

Hopefully that link to the manual will resolve your issue for caliper/pad adjustment otherwise.

FWIW even the best mechanical brake, the Avid BB7, has just one moving pad; there are a few brands that offer dual pad movement.
FWIW even the best mechanical brake, the Avid BB7, has just one moving pad; there are a few brands that offer dual pad movement.
Well there was that RST model...

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Yeah but the RST works better I bet as it actually makes both pistons grip the rotor. The IRD model works like a car brake. You apply the brake and it sucks the inner side towards the fork after the outer pad has made contact with the rotor via some set of springs or whatnot. So instead of pushing the rotor into a stationary pad it pulls the whole caliper to the rotor. Kinda unique actually.
Its the entire rotor, its nice and true. I'll look at that pdf and see what i can do with it.
if that doesn't have what I need I can take it up to the lbs and see if they will offer me some help, or there is a mtb beginners course offered for free I think by our local swamp club, I can try to attend that one day. somebody there for sure will know what to do.

thanks for the quick responses and help guys.
Update, fixed - sorta

All I had to do was take off the back wheel and with my allen wrench turn the outside adjuster deal, it was not up against the piston but the side plate and it has an adjuster.

However after moving it, now I can see the rotor does have a bit of a warp to it, its so small though that its hard to spot and I really dont think I can bend it back without making it worse. Its so minor that I will leave it as is. But now you hear just a faint noise when that part of the rotor goes over the brake mech.

I think my tire is not seated 100% ether. It looks like its warped if I spin it fast and look at the outside of the tire, but I can only see it on the tire not the hub or wheel so I guess just one part of the tire is bulging out a bit more, but when looking near the tire bead area I cant spot it.

I occurs to me that the proper way to fix the brake in my case is by bending the rotor, as moving the adjuster to give it clearance only makes my brakes engage later, but that can be accounted for by making the cable tighter on the brakes I guess if I had too, but it wouldnt be proper. I only had to move it like a fraction of a mm though so didnt really change the feel of the brake and now the wheel can spin freely with almost 0 friction.

Now my last thing, when spining the wheel I hear a knock in the wheel at the same point every rotation that I never heard before, I cant tell what the heck is making the noise. I hope its not the hub.

I think it all sounds worse than it is, the bike has not been ridden that much and its still got many miles left to go before I think it needs any overhauling.
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Don't get crazy with the bending of the rotor to true it, you can get it quite flat with a bit of patience using the caliper as a guide. Bike tires aren't perfectly molded, sometimes they'll have a bit of a hop even when properly seated, not a big deal.

Your noise might be the hub needing a bit of adjustment (any side to side play felt at the rim?), maybe a bearing on the way out, maybe the freehub is making a bit of noise...just eliminate possibilities to narrow things down a bit.
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